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Mersana Therapeutics

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FY2019 Annual Report · Mersana Therapeutics
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UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549
FORM 10-K

(Mark One)

☒ ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

For the fiscal year ended December 31, 2019.

OR

☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

For the transition period from                    to                   

Commission file number 001-38129
Mersana Therapeutics, Inc.
(Exact name of registrant as specified in its charter)

Delaware
(State or Other Jurisdiction of Incorporation or Organization)

840 Memorial Drive Cambridge, MA
(Address of Principal Executive Offices)

04-3562403
(I.R.S. Employer Identification No.)

02139
(Zip Code)

Registrant’s telephone number, including area code (617) 498-0020

Securities registered pursuant to Section 12(b) of the Act:

Title of each class

Common Stock, $0.0001 par value

Trading symbol(s)

MRSN

Name of each exchange on which registered

The Nasdaq Global Select Market

Securities registered pursuant to Section 12(g) of the Act:

NONE

Indicate by check mark if the registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act.

Yes  ☐  No  ☒

Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or Section 15(d) of the Act.

Yes  ☐  No  ☒

Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12
months (or for such shorter period that registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days. 
Yes  ☒  No 
☐

Indicate by check mark whether the registrant has submitted electronically every Interactive Data File required to be submitted pursuant to Rule 405 of Regulation S-T (§232.405 of
this chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submit such files).

Yes  ☒  No  ☐

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company, or an emerging growth company.
See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company,” and “emerging growth company” in Rule 12b-2 of the Exchange Act.

Large accelerated filer
Non-accelerated filer

☐
☐

Accelerated filer
Smaller reporting company
Emerging growth company

☒
☒
☒

If  an  emerging  growth  company,  indicate  by  check  mark  if  the  registrant  has  elected  not  to  use  the  extended  transition  period  for  complying  with  any  new  or  revised  financial
accounting standards provided pursuant to Section 13(a) of the Exchange Act.

☒

Indicate by check mark whether the registrant is a shell company (as defined by Rule 12b-2 of the Exchange Act).

Yes  ☐  No  ☒

As of June 28, 2019, the last business day of the registrant’s most recently completed second fiscal quarter, the aggregate market value of the registrant’s common stock held by
non-affiliates was $163,614,650, based on the last reported sale price of such stock on the Nasdaq Global Select Market as of such date. 

As of February 25, 2020, the registrant had 45,429,985 shares of common stock outstanding at a par value $0.0001 per share.

DOCUMENTS INCORPORATED BY REFERENCE
Portions of the registrant’s definitive proxy statement that will be filed for the 2020 Annual Meeting of Stockholders are incorporated by reference in Part III.

 
 
 
 
 
 
 
 
 
 
 
 
 
    
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Table of Contents

TABLE OF CONTENTS

PART I

Page

FORWARD LOOKING STATEMENTS 

ITEM 1. 

BUSINESS

ITEM 1A. 

RISK FACTORS

ITEM 1B. 

UNRESOLVED STAFF COMMENTS

ITEM 2. 

ITEM 3. 

ITEM 4. 

ITEM 5. 

ITEM 6. 

ITEM 7. 

PROPERTIES

LEGAL PROCEEDINGS

MINE SAFETY DISCLOSURES

PART II

FOR 

MARKET 
STOCKHOLDER  MATTERS  AND 
SECURITIES

REGISTRANT’S 

COMMON 

RELATED
ISSUER  PURCHASES  OF  EQUITY

EQUITY, 

SELECTED FINANCIAL DATA

MANAGEMENT’S DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION
AND RESULTS OF OPERATIONS

ITEM 7A. 

QUANTITATIVE AND QUALITATIVE DISCLOSURES ABOUT MARKET RISK  

ITEM 8. 

ITEM 9. 

FINANCIAL STATEMENTS AND SUPPLEMENTARY DATA

CHANGES 
ACCOUNTING AND FINANCIAL DISCLOSURE

IN  AND  DISAGREEMENTS  WITH  ACCOUNTANTS  ON

ITEM 9A. 

CONTROLS AND PROCEDURES

ITEM 9B. 

OTHER INFORMATION

PART III

ITEM 10. 

DIRECTORS, EXECUTIVE OFFICERS AND CORPORATE GOVERNANCE

ITEM 11  

EXECUTIVE COMPENSATION

ITEM 12. 

ITEM 13. 

SECURITY  OWNERSHIP  OF  CERTAIN  BENEFICIAL  OWNERS  AND
MANAGEMENT AND RELATED STOCKHOLDER MATTERS

CERTAIN  RELATIONSHIPS  AND  RELATED  TRANSACTIONS,  AND
DIRECTOR INDEPENDENCE

ITEM 14. 

PRINCIPAL ACCOUNTING FEES AND SERVICES

ITEM 15. 

EXHIBITS, FINANCIAL STATEMENT SCHEDULES

ITEM 16. 

FORM 10-K SUMMARY

PART IV

EXHIBIT INDEX 

SIGNATURES 

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FORWARD LOOKING STATEMENTS

PART I

This Annual Report on Form 10-K contains forward‑looking statements. Forward‑looking statements are neither historical
facts  nor  assurances  of  future  performance.  Instead,  they  are  based  on  our  current  beliefs,  expectations  and  assumptions
regarding the future of our business, future plans and strategies, our clinical results and other future conditions. The words
“aim,”  “anticipate,”  “believe,”  “contemplate,”  “continue,”  “could,”  “estimate,”  “expect,”  “goal,”  “intend,”  “may,”  “plan,”
“possible,”  “potential,”  “predict,”  “project,”  “seek,”  “should,”  “target,”  “will,”  “would”  or  the  negative  of  these  terms  or
other  similar  expressions  are  intended  to  identify  forward‑looking  statements,  although  not  all  forward‑looking  statements
contain these identifying words.

These forward‑looking statements include, among other things, statements about:

·

·

·

·

·

·

·

·

the  initiation,  cost,  timing,  progress  and  results  of  our  current  and  future  research  and  development  activities,
preclinical and clinical studies;

the timing of, and our ability to obtain and maintain, regulatory approvals for our product candidates;

unmet need of ovarian cancer and non-small cell lung cancer;

our ability to quickly and efficiently identify and develop additional product candidates;

our ability to advance any product candidate into, and successfully complete clinical studies;

our intellectual property position, including with respect to our trade secrets;

the potential benefits of strategic partnership agreements and our ability to enter into selective strategic partnerships;
and

our estimates regarding expenses, future revenues, capital requirements, the sufficiency of our current and expected
cash resources and our need for additional financing.

We  may  not  actually  achieve  the  plans,  intentions  or  expectations  disclosed  in  our  forward‑looking  statements,  and  you
should not place undue reliance on our forward‑looking statements. Actual results or events could differ materially from the
plans, intentions and expectations disclosed in the forward‑looking statements we make. We have included important factors
in the cautionary statements included in this Annual Report on Form 10-K, particularly in the “Risk factors” section, that we
believe  could  cause  actual  results  or  events  to  differ  materially  from  the  forward‑looking  statements  that  we  make.  Our
forward‑looking statements do not reflect the potential impact of any future acquisitions, mergers, dispositions, joint ventures
or investments we may make.

The forward‑looking statements contained herein represent our views as of the date of this Annual Report on Form 10-K. We
anticipate  that  subsequent  events  and  developments  will  cause  our  views  to  change.  However,  although  we  may  elect  to
update these forward‑looking statements at some point in the future, we have no current intention of doing so except to the
extent required by applicable law. You should, therefore, not rely on these forward‑looking statements as representing our
views as of any date subsequent to the date of this Annual Report on Form 10-K.

ITEM 1.              BUSINESS

Overview

We are a clinical-stage biopharmaceutical company focused on developing antibody drug conjugates, or ADCs, that offer a
clinically meaningful benefit for cancer patients with significant unmet need. We have leveraged 20 years of industry

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learning in the ADC field to develop proprietary and differentiated technology platforms that enable us to design ADCs to
have improved efficacy, safety and tolerability relative to existing ADC therapies.

Our  innovative  platforms,  which  include  Dolaflexin  and  Dolasynthen,  delivering  our  DolaLock  payload,  as  well  as
Immunosynthen,  delivering  a  novel  stimulator  of  interferon  genes,  or  STING,  agonist,  compose  a  highly  efficient  product
engine that has enabled a robust discovery pipeline for us and our partners. Our ADCs in preclinical and clinical studies are
first-in-class molecules that target multiple tumor types with high unmet medical need and have exhibited improved safety
and efficacy compared to ADCs developed using first-generation technology.

We have assembled a management team with extensive and relevant experience, including specific ADC experience, from
prior  work  at  leading  pharmaceutical  companies  such  as  Millennium  Pharmaceuticals,  Inc.,  Takeda,  Biogen,  Inc.,
MedImmune,  Inc.,  Bayer  AG,  Genzyme,  Tesaro,  Roche  and  Bristol-Myers  Squibb.  We  are  supported  by  our  board  of
directors and scientific advisory board, who offer complementary experience in drug discovery and development, as well as
expertise  in  building  public  companies,  management  and  business  development.  We  believe  that  our  highly  differentiated
platforms, together with the team we have assembled, position us well to generate best-in-class ADCs with the potential to
transform the lives of cancer patients.

Strategy

Our  goal  is  to  become  a  leading  oncology  company  by  leveraging  the  potential  of  our  innovative  and  differentiated  ADC
technologies and the experience and competencies of our management team to discover and develop promising ADC product
candidates  and  to  commercialize  cancer  therapeutics  that  address  unmet  medical  needs  or  provide  significant  benefit  to
patients. Key components of our strategy to achieve this goal are as follows:

·

·

·

·

·

Rapidly  advance  XMT‑1536.    Our  lead  product  candidate,  XMT-1536,  is  a  first-in-class  Dolaflexin  ADC  in  a
Phase  1  proof-of-concept  clinical  trial  in  patients  with  tumors  likely  to  express  NaPi2b,  an  antigen  broadly
expressed  in  ovarian  cancer  and  non-small  cell  lung  cancer,  or  NSCLC,  adenocarcinoma.  We  expect  to  report
multiple data disclosures in 2020 as we advance our proof-of-concept studies and prepare to initiate registrational
enabling studies.

Rapidly  Advance  XMT-1592.    Mersana’s  second  product  candidate  targeting  NaPi2b-expressing  tumors,  XMT-
1592, is an ADC created using our Dolasynthen platform. We expect to file an Investigational New Drug, or IND,
application  and  initiate  a  Phase  1  dose  escalation  study  of  XMT-1592  in  patients  with  tumors  likely  to  express
NaPi2b in the first half of 2020. We believe that we have a path to advance XMT-1592 through rapid dose escalation
and clinical validation.   

Expand  our  ADC  pipeline.    We  intend  to  establish  a  leading  position  in  the  field  of  ADCs  by  continuing  to
advance platform innovations that further broaden the potential of our ADCs to deliver clinically meaningful benefit
for cancer patients, by focusing on first-in-class targets and payloads, and by pursuing fast-to-market opportunities.
We  are  advancing  a  new,  potentially  first-in-class  ADC  targeting  B7-H4  which  leverages  our  DolaLock  payload
towards  IND-enabling  studies.  We  have  taken  ADCs  beyond  cytotoxics  by  developing  the  Immunosynthen
platform, an approach that may allow activation of the innate immune system in a targeted way. 

Attract  and  retain  talented  and  experienced  people.    In  addition  to  our  team’s  deep  experience  with  ADC
science, drug development and operational management, we believe that our accomplishments are a testament to the
talent  and  commitment  of  our  people.  Our  team  is  driven  by  a  shared  passion  to  advance  therapies  that  make  a
significant difference in the lives of cancer patients. We will continue to cultivate the collaborative and passionate
workplace culture that has allowed us to advance this mission.

Build strategic partnerships to maximize the value of our programs and platforms.  Our platform technologies,
and  product  discovery  and  development  capabilities,  drive  the  potential  for  multiple  clinically  meaningful
opportunities for cancer patients. In order to preserve a disciplined drug development and commercialization focus,
we may choose to enter into strategic partnerships that facilitate our ability to bring

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differentiated  product  candidates  to  more  patients.  Our  current  partnerships  with  Merck  KGaA  and  Asana
Biosciences exemplify different aspects of this strategy.

Our current pipeline is summarized in the chart below:

ADC Background

Traditional ADCs are a class of cancer biotherapeutics that combine the targeting capabilities of monoclonal antibodies with
the cancer-killing ability of cytotoxic drug payloads. Antibodies and payloads are chemically linked, allowing specific drug
delivery to cancer cells targeted by the antibody. After ADCs enter a cell, the conjugated payload is released and kills the
cell.  Despite  the  promise  of  ADCs,  companies  in  the  field  have  faced  certain  challenges  in  developing  product  candidates
that  achieve  the  optimal  therapeutic  index,  or  the  balance  between  efficacy  and  tolerability.  These  challenges  are
characterized as follows:

·

·

·

·

Linker  stability:    Linkers  must  be  stable  in  the  bloodstream  to  ensure  that  free  payload  is  not  released  into
circulation  prior  to  delivery  into  the  tumor.  Free  payload  in  circulation  causes  toxicity.  Efforts  to  design  better
linkers to increase stability have, in turn, reduced the efficiency of payload release once the ADC is internalized in
the tumor cell, resulting in decreased efficacy.

Drug‑to‑antibody ratio:  Increasing the number of payload molecules delivered per antibody internalization event
increases potency. However, the drug-to-antibody ratio, or DAR, has typically been limited to three to four payload
molecules per antibody due to aggregation, poor pharmacokinetics and loss of drug‑like properties of the ADC at
levels  above  this  threshold.  Other  attempts  to  increase  efficacy  have  involved  the  introduction  of  ultra‑potent
payloads, however these efforts appear to face safety and tolerability challenges, necessitating even further reduced
DAR to maintain acceptable pharmacokinetics and drug‑like properties.

Target  antigen  expression  level:    Tumor  cells  typically  require  a  threshold  number  of  payload  molecules  to  be
internalized in order to kill the cell. Antigens with lower levels of expression have proven less desirable as targets
for ADCs, as a result of fewer binding, internalization and payload delivery events to drive cell‑killing activity. In
turn, this has limited the number of cancers amenable to treatment with low-DAR ADC approaches, as the use of
ADCs requires antigen targets to be highly expressed on tumor cells.

Bystander effect:  Once ADCs release their cytotoxic payload into targeted cells, the drug is often able to cross cell
membranes, entering and potentially killing neighboring cells whether those cells are cancerous or not. This

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is  known  as  the  ‘bystander  effect,’  which  is  advantageous  when  bystander  cells  are  cancerous,  but  toxic  if  the
cytotoxic  drug  is  able  to  enter  adjacent  healthy  cells,  leading  to  dose-limiting  toxicities  such  as  neutropenia,
peripheral neuropathy, or ocular toxicity.

Our Technologies and Platforms

The development of ADCs is not a one-size-fits-all approach. In fact, a number of diverse factors impact the properties of an
ADC,  including  payload,  drug-to-antibody  ratio,  site  of  conjugation  and  homogeneity.  For  each  target  antigen,  there  is  an
optimal  combination  of  these  factors.  Our  novel  and  highly  differentiated  platforms  are  designed  to  allow  us  to  optimize
these properties for a given target and develop ADCs that best address patient needs.

DolaLock Payload

Our DolaLock payload is a proprietary auristatin cytotoxic drug and is a highly potent anti-tubulin agent selectively toxic to
rapidly dividing cells. The DolaLock payload has been shown in preclinical studies to control the bystander effect by locking
the cytotoxic drug inside cells after allowing a short period of diffusion throughout the tumor. As the drug diffuses through
neighboring tissue, the DolaLock payload is metabolized to a form that is still highly potent but is no longer able to cross the
cell membrane, effectively locking the drug inside cells and controlling the bystander effect for a safer and more effective
cancer therapy.

A  common  mechanism  of  resistance  in  cancer  is  the  up-regulation  of  multi-drug  resistance,  or  MDR,  pumps,  such  as  P-
glycoproteins, or PgPs, which actively pump drugs out of cancer cells to help them survive. Once metabolized, our DolaLock
payload cannot be pumped out by PgPs, thereby avoiding this resistance mechanism. In addition, our proprietary auristatin
payload  has  also  been  shown  in  preclinical  studies  to  cause  immunogenic  cell  death  and  to  stimulate  the  immune  system
through dendritic cell activation. Because of this, synergy with immuno-oncology agents such as PD-1 inhibitors has been
observed  in  preclinical  models.  Our  DolaLock  payload  with  controlled  bystander  effect  is  designed  to  allow  us  to  create
ADCs that produce a highly potent, well-tolerated and specifically-targeted cancer therapy.

Figure 1. DolaLock Payload with Controlled Bystander Effect

Dolaflexin Platform

The  Dolaflexin  platform  was  designed  to  increase  the  efficacy,  safety  and  tolerability  of  ADCs.  Dolaflexin  utilizes  our
proprietary  Fleximer  polymer,  a  biodegradable,  highly  biocompatible,  water-soluble  polymer  able  to  carry  multiple  drug
molecules.  Instead  of  direct  conjugation  to  an  antibody,  drug  molecules  are  attached  through  a  cleavable  linker  to  the
Fleximer  scaffold,  which  is  then  conjugated  to  the  antibody  through  a  non-cleavable  linker.  Fleximer  has  demonstrated
dramatically improved drug solubility, pharmacokinetics and immunogenicity, and an increased number of drug molecules
carried by each ADC compared with traditional ADC therapies.

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As a result, we believe Dolaflexin has the potential to offer the following benefits relative to traditional ADCs:

·

Proprietary DolaLock Payload: Dolaflexin is loaded with our proprietary auristatin chemotherapeutic drug, which
is a highly potent anti-tubulin agent selectively toxic to rapidly dividing cells, with the advantages of the DolaLock
controlled bystander effect.

· Higher Drug-to-Antibody Ratio: Historically, ADCs have been limited to a DAR of 3-4. The Dolaflexin platform
can deliver ADCs with DAR between 10-12, allowing for greater efficacy while also maintaining pharmacokinetics
and drug-like properties.

·

Expanded  Range  of  Addressable  Tumor  Targets:  The  higher  DAR  enabled  by  Dolaflexin  results  in  more
chemotherapeutic drug released into the tumor cell for every ADC internalized. As a result, Dolaflexin ADCs can
have efficacy against tumor targets with lower levels of antigen expression where traditional ADCs have not been
effective.

We  believe  these  advantageous  characteristics  of  our  Dolaflexin  platform  provide  a  substantial  opportunity  to  develop
clinically  meaningful  ADC  therapies  with  potential  to  address  a  broader  range  of  cancers  than  traditional  ADC-based
approaches. Our lead clinical candidate, XMT-1536, is a Dolaflexin ADC that targets NaPi2b. XMT-1536 is currently in a
proof-of-concept study in patients with ovarian cancer and NSCLC adenocarcinoma.

Dolasynthen Platform

The  Dolasynthen  platform  enables  an  iterative  approach  to  develop  the  right  ADC  for  a  given  indication  through
customization and optimization. Dolasynthen utilizes a synthetic scaffold for precise control of DAR, from 2-24, and site-
specific antibody bioconjugation. The platform is also able to homogeneously generate ADCs with precisely defined DARs
for consistent drug delivery to cancer cells. The Dolasynthen scaffold has been precisely designed to provide optimal water
solubility,  charge  balance,  linker  stability  and  DAR.  We  believe  that  Dolasynthen  retains  the  favorable  properties  of
Dolaflexin, including our proprietary DolaLock technology for a controlled bystander effect, with superior physicochemical
and pharmacokinetic properties.

Illustrated by our preclinical data, optimized Dolasynthen ADCs exhibit a broad therapeutic index as a cancer therapy. These
data  demonstrate  the  ability  of  the  Dolasynthen  platform  to  generate  and  identify  the  optimal  ADC  for  a  given  target  and
antibody.

We  believe  that  Dolasynthen  offers  the  benefits  of  Dolaflexin,  including  the  proprietary  DolaLock  payload,  and  has  the
potential to offer the following benefits relative to traditional ADCs:

·

·

Precise Control of DAR: The optimal DAR may vary between different targets and antigens. Dolasynthen allows
for precise DARs between 2-24, enabling optimization of the DAR for specific antigens and antibodies.

Site-Specific Bioconjugation: The site of scaffold bioconjugation to an antibody impacts the overall properties of
that ADC. Dolasynthen enables site-specific bioconjugation allowing further ADC optimization.

· Homogenous  ADC  Development:  The  DAR  and  antibody  bioconjugation  is  consistent  throughout  ADCs

developed with the Dolasynthen platform allowing for consistent and precise drug delivery to targeted cancer cells.

·

Increased Hydrophilicity:  The  precise  optimization  of  the  hydrophilic  moiety  on  Dolasynthen  ADCs  allows  for
increased aqueous solubility and enhanced pharmacokinetic properties.

We have selected XMT-1592, an ADC created using the Dolasynthen platform, as our next clinical candidate.

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Immunosynthen Platform

Immunosynthen  is  our  proprietary  immunostimulatory  ADC  platform  that  is  designed  to  take  ADCs  beyond  delivery  of
traditional  cytotoxic  drugs  to  immunomodulatory  molecules  that  can  stimulate  an  anti-tumor  innate  immune  response  in  a
targeted manner. Through the efficient delivery of immunomodulatory molecules, Immunosynthen ADCs have the potential
to address the challenges of systemic delivery and tolerability. The Immunosynthen platform utilizes a novel STING agonist,
which  has  emerged  as  an  innate  immune  pathway  capable  of  inducing  anti-tumor  immune  activity.  Preclinical  data
demonstrate that our STING agonist ADCs result in a greater than 100-fold increase in in vitro activity compared to a free
agonist. In addition, treatment with our STING agonist ADCs resulted in complete regression of tumors in vivo after a single,
well-tolerated  dose  in  a  variety  of  preclinical  tumor  models.  Increased  immune  cell  infiltration  and  cytokine  expression
within the tumor after dosing was also observed after treatment, consistent with the activation of STING. During preclinical
studies, Immunosynthen ADCs achieved extended plasma exposure yet limited induction of systemic cytokines. 

Immunosynthen ADCs are suited to potentially overcome the limitations of free STING agonists due to the following:

·

·

·

Systemic  Administration  with  Targeted  Delivery:  Immunosynthen  ADCs  have  the  convenience  of  systemic
administration while providing targeted delivery specifically to the tumor, including metastatic lesions.

Improved Therapeutic Index: Conjugation of the STING agonist provides protection in the systemic circulation to
minimize off-target effects while simultaneously providing targeted delivery to maximize effects in the tumor and
metastatic lesions.

Enhanced  Pharmacokinetic  Properties:  The  prolonged  pharmacokinetics  of  ADCs  and  active  uptake  through
targeting can overcome pharmacokinetic and permeability issues of the free agonists, resulting in sustained delivery
and activation of the innate immune response.

Our product candidates

We are leveraging our platforms to develop a robust pipeline of clinically meaningful cancer therapies. Our pipeline strategy
focuses on targets that have been biologically validated (either as ADCs or through another modality), where the advantages
of  our  platforms  may  lead  to  clinically  superior  therapeutic  benefits,  where  we  have  the  potential  to  achieve  first-in-class
status,  and  where  fast-to-market  opportunities  are  available.  Our  lead  product  candidate,  XMT-1536,  is  in  Phase  1  dose
escalation  and  proof-of-concept  expansion  studies  in  ovarian  cancer  and  NSCLC  adenocarcinoma.  Our  next  product
candidate, XMT-1592, is expected to initiate a Phase 1 dose escalation study in the first half of 2020.  We are also advancing
a  potentially  first-in-class  DolaLock  ADC  targeting  B7-H4  towards  IND-enabling  studies  and  are  progressing  towards
nomination of an Immunosynthen development candidate.  In addition, our partners have multiple ADC product candidates
leveraging our technology in development.

XMT‑1536: our NaPi2b‑targeted Dolaflexin ADC

XMT-1536, a first-in-class ADC targeting the sodium-dependent phosphate transport protein NaPi2b, utilizes the Dolaflexin
platform to deliver an average of 10-12 DolaLock payload molecules per antibody. The NaPi2b antigen is broadly expressed
in  NSCLC  adenocarcinoma  and  ovarian  cancer  with  limited  expression  in  normal  tissue.  We  are  actively  recruiting  and
dosing patients with ovarian cancer and NSCLC adenocarcinoma, where a majority of patients express NaPi2b, in a Phase 1
clinical trial.

In June 2019, we presented interim data from the ongoing XMT-1536 Phase 1 dose escalation study at the Annual Meeting of
the  American  Society  of  Clinical  Oncology,  or  the  ASCO  Meeting,  showing  encouraging  clinical  activity  with  confirmed
responses  and  prolonged  stable  disease  in  heavily  pretreated  patients,  without  pre-selection  for  NaPi2b  expression.  The
interim data showed that XMT-1536 was well-tolerated without the severe toxicities commonly seen with other ADCs such
as  neutropenia,  ocular  toxicities  or  peripheral  neuropathy.  Since  the  ASCO  Meeting,  we  have  made  further  progress  in
demonstrating both safety and activity at higher doses. Specifically, XMT-1536 has been well tolerated by patients at both the
36 mg/m  once-every-four-week and 43 mg/m  once-every-four-week dosing regimens initiated

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during the Phase 1 dose escalation study. The doses have been well-tolerated with primarily Grade 1 and Grade 2 treatment-
related  adverse  events  without  the  severe  toxicities  seen  with  other  ADCs,  such  as  neutropenia,  neuropathy,  or  ocular
toxicities. To date, a maximum tolerated dose, or MTD, has not been determined, and we have initiated evaluation of a 52
mg/m  once-every-four-week dose escalation cohort. 

2

Since  the  ASCO  Meeting,  we  have  also  expanded  in  more  homogenous,  earlier  line  patient  populations,  and  we  are
developing a patient selection strategy. Specifically, and in parallel with dose escalation, we have initiated proof-of-concept
expansion  cohorts  in  more  homogeneous  earlier  line  patient  populations  in  ovarian  cancer  and  NSCLC  adenocarcinoma.
Expansion cohorts were initiated at 36 mg/m  once-every-four-week dose regimens, and the dose regimen has been increased
to  43  mg/m   once-every-four-week  for  newly-dosed  patients.  We  have  also  developed  a  proprietary  biomarker  assay  for
patient selection and entered into a collaboration with a partner with expertise in the development of companion diagnostics.

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XMT-1592: our NaPi2b targeted Dolasynthen ADC

We have selected our next clinical product candidate, XMT-1592. XMT-1592 was created using our Dolasynthen platform
and  also  targets  NaPi2b.    XMT-1592  comprises  the  same  proprietary  NaPi2b  antibody  and  potent  auristatin  DolaLock
payload  with  controlled  bystander  effect  as  XMT-1536,  with  the  additional  features  of  homogeneous,  site-specific
bioconjugation  and  precise  DAR.  Preclinically,  XMT-1592  has  shown  a  differentiated  profile  particularly  in  NSCLC
adenocarcinoma,  where  it  was  four  times  more  efficacious  than  XMT-1536,  consistent  with  higher  tumor  penetration,  as
described in below in Figure 2. Based on these preclinical data, we believe that XMT-1592 has the potential to provide us
with  a  second  opportunity  to  treat  NSCLC  adenocarcinoma  patients.  We  plan  to  evaluate  the  clinical  differentiation  of
Dolasynthen by leveraging our experience in NaPi2b to rapidly progress XMT-1592 through dose escalation.  

Figure 2. XMT-1592 Shows Four-Fold Greater Efficacy in Lung Tumor Model

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Our B7-H4 targeted ADC candidate

Our  early  stage  programs  include  a  potentially  first-in-class  B7-H4-targeted  DolaLock  ADC  candidate  addressing  areas  of
high unmet medical need. The expression profile of B7-H4 is well suited for our unique DolaLock payload. B7-H4 can be
expressed  in  two  places:  on  tumor  cells  and  on  immunosuppressive  tumor  associated  macrophages,  or  TAMs,  which  may
lead  to  additional  processing  of  the  ADC  and  more  payload  in  the  tumor  environment.    DolaLock’s  dual  mechanisms  of
action  with  a  direct  cytotoxic  effect  as  well  as  an  immunostimulatory  effect  through  dendritic  cell  activation  and
immunogenic  cell  death  are  well  suited  to  the  biology  of  the  B7-H4  target.  We  have  favorable  efficacy  and  non-human
primate tolerability data with both Dolaflexin and Dolasynthen ADCs targeting B7-H4. Our objective is to rapidly progress
through  IND-enabling  studies  and  scale  up  manufacturing  activities  with  third  parties.  B7-H4  provides  significant
opportunities for development in areas of high unmet need such as breast cancer, NSCLC and ovarian cancer. We anticipate
potential fast-to-market clinical development opportunities because expressions of B7-H4 and PD-L1 are mutually exclusive,
creating an opportunity for high unmet need tumors where patients are ineligible for immune checkpoint inhibitors.  

Ovarian cancer unmet need and epidemiology

Worldwide, ovarian cancer had incidence of approximately 295,000 and caused an estimated 185,000 deaths in 2018.  With a
U.S.  incidence  of  approximately  25,000  new  cases  and  mortality  of  14,000  in  2018,  ovarian  cancer  was  the  second  most
common  gynecologic  malignancy  and  the  most  common  cause  of  gynecologic  cancer  death  in  the  United  States.  The
majority  of  ovarian  malignancies  (approximately  90%)  are  derived  from  epithelial  cells.  Diagnosis  is  made  histologically,
and  evaluation  is  commonly  performed  following  surgical  removal  of  an  ovary  or  fallopian  tube  or  biopsies  of  the
peritoneum.  The  ovarian  cancer  standard  of  care  is  characterized  by  initial  surgery  followed  by  platinum-containing
chemotherapy  followed  by  periods  of  either  observation  or  maintenance.  Nearly  85%  of  ovarian  cancer  patients  typically
relapse following initial treatment.  Subsequent treatment depends on the depth and duration of response to initial platinum
treatment. Ovarian cancer patients who progress within six months of completion of platinum-based therapy are considered
to have platinum-resistant disease. Unmet medical need is significant for patients with platinum-resistant ovarian cancer as
treatment options are mainly limited to single agent chemotherapies such as pegylated liposomal doxorubicin, topotecan and
paclitaxel.  Multiple  Phase  3  studies  of  single  agent  chemotherapies  in  patients  with  platinum-resistant  disease  and  one  to
three prior therapies have exhibited an overall response rate of 4-12% and median progression-free survival of 3-4 months. 

With  targeted  agents  approved  in  platinum-resistant  disease  increasingly  being  prescribed  in  earlier  lines  of  therapy,  the
unmet need is expected to remain severe. Bevacizumab in combination with chemotherapy is indicated to treat a subset of
platinum-resistant ovarian cancer patients with no more than two prior therapies but it is not always well-tolerated and has
shown  no  overall  survival  benefit.  Use  of  bevacizumab  in  combination  with  platinum-containing  chemotherapy  in  the
frontline and platinum-sensitive recurrent settings mean an increasing number of platinum-resistant patients are pre-treated
with bevacizumab and are not candidates for additional bevacizumab combination treatment. More recently, PARP inhibitors
have  been  approved  for  heavily-pretreated  ovarian  cancer  including  platinum-resistant  disease.  However,  they  are
predominantly used in a subset of patients with cancers harboring BRCA1 and BRCA2 mutations. Similarly, use of PARP
inhibitors  in  earlier  lines  of  recurrent  platinum-sensitive  maintenance  and  more  recently  frontline  maintenance  therapy
following  platinum-based  chemotherapy  means  an  increasing  number  of  platinum-resistant  patients  are  pre-treated  with
PARP inhibitors and are not candidates for additional PARP therapy.

NSCLC unmet need and epidemiology

Worldwide, lung cancer had an incidence of approximately 2.1 million and caused an estimated 1.7 million deaths in 2018.
With  a  U.S.  incidence  of  approximately  230,000  new  cases  and  over  150,000  deaths  in  2018,  lung  cancer  was  the  most
deadly form of cancer in the United States. The five year survival rate is less than 20% on average.  Approximately 95% of
all lung cancers are classified as either small cell lung cancer or NSCLC.  NSCLC can be further divided into squamous or
non-squamous. The majority of non-squamous NSCLC is classified as adenocarcinoma. These histological distinctions are
important for proper staging, treatment and prognosis. For patients with NSCLC, initial treatment is largely determined by
the stage of disease. Surgical resection offers the best opportunity for long-term survival and cure in patients with resectable
early-stage NSCLC. Locally-advanced NSCLC is treated by combinations of radiotherapy, immunotherapy,

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chemotherapy  and  surgery.  The  majority  of  patients  present  with  inoperable  disease.    Metastatic  NSCLC  is  managed  with
systemic chemotherapy and immunotherapy. 

The standard of care is evolving for NSCLC with the introduction of immunotherapies for patients without oncogenic driver
mutations and new targeted therapies for patients with EGFR, ALK, ROS-1, NTRK or BRAF mutations. For patients with
metastatic  disease  without  oncogenic  driver  mutations,  frontline  platinum-based  chemotherapy  is  being  combined  with,  or
depending on PD-L1 expression status, replaced by immunotherapy using anti-PD-1 or anti-PD-L1 monoclonal antibodies.
For  patients  with  metastatic  disease  harboring  oncogenic  driver  mutations,  several  generations  of  targeted  agents  are
available  with  different  resistance  profiles.  Frontline  therapy  is  often  followed  by  relapse  and  recurrence  and  treatment
options  for  these  patients  are  substantially  more  limited.  The  standard  of  care  of  docetaxel  alone  or  in  combination  with
targeted agents has an overall response rate of 14-23%, median progression-free survival of 3-4 months and median overall
survival of 9-12 months.

With PD-1 and PD-L1 inhibitors and next generation targeted therapies moving into frontline, the unmet need in recurrent
lung cancer is expected to remain severe.

NaPi2b Background

NaPi2b  is  a  member  of  the  SLC34  family  of  sodium-dependent  transporters  and  plays  an  important  role  in  maintaining
phosphate homeostasis.  NaPi2b is expressed in a high proportion of ovarian cancer and NSCLC adenocarcinoma.  There are
currently no FDA‑approved tests to measure NaPi2b expression on tumor cells. Given the prevalence of its expression on
epithelial  ovarian  and  NSCLC  adenocarcinoma  tumors,  however,  our  initial  clinical  studies  of  XMT‑1536  are  being
conducted  without  prospective  identification  of  patients  with  NaPi2b‑expressing  tumors.  Nonetheless,  we  have  developed
and  technically  validated  an  immunohistochemistry  assay  to  measure  NaPi2b  expression  which  we  intend  to  use
retrospectively to confirm the broad prevalence of NaPi2b expression in our target patient populations while correlating those
expression levels with the efficacy observed in such patients. We are currently collaborating with a third party to create and
obtain regulatory approval for our assay as a companion diagnostic. 

Strategic partnerships

Strategic partnerships with leading biopharmaceutical companies to advance Fleximer ADC product candidates

We believe that our ADC platforms have broad applicability across a number of targets. We have used strategic partnering to
accelerate bringing Fleximer ADCs to patients. Fleximer is our proprietary, biodegradable, highly biocompatible and water-
soluble polymer that is able to carry multiple drug molecules, and it is a key component of our Dolaflexin platform. Since
2012, we have entered into strategic research and development partnerships with Merck KGaA and Asana BioSciences, LLC
(by  assignment  from  Endo  Pharmaceuticals  Inc.)  to  enable  development  of  certain  ADC  product  candidates  utilizing
Fleximer.  In  establishing  each  of  these  partnerships,  our  primary  objectives  were  to  collaborate  with  leading
biopharmaceutical  companies  to  validate  the  potential  of  ADC  product  candidates  utilizing  Fleximer,  gain  meaningful
near‑term  funding  and  drive  significant  long‑term  value.  Under  each  of  our  partnerships,  we  own  the  rights  to  any
improvements to our ADC platform. The details of our material existing strategic partnerships are as follows:

Merck KGaA strategic research and development partnership

In June 2014, we entered into a collaboration agreement with Merck KGaA for the development and commercialization of
ADC product candidates utilizing Fleximer for up to six target antigens. We formed a strategic partnership with Merck KGaA
because  of  their  expertise  in  oncology  drug  development.  Under  this  agreement,  we  are  responsible  for  generating  ADC
product  candidates  against  Merck  KGaA‑selected  target  antigens.  Merck  KGaA  received  rights  to  select  up  to  six  target
antigens, of which it has selected all six. Merck KGaA is responsible for generating antibodies against the target antigens,
and we are responsible for generating Fleximer and our proprietary payloads and conjugating this to such antibodies to create
the  ADC  product  candidates.  With  respect  to  each  target  antigen  selected  by  Merck  KGaA,  we  granted  Merck  KGaA  an
exclusive, worldwide license under certain of our Fleximer ADC‑related patents and know‑how to develop, manufacture and
commercialize  ADC  product  candidates  directed  to  such  target  antigen.  Merck  KGaA  is  then  responsible  for  the  further
development and commercialization of these ADC product candidates. In addition, if Merck

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KGaA advances candidates, we are responsible for manufacturing these ADC product candidates for GLP toxicology studies
and Phase 1 clinical studies at Merck KGaA’s expense and Merck KGaA is responsible for all further manufacture of these
ADC  product  candidates.  Merck  KGaA  is  required  to  pay  its  own  costs  in  the  development,  commercialization  and
manufacture of these ADC product candidates and to reimburse us for our costs incurred in performing our research activities
under this agreement. The most advanced product candidates in this partnership are in the lead optimization stage.

Through  December  31,  2019,  we  have  received  an  upfront  payment  of  $12  million  and  milestone  payments  of  $3  million
under  this  agreement.  If  products  are  successfully  developed  and  commercialized  against  all  six  target  antigens,  we  are
entitled  to  receive  future  development,  regulatory  and  commercial  milestones  of  up  to  $777  million.  We  are  entitled  to
receive tiered royalties in the low‑ to mid‑single digit percentages on net sales of products targeting Merck KGaA’s target
antigens  during  the  applicable  royalty  term  if  products  are  successfully  developed  and  commercialized  by  Merck  KGaA
under this agreement.

Unless  earlier  terminated,  this  agreement  will  expire  upon  the  expiration  of  the  last  royalty  term  for  a  product  under  the
agreement  in  all  countries  or,  if  Merck  KGaA  does  not  designate  any  ADC  product  candidates  produced  by  us  under  the
agreement  as  preclinical  development  candidates,  upon  the  expiration  of  the  last‑to‑expire  research  program.  The  royalty
term means, on a product‑by‑product and country‑by‑country basis, the period commencing upon the first commercial sale
of a product and ending upon the later to occur of: (i) the expiration of the last Mersana patent right that covers or claims the
exploitation of such product in such country, or (ii) 10 years from the date of first commercial sale of such product in such
country. Upon the expiration of each royalty term for each product on a country‑by‑country basis, Merck KGaA’s exclusive
license will convert to a perpetual, non‑exclusive, royalty‑free license with respect to such product in such country. Merck
KGaA may terminate this agreement in its entirety or with respect to any target antigen for convenience upon 60 days’ prior
written notice. Each party may terminate this agreement in its entirety upon an uncured material breach of the agreement by
the other party.

Asana Biosciences collaboration agreement

In  March  2012,  we  entered  to  a  collaboration  agreement  with  Asana  Biosciences,  or  Asana,  formerly  part  of  Endo
Pharmaceuticals,  to  develop  next-generation  ADCs.  Under  this  agreement,  Asana  paid  us  an  upfront  fee  for  the  right  to
utilize  our  Fleximer  technology  to  develop  novel  ADC  candidates  against  a  single  cancer  target.  We  are  responsible  for
conducting research and creating ADCs that are conjugates of our diverse, highly potent cytotoxic payloads, our Fleximer
polymer and custom linkers, and Asana’s novel antibodies. In addition to providing novel antibodies, Asana is responsible for
product development, manufacturing and commercialization of any Fleximer ADC products. Through December 31, 2019,
we have received an upfront payment of $0.8 million and milestone payments of $3.3 million under this agreement.

Strategic partnerships to access antibodies to progress our proprietary pipeline

Our focus is to progress our proprietary pipeline of ADCs. For this reason, we have partnered with biotechnology companies
that have the capability to generate high quality antibodies or that have existing antibodies that we can license for inclusion in
our ADCs. These strategic partnerships have facilitated the acceleration of our proprietary pipeline.

Recepta license for the NaPi2b antibody

In July 2015, we entered into a license agreement with Recepta Biopharma S.A., or Recepta, a Brazilian biopharmaceutical
company,  licensing  Recepta’s  NaPi2b  antibody  for  use  in  XMT‑1536  and  XMT-1592  and  granting  Recepta  the  exclusive
right to commercialize XMT‑1536 and XMT-1592 in Brazil. Under this agreement, Recepta granted us an exclusive license
and  sub‑license  with  respect  to  certain  patents  licensed  by  Recepta  from  Ludwig  Institute  for  Cancer  Research  and
technology owned by Recepta to develop and exploit products containing Recepta’s NaPi2b antibody, including XMT‑1536
and XMT-1592, worldwide for the diagnosis, prophylaxis and treatment of human cancer. We granted Recepta an exclusive
license  under  our  rights  in  such  patents  and  technology  and  certain  of  our  ADC‑related  patents  and  technology  to
commercialize any such products developed by us, including XMT‑1536 and XMT-1592, in Brazil. We are responsible for
the  worldwide  development  and  commercialization  of  products  under  this  agreement  at  our  own  expense  in  certain  major
markets, including at least one study site in our Phase 3 clinical studies in Brazil. Recepta may conduct development

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activities in Brazil at its own expense after providing us the opportunity to first conduct such activities at Recepta’s expense.
If a product is successfully developed and commercialized by Recepta in Brazil, we will use diligent efforts to enter into an
agreement for the supply of such products to Recepta for sale in Brazil.

Under this agreement, we paid Recepta an upfront payment of $1 million during the year ended December 31, 2015 and are
obligated to pay Recepta up to $65.5 million in development, regulatory and commercial milestones and tiered royalties in
the low‑single digit percentages on net sales of products outside of Brazil until the expiration of the royalty term if products
are  successfully  developed  and  commercialized.  Through  December  31,  2019,  we  have  paid  $1.9  million  in  milestone
payments. We are entitled to receive tiered royalties in the low‑ to mid‑single digit percentages on net sales of products in
Brazil until the expiration of the royalty term if products are successfully developed and commercialized. The royalty term
means, on a product‑by‑product and country‑by‑country basis, the period ending upon the later of (i) with respect to products
commercialized  by  Mersana,  the  expiration  of  the  last‑to‑expire  Recepta  patent  that  covers  the  product  in  such  country
(including  the  term  of  any  applicable  supplementary  protection  certificate)  or  with  respect  to  products  commercialized  by
Recepta,  the  expiration  of  the  last‑to‑expire  Mersana  Patent  that  covers  the  product  in  Brazil  (including  the  term  of  any
applicable supplementary protection certificate) or (ii) 10 years from the date of first commercial sale of such product in such
country. Upon the expiration of each royalty term in each country for each applicable product, the exclusive licenses granted
to  each  party  under  the  agreement  will  become  fully‑paid  up  and  royalty‑free.  This  agreement  will  remain  in  effect  until
otherwise  terminated  as  set  forth  below.  We  may  terminate  this  agreement  for  convenience  in  its  entirety  or  on  a
country‑by‑country basis (except with respect to Brazil) or product‑by‑product basis upon 180 days’ prior written notice for
a  termination  in  its  entirety  or  upon  45  days’  prior  written  notice  for  a  termination  in  part.  Each  party  may  terminate  this
agreement in its entirety upon bankruptcy or similar proceedings of the other party, upon a patent challenge by the other party
or upon an uncured material breach of the agreement by the other party. However, if such breach only relates to one country,
the agreement may only be terminated with respect to such country.

Manufacturing

We  do  not  own  or  operate  and  currently  have  no  plans  to  establish  any  cGMP  compliant  manufacturing  facilities.  We
currently  rely,  and  expect  to  continue  to  rely,  on  external  Contract  Manufacturing  Organizations,  or  CMOs,  for  the
manufacture of product to support clinical study. In the future, we expect to use CMOs to manufacture commercial supply of
our products. The Dolaflexin manufacturing process involves readily available starting materials and uses unit operations that
are  well‑precedented  in  the  field  of  chemical/pharmaceutical  production.  The  current  XMT-1536  supply  chain  utilizes  the
same vendors the company could use for commercialization.

Government regulation

Government  authorities  in  the  United  States,  at  the  federal,  state  and  local  level,  and  in  other  countries  and  jurisdictions,
including the European Union, extensively regulate, among other things, the research, development, clinical and preclinical
studies, manufacture, packaging, storage, recordkeeping, labeling, advertising, promotion, distribution, marketing and import
and export of pharmaceutical products. The processes for obtaining regulatory approvals in the United States and in foreign
countries and jurisdictions, along with subsequent compliance with applicable statutes and regulations and other regulatory
authorities,  require  the  expenditure  of  substantial  time  and  financial  resources.  Failure  to  comply  with  the  applicable
requirements  at  any  time  during  the  product  development  process,  approval  process  or  after  approval  may  subject  an
applicant and/or sponsor to a variety of administrative or judicial sanctions, including imposition of a clinical hold, refusal to
approve marketing applications, withdrawal of an approval, import/export delays, issuance of warning letters and other types
of enforcement letters, product recalls, product seizures, total or partial suspension of production or distribution, injunctions,
fines, refusals of government contracts, restitution, disgorgement of profits or civil or criminal investigations and penalties.

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Review and approval in the United States

In  the  United  States,  our  ADC  product  candidates  are  subject  to  regulation  by  the  FDA  as  biologics.  The  FDA  regulates
biologics  under  the  Federal  Food,  Drug,  and  Cosmetic  Act,  or  FDCA,  the  Public  Health  Service  Act,  or  PHS  Act,  and
associated  implementing  regulations.  The  failure  to  comply  with  the  FDCA,  the  PHS  Act  and  other  applicable  U.S.
requirements  at  any  time  during  the  product  development  process,  approval  process  or  after  approval  may  subject  an
applicant and/or sponsor to a variety of administrative or judicial sanctions, including refusal by the FDA to approve pending
applications,  withdrawal  of  an  approval,  imposition  of  a  clinical  hold,  issuance  of  warning  letters  and  other  types  of
enforcement‑related  letters,  product  recalls,  product  seizures,  total  or  partial  suspension  of  production  or  distribution,
injunctions, fines, refusals of government contracts, restitution, disgorgement of profits or civil or criminal investigations and
penalties brought by the FDA and the Department of Justice, or DOJ, or other governmental entities.

The steps before a biological product may be approved for marketing in the United States generally include:

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completion of preclinical laboratory tests, animal studies and formulation studies in compliance with the FDA’s GLP
regulations;

the  submission  to  the  FDA  of  an  Investigational  New  Drug,  or  IND  application  which  must  take  effect  before
human clinical studies may begin in the United States;

approval by an independent Institutional Review Board, or IRB representing each clinical site before each clinical
study may be initiated;

performance  of  adequate  and  well‑controlled  clinical  studies  to  establish  the  safety  and  efficacy  of  the  proposed
product for each indication, conducted in accordance with GCP;

preparation and submission to the FDA of a Biologics License Application, or BLA;

FDA acceptance, review and approval of the BLA, which might include an Advisory Committee review;

satisfactory  completion  of  one  or  more  FDA  inspections  of  the  manufacturing  facility  or  facilities  at  which  the
product, or components thereof, are produced to assess compliance with cGMP requirements and to assure that the
facilities, methods and controls are adequate to preserve the product’s identity, strength, quality and purity;

satisfactory completion of any FDA audits of clinical study sites to assure compliance with GCPs and the integrity
of the clinical data;

payment of user fees, if any, for FDA review of the BLA; and

compliance with any post‑approval requirements, including a Risk Evaluation and Mitigation Strategy, or REMS,
where applicable, and post‑approval studies required by the FDA as a condition of approval.

The testing and approval process requires substantial time, effort and financial resources, and the receipt and timing of any
approval is uncertain.

Preclinical studies

Preclinical studies include laboratory evaluation of the product candidate, as well as in vitro and animal studies to assess the
potential  safety  and  efficacy  of  the  product  candidate  for  use  in  humans.  The  conduct  of  preclinical  studies  is  subject  to
federal  regulations  and  requirements,  including  GLP  regulations.  The  results  of  the  preclinical  studies,  together  with
manufacturing information, analytical data, any available clinical data or literature and plans for clinical studies, among other
things, are submitted to the FDA as part of an IND. Additional preclinical testing, such as toxicity studies, may continue after
the IND is submitted.

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Clinical studies

Clinical  studies  involve  the  administration  of  the  product  candidate  to  human  subjects  under  the  supervision  of  qualified
investigators in accordance with GCP requirements. GCP requirements include, among other things, conducting the study in
accordance with a written protocol, obtaining informed consent from study subjects and approval and ongoing review of the
study by an IRB at each site where the study will be conducted.

A  protocol  for  each  clinical  study  and  any  subsequent  protocol  amendments  must  be  submitted  to  the  FDA  as  part  of  the
IND.  An  IND  automatically  becomes  effective  30  days  after  receipt  by  the  FDA,  unless  before  that  time  the  FDA  raises
concerns or questions related to a proposed clinical study or places the study on clinical hold. In such a case, the IND sponsor
and the FDA must resolve any outstanding concerns before the clinical study can begin.

Clinical studies are typically conducted in three sequential phases prior to approval, which may overlap or be combined:

Phase 1:  The product candidate is initially introduced into healthy human subjects or, in some cases, patients with
the target disease (e.g., cancer) or condition. In Phase 1, the product candidate is typically tested for safety, dosage
tolerance,  absorption,  metabolism,  distribution,  excretion  and,  if  possible,  to  gain  an  early  indication  of  its
effectiveness and to determine optimal dosage.

Phase 2:  The product candidate is administered to a limited patient population to preliminarily evaluate the efficacy
of the product for specific targeted diseases, to identify possible adverse effects and safety risks and to determine
dosage tolerance and optimal dosage.

Phase  3:    The  product  candidate  is  administered  to  an  expanded  patient  population,  generally  at  geographically
dispersed clinical study sites, in well‑controlled clinical studies to generate enough data to statistically evaluate the
efficacy  and  safety  of  the  product  for  approval,  to  establish  the  overall  risk‑benefit  profile  of  the  product  and  to
provide adequate information for the labeling of the product.

Phase  4  clinical  studies  may  be  conducted  after  initial  marketing  approval.  These  studies  are  used  to  gain  additional
experience from the treatment of patients in the intended therapeutic indication and to document a clinical benefit in the case
of  products  approved  under  accelerated  approval  regulations  or  when  otherwise  requested  by  the  FDA  in  the  form  of
post‑market requirements or commitments.

Clinical  studies  at  each  phase  of  development  may  not  be  completed  successfully  within  any  specified  period,  or  at  all.
Furthermore,  the  FDA,  an  IRB,  the  sponsor  or  the  data  monitoring  committee,  if  applicable,  may  suspend  or  terminate  a
clinical  study  at  any  time  on  various  grounds,  including  a  finding  that  the  research  subjects  are  being  exposed  to  an
unacceptable health risk. The FDA will typically inspect one or more clinical sites to assure compliance with GCP and the
integrity of the clinical data submitted.

Submission of a marketing application to the FDA

Assuming successful completion of required clinical testing and other requirements, the results of the preclinical studies and
clinical  studies,  together  with  detailed  information  relating  to  the  product’s  chemistry,  manufacture,  controls  and  proposed
labeling, among other things, are submitted to the FDA as part of a BLA requesting approval to market the product for one or
more indications.

BLA pathway

Our ADC product candidates must be licensed via FDA approval of a BLA under Section 351 of the PHS Act on the basis of
a  demonstration  that  the  product  is  safe,  pure  and  potent.  Once  a  BLA  has  been  accepted  for  filing,  the  FDA’s  goal  is  to
review BLAs within ten months of the filing date for standard review or six months of the filing date for priority review. The
review  process  is  often  significantly  extended  by  FDA  requests  for  additional  information  or  clarification.  The  FDA  may
refer the application to an advisory committee for review, evaluation and recommendation as to whether the

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application should be approved. The FDA is not bound by the recommendation of an advisory committee, but it generally
follows such recommendations.

Before approving the BLA, the FDA will inspect the facilities at which the biological product is manufactured and will not
approve the product unless the facility is compliant with cGMPs. Additionally, the FDA will typically inspect one or more
clinical study sites for compliance with GCP and integrity of the data supporting safety and efficacy.

During the approval process, the FDA also will determine whether to require post‑approval testing, including Phase 4 clinical
studies and surveillance programs to monitor the effect of approved biologics after they are commercialized. In addition, the
FDA will determine whether the biologic will require a REMS to ensure that the benefits of the product outweigh its risks,
which  could  include  medication  guides,  physician  communication  plans  or  elements  to  assure  safe  use,  such  as  restricted
distribution methods, patient registries and other risk minimization tools.

On the basis of the FDA’s evaluation of the BLA and accompanying information, including the results of the inspection of
the manufacturing facilities, the FDA will issue either an approval of the BLA or a Complete Response Letter, detailing the
deficiencies in the submission and the additional testing or information required for reconsideration of the application. Even
with  submission  of  this  additional  information,  the  FDA  ultimately  may  decide  that  the  application  does  not  satisfy  the
regulatory criteria for approval.

If the FDA approves a product, it may limit the approved indications for use for the product, require that contraindications,
warnings  or  precautions  be  included  in  the  product  labeling,  require  that  post‑approval  studies,  including  Phase  4  clinical
studies,  be  conducted  to  further  assess  the  product’s  safety  after  approval,  require  testing  and  surveillance  programs  to
monitor the product after commercialization or impose other conditions, including a REMS, which can materially affect the
potential market and profitability of the product. The FDA may prevent or limit further marketing of a product based on the
results of post‑market studies or surveillance programs. After approval, many types of changes to the approved product, such
as adding new indications, manufacturing changes and additional labeling claims, are subject to further testing requirements
and FDA review and approval.

Fast track, breakthrough therapy and priority review designations

The FDA is authorized to designate certain products for expedited review if they are intended to address an unmet medical
need  in  the  treatment  of  a  serious  or  life‑threatening  disease  or  condition.  These  programs  are  fast  track  designation,
breakthrough therapy designation and priority review designation.

First,  the  FDA  may  designate  a  product  for  “fast  track”  review  if  it  is  intended  for  the  treatment  of  a  serious  or
life‑threatening  disease  or  condition  and  it  demonstrates  the  potential  to  address  unmet  medical  needs  for  such  disease  or
condition. For fast track products, sponsors may have greater interactions with the FDA, and the FDA may initiate review of
sections  of  a  fast  track  product’s  BLA  before  the  application  is  complete.  This  “rolling  review”  is  available  if  the  FDA
determines, after preliminary evaluation of clinical data submitted by the sponsor, that a fast track product may be effective.
The sponsor must also provide, and the FDA must approve, a schedule for the submission of the remaining information and
the sponsor must pay applicable user fees.

Second,  the  FDA  may  designate  a  product  as  a  breakthrough  therapy  if  it  is  intended  to  treat  a  serious  or  life‑threatening
disease or condition and preliminary clinical evidence indicates that the product may demonstrate substantial improvement
over  existing  therapies  on  one  or  more  clinically  significant  endpoints.  The  FDA  may  take  certain  actions  with  respect  to
breakthrough therapies, including holding meetings with the sponsor throughout the development process, providing timely
advice  to  the  product  sponsor  regarding  development  and  approval,  involving  more  senior  staff  in  the  review  process,
assigning  a  cross‑disciplinary  project  lead  for  the  review  team  and  taking  other  steps  to  design  the  clinical  studies  in  an
efficient manner.

Third, the FDA may designate a product for priority review if it treats a serious condition and, if approved, would provide a
significant improvement in safety or effectiveness. A priority designation is intended to direct overall attention and resources
to  the  evaluation  of  such  applications  and  shortens  the  FDA’s  goal  for  taking  action  on  a  marketing  application  from  ten
months to six months from the filing date.

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Accelerated approval pathway

The  FDA  may  grant  accelerated  approval  to  a  product  for  a  serious  or  life‑threatening  condition  that  provides  meaningful
therapeutic advantage to patients over existing treatments. A product eligible for accelerated approval may be approved on
the basis of either a surrogate endpoint that is reasonably likely to predict clinical benefit, or on a clinical endpoint that can be
measured  earlier  than  irreversible  morbidity  or  mortality,  that  is  reasonably  likely  to  predict  an  effect  on  irreversible
morbidity or mortality or other clinical benefit, taking into account the severity, rarity or prevalence of the condition and the
availability or lack of alternative treatments.

The accelerated approval pathway is most often used in settings in which the course of a disease is long and an extended
period  of  time  is  required  to  measure  the  intended  clinical  benefit  of  a  product,  even  if  the  effect  on  the  surrogate  or
intermediate clinical endpoint occurs rapidly. Thus, accelerated approval has been used extensively in the development and
approval of products for treatment of a variety of cancers in which the goal of therapy is generally to improve survival or
decrease morbidity and the duration of the typical disease course requires lengthy and sometimes large studies to demonstrate
a clinical or survival benefit.

The accelerated approval pathway is usually contingent on a sponsor’s agreement to conduct, in a diligent manner, additional
post‑approval  confirmatory  studies  to  verify  and  describe  the  product’s  clinical  benefit.  As  a  result,  a  product  candidate
approved on this basis is subject to rigorous post‑marketing compliance requirements, including the completion of Phase 4 or
post‑approval clinical studies to confirm the effect on the clinical endpoint. Failure to conduct required post‑approval studies,
or to confirm a clinical benefit during post‑marketing studies, would allow the FDA to withdraw the product from the market
on an expedited basis. All promotional materials for product candidates approved under accelerated regulations are subject to
prior review by the FDA.

Post‑approval requirements

Products manufactured or distributed pursuant to FDA approvals are subject to pervasive and continuing regulation by the
FDA,  including,  among  other  things,  requirements  relating  to  recordkeeping,  periodic  reporting,  product  sampling  and
distribution, advertising and promotion and reporting of adverse experiences with the product. After approval, most changes
to  the  approved  product,  such  as  adding  new  indications  or  other  labeling  claims,  are  subject  to  prior  FDA  review  and
approval. There also are continuing, annual user fee requirements for any marketed products and the establishments at which
such products are manufactured, as well as new application fees for certain supplemental applications.

In addition, manufacturers and other entities involved in the manufacture and distribution of approved products are required
to register their establishments with the FDA and state agencies and are subject to periodic unannounced inspections by the
FDA  and  these  state  agencies  for  compliance  with  cGMP  requirements.  Changes  to  the  manufacturing  process  are  strictly
regulated and often require prior FDA approval before being implemented. FDA regulations also require investigation and
correction of any deviations from cGMP and impose reporting and documentation requirements upon the sponsor and any
third‑party  manufacturers  that  the  sponsor  may  decide  to  use.  Accordingly,  manufacturers  must  continue  to  expend  time,
money and effort in the area of production and quality control to maintain cGMP compliance.

Once an approval is granted, the FDA may withdraw the approval if compliance with regulatory requirements and standards
is not maintained or if problems occur after the product reaches the market. Later discovery of previously unknown problems
with a product, including adverse events of unanticipated severity or frequency, or with manufacturing processes, or failure to
comply  with  regulatory  requirements,  may  result  in  revisions  to  the  approved  labeling  to  add  new  safety  information,
imposition  of  post‑market  studies  or  clinical  studies  to  assess  new  safety  risks  or  imposition  of  distribution  or  other
restrictions under a REMS program. Other potential consequences include, among other things:

·

·

restrictions on the marketing or manufacturing of the product, suspension of the approval, complete withdrawal of
the product from the market or product recalls;

fines, warning or other enforcement‑related letters or holds on post‑approval clinical studies;

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·

·

·

refusal  of  the  FDA  to  approve  pending  BLAs  or  supplements  to  approved  BLAs,  or  suspension  or  revocation  of
product license approvals;

product seizure or detention, or refusal to permit the import or export of products; or

injunctions or the imposition of civil or criminal penalties.

The FDA strictly regulates marketing, labeling, advertising and promotion of products that are placed on the market. Such
products may be promoted only for the approved indications and in accordance with the provisions of the approved label.
The  FDA  and  other  agencies  actively  enforce  the  laws  and  regulations  prohibiting  the  promotion  of  off‑label  uses,  and  a
company that is found to have improperly promoted off‑label uses may be subject to significant liability.

Biosimilars and exclusivity

The Patient Protection and Affordable Care Act, as amended by the Health Care and Education Reconciliation Act, signed
into law on March 23, 2010, or the Health Care Reform Act, includes a subtitle called the Biologics Price Competition and
Innovation Act of 2009, or the BPCIA, which created an abbreviated approval pathway for biological products shown to be
biosimilar to, or interchangeable with, an FDA‑licensed reference biological product. Biosimilarity requires a showing that
the product is “highly similar” to the reference product notwithstanding minor differences in clinically inactive components
and that there are no clinically meaningful differences between the biological product and the reference product in terms of
safety, purity and potency. Interchangeability requires that a product is biosimilar to the reference product and the product
must demonstrate that it can be expected to produce the same clinical results as the reference product in any given patient
and, for products administered multiple times, the biologic and the reference biologic may be switched after one has been
previously  administered  without  increasing  safety  risks  or  risks  of  diminished  efficacy  relative  to  exclusive  use  of  the
reference  biologic.  To  date,  the  FDA  has  approved  more  than  25  biosimilar  applications,  although  less  than  half  of  those
products are currently being marketed due largely to ongoing patent litigation or as a result of patent settlements. The FDA
has yet to approve an interchangeable biosimilar and is continuing to issue guidance documents outlining its approach to the
review and approval of interchangeable biosimilars.

A reference biologic is entitled to 12 years of exclusivity from the time of first licensure of the product. In addition, the first
biological product submitted under the abbreviated approval pathway that is determined to be interchangeable with, not just
biosimilar  to,  the  reference  product  has  exclusivity  against  other  biologics  submitting  under  the  abbreviated  approval
pathway for the lesser of (i) one year after the first commercial marketing, (ii) 18 months after approval if there is no legal
challenge,  (iii)  18  months  after  the  resolution  in  the  applicant’s  favor  of  a  lawsuit  challenging  the  biologics’  patents  if  an
application has been submitted or (iv) 42 months after the application has been approved if a lawsuit is ongoing within the
42‑month period.

The BPCIA is complex and as noted above, elements of the law, such as interchangeability, are still being developed by the
FDA.  In addition, there is continued debate as to whether recent government proposals that have sought to reduce the 12-
year  reference  product  exclusivity  period  should  be  reduced.  Further,  since  the  BPCIA  was  enacted  as  part  of  the  overall
Health Care Reform Act, current litigation challenges to that Act, discussed more in full below, could impact the validity of
the BPCIA. As a result, there still remains significant uncertainty as to the ultimate impact, implementation and meaning of
the BPCIA.

Pediatric studies and exclusivity

Under the Pediatric Research Equity Act of 2003, all applications for new active ingredients, new indications, new dosage
forms,  new  dosing  regimens  or  new  routes  of  administration  are  required  to  contain  an  assessment  of  the  safety  and
effectiveness  of  the  product  for  the  claimed  indication  in  pediatric  patients  unless  this  requirement  is  waived,  deferred  or
inapplicable.

Under the Best Pharmaceuticals for Children Act, a product may be eligible for pediatric exclusivity, which, if granted, adds
six months to existing exclusivity periods and patent terms. This six‑month exclusivity, which runs from the end of

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other  exclusivity  protection  or  patent  term,  may  be  granted  based  on  the  voluntary  completion  of  a  pediatric  study  in
accordance with an FDA‑issued written request for such a study.

Orphan drug designation and exclusivity

Under the Orphan Drug Act, the FDA may designate a product, including a biological product, as an “orphan drug” if it is
intended  to  treat  a  rare  disease  that  affects  fewer  than  200,000  individuals  in  the  United  States  or,  if  it  affects  more  than
200,000 individuals in the United States, a disease for which there is no reasonable expectation that the cost of developing
and making the product for this type of disease or condition will be recovered from sales in the United States.

A product that receives the first FDA approval for a product for the indication for which it has orphan designation is entitled
to orphan drug exclusivity, which means the FDA may not approve any other application to market the same product for the
same indication for a period of seven years, except in limited circumstances, such as a showing of clinical superiority over
the product with orphan exclusivity.

Patent term restoration

A patent claiming a new product may be eligible for a limited patent term extension under the Hatch‑Waxman Amendments,
which  permits  a  patent  restoration  of  up  to  five  years  for  patent  term  lost  during  product  development  and  the  FDA
regulatory review. The restoration period granted is typically one‑half the time between the effective date of an IND and the
submission date of a BLA, plus the time between the submission date of a BLA and the ultimate approval date. Patent term
restoration cannot be used to extend the remaining term of a patent past a total of 14 years from the product’s approval date.
Only one patent applicable to an approved drug product is eligible for the extension, and the application for the extension
must be submitted prior to the expiration of the patent in question. The USPTO, reviews and approves the application for any
patent term extension or restoration in consultation with the FDA.

Review and approval outside the United States

In order to market any product outside of the United States, we would need to comply with numerous and varying regulatory
requirements  of  other  countries  and  jurisdictions  governing,  among  other  things,  clinical  studies,  marketing  authorization,
commercial sales and distribution of our products. Whether or not we obtain FDA approval for a product, we would need to
obtain the necessary approvals by the comparable foreign regulatory authorities before we can commence clinical studies or
marketing of the product in foreign countries and jurisdictions. Although many of the issues discussed above with respect to
the United States apply similarly in the context of the European Union and other geographies, the approval process varies
between countries and jurisdictions and can involve additional product testing and additional administrative review periods.
The time required to obtain approval in other countries and jurisdictions might differ from and be longer than that required to
obtain FDA approval. Regulatory approval in one country or jurisdiction does not ensure regulatory approval in another, but
a failure or delay in obtaining regulatory approval in one country or jurisdiction may negatively impact the regulatory process
in others.

Certain countries outside of the United States have a process that requires the submission of a clinical trial application, or
CTA, much like the IND prior to the commencement of human clinical studies. In the European Union, for example, a CTA
must be submitted for each clinical trial to the national health authority and an independent ethics committee in each country
in  which  the  company  intends  to  conduct  clinical  trials.  Once  the  CTA  is  approved  in  accordance  with  a  country’s
requirements, the clinical trial may proceed. In all cases, the clinical trials must be conducted in accordance with GCPs and
other applicable regulatory requirements and ethical principles.

To  obtain  regulatory  approval  of  an  investigational  product  under  European  Union  regulatory  systems,  we  must  submit  a
marketing  authorization  application  under  either  a  centralized  or  decentralized  procedure.  The  centralized  procedure  is
compulsory for medicinal products produced by biotechnology. The application used to file the BLA in the United States is
similar  to  that  required  in  the  European  Union,  with  the  exception  of,  among  other  things,  region-specific  document
requirements.

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The  European  Union  also  provides  opportunities  for  market  exclusivity.  For  example,  upon  receiving  marketing
authorization, innovative medicinal products generally receive eight years of data exclusivity and an additional two years of
market  exclusivity.  If  grated,  data  exclusivity  prevents  regulatory  authorities  in  the  European  Union  from  referencing  the
innovator’s data to assess a generic or biosimilar application. There is no guarantee that a product will be considered by the
European  Union’s  regulatory  authorities  to  be  an  innovative  medicinal  product,  and  products  may  not  qualify  for  data
exclusivity. Products receiving orphan designation in the European Union can receive ten years of market exclusivity, during
which time no similar medicinal product for the same indication may be placed on the market. An orphan product can also
obtain  an  additional  two  years  of  market  exclusivity  in  the  European  Union  for  pediatric  studies.  No  extension  to  any
supplementary protection certificate can be granted on the basis of pediatric studies for orphan indications.

The collection, use, disclosure, transfer or other processing of personal data regarding individuals in the European Economic
Area,  including  personal  health  data,  is  subject  to  the  Regulation  (EU)  2016/679  (General  Data  Protection  Regulation,  or
GDPR), which became effective on May 25, 2018. The GDPR is wide-ranging in scope and imposes numerous requirements
on  companies  that  process  personal  data,  including  requirements  relating  to  processing  health  and  other  sensitive  data,
obtaining consent of the individuals to whom the personal data relates, providing information to individuals regarding data
processing  activities,  implementing  safeguards  to  protect  the  security  and  confidentiality  of  personal  data,  providing
notification of data breaches and taking certain measures when engaging third-party data processors. The GDPR also imposes
strict rules on the transfer of personal data to countries outside the European Economic Area, including the United States, and
permits data protection authorities to impose large penalties for violations of the GDPR, including potential fines of up to €20
million  or  4%  of  annual  global  revenues,  whichever  is  greater.  The  GDPR  also  confers  a  private  right  of  action  on  data
subjects  and  consumer  associations  to  lodge  complaints  with  supervisory  authorities,  seek  judicial  remedies  and  obtain
compensation for damages resulting from violations of the GDPR. Compliance with the GDPR will be a rigorous and time-
intensive  process  that  may  increase  the  cost  of  doing  business  or  require  companies  to  change  their  business  practices  to
ensure full compliance.

If  we  fail  to  comply  with  applicable  foreign  regulatory  requirements,  we  may  be  subject  to,  among  other  things,  fines,
suspension  or  withdrawal  of  regulatory  approvals,  product  recalls,  seizure  of  products,  operating  restrictions  and  criminal
prosecution.

Pharmaceutical coverage, pricing and reimbursement

Significant  uncertainty  exists  as  to  the  coverage  and  reimbursement  status  of  products  approved  by  the  FDA  and  other
government  authorities.  Sales  of  pharmaceutical  products  depend  in  significant  part  on  the  availability  and  adequacy  of
third‑party reimbursement. Third‑party payors include government health administrative authorities, including authorities at
the U.S. federal and state level, managed care providers, private health insurers and other organizations. Third‑party payors
are increasingly challenging the prices charged for, examining the medical necessity of and assessing the cost‑effectiveness
of medical products and services.

In  order  to  secure  coverage  and  reimbursement  for  any  product  that  might  be  approved  for  sale,  a  company  may  need  to
conduct  expensive  pharmacoeconomic  studies  in  order  to  demonstrate  the  medical  necessity  and  cost‑effectiveness  of  the
product,  in  addition  to  the  costs  required  to  obtain  FDA  or  other  comparable  regulatory  approvals.  A  payor’s  decision  to
provide  coverage  for  a  product  does  not  imply  that  an  adequate  reimbursement  rate  will  be  approved.  Third‑party
reimbursement may not be sufficient to maintain price levels high enough to realize an appropriate return on investment in
product development.

The containment of healthcare costs also has become a priority of federal, state and foreign governments and the prices of
drugs  and  biologics  have  been  a  focus  in  this  effort.  Governments  have  shown  significant  interest  in  implementing
cost‑containment  programs,  including  price  controls,  restrictions  on  reimbursement  and  requirements  for  substitution  of
generic  products.  Adoption  of  price  controls  and  cost‑containment  measures,  and  adoption  of  more  restrictive  policies  in
jurisdictions  with  existing  controls  and  measures,  could  further  limit  a  company’s  revenue  generated  from  the  sale  of  any
approved  products.  Coverage  policies  and  third‑party  reimbursement  rates  may  change  at  any  time.  Even  if  favorable
coverage  and  reimbursement  status  is  attained  for  one  or  more  products  for  which  a  company  or  its  collaborators  receive
marketing approval, less favorable coverage policies and reimbursement rates may be implemented in the future.

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In the European Union, pricing and reimbursement schemes vary widely from country to country. Some countries provide
that products may be marketed only after a reimbursement price has been agreed. Some countries may require the completion
of additional studies that compare the cost‑effectiveness of a particular product candidate to currently available therapies, or
so  called  health  technology  assessments,  to  obtain  reimbursement  or  pricing  approval.  For  example,  the  European  Union
provides  options  for  its  member  states  to  restrict  the  range  of  products  for  which  their  national  health  insurance  systems
provide reimbursement and to control the prices of medicinal products for human use. European Union member states may
approve a specific price for a product or may instead adopt a system of direct or indirect controls on the profitability of the
company.

The downward pressure on healthcare costs in general, particularly prescription drugs and biologics, has become intense. As
a result, increasingly high barriers are being erected to the entry of new products. In addition, in some countries, cross‑border
imports from low‑priced markets exert competitive pressure that may reduce pricing within a country. Any country that has
price controls or reimbursement limitations for products may not allow favorable reimbursement and pricing arrangements.

Healthcare law and regulation

Within  the  United  States,  the  activities  of  pharmaceutical  companies  are  subject  to  extensive  regulation  and  our  activities
could  possibly  be  subject  to  challenge  as  a  result.  Laws  and  regulations  that  may  affect  our  ability  to  operate  (including
certain laws that will apply if and when we have a product approved for marketing) include:

·

·

·

·

·

·

·

federal false claims, false statements and civil monetary penalties laws prohibiting, among other things, any person
from knowingly presenting, or causing to be presented, a false claim for payment of government funds or knowingly
making, or causing to be made, a false statement to get a false claim paid;

the  federal  anti‑kickback  law,  which  prohibits,  among  other  things,  persons  from  soliciting,  offering,  receiving  or
providing remuneration, directly or indirectly, to induce either the referral of an individual, for an item or service or
the purchasing or ordering of a good or service, for which payment may be made, under federal healthcare programs
such as Medicare and Medicaid;

the federal anti-kickback prohibition known as Eliminating Kickbacks in Recovery Act or EKRA, enacted in 2018,
which  prohibits  certain  payments  related  to  referrals  of  patients  to  certain  providers  (recovery  homes,  clinical
treatment  facilities  and  laboratories)  and  applies  to  services  reimbursed  by  private  health  plans  as  well  as
government health care programs;

the federal law known as HIPAA, which, in addition to privacy protections applicable to healthcare providers and
other entities (see “Government regulation – Data privacy and security”), prohibits executing a scheme to defraud
any  healthcare  benefit  program  (which  may  include  private  health  plans)  or  making  false  statements  relating  to
healthcare matters;

the  FDCA,  which  among  other  things,  strictly  regulates  drug  marketing,  prohibits  manufacturers  from  marketing
such products for off-label use and regulates the distribution of samples;

the  federal  laws  that  require  pharmaceutical  manufacturers  to  report  certain  calculated  product  prices  to  the
government or provide certain discounts or rebates to government authorities or private entities, often as a condition
of reimbursement under government healthcare programs;

the so-called “federal sunshine” law, which requires pharmaceutical and medical device companies to monitor and
report certain financial interactions with certain healthcare providers to the federal government for re-disclosure to
the public (the scope of which reportable interactions will increase for interactions occurring on or after 2021); and

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·

state law analogues of the above federal laws, such as anti‑kickback and false claims laws which may apply to items
or services reimbursed by any third‑party payor, including private health plans, and state laws regulating interactions
between  pharmaceutical  manufacturers  and  healthcare  providers,  many  of  which  differ  from  each  other  in
significant ways and often are not preempted by federal laws, thus complicating compliance efforts.

We will be required to spend substantial time and money to ensure that our business arrangements with third parties comply
with applicable healthcare laws and regulations. Violations of these laws can subject us to criminal, civil and administrative
sanctions  including  monetary  penalties,  damages,  fines,  disgorgement,  individual  imprisonment  and  exclusion  from
participation in government funded healthcare programs, such as Medicare and Medicaid, additional reporting requirements
and  oversight  if  we  become  subject  to  a  corporate  integrity  agreement  or  similar  agreement  to  resolve  allegations  of
non‑compliance  with  these  laws,  and  reputational  harm.  Additionally,  we  may  be  required  to  curtail  or  restructure  our
operations.  Moreover,  we  expect  that  there  will  continue  to  be  federal  and  state  laws  and  regulations,  proposed  and
implemented, that could impact our future operations and business.

Healthcare reform

Our  revenue  and  operations  could  be  affected  by  changes  in  healthcare  spending  and  policy  in  the  United  States  and
elsewhere. We operate in a highly regulated industry and new laws, regulations or judicial decisions, or new interpretations of
existing  laws,  regulations  or  decisions,  related  to  healthcare  availability,  the  method  of  delivery  or  payment  for  healthcare
products and services could negatively impact our business, operations and financial condition.

In the United States, there have been and continue to be a number of significant legislative initiatives to contain healthcare
costs. Federal and state governments continue to propose and pass legislation designed to reform delivery of, or payment for,
health  care,  which  include  initiatives  to  reduce  the  cost  of  healthcare.  For  example,  the  Healthcare  Reform  Act,  which
expanded  health  care  coverage  through  Medicaid  expansion  and  the  implementation  of  the  individual  mandate  for  health
insurance  coverage  and  which  included  changes  to  the  coverage  and  reimbursement  of  drug  products  under  government
healthcare  programs.  Under  the  Trump  administration,  there  have  been  ongoing  efforts  to  modify  or  repeal  all  or  certain
provisions of the Healthcare Reform Act. For example, tax reform legislation was enacted at the end of 2017 that eliminated
the  tax  penalty  established  under  Healthcare  Reform  Act  for  individuals  who  do  not  maintain  mandated  health  insurance
coverage beginning in 2019. The Healthcare Reform Act has also been subject to judicial challenge.  In December 2018, a
federal  district  court,  in  a  challenge  brought  by  a  number  of  state  attorneys  general,  found  the  Healthcare  Reform  Act
unconstitutional in its entirety because, once Congress repealed the individual mandate provision, there was no longer a basis
to rely on Congressional taxing authority to support enactment of the law.  In December 2019, a federal appeals court agreed
that the individual mandate provision was unconstitutional, but remanded the case back to the district court to assess more
carefully  whether  any  provisions  of  the  Healthcare  Reform  Act  were  severable  and  could  survive.    Pending  action  by  the
district court and resolution of any appeals, which could take some time, the Healthcare Reform Act is still operational in all
respects.

There have also been other reform initiatives under the Trump Administration, including initiatives focused on drug pricing.
For  example,  the  Bipartisan  Budget  Act  of  2018  contained  various  provisions  that  affect  coverage  and  reimbursement  of
drugs,  including  an  increase  in  the  discount  that  manufacturers  of  Medicare  Part  D  brand  name  drugs  must  provide  to
Medicare Part D beneficiaries during the coverage gap from 50% to 70% which started in 2019. As another example, in May
of 2018, President Trump and the Secretary of the Department of Health and Human Services released a “blueprint” to lower
prescription  drug  prices  and  out-of-pocket  costs.  Certain  proposals  in  the  blueprint,  and  related  drug  pricing  measures
proposed since the blueprint, could cause significant operational and reimbursement changes for the pharmaceutical industry.
As  another  example,  legislation  passed  in  2019  revised  how  certain  prices  reported  by  manufacturers  under  the  Medicaid
Drug Rebate Program are calculated, a revision that the Congressional Budget Office has estimated will save the Medicaid
program approximately $3 billion in the next ten years.

There have also been efforts by federal and state government officials or legislators to implement measures to regulate prices
or  payment  for  pharmaceutical  products,  including  legislation  on  drug  importation.  Recently,  there  has  been  considerable
public and government scrutiny of pharmaceutical pricing and proposals to address the perceived high cost

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of pharmaceuticals. There have also been recent state legislative efforts to address drug costs, which generally have focused
on increasing transparency around drug costs or limiting drug prices.

Data privacy and security

We may be subject to privacy and security laws in the various jurisdictions in which we operate, obtain or store personally
identifiable  information.  The  legislative  and  regulatory  landscape  for  privacy  and  data  protection  continues  to  evolve,  and
there has been an increasing focus on privacy and data protection issues with the potential to affect our business.

Within the United States, our operations may be affected by the Health Insurance Portability and Accountability Act of 1996
as amended by the Health Information Technology for Economic and Clinical Health Act and its implementing regulations,
collectively,  HIPAA,  which  impose  obligations  on  certain  “covered  entities”  (healthcare  providers,  health  plans  and
healthcare  clearinghouses)  and  certain  of  their  “business  associate”  contractors  with  respect  to  safeguarding  the  privacy,
security and transmission of individually identifiable health information. Although we believe that we currently are neither a
“covered entity” nor a “business associate” under the legislation, HIPAA may affect our interactions with customers who are
covered  entities  or  their  business  associates  because  HIPAA  affects  the  ability  of  these  entities  to  disclose  patient  health
information  to  us.  Various  states  also  have  laws  that  regulate  the  privacy  and  security  of  patient  information  and  so  may
affect our business operations. For example, we are subject to the California Consumer Privacy Act, or CCPA, that became
effective  on  January  1,  2020.  The  CCPA  gives  California  consumers  (defined  to  include  all  California  residents)  certain
rights,  including  the  right  to  ask  companies  to  disclose  the  types  of  personal  information  collected,  specific  pieces  of
information  collected  by  a  company,  the  categories  of  sources  from  which  such  information  was  collected,  the  business
purpose  for  collecting  or  selling  the  consumer’s  personal  information,  and  the  categories  of  third  parties  with  whom  a
company  shares  personal  information.  The  CCPA  also  imposes  several  obligations  on  companies  to  provide  notice  to
California consumers regarding a company’s data processing activities. Additionally, the CCPA gives California consumers
the right to ask companies to delete a consumer’s personal information and it places limitations on a company’s ability to sell
personal information, including providing consumers a right to opt out of sales of their personal information.

Outside the United States, other data privacy and security regulations may apply.  For example, the processing of personal
data in the European Economic Area, or the EEA, is subject to the General Data Protection Regulation, or the GDPR, which
took  effect  in  May  2018.  The  GDPR  increases  obligations  with  respect  to  clinical  trials  conducted  in  the  EEA,  such  as  in
relation  to  the  provision  of  fair  processing  notices,  exercising  data  subject  rights  and  reporting  certain  data  breaches  to
regulators  and  affected  individuals,  as  well  as  how  we  document  our  relationships  with  third  parties  that  process  GDPR-
covered  personal  data  on  our  behalf.  The  GDPR  also  increases  the  scrutiny  applied  to  transfers  of  personal  data  from  the
EEA (including from clinical trial sites in the EEA) to countries that are considered by the European Commission to lack an
adequate level of data protection, such as the United States.  

Compliance with data privacy and security regulation can require allocation of resources as well as changes in operations and
non-compliance can result in substantial penalties. For example, the GDPR and the CCPA impose substantial fines and other
regulatory penalties for breaches of data protection requirements, and they confer a private right of action on data subjects (in
the  case  of  the  GDPR)  and  consumers  (in  the  case  of  the  CCPA)  and  their  representatives  for  breaches  of  certain  data
protection requirements.

Additional regulation

In addition to the foregoing, state and federal laws regarding environmental protection and hazardous substances, including
the Occupational Safety and Health Act, the Resource Conservation and Recovery Act and the Toxic Substances Control Act,
affect our business. These and other laws govern the use, handling and disposal of various biologic, chemical and radioactive
substances  used  in,  and  wastes  generated  by,  operations.  If  our  operations  result  in  contamination  of  the  environment  or
expose individuals to hazardous substances, we could be liable for damages and governmental fines. Equivalent laws have
been adopted in foreign countries that impose similar obligations.

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Intellectual property

We actively seek to protect the proprietary technology that we consider important to our business, including pursuing patents
that  cover  our  ADC  platform,  proprietary  composition  of  matter,  ADC  product  candidates  and  methods  of  using  and
manufacturing  the  same,  as  well  as  any  other  relevant  inventions  and  improvements  that  are  considered  commercially
important  to  the  development  of  our  business.  We  also  rely  on  trade  secrets,  know  how  and  continuing  technological
innovation to develop and maintain our proprietary and intellectual property position.

Our  commercial  success  will  depend  significantly  on  our  ability  to  obtain  and  maintain  patents  and  other  proprietary
protection for the technology, inventions and improvements we consider important to our business, and to defend our patents,
preserve  the  confidentiality  of  our  trade  secrets  and  operate  without  infringing  the  patents  and  proprietary  rights  of  third
parties.  Our  policy  is  to  seek  to  protect  our  proprietary  and  intellectual  property  position  by,  among  other  methods,  filing
U.S.,  international  (under  Patent  Cooperation  Treaty,  or  PCT)  and  foreign  patent  applications  related  to  our  proprietary
technology,  inventions  and  improvements  that  we  consider  to  be  important  to  the  development  and  implementation  of  our
business.

The term of individual patents depends upon the legal term for patents in the countries in which they are obtained. In most
countries,  including  the  United  States,  the  patent  term  is  20  years  from  the  earliest  filing  date  of  a  non-provisional  patent
application. In the United States, a patent’s term may be lengthened by patent term adjustment, which compensates a patentee
for  administrative  delays  by  the  USPTO  in  examining  and  granting  a  patent  or  may  be  shortened  if  a  patent  is  terminally
disclaimed over an earlier filed patent. The term of a patent that covers a drug or biological product may also be eligible for
patent term extension when FDA approval is granted, provided statutory and regulatory requirements are met. In the future, if
and when our drug candidates receive approval by the FDA or foreign regulatory authorities, we expect to apply for patent
term extensions on issued patents covering those drugs, depending upon the length of the clinical studies for each drug and
other factors. There can be no assurance that any of our pending patent applications will issue or that we will benefit from
any patent term extension or favorable adjustments to the terms of any of our patents.

As  with  other  biotechnology  and  pharmaceutical  companies,  our  ability  to  maintain  and  solidify  our  proprietary  and
intellectual  property  position  for  our  drug  candidates  and  technologies  will  depend  on  our  success  in  obtaining  effective
patent claims and enforcing those claims if granted. However, our pending patent applications, and any patent applications
that we may in the future file or license from third parties, may not result in the issuance of patents. We also cannot predict
the  breadth  of  claims  that  may  be  allowed  or  enforced  in  our  patents.  Any  issued  patents  that  we  may  currently  own  or
license or may receive in the future may be challenged, invalidated, circumvented or have the scope of their claims narrowed.
For example, we cannot be certain of the priority of inventions covered by pending third party patent applications. If third
parties prepare and file patent applications in the United States that also claim technology or therapeutics to which we have
rights, we may have to participate in interference proceedings in the USPTO to determine priority of invention, which could
result in substantial costs to us, even if the eventual outcome is favorable to us, which is highly unpredictable. In addition,
because of the extensive time required for clinical development and regulatory review of a drug candidate we may develop, it
is possible that, before any of our drug candidates can be commercialized, any related patent may expire or remain in force
for only a short period following commercialization, thereby limiting the protection such patent would afford the respective
product  and  any  competitive  advantage  such  patent  may  provide.  For  more  information  regarding  the  risks  related  to  our
intellectual property, please see “Risk factors—Risks related to our intellectual property.”

As of January 31, 2020, we owned, in all of our patent portfolios, 18 issued U.S. patents, 12 pending non-provisional U.S.
patent  applications  (including  two  allowed  U.S.  patent  applications),  7  pending  provisional  U.S.  patent  applications,  81
issued foreign patents, five pending PCT patent applications and 88 pending foreign patent applications (including 6 allowed
foreign patent applications) in a number of jurisdictions, including, but being not limited to, Australia, Brazil, Canada, China,
Europe, Eurasia, Gulf Cooperation Council, Hong Kong, Israel, India, Indonesia, Iran, Japan, Mexico, Macau, New Zealand,
Russia,  South  Korea,  South  Africa,  and  Taiwan.  Our  nine  issued  U.S.  patents  covering  our  Fleximer  ADC  platform  are
projected  to  expire  in  2032,  excluding  any  additional  term  for  patent  term  adjustments  or  patent  term  extensions;  our  one
issued U.S. patent covering our Dolaflexin ADC platform is projected to expire in 2034, excluding any additional term for
patent term adjustments or patent term extensions; our additional eight issued U.S. patents are projected to expire in 2030 and
2037, excluding any additional term for patent term adjustments or patent term extensions;

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and any patent that may issue from our pending U.S. applications is projected to expire between 2032 and 2041, in each case,
excluding  any  additional  term  for  patent  term  adjustments  or  patent  term  extensions.  In  addition,  we  have  exclusively  in
licensed four issued U.S. patents and one issued European patent for the NaPi2b antibody from Recepta. These in licensed
issued U.S. and foreign patents are projected to expire in 2029, excluding any additional term for patent term adjustments or
patent term extensions. We have so far not filed for patent protection in all national and regional jurisdictions where such
protection may be available. In addition, we may decide to abandon national and regional patent applications before they are
granted. Finally, the grant proceeding of each national or regional patent is an independent proceeding which may lead to
situations in which applications might in some jurisdictions be refused by the relevant registration authorities, while granted
by others. It is also quite common that depending on the country, various scopes of patent protection may be granted on the
same product candidate or technology.

The  intellectual  property  portfolio  of  our  ADC  platform,  our  ADC  product  candidates  and  components  thereof  and
companion diagnostics are summarized below. Some of these portfolios are in very early stages and prosecution has yet to
commence on most of the pending patent applications. Prosecution is a lengthy process, during which the scope of the claims
initially submitted for examination by the USPTO may be narrowed (sometimes significantly) by the time they issue, if they
issue at all. We expect this to be the case with respect to our pending patent applications referred to below.

Fleximer ADC platform

The  intellectual  property  portfolio  for  our  Fleximer  ADC  platform  is  directed  to  compositions  of  matter  for  the  Fleximer
ADCs, as well as methods of using and making these novel conjugates, compositions of matter for Fleximer drug conjugates
prior to conjugation with the antibody or antibody fragment and methods of making the same, and compositions of matter for
our  proprietary  auristatin  compounds  (and  by  extension  our  proprietary  DolaLock  feature)  and  conjugates  thereof  (e.g.,  to
Fleximer and/or an antibody or antibody fragment). As of January 31, 2020, we owned nine issued U.S. patents, two pending
U.S.  patent  applications  (including  one  allowed  application),  41  issued  foreign  patents,  and  9  pending  foreign  patent
applications (including three allowed applications) in a number of jurisdictions, including Australia, Brazil, Canada, China,
Europe,  Hong  Kong,  Israel,  India,  Japan,  Macau,  Mexico,  Russia,  South  Korea,  and  Taiwan.  Any  U.S.  or  foreign  patent
issuing  from  the  pending  applications  covering  the  Fleximer  ADC  platform  is  projected  to  expire  in  2032,  excluding  any
additional term for patent term adjustments or patent term extensions.

Dolaflexin ADC platform

The intellectual property portfolio for our Dolaflexin ADC platform is directed to compositions of matter for the Dolaflexin
ADCs,  as  well  as  methods  of  using  and  making  these  novel  conjugates,  compositions  of  matter  for  Dolaflexin  drug
conjugates prior to conjugation with the antibody or antibody fragment and methods of making the same. As of January 31,
2020, we owned one issued U.S. patent, and two pending U.S. patent applications, 27 issued foreign patent, and 16 pending
foreign  patent  applications  (including  three  allowed  applications)  in  a  number  of  jurisdictions,  including  Australia,  Brazil,
Canada,  China,  Eurasia,  Europe,  Israel,  India,  Japan,  South  Korea,  Mexico  and  South  Africa.  Any  U.S.  or  foreign  patent
issuing  from  the  pending  applications  covering  Dolaflexin  ADC  platform  is  projected  to  expire  in  October  2034,  and  any
U.S. or foreign patent issuing from the pending applications covering the method of making the Dolaflexin ADC is projected
to expire in 2038, excluding any additional term for patent term adjustments or patent term extensions.

XMT-1536 ADC

The intellectual property portfolio for our NaPi2b ADC product candidate, XMT-1536, is directed to compositions of matter
for  our  novel  ADC  based  on  exclusively  in  licensed  NaPi2b  antibody  and  our  Dolaflexin  platform,  as  well  as  methods  of
using,  making  these  novel  conjugates,  methods  of  administration  and  companion  diagnostics.  As  of  January  31,  2020,  we
owned  six  pending  U.S.  patent  applications  (including  three  pending  provisional  U.S.  patent  applications),  21  pending
foreign patent applications, and two pending PCT applications directed to the composition of matter for XMT-1536, methods
of using and making same, companion diagnostics for XMT-1536 ADC and XMT-1536 dosing regimens. We also intend to
enter the national/regional phase of the pending PCT patent application in foreign jurisdictions, including Australia, Brazil,
Canada,  China,  Eurasia,  Europe,  Israel,  India,  Japan,  South  Korea,  Mexico  and  South  Africa.  Any  U.S.  or  foreign  patent
issuing  from  the  pending  applications  covering  XMT-1536  is  projected  to  expire  in  2037,  and  any  U.S.  or  foreign  patent
issuing from the pending applications covering XMT-1536 companion diagnostics is projected to expire

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in 2038, excluding any additional term for patent term adjustments or patent term extensions, and any U.S. or foreign patent
issuing from the pending applications covering the XMT-1536 dosing regimens is projected to expire in 2039 or 2041.

In addition, we have exclusively in licensed four issued U.S. patents and one issued European patent for the novel NaPi2b
antibody from Recepta, which Recepta licensed from Ludwig Institute for Cancer Research. These in licensed issued U.S.
and European patents are projected to expire in 2029, excluding any additional term for patent term adjustments or patent
term extensions. Recepta still owns one pending Brazilian patent application for the NaPi2b antibody, which is not licensed
to us. A patent issuing from this Brazilian patent application is projected to expire in 2029.

Dolasynthen ADC platform

The  intellectual  property  portfolio  for  our  novel  Dolasynthen  platform  is  directed  to  compositions  of  matter  for  the  novel
scaffold and ADCs thereof, as well as methods of using and making these novel conjugates and scaffolds. As of January 31,
2020, we owned one pending U.S. patent application, 15 pending foreign patent applications, and one pending PCT patent
application.  We  intend  to  enter  the  national/regional  phase  of  the  PCT  patent  applications  in  a  number  of  jurisdictions,
including Australia, Brazil, Canada, China, Europe, Hong Kong, Israel, India, Japan, Macau, Mexico, Russia, South Korea,
and Taiwan. Any U.S. or foreign patent issuing from the pending applications covering the novel DNA alkylators and novel
scaffold platforms is projected to expire between 2037 and 2039, excluding any additional term for patent term adjustments
or patent term extensions.

XMT-1592 ADC

The  intellectual  property  portfolio  for  our  site  specific  NaPi2b  ADC  product  candidate,  XMT-1592,  is  directed  to
compositions of matter for our novel ADC based on exclusively in licensed NaPi2b antibody and our Dolasynthen platform,
as well as methods of using, making these novel conjugates and administration of these novel conjugates. As of January 31,
2020, we owned one pending provisional U.S. patent application related to XMT-1592. Any U.S. or foreign patent issuing
from the pending applications covering XMT-1592 is projected to expire in 2041, excluding any additional term for patent
term adjustments or patent term extensions.

Immunosynthen ADC platform

The intellectual property portfolio for our novel Immunosynthen platform is directed to compositions of matter for the novel
STING  agonists,  as  well  as  methods  of  using  and  methods  of  making  these  novel  payloads.  As  of  January  31,  2020,  we
owned three pending provisional U.S. patent applications related to Immunosynthen. Any U.S. or foreign patent issuing from
the pending applications is projected to expire in 2040, excluding any additional term for patent term adjustments or patent
term extensions.

In  addition  to  patents,  we  rely  upon  unpatented  trade  secrets  and  know-how  and  continuing  technological  innovation  to
develop  and  maintain  our  competitive  position.  We  seek  to  protect  our  proprietary  information,  in  part,  by  executing
confidentiality  agreements  with  our  collaborators  and  scientific  advisors  and  non-competition,  non-solicitation,
confidentiality and invention assignment agreements with our employees and consultants. We have also executed agreements
requiring  assignment  of  inventions  with  selected  scientific  advisors  and  collaborators.  The  confidentiality  agreements  we
enter  into  are  designed  to  protect  our  proprietary  information  and  the  agreements  or  clauses  requiring  assignment  of
inventions  to  us  are  designed  to  grant  us  ownership  of  technologies  that  are  developed  through  our  relationship  with  the
respective  counterparty.  We  cannot  guarantee,  however,  that  we  will  have  executed  such  agreements  with  all  applicable
employees  and  contractors,  or  that  these  agreements  will  afford  us  adequate  protection  of  our  intellectual  property  and
proprietary information rights. With respect to the building of our proprietary compound library, we consider trade secrets
and know-how to be our primary intellectual property. Trade secrets and know-how can be difficult to protect. In particular,
we anticipate that with respect to this technology platform, these trade secrets and know-how will over time be disseminated
within  the  industry  through  independent  development  and  public  presentations  describing  the  methodology.  For  more
information regarding the risks associated with our trade secrets, please see “Risk factors—Risks related to our intellectual
property—Confidentiality  agreements  with  employees  and  third  parties  may  not  prevent  unauthorized  disclosure  of  trade
secrets and other proprietary information.”

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Competition

The  biotechnology  and  biopharmaceutical  industries,  and  the  oncology  subsector,  are  characterized  by  rapid  evolution  of
technologies,  fierce  competition  and  strong  defense  of  intellectual  property.  Any  product  candidates  that  we  successfully
develop and commercialize will have to compete with existing therapies and new therapies that may become available in the
future. While we believe that our proprietary ADC platforms and scientific expertise provide us with competitive advantages,
a  wide  variety  of  institutions,  including  large  biopharmaceutical  companies,  specialty  biotechnology  companies,  academic
research  departments  and  public  and  private  research  institutions,  are  actively  developing  potentially  competitive  products
and technologies. These competitors generally fall within the following categories:

New cancer treatments:  Many global pharmaceutical companies, as well as medium and small biotechnology companies,
are pursuing new cancer treatments whether small molecules, biologics or ADCs. Any of these treatments could prove to be
superior clinically to our products.

ADC  platforms:    Although  Dolaflexin,  Dolasynthen  and  the  new  platform  initiatives  we  have  underway  are  highly
differentiated  and  proprietary,  many  companies  continue  to  invest  in  innovation  in  the  ADC  field  including  new  payload
classes, new conjugation approaches and new targeting moieties. Any of these initiatives could lead to a platform that has
superior properties to ours. We are also aware of multiple companies with ADC technologies that may be competitive to our
platforms, including Astellas, AstraZeneca, Daiichi Sankyo, ImmunoGen, Immunomedics, Pfizer and Seattle Genetics. These
companies or their partners, including AbbVie, Genentech and Takeda, may develop product candidates which compete in
the same indications as our current and future product candidates. We expect to compete on improved efficacy, safety and
tolerability  compared  to  other  product  candidates  and  if  our  products  are  not  demonstrably  superior  in  these  respects
compared to other approved therapeutics, we may not be able to compete effectively.

Many  of  our  competitors,  either  alone  or  with  strategic  partners,  have  substantially  greater  financial,  technical  and  human
resources than we do. Accordingly, our competitors may be more successful than us in obtaining approval for treatments and
achieving  widespread  market  acceptance,  rendering  our  treatments  obsolete  or  non-competitive.  Accelerated  merger  and
acquisition  activity  in  the  biotechnology  and  biopharmaceutical  industries  may  result  in  even  more  resources  being
concentrated among a smaller number of our competitors. These companies also compete with us in recruiting and retaining
qualified  scientific  and  management  personnel,  establishing  clinical  study  sites  and  patient  registration  for  clinical  studies
and  acquiring  technologies  complementary  to,  or  necessary  for,  our  programs.  Smaller  or  early  stage  companies  may  also
prove  to  be  significant  competitors,  particularly  through  collaborative  arrangements  with  large  and  established  companies.
Our  commercial  opportunity  could  be  substantially  limited  in  the  event  that  our  competitors  develop  and  commercialize
products  that  are  more  effective,  safer,  less  toxic,  more  convenient  or  less  expensive  than  our  comparable  products.  In
geographies that are critical to our commercial success, competitors may also obtain regulatory approvals before us, resulting
in our competitors building a strong market position in advance of our products’ entry. We believe the factors determining the
success of our programs will be the efficacy, safety and tolerability of our product candidates.

Employees

As of January 31, 2020, we had 83 full time employees, including 63 with M.D., Ph.D. or other advanced degrees. Of these
full time employees, 66 are engaged in research and development and 17 are engaged in general and administrative activities.
None of our employees are represented by a labor union or covered by a collective bargaining agreement. We consider our
relationship with our employees to be good.

Facilities

Our corporate headquarters are located in Cambridge, Massachusetts. We occupy approximately 34,000 square feet of office
and laboratory space that we lease in the multi-tenant building in which our corporate headquarters are located. We have an
option  to  extend  the  lease  term  for  an  additional  five  years  thereafter.  We  believe  that  this  office  and  laboratory  space  is
sufficient to meet our current needs and that suitable additional space will be available as and when needed.

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Corporate Information

We were incorporated in 2001 as a Delaware corporation. Our principal executive offices are located at 840 Memorial Drive,
Cambridge,  MA  02139,  and  our  telephone  number  is  617-498-0020.  Our  internet  site  is  www.mersana.com.  We  routinely
make  available  important  information  free  of  charge,  including  copies  of  our  Annual  Reports  on  Form  10-K,  Quarterly
Reports on Form 10-Q, Current Reports on Form 8-K and amendments to those reports filed or furnished pursuant to Section
13(a)  or  15(d)  of  the  Exchange  Act,  as  soon  as  reasonably  practicable  after  such  reports  are  electronically  filed  with,  or
furnished to, the SEC. We recognize our website as a key channel of distribution to reach public investors and as a means of
disclosing material non-public information to comply with our disclosure obligations under SEC Regulation FD. Information
contained on our website shall not be deemed incorporated into, or to be part of this Annual Report on Form 10-K, and any
website references are not intended to be made through active hyperlinks.

ITEM 1A.           RISK FACTORS

The  following  risk  factors  and  other  information  included  in  this  Annual  Report  on  Form  10-K  should  be  carefully
considered. The risks and uncertainties described below are not the only ones we face. Additional risks and uncertainties not
presently  known  to  us  or  that  we  currently  believe  to  be  immaterial  may  also  adversely  affect  our  business.  If  any  of  the
following risks occur, our business, financial condition, results of operations and future growth prospects could be materially
and adversely affected.

Risks related to our financial position and need for additional capital

We have incurred net losses since our inception, we have no products approved for commercial sale and we anticipate that
we  will  continue  to  incur  substantial  operating  losses  for  the  foreseeable  future.  We  may  never  achieve  or  sustain
profitability.

We have incurred net losses since our inception. Our net loss was $28.2 million for the year ended December 31, 2019. As of
December 31, 2019, we had an accumulated deficit of $192.4 million. We do not know when or whether we will become
profitable. To date, we have not commercialized any products and therefore have never generated any revenues from the sale
of  products,  and  we  do  not  expect  to  generate  any  product  revenues  in  the  foreseeable  future.  Our  losses  have  resulted
principally from costs incurred in our discovery and development activities. Our net losses may fluctuate significantly from
quarter to quarter and year to year.

We  have  devoted  most  of  our  financial  resources  to  research  and  development,  including  our  clinical  and  preclinical
development activities. To date, we have financed our operations primarily through the sale of equity securities, the receipt of
funds through strategic partnerships with third parties and our credit facility. The amount of our future net losses will depend,
in part, on the rate of our future expenditures. We have not completed pivotal clinical studies for any product candidate and
only have one product candidate in a clinical study. It will be several years, if ever, before we have a product candidate ready
for  commercialization.  Even  if  we  obtain  regulatory  approval  to  market  a  product  candidate,  our  future  revenues  would
depend  upon  the  size  of  the  market  or  markets  in  which  our  product  candidates  received  such  approval  and  our  ability  to
achieve  sufficient  market  acceptance,  reimbursement  from  third‑party  payors  and  adequate  market  share  for  our  product
candidates in those markets.

We expect to continue to incur significant expenses and increasing net losses for at least the next several years. We expect our
expenses will increase substantially in connection with our ongoing activities, as we:

·

·

·

conduct clinical development of XMT-1536, our lead product candidate, and any other current or future product
candidates;

seek regulatory approval for XMT‑1536, and any other current or future product candidates, if our development
efforts are successful;

add personnel to support our product development efforts;

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·

·

continue our research and development efforts for new product opportunities; and

continue to operate as a public company.

If  we  are  required  by  the  United  States  Food  and  Drug  Administration,  or  FDA,  or  any  equivalent  foreign  regulatory
authority to perform clinical studies or preclinical studies in addition to those we currently expect to conduct, or if there are
any delays in completing the clinical studies of XMT‑1536 or any other current or future product candidates, our expenses
could increase.

To become and remain profitable, we must succeed in developing our product candidates, obtaining regulatory approval for
them, and manufacturing, marketing and selling those products for which we may obtain regulatory approval. We may not
succeed  in  these  activities,  and  we  may  never  generate  revenue  from  product  sales  or  strategic  partnerships  in  an  amount
sufficient to achieve profitability. Even if we achieve profitability in the future, we may not be able to sustain profitability in
subsequent periods. Our failure to become or remain profitable would depress our market value and could impair our ability
to raise capital, expand our business, discover or develop other product candidates or continue our operations.

We will require substantial additional financing to achieve our goals, and a failure to obtain this necessary capital when
needed could force us to delay, limit, reduce or terminate our product development or commercialization efforts.

Our  cash,  cash  equivalents  and  short-term  marketable  securities  were  $99.8  million  as  of  December  31,  2019.  We  have
utilized substantial amounts of cash since our inception and expect that we will continue to expend substantial resources for
the foreseeable future developing XMT‑1536, our lead product candidate, and any other current or future product candidates.
These expenditures may include costs associated with research and development, conducting preclinical studies and clinical
studies,  potentially  obtaining  regulatory  approvals  and  manufacturing  products,  as  well  as  marketing  and  selling  products
approved  for  sale,  if  any,  and  potentially  acquiring  new  technologies.  In  addition,  other  unanticipated  costs  may  arise.
Because the outcome of our planned and anticipated clinical studies is highly uncertain, we cannot reasonably estimate the
actual amounts necessary to successfully complete the development and commercialization of our product candidates. Our
costs will increase if we experience any delays in our clinical studies for XMT‑1536 or any other current or future product
candidates,  including  delays  in  enrollment  of  patients.  We  also  incur  costs  associated  with  operating  as  a  public  company,
hiring additional personnel and expanding our facilities.

Our future capital requirements depend on many factors, including:

·

·

·

·

·

·

the scope, progress, results and costs of researching and developing XMT‑1536 and any other current or future
product candidates and conducting preclinical studies and clinical studies;

the timing of, and the costs involved in, obtaining regulatory approvals for XMT‑1536 and any other current or
future product candidates if preclinical studies and clinical studies are successful;

the cost of manufacturing XMT‑1536 and any other current or future product candidates for clinical studies in
preparation for regulatory approval and in preparation for commercialization;

the cost of commercialization activities for XMT‑1536 and any other current or future product candidates, if any
product candidates are approved for sale, including manufacturing, marketing, sales and distribution costs;

our ability to establish and maintain strategic partnerships, licensing or other arrangements and the financial terms of
such agreements;

the costs involved in preparing, filing, prosecuting, maintaining, defending and enforcing patent claims, including
litigation costs and the outcome of such litigation; and

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the timing, receipt and amount of sales of, or royalties on, our future products, if any, or products developed by our
partners.

As further explained in Item 7. Management’s Discussion and Analysis of Financial Condition and Results of Operation of
this  Form  10-K,  based  on  our  current  operating  plan,  we  estimate  that  our  existing  cash,  cash  equivalents  and  marketable
securities will be sufficient to fund our projected operating requirements through at least the next twelve months following
the  filing  of  our  Annual  Report  on  Form  10-K,  including  our  Phase  1  clinical  study  for  XMT‑1536  and  our  planned  dose
escalation study for XMT-1592. Our operating plan, however, may change as a result of many factors currently unknown to
us and we may need additional funds sooner than planned. Additional funds may not be available when we need them on
terms that are acceptable to us, or at all. If adequate funds are not available to us on a timely basis, we may be required to
delay, limit, reduce or terminate preclinical studies, clinical studies or other development activities for one or more of our
product candidates or delay, limit, reduce or terminate our establishment of sales and marketing capabilities or other activities
that may be necessary to commercialize our product candidates. In addition, we may seek additional capital due to favorable
market conditions or strategic considerations even if we believe we have sufficient funds for our current or future operating
plans.

Raising  additional  capital  may  cause  dilution  to  our  existing  stockholders,  restrict  our  operations  or  require  us  to
relinquish rights to our technologies or ADC product candidates on unfavorable terms to us.

We may seek additional capital through a variety of means, including through private and public equity offerings and debt
financings.  To  the  extent  that  we  raise  additional  capital  through  the  sale  of  equity  or  convertible  debt  securities,  the
ownership interests of our common stockholders will be diluted, and the terms of such equity or convertible debt securities
may  include  liquidation  or  other  preferences  that  are  senior  to  or  otherwise  adversely  affect  the  rights  of  our  common
stockholders. Additional debt financing, if available, may involve agreements that include covenants limiting or restricting
our  ability  to  take  certain  actions,  such  as  incurring  future  debt,  making  capital  expenditures,  declaring  dividends  or
encumbering  our  assets  to  secure  future  indebtedness,  each  of  which  could  adversely  impact  our  ability  to  conduct  our
business and execute our operating plan. If we raise additional funds through strategic partnerships with third parties, we may
have to relinquish valuable rights to our technologies, including our  platforms, or product candidates, or grant licenses on
terms that are not favorable to us. If we are unable to raise additional funds through equity or debt financing when needed,
we  may  be  required  to  delay,  limit,  reduce  or  terminate  our  product  development  or  commercialization  efforts  for
XMT‑1536, our lead product candidate, or any other current or future product candidates, or grant rights to third parties to
develop and market product candidates that we would otherwise prefer to develop and market ourselves.

We have a credit facility that requires us to meet certain operating and financial covenants and place restrictions on our
operating and financial flexibility. 

On May 8, 2019, we entered into a loan and security agreement, or the Credit Facility, with Silicon Valley Bank, or SVB,
pursuant  to  which  we  may  borrow,  at  our  option,  up  to  $20.0  million,  through  August  31,  2020.    The  Credit  Facility  is
secured  by  substantially  all  of  our  assets,  except  for  our  intellectual  property,  which  is  subject  to  a  negative  pledge,  and
certain other customary exclusions, which ensures that SVB’s rights to repayment would be senior to the rights of the holders
of our common stock in the event of liquidation.

The Credit Facility includes customary covenants including covenants requiring us to maintain our corporate existence and
governmental  approvals,  deliver  certain  financial  reports,  maintain  insurance  coverage  and  maintain  a  liquidity  ratio.
Additionally,  we  are  restricted  in  our  ability  to  transfer  collateral,  incur  additional  indebtedness,  engage  in  mergers  or
acquisitions, pay dividends or make other distributions, make investments, create liens, sell assets and agree to a change in
control.  Upon the occurrence of an event of default, which includes our failure to satisfy our payment obligations under the
Credit Facility, the breach of certain of the covenants under the Credit Facility, or the occurrence of a material adverse change
in our business, SVB is entitled to increase the applicable interest rate, accelerate amounts due under the Credit Facility and
dispose the collateral as permitted under applicable law. Any declaration by SVB of an event of default could significantly
harm our business and prospects and could cause the price of our common stock to decline.

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We may expend our resources to pursue a particular product candidate and fail to capitalize on product candidates that
may be more profitable or for which there is a greater likelihood of success.

Because we have limited financial and managerial resources, we focus on specific product candidates. As a result, we may
forgo or delay pursuit of opportunities with other product candidates that later prove to have greater commercial potential.
Our  resource  allocation  decisions  may  cause  us  to  fail  to  capitalize  on  viable  commercial  products  or  profitable  market
opportunities. Failure to properly assess potential product candidates could result in our focus on product candidates with low
market potential, which would harm our business and financial condition. Our spending on current and future research and
development  programs  and  product  candidates  for  specific  indications  may  not  yield  any  commercially  viable  product
candidates. If we do not accurately evaluate the commercial potential or target market for a particular product candidate, we
may relinquish valuable rights to that product candidate through partnering, licensing or other royalty arrangements in cases
in  which  it  would  have  been  more  advantageous  for  us  to  retain  sole  development  and  commercialization  rights  to  such
product candidate.

Risks related to development and approval of our ADC product candidates

Failure of a discovery program or product candidate may occur at any stage of preclinical or clinical development, and,
because our and our partner’s discovery programs and our product candidates are in early stages of preclinical or clinical
development, there is a relatively higher risk of failure and we or our partners may never succeed in generating revenue
from such discovery programs or product candidates.

Our early encouraging preclinical results for XMT‑1536, our lead product candidate, or any other current or future product
candidates,  are  not  necessarily  predictive  of  the  results  of  our  ongoing  or  future  discovery  programs  or  clinical  studies.
Promising results in preclinical studies of a drug candidate may not be predictive of similar results in later‑stage preclinical
studies  or  in  humans  during  clinical  studies.  Many  companies  in  the  pharmaceutical  and  biotechnology  industries  have
suffered  significant  setbacks  in  late‑stage  clinical  studies  after  achieving  positive  results  in  early‑stage  development,
including  early‑stage  clinical  studies,  and  we  cannot  be  certain  that  we  will  not  face  similar  setbacks.  These  companies’
setbacks have been caused by, among other things, preclinical findings made while clinical studies were underway or safety
or efficacy observations made in preclinical studies and clinical studies, including previously unreported adverse events.

Any  clinical  studies  that  we  may  conduct  may  not  demonstrate  the  efficacy  and  safety  necessary  to  obtain  regulatory
approval  to  market  our  product  candidates.  In  addition,  clinical  trial  results  for  one  of  our  product  candidates  or  for
competitor  products  utilizing  similar  technology,  may  raise  concerns  about  the  safety  or  efficacy  of  other  products  in  our
pipeline. If the results of our ongoing or future clinical studies are inconclusive with respect to the efficacy of our product
candidates or if we do not meet the clinical endpoints with statistical significance or if there are safety concerns or adverse
events  associated  with  our  product  candidates,  we  may  be  prevented  or  delayed  in  obtaining  marketing  approval  for  our
product candidates. There can be significant variability in safety or efficacy results between different clinical studies of the
same product candidate due to numerous factors, including changes in study procedures set forth in protocols, differences in
the size and type of the patient populations, changes in and adherence to the clinical study protocols and the rate of dropout
among clinical study participants. Moreover, preclinical and clinical data are often susceptible to varying interpretations and
analyses,  and  many  companies  that  believed  their  product  candidates  performed  satisfactorily  in  preclinical  studies  and
clinical studies nonetheless failed to obtain FDA approval.

Alternatively, even if we obtain regulatory approval, that approval may be for indications or patient populations that are not
as  broad  as  intended  or  desired  or  may  require  labeling  that  includes  significant  use  or  distribution  restrictions  or  safety
warnings. We may also be required to perform additional or unanticipated clinical studies to obtain approval or be subject to
additional  post‑marketing  testing  requirements  to  maintain  regulatory  approval.  In  addition,  regulatory  authorities  may
withdraw their approval of a product or impose restrictions on its distribution, such as in the form of a risk evaluation and
mitigation  strategy  (REMS)  program.  The  failure  to  obtain  timely  regulatory  approval  of  product  candidates,  any  product
marketing  limitations  or  a  product  withdrawal  would  negatively  impact  our  business,  results  of  operations  and  financial
condition.

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Interim, top-line and preliminary data from our clinical trials that we announce or publish from time to time may change
as more patient data become available and are subject to audit and verification procedures that could result in material
changes in the final data.

From time to time, we may publish interim, “top-line” or preliminary data from our clinical studies. Positive preliminary data
may not be predictive of such trial’s subsequent or overall results. Interim data from clinical trials that we may complete are
subject to the risk that one or more of the clinical outcomes may materially change as patient enrollment continues and more
patient  data  become  available.  Preliminary  or  “top-line”  data  also  remain  subject  to  audit  and  verification  procedures  that
may result in the final data being materially different from the preliminary data we previously published. As a result, interim
and  preliminary  data  should  be  viewed  with  caution  until  the  final  data  are  available.  Adverse  differences  between
preliminary or interim data and final data could significantly harm our business prospects.

We currently have only one ADC product candidate, XMT-1536, in a clinical study. A failure of this product candidate in
clinical development would adversely affect our business and may require us to discontinue development of other ADC
product candidates based on the same technology.

XMT-1536  is  currently  our  only  clinical‑stage  development  product  candidate.  While  we  have  certain  other  preclinical
programs  in  development  and  we  intend  to  develop  other  product  candidates,  including  XMT-1592,  it  will  take  additional
investment and time for such programs to reach the same stage of development as XMT-1536. In addition, we have other
product candidates in our current pipeline that are based on the same platform. If XMT-1536 fails in development as a result
of any underlying problem with our platform, then we may be required to discontinue development of the product candidates
that are based on the same technology. If we were required to discontinue development of XMT-1536 or if XMT-1536 were
to fail to receive regulatory approval or were to fail to achieve sufficient market acceptance, we could be prevented from or
significantly delayed in achieving profitability.

Events that may delay or prevent successful commencement, enrollment or completion of clinical studies of our product
candidates could result in increased costs to us as well as a delay in obtaining, or failure to obtain, regulatory approval, or
cause us to suspend or terminate a clinical trial, which could prevent us from commercializing our product candidates on
a timely basis, or at all.

We cannot guarantee that clinical studies, including our ongoing Phase 1b clinical study and anticipated additional clinical
studies for XMT-1536, our lead product candidate, will be conducted as planned or completed on schedule, if at all. A failure
of one or more clinical studies can occur at any stage of testing, and other events may cause us to temporarily or permanently
cease  a  clinical  study.  Events  that  may  prevent  successful  or  timely  commencement,  enrollment  or  completion  of  clinical
development include, among others:

·

·

·

·

·

·

·

delays by us in reaching a consensus with regulatory agencies on study design;

delays in reaching, or failing to reach, agreement on acceptable terms with prospective clinical research
organizations, or CROs, and clinical study sites;

difficulties in obtaining required Institutional Review Board, or IRB, approval at each clinical study site;

challenges in recruiting and enrolling suitable patients to participate in clinical studies that meet the criteria of the
protocol for the clinical study;

imposition of a clinical hold by regulatory agencies or IRBs for any reason, including safety concerns or after an
inspection of clinical operations or study sites;

failure by CROs, other third parties or us to adhere to clinical study requirements;

failure to perform in accordance with the FDA’s good clinical practices, or GCP, or applicable regulatory guidelines
in other countries;

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·

·

·

·

·

·

inadequate quantity or quality of a product candidate or other materials necessary to conduct clinical studies,
including, for example, delays in the testing, validation, manufacturing or delivery of the product candidates to the
clinical sites;

patients not completing participation in a study or not returning for post‑treatment follow‑up;

clinical study sites or patients dropping out of a study;

safety issues, including occurrence of serious adverse events, or SAEs, in clinical studies that are associated with the
product candidates that are viewed to outweigh their potential benefits or unforeseen safety issues in our ongoing
preclinical studies;

changes in regulatory requirements or guidance that require amending or submitting new clinical protocols; or

lack of adequate funding to continue the clinical study.

Delays,  including  delays  caused  by  the  above  factors,  can  be  costly  and  could  negatively  affect  our  ability  to  complete  a
clinical study. If we or our partners are not able to successfully complete clinical studies, we or they will not be able to obtain
regulatory approval and will not be able to commercialize our product candidates or our partners’ product candidates based
on our technology.

An  inability  to  enroll  sufficient  numbers  of  patients  in  our  clinical  studies  could  result  in  increased  costs  and  longer
development periods for our product candidates.

Clinical studies require sufficient patient enrollment, which is a function of many factors, including:

·

·

·

·

·

·

·

·

the size and nature of the patient population;

the severity of the disease under investigation;

the nature and complexity of the study protocol, including eligibility criteria for the study;

the number of clinical study sites and the proximity of patients to those sites;

standard of care in the diseases under investigation;

the commitment of clinical investigators to identify eligible patients;

competing studies or trials; and

clinicians’ and patients’ perceptions as to the potential advantages and risks of the drug being studied in relation to
other available therapies, including any new drugs that may be approved for the indications we are investigating.

Challenges in recruiting and enrolling suitable patients to participate in clinical studies that meet the criteria of the protocol
for clinical studies could increase costs and result in delays to our current development plan for XMT‑1536, our lead product
candidate, or any other current or future product candidate.

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We may seek a Breakthrough Therapy Designation or Fast Track Designation by the FDA for any of our ADC product
candidates,  and  we  may  be  unsuccessful.  If  we  are  successful,  the  designation  may  not  actually  lead  to  a  faster
development  or  regulatory  review  or  approval  process,  and  it  does  not  increase  the  likelihood  that  any  ADC  product
candidate would receive marketing approval.

We  may  seek  a  Breakthrough  Therapy  Designation  or  Fast  Track  Designation  for  any  of  our  product  candidates.  A
breakthrough therapy is defined as a drug that is intended, alone or in combination with one or more other drugs, to treat a
serious  or  life-threatening  disease  or  condition,  and  preliminary  clinical  evidence  indicates  that  the  drug  may  demonstrate
substantial  improvement  over  currently  approved  therapies  on  one  or  more  clinically  significant  endpoints,  such  as
substantial treatment effects observed early in clinical development. Fast Track Designation may be available if a product is
intended for the treatment of a serious or life-threatening condition and preclinical or clinical data demonstrate the potential
to  address  an  unmet  medical  need  for  this  condition.  Drugs  that  receive  Breakthrough  Therapy  Designation  or  Fast  Track
Designation by the FDA may also be eligible for accelerated approval and/or priority review if they satisfy the criteria for
those programs.

The FDA has broad discretion whether or not to grant Breakthrough Therapy Designation or Fast Track Designation. Even if
we receive Breakthrough Therapy Designation or Fast Track Designation for a product candidate, such designation may not
result in a faster development process, review or approval compared to conventional FDA procedures and does not assure
ultimate approval by the FDA. In addition, even if any of our product candidates receives Breakthrough Therapy Designation
or Fast Track Designation, the FDA may later decide that the drugs no longer meet the conditions for qualification and
rescind the designation.

We may not be able to obtain orphan drug designation for our ADC product candidates, and even if we do, we may be
unable to maintain the benefits associated with orphan drug designation, including the potential for market exclusivity.

We may seek orphan drug designation status for one of our current or future product candidates, and we may be unsuccessful.
In the United States, orphan drug designation entitles a party to financial incentives such as opportunities for grant funding
towards clinical trial costs, tax advantages and user-fee waivers. In Europe, orphan drug designation entitles a party to a
number of incentives, such as protocol assistance and scientific advice specifically for designated orphan medicines, and
potential fee reductions depending on the status of the sponsor. Generally, if a drug with an orphan drug designation
subsequently receives the first marketing approval for the indication for which it has such designation, the drug is entitled to
a period of marketing exclusivity, which precludes the European Medicines Agency or the FDA from approving another
marketing application for the same drug and indication for a set time period, except in limited circumstances. Even if we
obtain orphan drug exclusivity for a drug, that exclusivity may not effectively protect the drug from competition because
different drugs can be approved for the same condition, or the drug may be used off-label. Even after an orphan drug is
approved, the FDA can subsequently approve another drug for the same condition if the FDA concludes that the other drug is
clinically superior. In addition, a designated orphan drug may not receive orphan drug exclusivity if it is approved for a use
that is broader than the indication for which it received orphan designation. Moreover, orphan drug exclusive marketing
rights in the United States may be lost if the FDA later determines that the request for designation was materially defective or
if the manufacturer is unable to assure sufficient quantity of the drug to meet the needs of patients with the rare disease or
condition. Orphan drug designation neither shortens the development time or regulatory review time of a drug nor gives the
drug any advantage in the regulatory review or approval process. While we may seek orphan drug designation for applicable
indications for our current or future product candidates, we may never receive such designations. Even if we do receive such
designations, there is no guarantee that we will enjoy the benefits of those designations.

Clinical development, regulatory review and approval by the FDA and comparable foreign authorities are lengthy, time
consuming and inherently unpredictable. If we or our partners are ultimately unable to obtain regulatory approval for our
ADC product candidates, our business will be substantially harmed.

The preclinical studies and clinical studies of our product candidates are, and the manufacturing and marketing of our product
candidates will be, subject to extensive and rigorous review and regulation by numerous government authorities in the United
States and in other countries where we intend to test and, if approved, market any such product candidate.

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These  government  regulations  relate  to,  among  other  things,  development,  clinical  studies,  manufacturing  and
commercialization.  In  order  to  obtain  regulatory  approval  for  the  commercial  sale  of  any  product  candidates,  we  or  our
partners  must  demonstrate  through  extensive  preclinical  studies  and  clinical  studies  that  the  product  candidate  is  safe  and
effective for use in each target indication.

The time required to obtain approval by the FDA and comparable foreign authorities is unpredictable, typically takes many
years following the commencement of clinical studies and depends upon numerous factors. Of the large number of drugs in
development in the United States, only a small percentage will successfully complete the FDA regulatory approval process
and  will  be  commercialized.  Accordingly,  even  if  we  are  able  to  obtain  the  requisite  financing  to  continue  to  fund  our
development  and  preclinical  studies  and  clinical  studies,  we  cannot  be  assured  that  any  of  our  product  candidates  will  be
successfully developed or commercialized.

In  addition,  approval  policies,  regulations  or  the  type  and  amount  of  clinical  data  necessary  to  gain  approval  may  change
during the course of a product candidate’s clinical development and may vary among jurisdictions, which may cause delays
in the approval of or the decision not to approve an application. Regulatory approval has not been obtained for any product
candidate based on our technologies, and it is possible that none of our existing product candidates or any product candidates
we may seek to develop in the future will ever obtain regulatory approval. In addition, we may gain regulatory approval for
XMT‑1536, our lead product candidate, or any other current or future product candidates in some but not all of the territories
for which we seek approval or some but not all of the target indications, resulting in limited commercial opportunity for the
approved product candidates.

Applications  for  our  or  our  partners’  product  candidates  could  be  delayed  or  could  fail  to  receive  regulatory  approval  for
many reasons, including, but not limited to the following:

·

·

·

·

·

·

·

·

·

the FDA or comparable foreign regulatory authorities may disagree with the number, design or implementation of
our clinical studies;

the population studied in the clinical program may not be sufficiently broad or representative to assure safety in the
full population for which we seek approval;

the FDA or comparable foreign regulatory authorities may disagree with our interpretation of data from preclinical
studies or clinical studies;

the data collected from clinical studies of our product candidates may not meet the level of statistical or clinical
significance required by the FDA or comparable foreign regulatory authorities for marketing approval or may
otherwise not be sufficient to support the submission of a new drug application or biologics license application, or
other submission or to obtain regulatory approval in the United States or elsewhere;

the FDA may not accept data generated at our preclinical studies and clinical study sites;

the FDA may require us to conduct additional preclinical studies and clinical studies;

we may be unable to demonstrate to the FDA or comparable foreign regulatory authorities that a product candidate’s
risk‑benefit ratio for its proposed indication is acceptable;

the FDA or comparable foreign regulatory authorities may fail to approve the manufacturing processes, test
procedures and specifications or facilities of third‑party manufacturers with which we contract for clinical and
commercial supplies;

we or any third‑party service providers may be unable to demonstrate compliance with current Good Manufacturing
Practices, or cGMPs, to the satisfaction of the FDA or comparable foreign regulatory authorities, which could result
in delays in regulatory approval or require us to withdraw or recall products and interrupt commercial supply of our
products; or

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the approval policies or regulations of the FDA or comparable foreign regulatory authorities may significantly
change in a manner rendering our clinical data insufficient for approval.

Any of these factors, many of which are beyond our control, may result in our failing to obtain regulatory approval to market
any of our product candidates, which would significantly harm our business, results of operations and prospects.

We may conduct clinical trials for ADC product candidates at sites outside the United States, and the FDA may not accept
data from trials conducted in such locations. 

We may conduct clinical trials outside the United States. Although the FDA may accept data from clinical trials conducted
outside the United States, acceptance of these data is subject to conditions imposed by the FDA. For example, the clinical
trial must be well designed and conducted and be performed by qualified investigators in accordance with ethical principles.
If the foreign data is the sole basis for a marketing application, then the data must be applicable to the U.S. population and
U.S.  medical  practice  in  ways  that  the  FDA  deems  clinically  meaningful  and  the  FDA  must  be  able  to  validate  the  data
through an on-site inspection, if necessary. In addition, while these clinical trials are subject to the applicable local laws, FDA
acceptance  of  the  data  will  depend  on  its  determination  that  the  trials  also  complied  with  all  applicable  U.S.  laws  and
regulations.  If  the  FDA  does  not  accept  the  data  from  any  trial  that  we  conduct  outside  the  United  States,  it  would  likely
result  in  the  need  for  additional  trials,  which  would  be  costly,  time-consuming  and  could  delay  or  permanently  halt  our
development of the applicable product candidates.

If  we  fail  to  obtain  regulatory  approval  in  jurisdictions  outside  the  United  States,  we  will  not  be  able  to  market  our
products in those jurisdictions.

We intend to market our product candidates, including XMT‑1536, our lead product candidate, if approved, in international
markets either directly or through partnerships. Such marketing will require separate regulatory approvals in each market and
compliance with numerous and varying regulatory requirements. The approval procedures vary from country to country and
may  require  additional  testing  that  we  are  not  required  to  perform  to  obtain  regulatory  approval  in  the  United  States.
Moreover, the time required to obtain approval in countries outside the United States may differ from that required to obtain
FDA approval. In addition, in many countries outside the United States, a drug must be approved for reimbursement before it
can be approved for sale in that country. Approval by the FDA does not ensure approval by regulatory authorities in other
countries or jurisdictions, and approval by one foreign regulatory authority does not ensure approval by regulatory authorities
in other foreign countries or by the FDA. The foreign regulatory approval process may include all of the risks associated with
obtaining FDA approval. We or our partners may not obtain foreign regulatory approvals on a timely basis, if at all. We or
our partners may not be able to file for regulatory approvals and may not receive necessary approvals to commercialize our
products in any market. If we or any existing or future partner are unable to obtain regulatory approval for XMT‑1536 or any
of  our  other  current  or  future  product  candidates  in  one  or  more  significant  foreign  jurisdictions,  then  the  commercial
opportunity for such product candidate and our financial condition will be adversely affected.

Even  if  we  receive  regulatory  approval  for  our  ADC  product  candidates,  such  products  will  be  subject  to  ongoing
regulatory  review,  which  may  result  in  significant  additional  expense.  Additionally,  our  ADC  product  candidates,  if
approved, could be subject to labeling and other restrictions, and we may be subject to penalties if we fail to comply with
regulatory requirements or experience unanticipated problems with our products.

Any  regulatory  approvals  that  we  receive  for  our  product  candidates  may  also  be  subject  to  limitations  on  the  approved
indicated uses for which the product may be marketed or to conditions of approval, or contain requirements for potentially
costly post‑marketing testing and surveillance to monitor safety and efficacy. In addition, if the FDA or any other governing
regulatory  body  approves  any  of  our  product  candidates,  the  manufacturing  processes,  labeling,  packaging,  distribution,
adverse event reporting, storage, advertising, promotion and recordkeeping for the product will be subject to extensive and
ongoing  regulatory  requirements.  These  requirements  include  submissions  of  safety  and  other  post‑marketing  information
and  reports,  registration,  as  well  as  continued  compliance  with  cGMP  and  GCP,  for  any  clinical  studies  that  we  conduct
post‑approval.

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Later discovery of previously unknown problems with an approved drug, including adverse events of unanticipated severity
or frequency, or with manufacturing operations or processes, or failure to comply with regulatory requirements, may result in,
among other things:

·

·

·

·

·

restrictions on the marketing or manufacturing of the product, withdrawal of the product from the market or
voluntary or mandatory product recalls;

fines, warning letters or holds on clinical studies;

refusal by the FDA or any other governing regulatory body to approve pending applications or supplements to
approved applications filed by us, or suspension or revocation of product license approvals;

product seizure or detention, or refusal to permit the import or export of products; and

injunctions or the imposition of civil or criminal penalties.

The policies of the FDA or any other governing regulatory body may change and additional government regulations may be
enacted that could prevent, limit or delay regulatory approval of our product candidates. We cannot predict the likelihood,
nature or extent of government regulation that may arise from future legislation or administrative action, either in the United
States or abroad. If we are slow or unable to adapt to changes in existing requirements or the adoption of new requirements or
policies, or not able to maintain regulatory compliance, we may lose any marketing approval that may have been obtained
and we may not achieve or sustain profitability, which would adversely affect our business.

Our ADC product candidates or ADCs developed or commercialized by our competitors may cause undesirable side effects
or  have  other  properties  that  delay  or  prevent  regulatory  approval  of  our  ADC  product  candidates  or  limit  their
commercial potential.

Undesirable side effects caused by our product candidates or ADCs being developed or commercialized by our partners or
competitors  could  cause  us  or  regulatory  authorities  to  interrupt,  delay  or  halt  clinical  studies  and  could  result  in  a  more
restrictive label or the denial of regulatory approval by the FDA or other regulatory authorities and potential product liability
claims. Further, clinical studies by their nature utilize a sample of the potential patient population. With a limited number of
subjects and limited duration of exposure, rare and severe side effects of our product candidates or those of our competitors
may only be uncovered with a significantly larger number of patients exposed to the drug. SAEs deemed to be caused by our
product candidates or those of our competitors, either before or after receipt of marketing approval, could have a material
adverse effect on the development of our product candidates and our business as a whole.

If we or others identify undesirable side effects caused by our product candidates or those of our competitors either before or
after receipt of marketing approval, a number of potentially significant negative consequences could result, including:

·

·

·

·

·

·

our clinical studies may be put on hold;

we may be unable to obtain regulatory approval for our product candidates;

regulatory authorities may withdraw or limit their approvals of our product candidates;

regulatory authorities may require the addition of labeling statements, such as a contraindication, black box
warnings or additional warnings;

the FDA may require development of a REMS with Elements to Assure Safe Use as a condition of approval or
post‑approval;

we may decide to remove such product candidates from the marketplace;

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·

·

·

we may be subject to regulatory investigations and government enforcement actions;

we could be sued and held liable for harm caused to patients; and

our reputation may suffer.

Any of these events could prevent us from achieving or maintaining market acceptance of our product candidates and could
substantially increase commercialization costs.

If  we  or  our  third‑party  collaborators  are  unable  to  successfully  develop  and  commercialize  any  required  companion
diagnostics  for  our  product  candidates  or  engage  a  third  party  to  do  so,  or  we  or  they  experience  significant  delays  in
doing so, we may not realize the full potential of our ADC product candidates.

If a companion diagnostic is required for the label for XMT‑1536, our lead product candidate, or any of our other current or
future product candidates, therefore conditioning our ability to market such product candidates on the commercial availability
of an approved companion diagnostic, we may seek approval for our validated assay as a companion diagnostic or we may
contract  with  third  parties  to  create  and  obtain  approval  for  a  companion  diagnostic.  To  be  successful  in  developing  and
commercializing such a companion diagnostic, we need to address a number of scientific, technical and logistical challenges.
We have little experience in the development and commercialization of diagnostics and may not be successful in developing
and commercializing appropriate diagnostics to pair with XMT‑1536 or any of our other current or future product candidates.
Companion diagnostics are subject to regulation by the FDA and equivalent foreign regulatory authorities as medical devices
and  require  separate  regulatory  approval  prior  to  commercialization.  Given  our  limited  experience  in  developing  and
commercializing  diagnostics,  we  may  rely  in  part  or  in  whole  on  third  parties  for  their  design,  manufacture  and
commercialization.  We,  our  collaborators  or  such  third  parties  may  encounter  difficulties  in  developing  and  obtaining
approval  for  the  companion  diagnostics,  including  issues  relating  to  selectivity/specificity,  analytical  validation,
reproducibility or clinical validation. Any delay or failure by us, our collaborators or such third parties to develop or obtain
regulatory approval of the companion diagnostics could delay or prevent approval of our product candidates. If we, or any
third  parties  that  we  may  contract  with  to  assist  us,  are  unable  to  successfully  develop  and  commercialize  companion
diagnostics for our product candidates, or experience delays in doing so:

·

·

·

the development of XMT‑1536 and our other current or future product candidates, may be adversely affected if we
are unable to appropriately select patients for enrollment in our clinical trials;

our product candidates may not receive marketing approval if safe and effective use of a therapeutic product
candidate depends on the availability of an in vitro diagnostic; and

we may not realize the full commercial potential of any product candidates that receive marketing approval if,
among other reasons, we are unable to appropriately select patients who are likely to benefit from therapy with our
products.

As a result, our business would be harmed, possibly materially.

In addition, third‑party collaborators may encounter production difficulties that could constrain the supply of the companion
diagnostics, and both they and we may have difficulties gaining acceptance of the use of the companion diagnostics in the
clinical  community.  If  such  companion  diagnostics  fail  to  gain  market  acceptance,  it  would  have  an  adverse  effect  on  our
ability to derive revenues from sales of our product candidates, if approved. In addition, any diagnostic company with whom
we  contract  may  decide  to  discontinue  selling  or  manufacturing  the  companion  diagnostic  that  we  anticipate  using  in
connection  with  development  and  commercialization  of  our  product  candidates  or  our  relationship  with  such  diagnostic
company may otherwise terminate. We may not be able to enter into arrangements with another diagnostic company to obtain
supplies of an alternative diagnostic test for use in connection with the development and commercialization of our product
candidates  or  do  so  on  commercially  reasonable  terms,  which  could  adversely  affect  and/or  delay  the  development  or
commercialization of our product candidates.

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We or our partners may fail to discover and develop additional potential product candidates.

Our and our partners’ research programs to identify new product candidates will require substantial technical, financial and
human resources, and we or our partners may be unsuccessful in our or their efforts to identify new product candidates. If we
or our partners are unable to identify suitable additional product candidates for preclinical and clinical development, our or
their ability to develop product candidates and our ability to obtain revenues from commercializing our products or to receive
royalties from our partners’ sales of their products in future periods could be compromised, which could result in significant
harm to our financial position and adversely impact our stock price.

Risks related to our reliance on third parties

Because we rely on third‑party manufacturing and supply partners, our supply of research and development, preclinical
and clinical development materials may become limited or interrupted or may not be of satisfactory quantity or quality.

We rely on third‑party contract manufacturers to manufacture our preclinical and clinical study product supplies, and we lack
the  internal  resources  and  the  capability  to  manufacture  any  product  candidates  on  a  clinical  or  commercial  scale.  The
facilities used by our contract manufacturers to manufacture the active pharmaceutical ingredient and final drug product must
be acceptable to the FDA and other comparable foreign regulatory agencies pursuant to inspections that would be conducted
after  we  submit  our  marketing  application  or  relevant  foreign  regulatory  submission  to  the  applicable  regulatory  agency.
There can be no assurance that our preclinical and clinical development product supplies will be sufficient, uninterrupted or
of  satisfactory  quality  or  continue  to  be  available  at  acceptable  prices.  If  our  contract  manufacturers  cannot  successfully
manufacture  material  that  conforms  to  our  specifications  and  the  strict  regulatory  requirements  of  the  FDA  or  applicable
foreign regulatory agencies, they will not be able to secure or maintain regulatory approval for their manufacturing facilities.
Any replacement of our manufacturers could require significant effort and expertise because there may be a limited number
of qualified replacements.

The manufacturing process for a product candidate is subject to FDA and foreign regulatory authority review. Suppliers and
manufacturers must meet applicable manufacturing requirements and undergo rigorous facility and process validation tests
required  by  regulatory  authorities  in  order  to  comply  with  regulatory  standards,  such  as  cGMP.  We  have  no  direct  control
over our contract manufacturers’ ability to maintain adequate quality control, quality assurance and qualified personnel. In
the event that any of our manufacturers fails to comply with regulatory requirements or to perform its obligations to us in
relation to quality, timing or otherwise, or if our supply of components or other materials becomes limited or interrupted for
other reasons, we may be forced to manufacture the materials ourselves, for which we currently do not have the capabilities
or resources, or enter into an agreement with another third party, which we may not be able to do on reasonable terms, if at
all.  In  some  cases,  the  technical  skills  or  technology  required  to  manufacture  our  product  candidates  may  be  unique  or
proprietary  to  the  original  manufacturer  and  we  may  have  difficulty  transferring  such  skills  or  technology  to  another  third
party and a feasible alternative may not exist. These factors would increase our reliance on such manufacturer or require us to
obtain a license from such manufacturer in order to have another third-party manufacture our product candidates. If we are
required to change manufacturers for any reason, we will be required to verify that the new manufacturer maintains facilities
and procedures that comply with quality standards and with all applicable regulations and guidelines. The delays associated
with  the  verification  of  a  new  manufacturer  could  negatively  affect  our  ability  to  develop  product  candidates  in  a  timely
manner or within budget. Our reliance on contract manufacturers also exposes us to the possibility that they, or third parties
with access to their facilities, will have access to and may appropriate our trade secrets or other proprietary information.

We expect to continue to rely on third‑party manufacturers if we receive regulatory approval for any product candidate. To
the extent that we have existing, or enter into future, manufacturing arrangements with third parties, we will depend on these
third  parties  to  perform  their  obligations  in  a  timely  manner  consistent  with  contractual  and  regulatory  requirements,
including those related to quality control and assurance. If we are unable to obtain or maintain third‑party manufacturing for
product candidates, or to do so on commercially reasonable terms, we may not be able to develop and commercialize our
product candidates successfully. Our or a third party’s failure to execute on our manufacturing requirements and comply with
cGMP could adversely affect our business in a number of ways, including:

·

an inability to initiate or continue clinical studies of product candidates under development;

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·

·

·

·

·

delay in submitting regulatory applications, or receiving regulatory approvals, for product candidates;

loss of the cooperation of an existing or future strategic partner;

subjecting third‑party manufacturing facilities or our manufacturing facilities to additional inspections by regulatory
authorities;

a requirement to cease distribution or to recall batches of our product candidates; and

in the event of approval to market and commercialize a product candidate, an inability to meet commercial demands
for our products.

We,  or  our  third‑party  manufacturers,  may  be  unable  to  successfully  scale‑up  manufacturing  of  our  ADC  product
candidates  in  sufficient  quality  and  quantity,  which  would  delay  or  prevent  us  from  developing  our  ADC  product
candidates and commercializing approved products, if any.

In order to conduct clinical studies of our product candidates and commercialize any approved product candidates, we, or our
manufacturing partners, will need to manufacture them in large quantities. We, or our manufacturing partners, may be unable
to successfully increase the manufacturing capacity for any of our product candidates in a timely or cost‑effective manner, or
at  all.  In  addition,  quality  issues  may  arise  during  scale‑up  activities.  If  we,  or  any  manufacturing  partners,  are  unable  to
successfully scale up the manufacture of our product candidates in sufficient quality and quantity, the development, testing
and clinical studies of that product candidates may be delayed or infeasible, and regulatory approval or commercial launch of
any resulting product may be delayed or not obtained, which could significantly harm our business. We have evaluated which
third‑party manufactures to engage for scale‑up to commercial supply of our product candidates, including XMT‑1536, our
lead  product  candidate,  and  we  have  begun  transfer  and  scale-up  of  certain  manufacturing  activities.  If  we  are  unable  to
obtain  or  maintain  third‑party  manufacturing  for  commercial  supply  of  product  candidates,  or  to  do  so  on  commercially
reasonable terms, we may not be able to develop and commercialize our product candidates successfully.

We  rely  on  third  parties  to  conduct  preclinical  studies  and  clinical  studies  for  our  product  candidates,  including
XMT‑1536,  our  lead  product  candidate,  and  if  such  third  parties  do  not  properly  and  successfully  perform  their
obligations to us, we may not be able to obtain regulatory approvals for XMT‑1536 or any other current or future ADC
product candidates.

We  have  designed  the  Phase  1  clinical  study  for  XMT-1536,  our  lead  product  candidate,  and  intend  to  design  any  future
clinical  study  for  any  future  unpartnered  product  candidates  that  we  may  develop  if  preclinical  studies  are  successful.
However,  we  rely  on  CROs  and  other  third  parties  to  assist  in  managing,  monitoring  and  otherwise  carrying  out  many  of
these studies. As a result, we have less direct control over the conduct, timing and completion of these clinical studies and the
management of data developed through clinical studies than would be the case if we were relying entirely upon our own staff.
These CROs and other third parties are not our employees and we have limited control over the amount of time and resources
that they dedicate to our programs. We compete with many other companies for the resources of these third parties. These
third parties may have contractual relationships with other entities, some of which may be our competitors, which may draw
time and resources from our programs. The third parties with whom we contract might not be diligent, careful or timely in
conducting our preclinical studies or clinical studies, resulting in the preclinical studies or clinical studies being delayed or
unsuccessful.

The  third  parties  on  whom  we  rely  generally  may  terminate  their  engagements  at  any  time,  and  having  to  enter  into
alternative arrangements would delay development and commercialization of our product candidates. Communicating with
outside  parties  can  also  be  challenging,  potentially  leading  to  mistakes  as  well  as  difficulties  in  coordinating  activities.
Outside parties may:

·

have staffing difficulties;

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·

·

·

·

fail to comply with contractual obligations;

experience regulatory compliance issues;

undergo changes in priorities or become financially distressed; or

form relationships with other entities, some of which may be our competitors.

The FDA and comparable foreign regulatory authorities require compliance with regulations and standards, including GCP,
for designing, conducting, monitoring, recording, analyzing and reporting the results of clinical studies to assure that the data
and  results  are  credible  and  accurate  and  that  the  rights,  integrity  and  confidentiality  of  study  participants  are  protected.
Although we rely, and intend to continue to rely, on third parties to conduct our clinical studies, they are not our employees,
and  we  are  responsible  for  ensuring  that  each  of  these  clinical  studies  is  conducted  in  accordance  with  its  general
investigational  plan,  protocol  and  other  requirements.  Our  reliance  on  these  third  parties  for  research  and  development
activities will reduce our control over these activities but will not relieve us of our responsibilities.

If these third parties do not successfully carry out their duties under their agreements, if the quality or accuracy of the data
they obtain is compromised due to their failure to adhere to clinical study protocols or to regulatory requirements, or if they
otherwise  fail  to  comply  with  clinical  study  protocols  or  meet  expected  deadlines,  the  clinical  studies  of  our  product
candidates  may  not  meet  regulatory  requirements.  The  FDA  enforces  GCP  regulations  through  periodic  inspections  of
clinical study sponsors, principal investigators and study sites. If we or our CROs fail to comply with applicable GCPs or
other regulatory requirements, the clinical data generated in our clinical studies may be deemed unreliable, third parties may
need  to  be  replaced  and  preclinical  development  activities  or  clinical  studies  may  be  extended,  delayed,  suspended  or
terminated. If any of these events occur, we may not be able to obtain regulatory approval of our product candidates on a
timely basis or at all.

We depend on strategic partnerships with other companies to assist in the research, development and commercialization of
our ADC platforms and ADC product candidates. If our existing partners do not perform as expected, this may negatively
affect  our  ability  to  commercialize  our  ADC  product  candidates,  generate  revenues  through  technology  licensing,  or
otherwise negatively affect our business.

We  have  established  strategic  partnerships  and  intend  to  continue  to  establish  strategic  partnerships  with  third  parties  to
research,  develop  and  commercialize  our  platforms  and  existing  and  future  product  candidates.  We  entered  into  a
collaboration  agreement  with  Merck  KGaA  for  the  development  and  commercialization  of  other  product  candidates.  For
certain of these programs, we will depend on our partners to design and conduct their clinical studies. As a result, we may not
be able to conduct these programs in the manner or on the time schedule we currently contemplate, which may negatively
impact  our  business  operations.  In  addition,  if  any  of  these  partners  withdraw  support  for  these  programs  or  proposed
products or otherwise impair their development or experience negative results, our business and our product candidates could
be negatively affected.

Our  partners  may  terminate  their  agreements  with  us  for  cause  under  certain  circumstances  or  at  will  in  certain  cases  and
discontinue  use  of  our  technologies.  In  addition,  we  cannot  control  the  amount  and  timing  of  resources  our  partners  may
devote  to  products  utilizing  or  incorporating  our  technology.  Moreover,  our  relationships  with  our  partners  may  divert
significant time and effort of our scientific staff and management team and require effective allocation of our resources to
multiple  internal  and  collaborative  projects.  Our  partners  may  fail  to  perform  their  obligations  under  the  collaboration
agreements or may not perform their obligations in a timely manner. If conflicts arise between our partners and us, the other
party  may  act  in  a  manner  adverse  to  us  and  could  limit  our  ability  to  implement  our  strategies.  If  any  of  our  partners
terminate or breach our agreements with them, or otherwise fail to complete their obligations in a timely manner, it may have
a detrimental effect on our financial position by reducing or eliminating the potential for us to receive technology access and
license  fees,  milestones  and  royalties,  reimbursement  of  development  costs,  as  well  as  possibly  requiring  us  to  devote
additional efforts and incur costs associated with pursuing internal development of product candidates. Furthermore, if our
partners  do  not  prioritize  and  commit  sufficient  resources  to  programs  associated  with  our  product  candidates  or
collaboration product candidates, we or our partners may be unable to commercialize these product candidates, which would
limit our ability to generate revenue and become profitable.

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Our partners may separately pursue competing products, therapeutic approaches or technologies to develop treatments for the
diseases targeted by us or our partners. Competing products, either developed by the partners or to which the partners have
rights,  may  result  in  the  withdrawal  of  partner  support  for  our  product  candidates.  Even  if  our  partners  continue  their
contributions  to  the  strategic  partnerships,  they  may  nevertheless  determine  not  to  actively  pursue  the  development  or
commercialization  of  any  resulting  products.  Additionally,  if  our  partners  pursue  different  clinical  or  regulatory  strategies
with  their  product  candidates  based  on  our  platforms  or  technologies,  adverse  events  with  their  product  candidates  could
negatively affect our product candidates utilizing similar technologies.  Any of these developments could harm our product
development efforts.

To date, we have depended on a small number of partners for a substantial portion of our revenue. The loss of any one of
these partners could result in a material decline in our revenue.

We have strategic partnerships with a limited number of companies. To date, a substantial portion of our revenue has resulted
from payments made under agreements with our strategic partners, and we expect that a portion of our revenue will continue
to come from strategic partnerships. The loss of any of our partners, or the failure of our partners to perform their obligations
under  their  agreements  with  us,  including  paying  license  or  technology  fees,  milestone  payments,  royalties  or
reimbursements, could have a material adverse effect on our financial performance. Payments under our existing and future
strategic partnerships are also subject to significant fluctuations in both timing and amount, which could cause our revenue to
fall below the expectations of securities analysts and investors and cause a decrease in our stock price.

We may not be successful in establishing and maintaining additional strategic partnerships, which could adversely affect
our ability to develop and commercialize products, negatively impacting our operating results.

We  continue  to  strategically  evaluate  our  partnerships  and,  as  appropriate,  we  expect  to  enter  into  additional  strategic
partnerships  in  the  future,  including  potentially  with  major  biotechnology  or  biopharmaceutical  companies.  We  face
significant  competition  in  seeking  appropriate  partners  for  our  product  candidates,  and  the  negotiation  process  is
time‑consuming  and  complex.  In  order  for  us  to  successfully  partner  our  product  candidates,  potential  partners  must  view
these product candidates as economically valuable in markets they determine to be attractive in light of the terms that we are
seeking and other available products for licensing by other companies. Even if we are successful in our efforts to establish
strategic partnerships, the terms that we agree upon may not be favorable to us, and we may not be able to maintain such
strategic  partnerships  if,  for  example,  development  or  approval  of  a  product  candidate  is  delayed  or  sales  of  an  approved
product are disappointing. Any delay in entering into strategic partnership agreements related to our product candidates could
delay  the  development  and  commercialization  of  such  candidates  and  reduce  their  competitiveness  even  if  they  reach  the
market. If we are not able to generate revenue under our strategic partnerships when and in accordance with our expectations
or the expectations of industry analysts, this failure could harm our business and have an immediate adverse effect on the
trading price of our common stock.

If we fail to establish and maintain additional strategic partnerships related to our unpartnered product candidates, we will
bear all of the risk and costs related to the development of any such product candidate, and we may need to seek additional
financing, hire additional employees and otherwise develop expertise, such as regulatory expertise, for which we have not
budgeted.  If  we  were  not  successful  in  seeking  additional  financing,  hiring  additional  employees  or  developing  additional
expertise,  our  cash  burn  rate  would  increase  or  we  would  need  to  take  steps  to  reduce  our  rate  of  product  candidate
development. This could negatively affect the development of any unpartnered product candidate.

Risks related to commercialization of our ADC product candidates

Our future commercial success depends upon attaining significant market acceptance of our ADC product candidates, if
approved, among physicians, patients and health care payors.

Even  if  we  obtain  regulatory  approval  for  XMT‑1536,  our  lead  product  candidate,  or  any  other  current  or  future  product
candidates that we may develop or acquire in the future, the product candidate may not gain market acceptance among

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physicians, health care payors, patients and the medical community. Market acceptance of any approved products depends on
a number of factors, including:

·

·

·

·

·

·

·

·

the efficacy and safety of the product, as demonstrated in clinical studies;

the indications for which the product is approved and the label approved by regulatory authorities for use with the
product, including any warnings that may be required on the label;

acceptance by physicians and patients of the product as a safe and effective treatment;

the cost, safety and efficacy of treatment in relation to alternative treatments;

the availability of adequate reimbursement and pricing by third‑party payors and government authorities;

relative convenience and ease of administration;

the prevalence and severity of adverse side effects; and

the effectiveness of our sales and marketing efforts.

Perceptions of any product are influenced by perceptions of competitors’ products that are in the same class of drugs or have
a similar mechanism of action. As a result, adverse public perception of our competitors’ products may negatively impact the
market acceptance of our product candidates. Market acceptance is critical to our ability to generate significant revenue and
become profitable. Any therapeutic candidate, if approved and commercialized, may be accepted in only limited capacities or
not  at  all.  If  any  approved  products  are  not  accepted  by  the  market  to  the  extent  that  we  expect,  we  may  not  be  able  to
generate significant revenue and our business would suffer.

The  incidence  and  prevalence  for  target  patient  populations  of  our  drug  candidates  have  not  been  established  with
precision.  If  the  market  opportunities  for  our  drug  candidates  are  smaller  than  we  estimate  or  if  any  approval  that  we
obtain is based on a narrower definition of the patient population, our revenue and ability to achieve profitability will be
adversely affected, possibly materially.

The  precise  incidence  and  prevalence  of  epithelial  ovarian  cancer  and  non‑squamous  NSCLC  with  NaPi2b  expression  are
unknown. Our projections of both the number of people who have these diseases, as well as the subset of people with these
diseases  who  have  the  potential  to  benefit  from  treatment  with  our  drug  candidates,  are  based  on  estimates.  The  total
addressable  market  opportunity  for  XMT‑1536  or  XMT-1592  for  the  treatment  of  epithelial  ovarian  cancer  and
non‑squamous  NSCLC  with  NaPi2b  expression  will  ultimately  depend  upon,  among  other  things,  the  diagnosis  criteria
included in the final label for XMT‑1536 or XMT-1592, if our drug candidates are approved for sale for these indications,
acceptance by the medical community and patient access, drug pricing and reimbursement. The number of patients who can
be  treated  with  our  drug  candidates  may  turn  out  to  be  lower  than  expected,  patients  may  not  be  otherwise  amenable  to
treatment with our drugs, or new patients may become increasingly difficult to identify or gain access to, all of which would
adversely affect our results of operations and our business.

If we are unable to establish sales, marketing and distribution capabilities, we may not be successful in commercializing
our product candidates if and when they are approved.

We do not have a sales or marketing infrastructure and have no experience in the sale, marketing or distribution of products.
To achieve commercial success for any product for which we have obtained marketing approval, we will need to establish a
sales and marketing organization.

In  the  future,  we  expect  to  build  a  focused  sales  and  marketing  infrastructure  to  market  XMT‑1536,  our  lead  product
candidate,  and  any  other  current  or  future  product  candidates  in  the  United  States  and  certain  foreign  jurisdictions,  if  and
when they are approved. There are risks involved with establishing our own sales, marketing and distribution capabilities.

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For example, recruiting and training a sales force is expensive and time consuming and could delay any product launch. If the
commercial launch of a product candidate for which we recruit a sales force and establish marketing capabilities is delayed or
does not occur for any reason, we would have prematurely or unnecessarily incurred these commercialization expenses. This
may be costly, and our investment would be lost if we cannot retain or reposition our sales and marketing personnel.

Factors that may inhibit our efforts to commercialize our products on our own include:

·

·

·

·

·

our inability to recruit, train and retain adequate numbers of effective sales and marketing personnel;

the inability of sales personnel to obtain access to physicians;

the lack of adequate numbers of physicians to prescribe any future products;

the lack of complementary products to be offered by sales personnel, which may put us at a competitive
disadvantage relative to companies with more extensive product lines; and

unforeseen costs and expenses associated with creating an independent sales and marketing organization.

If  we  are  unable  to  establish  our  own  sales,  marketing  and  distribution  capabilities  and  enter  into  arrangements  with  third
parties to perform these services, our product revenues and our profitability, if any, are likely to be lower than if we were to
market, sell and distribute any products that we develop ourselves.

In addition, we may not be successful in entering into arrangements with third parties to sell, market and distribute certain of
our product candidates outside of the United States or may be unable to do so on terms that are favorable to us. We likely will
have limited control over such third parties, and any of them may fail to devote the necessary resources and attention to sell
and market our products effectively. If we do not establish sales, marketing and distribution capabilities successfully, either
on our own or in collaboration with third parties, we will not be successful in commercializing our product candidates.

Reimbursement may be limited or unavailable in certain market segments for our ADC product candidates, which could
make it difficult for us to sell our products profitably.

In both domestic and foreign markets, sales of any of our product candidates, if approved, will depend, in part, on the extent
to which the costs of our products will be covered by third‑party payors, such as government health programs, commercial
insurance and managed health care organizations. These third-party payors decide which drugs will be covered and establish
reimbursement levels for those drugs. The containment of health care costs has become a priority of foreign and domestic
governments  as  well  as  private  third-party  payors.  The  prices  of  drugs  have  been  a  focus  in  this  effort.  Governments  and
private  third‑party  payors  have  attempted  to  control  costs  by  limiting  coverage  and  the  amount  of  reimbursement  for
particular medications, which could affect our ability to sell our product candidates profitably. Cost‑control initiatives could
cause us to decrease the price we might establish for products, which could result in lower than anticipated product revenues.

Reimbursement by a third‑party payor may depend upon a number of factors, including the third‑party payor’s determination
that use of a product is:

·

·

·

·

a covered benefit under its health plan;

safe, effective and medically necessary;

appropriate for the specific patient;

cost‑effective; and

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·

neither experimental nor investigational.

Adverse pricing limitations may hinder our ability to recoup our investment in XMT‑1536, our lead product candidate or any
other current or future product candidates, even if such product candidates obtain marketing approval.

Obtaining  coverage  and  reimbursement  approval  for  a  product  from  a  government  or  other  third‑party  payor  is  a  time
consuming and costly process that could require us to provide supporting scientific, clinical and cost‑effectiveness data for
the  use  of  our  products  to  the  payor.  Further,  there  is  significant  uncertainty  related  to  third‑party  payor  coverage  and
reimbursement of newly approved drugs. We may not be able to provide data sufficient to gain acceptance with respect to
coverage and reimbursement. We cannot be sure that coverage or adequate reimbursement will be available for any of our
product candidates. Also, we cannot be sure that reimbursement amounts will not reduce the demand for, or the price of, our
products. If reimbursement is not available or is available only to limited levels, we may not be able to commercialize certain
of our products. In addition, in the United States, third‑party payors are increasingly attempting to contain health care costs
by  limiting  both  coverage  and  the  level  of  reimbursement  of  new  drugs.  As  a  result,  significant  uncertainty  exists  as  to
whether and how much third‑party payors will reimburse patients for their use of newly approved drugs, which in turn will
put pressure on the pricing of drugs.

Price controls may be imposed in foreign markets, which may adversely affect our future profitability.

In  some  countries,  including  member  states  of  the  European  Union,  the  pricing  of  prescription  drugs  is  subject  to
governmental  control.  Additional  countries  may  adopt  similar  approaches  to  the  pricing  of  prescription  drugs.  In  such
countries, pricing negotiations with governmental authorities can take considerable time after receipt of marketing approval
for  a  product.  In  addition,  there  can  be  considerable  pressure  by  governments  and  other  stakeholders  on  prices  and
reimbursement levels, including as part of cost containment measures. Political, economic and regulatory developments may
further  complicate  pricing  negotiations,  and  pricing  negotiations  may  continue  after  reimbursement  has  been  obtained.
Reference pricing used by various European Union member states and parallel distribution, or arbitrage between low‑priced
and high‑priced member states, can further reduce prices. In some countries, we may be required to conduct a clinical study
or other studies that compare the cost‑effectiveness of our product candidates to other available therapies in order to obtain or
maintain reimbursement or pricing approval. We cannot be sure that such prices and reimbursement will be acceptable to us
or  our  strategic  partners.  Publication  of  discounts  by  third‑party  payors  or  authorities  may  lead  to  further  pressure  on  the
prices or reimbursement levels within the country of publication and other countries. If pricing is set at unsatisfactory levels
or  if  reimbursement  of  our  products  is  unavailable  or  limited  in  scope  or  amount,  our  revenues  from  sales  by  us  or  our
strategic partners and the potential profitability of our product candidates in those countries would be negatively affected.

The impact of health care reform legislation and other changes in the health care industry and in health care spending on
us is currently unknown and may adversely affect our business model.

Our revenue prospects could be affected by changes in health care spending and policy in the United States and abroad. We
operate in a highly regulated industry and new laws, regulations or judicial decisions, or new interpretations of existing laws,
regulations or decisions, related to health care availability, the method of delivery or payment for health care products and
services could negatively impact our business, operations and financial condition.

Within the United States, there have been ongoing government efforts at the federal and state levels to reform the provision
or control the cost of health care.  There have been a number of legislative and regulatory changes to the healthcare system,
such as the enactment and subsequent modification of the Health Care Reform Act,  that could affect our future results of
operations or the commercial success of our products, if approved.   See “BUSINESS-Government regulation - Healthcare
reform”.  We  continue  to  evaluate  the  effect  that  healthcare  reform  efforts  may  have  on  our  business,  but  expect  that
healthcare reform measures that may be adopted in the future could have a material adverse effect on our industry generally
and on our ability to successfully commercialize our product candidates, if approved. Healthcare reform efforts to contain or
reduce costs of health care may adversely affect:

·

the demand for any products for which we may obtain regulatory approval;

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·

·

·

·

our ability to set a price that we believe is fair for our products;

our ability to obtain coverage and reimbursement approval for a product;

our ability to generate revenues and achieve or maintain profitability; and

the level of taxes that we are required to pay.

We cannot predict the ultimate content, timing or effect of any such reforms.

In addition, other legislative changes have been proposed and adopted that affect health care spending. The Budget Control
Act of 2011, includes provisions to reduce the federal deficit. The Budget Control Act, as amended, resulted in the imposition
of  2%  reductions  in  Medicare  payments  to  providers  which  began  in  April  2013,  and  will  remain  in  effect  through  2029
unless additional Congressional action is taken. Any significant spending reductions affecting Medicare, Medicaid  or other
publicly  funded  or  subsidized  health  programs  that  may  be  implemented  and/or  any  significant  taxes  or  fees  that  may  be
imposed  on  us,  as  part  of  any  broader  deficit  reduction  effort  or  legislative  replacement  to  the  Budget  Control  Act,
could  have an adverse impact on our results of operations.

We face substantial competition, which may result in others discovering, developing or commercializing products before,
or more successfully than, we do.

The  biotechnology  and  biopharmaceutical  industries  are  characterized  by  rapidly  advancing  technologies,  intense
competition  and  a  strong  emphasis  on  proprietary  products.  Many  third  parties  compete  with  us  in  developing  various
approaches to cancer therapy. They include pharmaceutical companies, biotechnology companies, academic institutions and
other research organizations. Any treatments developed by our competitors could be superior to our product candidates. It is
possible that these competitors will succeed in developing technologies that are more effective than our platforms or product
candidates  or  that  would  render  our  platforms  obsolete  or  noncompetitive.  We  anticipate  that  we  will  face  increased
competition  in  the  future  as  additional  companies  enter  our  market  and  scientific  developments  surrounding  other  cancer
therapies continue to accelerate.

We  are  also  aware  of  multiple  companies  with  ADC  technologies  that  may  be  competitive  to  our  platforms,  including
Astellas, AstraZeneca, Daiichi Sankyo, ImmunoGen, Immunomedics, Pfizer and Seattle Genetics. These companies or their
partners, including AbbVie, Genentech and Takeda, may develop product candidates which compete in the same indications
as our current and future product candidates. We expect to compete on improved efficacy, safety and tolerability compared to
other  product  candidates  and  if  our  products  are  not  demonstrably  superior  in  these  respects  compared  to  other  approved
therapeutics, we may not be able to compete effectively.

Many  of  our  competitors  have  significantly  greater  financial  resources  and  expertise  in  research  and  development,
manufacturing, preclinical studies, conducting clinical studies, obtaining regulatory approval and marketing than we do. In
addition,  many  of  these  competitors  are  active  in  seeking  patent  protection  and  licensing  arrangements  in  anticipation  of
collecting royalties for use of technology that they have developed. Smaller or early‑stage companies may also prove to be
significant competitors, particularly through strategic partnerships with large and established companies. These third parties
compete  with  us  in  recruiting  and  retaining  qualified  scientific  and  management  personnel,  as  well  as  in  acquiring
technologies complementary to our programs.

In  addition,  if  our  product  candidates  are  approved  and  commercialized,  we  may  face  competition  from  biosimilars.  The
route to market for biosimilars was established with the passage of the Health Care Reform Act in March 2010. The Health
Care  Reform  Act  establishes  a  pathway  for  the  FDA  approval  of  follow‑on  biologics  and  provides  twelve  years  data
exclusivity  for  reference  products  and  an  additional  six  months  exclusivity  period  if  pediatric  studies  are  conducted.  In
December 2018, however, a federal district court judge, in a challenge brought by a number of state attorneys general, found
the Health Care Reform Act unconstitutional in its entirety. Given the court’s decision struck down the Health Care Reform
Act in its entirety, the decision means numerous reforms enacted as part of the Health Care Reform Act, but not specifically
related  to  health  insurance,  such  as  the  BPCIA,  are  invalid  as  well.  While  the  Trump  administration  and  CMS  have  both
stated that the ruling will have no immediate effect, it is unclear how this decision, subsequent appeals, if any,

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and  other  efforts  to  repeal  and  replace  the  Health  Care  Reform  Act  will  impact  the  biosimilar  framework  created  by  the
Health Care Reform Act and our Business.

In Europe, the European Medicines Agency has issued guidelines for approving products through an abbreviated pathway,
and biosimilars have been approved in Europe. If a biosimilar version of one of our potential products were approved in the
United States or Europe, it could have a negative effect on sales and gross profits of the potential product and our financial
condition.

With  respect  to  our  current  and  potential  future  product  candidates,  we  believe  that  our  ability  to  compete  effectively  and
develop products that can be manufactured cost‑effectively and marketed successfully will depend on our ability to:

·

·

·

·

·

·

·

·

advance our technology platforms;

obtain and maintain intellectual property protection for our technologies and products;

obtain required government and other public and private approvals on a timely basis;

attract and retain key personnel;

commercialize effectively;

obtain reimbursement for our products in approved indications;

comply with applicable laws, regulations and regulatory requirements and restrictions with respect to the
commercialization of our products, including with respect to any changed or increased regulatory restrictions; and

enter into additional strategic partnerships to advance the development and commercialization of our product
candidates.

Risks related to our intellectual property

If we are unable to obtain or protect intellectual property rights related to our technology and ADC product candidates, or
if our intellectual property rights are inadequate, we may not be able to compete effectively.

Our success depends in large part on our ability to obtain and maintain protection with respect to our intellectual property and
proprietary  technology.  We  rely  upon  a  combination  of  patents,  trade  secret  protection  and  confidentiality  agreements  to
protect the intellectual property related to our  platforms and our product candidates, including our lead product candidate,
XMT‑1536.  The  patent  position  of  biopharmaceutical  companies  is  generally  uncertain  because  it  involves  complex  legal
and  factual  considerations  and  has,  in  recent  years,  been  the  subject  of  much  litigation.  As  a  result,  the  issuance,  scope,
validity, enforceability and commercial value of our patent rights is highly uncertain. The standards applied by the United
States  Patent  and  Trademark  Office,  or  USPTO,  and  foreign  patent  offices  in  granting  patents  are  not  always  applied
uniformly or predictably. For example, there is no uniform worldwide policy regarding patentable subject matter or the scope
of claims allowable in patents. In addition, changes in either the patent laws or interpretation of the patent laws in the United
States  and  other  countries  may  diminish  the  value  of  our  patents  or  narrow  the  scope  of  our  patent  protection.  The  patent
prosecution process is expensive, complex and time‑consuming, and we may not be able to file, prosecute, maintain, enforce
or  license  all  necessary  or  desirable  patents  and  patent  applications  at  a  reasonable  cost  or  in  a  timely  manner.  It  is  also
possible that we fail to identify patentable aspects of our research and development output before it is too late to obtain patent
protection. There is no assurance that all potentially relevant prior art relating to our patents and patent applications has been
found.  We  may  be  unaware  of  prior  art  that  could  be  used  to  invalidate  an  issued  patent  or  prevent  our  pending  patent
applications from issuing as patents.

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The patent applications that we own or in‑license may fail to result in issued patents, and even if they do issue as patents,
such patents may not cover our platforms and product candidates in the United States or in other countries. The issuance of a
patent  is  not  conclusive  as  to  its  inventorship,  scope,  validity  or  enforceability,  and  our  patents  may  be  challenged  in  the
courts or patent offices in the United States and abroad. Such challenges may result in loss of exclusivity or in patent claims
being  narrowed,  invalidated  or  held  unenforceable,  which  could  limit  our  ability  to  stop  others  from  using  or
commercializing similar or identical technology and products, or limit the duration of the patent protection of our technology
and product candidates. For example, even if patent applications we license or own do successfully issue as patents and even
if such patents cover our platforms and product candidates, third parties may challenge their validity, enforceability or scope,
which may result in such patents being narrowed or invalidated. Furthermore, even if they are unchallenged, our patents and
patent applications may not provide adequate protection or exclusivity for our ADC platform or product candidates, prevent
others from designing around our claims or otherwise provide us with a competitive advantage. Any of these outcomes could
impair our ability to prevent competition from third parties, which may have an adverse impact on our business.

If  patent  applications  we  own  or  have  in‑licensed  with  respect  to  our  platforms  or  our  product  candidates  fail  to  issue  as
patents,  if  their  breadth  or  strength  of  protection  is  threatened,  or  if  they  fail  to  provide  meaningful  exclusivity,  it  could
dissuade companies from collaborating with us. We cannot offer any assurances about which, if any, patents will issue, the
breadth of any such patents or whether any issued patents will be found invalid and unenforceable or will be threatened by
third parties. Any successful challenge to these patents or any other patents owned by or licensed to us could deprive us of
rights necessary for the successful development and commercialization of any product candidate. Since patent applications in
the United States and most other countries are confidential for a period of time after filing, and some remain so until issued,
we cannot be certain that we were the first to file any patent application related to a product candidate. Furthermore, if third
parties have filed such patent applications, an interference proceeding in the United States can be initiated by the USPTO or a
third‑party to determine who was the first to invent any of the subject matter covered by the patent claims of our applications.
In addition, patents have a limited lifespan. In the United States, the natural expiration of a patent is generally 20 years after it
is filed. Various extensions may be available; however, the life of a patent and the protection it affords is limited. Given the
amount  of  time  required  for  the  development,  testing  and  regulatory  review  of  new  product  candidates,  our  owned  or
in‑licensed patents protecting such candidates might expire before or shortly after such candidates are commercialized. If we
encounter  delays  in  obtaining  regulatory  approvals,  the  period  of  time  during  which  we  could  market  a  drug  under  patent
protection could be further reduced. Even if patents covering our product candidates are obtained, once the patent life has
expired for a product, we may be open to competition from similar or generic products. The launch of a generic version of
one of our products in particular would be likely to result in an immediate and substantial reduction in the demand for our
product, which could have a material adverse effect on our business, financial condition, results of operations and prospects.

On September 16, 2011, the Leahy‑Smith America Invents Act, or the Leahy‑Smith Act, was signed into law, which could
increase the uncertainties and costs surrounding the prosecution of our patent applications and the enforcement or defense of
our  issued  patents.  The  Leahy‑Smith  Act  includes  a  number  of  significant  changes  to  U.S.  patent  law.  These  include
provisions that affect the way patent applications are prosecuted, redefine prior art, may affect patent litigation and switch the
U.S. patent system from a “first‑to‑invent” system to a “first‑to‑file” system. Under a first‑to‑file system, assuming the other
requirements for patentability are met, the first inventor to file a patent application generally will be entitled to the patent on
an invention regardless of whether another inventor had made the invention earlier. These provisions also allow third‑party
submission of prior art to the USPTO during patent prosecution and set forth additional procedures to attack the validity of a
patent by the USPTO administered post grant proceedings. The USPTO developed additional regulations and procedures to
govern  administration  of  the  Leahy‑Smith  Act,  and  many  of  the  substantive  changes  to  patent  law  associated  with  the
Leahy‑Smith Act, and, in particular, the first‑to‑file provisions, only became effective on March 16, 2013. Accordingly, it is
not clear what, if any, impact the Leahy‑Smith Act will have on the operation of our business. The Leahy‑Smith Act and its
implementation  could  increase  the  uncertainties  and  costs  surrounding  the  prosecution  of  our  patent  applications  and  the
enforcement  or  defense  of  our  issued  patents,  all  of  which  could  have  a  material  adverse  effect  on  our  business,  financial
condition, results of operations and prospects.

Any loss of patent protection could have a material adverse impact on our business. We may be unable to prevent competitors
from entering the market with a product that is similar to or the same as our product candidates.

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Issued patents covering XMT‑1536, our lead product candidate, and any other current or future ADC product candidates
could be found invalid or unenforceable if challenged in court or before the USPTO or comparable foreign authority.

If we or one of our licensing partners initiate legal proceedings against a third party to enforce a patent covering XMT‑1536,
our lead product candidate, or any other current or future product candidates, the defendant could counterclaim that the patent
covering our product candidate is invalid or unenforceable. In patent litigation in the United States, defendant counterclaims
alleging invalidity or unenforceability are commonplace, and there are numerous grounds upon which a third party can assert
invalidity or unenforceability of a patent. Grounds for a validity challenge could be, among other things, an alleged failure to
meet  any  of  several  statutory  requirements,  including  lack  of  novelty,  obviousness,  lack  of  written  description  or
non‑enablement.  Grounds  for  an  unenforceability  assertion  could  be,  among  other  things,  an  allegation  that  someone
connected with prosecution of the patent withheld relevant information from the USPTO, or made a misleading statement,
during prosecution. Third parties may also raise similar claims before administrative bodies in the United States or abroad,
even  outside  the  context  of  litigation.  Such  mechanisms  include  re‑examination,  inter  partes  review,  post‑grant  review,
interference  proceedings,  derivation  proceedings  and  equivalent  proceedings  in  foreign  jurisdictions  (e.g.,  opposition
proceedings). Such proceedings could result in revocation, cancellation or amendment to our patents in such a way that they
no longer cover and protect our product candidates. The outcome following legal assertions of invalidity and unenforceability
is unpredictable. With respect to the validity of our patents, for example, we cannot be certain that there is no invalidating
prior art of which we, our licensors, our patent counsel and the patent examiner were unaware during prosecution. If a third
party were to prevail on a legal assertion of invalidity or unenforceability, we would lose at least part, and perhaps all, of the
patent protection on one or more of our product candidates. Any such loss of patent protection could have a material adverse
impact on our business, financial condition, results of operations and prospects.

If we fail to comply with our obligations under any license, strategic partnership or other agreements, we may be required
to  pay  damages  and  could  lose  intellectual  property  rights  that  are  necessary  for  developing  and  protecting  our  ADC
product candidates.

We rely, in part, on license, collaboration and other agreements. We may need to obtain additional licenses from others to
advance our research or allow commercialization of our product candidates and it is possible that we may be unable to obtain
additional licenses at a reasonable cost or on reasonable terms, if at all. The licensing or acquisition of third party intellectual
property rights is a competitive area, and several more established companies may pursue strategies to license or acquire third
party  intellectual  property  rights  that  we  may  consider  attractive.  These  established  companies  may  have  a  competitive
advantage over us due to their size, capital resources and greater clinical development and commercialization capabilities. In
addition, companies that perceive us to be a competitor may be unwilling to assign or license rights to use. We also may be
unable to license or acquire third-party intellectual property rights on terms that would allow us to make an appropriate return
on our investment.

In  addition,  our  existing  licenses  and  collaboration  agreements,  including  our  license  with  Recepta  Biopharma  S.A.,  or
Recepta,  for  intellectual  property  covering  the  NaPi2b  antibody  in  XMT‑1536  and  XMT-1592,  impose,  and  any  future
licenses,  collaborations  or  other  agreements  we  enter  into  are  likely  to  impose,  various  development,  commercialization,
funding, milestone, royalty, diligence, sublicensing, insurance, patent prosecution and enforcement or other obligations on us.
If we breach any of these obligations, or use the intellectual property licensed to us in an unauthorized manner, we may be
required to pay damages and the licensor may have the right to terminate the license, including, in the case of our agreement
with Recepta, the license for the rights covering the NaPi2b antibody in XMT‑1536 and XMT-1592. Any of the foregoing
could  result  in  us  being  unable  to  develop,  manufacture  and  sell  products  that  are  covered  by  the  licensed  technology  or
enable a competitor to gain access to the licensed technology. Disputes may arise regarding intellectual property subject to a
licensing, collaboration or other agreements, including:

·

·

the scope of rights granted under the license agreement and other interpretation related issues;

the extent to which our technology and processes infringe on intellectual property of the licensor that is not subject
to the licensing agreement;

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·

·

·

·

the sublicensing of patent and other rights under our collaborative development relationships;

our diligence obligations under the license agreement and what activities satisfy those diligence obligations;

the inventorship and ownership of inventions and know how resulting from the joint creation or use of intellectual
property by our licensors and us and our partners; and

the priority of invention of patented technology.

In addition, the agreements under which we currently license intellectual property or technology to or from third parties are
complex,  and  certain  provisions  in  such  agreements  may  be  susceptible  to  multiple  interpretations.  The  resolution  of  any
contract interpretation disagreement that may arise could narrow what we believe to be the scope of our rights to the relevant
intellectual property or technology, or increase what we believe to be our financial or other obligations under the relevant
agreement, either of which could have a material adverse effect on our business, financial condition, results of operations and
prospects. Moreover, if disputes over intellectual property that we have licensed prevent or impair our ability to maintain our
current  licensing  arrangements  on  commercially  acceptable  terms,  we  may  be  unable  to  successfully  develop  and
commercialize the affected product candidates.

In some circumstances, we may not have the right to control the preparation, filing and prosecution of patent applications, or
to  maintain  the  patents,  covering  the  technology  that  we  license  from  third  parties.  For  example,  pursuant  to  our  license
agreement with Recepta, Ludwig Institute for Cancer Research Ltd., a co‑owner of the intellectual property, retains control of
such  activities.  Therefore,  we  cannot  be  certain  that  these  patents  and  applications  will  be  prosecuted,  maintained  and
enforced  in  a  manner  consistent  with  the  best  interests  of  our  business.  If  our  licensors  fail  to  obtain  or  maintain  such
intellectual  property,  or  lose  rights  to  such  intellectual  property,  the  rights  we  have  licensed  and  our  exclusivity  may  be
reduced or eliminated and our right to develop and commercialize any of our products that are subject to such licensed rights
could be adversely affected.

Moreover, our rights to our in‑licensed patents and patent applications are dependent, in part, on inter‑institutional or other
operating agreements between the joint owners of such in‑licensed patents and patent applications. If one or more of such
joint  owners  breaches  such  inter‑institutional  or  operating  agreements,  our  rights  to  such  in‑licensed  patents  and  patent
applications  may  be  adversely  affected.  In  addition,  while  we  cannot  currently  determine  the  amount  of  the  royalty
obligations we would be required to pay on sales of future products, if any, the amounts may be significant. The amount of
our future royalty obligations will depend on the technology and intellectual property we use in products that we successfully
develop  and  commercialize,  if  any.  Therefore,  even  if  we  successfully  develop  and  commercialize  products,  we  may  be
unable  to  achieve  or  maintain  profitability.  Any  of  the  foregoing  could  have  a  material  adverse  effect  on  our  competitive
position, business, financial conditions, results of operations and prospects.

If  we  are  unable  to  successfully  obtain  rights  to  required  third-party  intellectual  property  rights  or  maintain  the  existing
intellectual property rights we have, we may have to abandon development of the relevant program or product candidate and
our business, financial condition, results of operations and prospects could suffer.

We  may  become  involved  in  lawsuits  to  protect  or  enforce  our  intellectual  property  or  to  defend  against  intellectual
property claims, which could be expensive, time consuming and unsuccessful.

Competitors  and  other  third  parties  may  infringe  our  patents  or  misappropriate  or  otherwise  violate  our  owned  and
in‑licensed intellectual property rights. To counter infringement or unauthorized use, litigation or other intellectual property
proceedings may be necessary to enforce or defend our owned and in‑licensed intellectual property rights, to protect our trade
secrets or to determine the validity and scope of our own intellectual property rights or the proprietary rights of others. Such
litigation  or  proceedings  can  be  expensive  and  time  consuming,  and  any  such  claims  could  provoke  defendants  to  assert
counterclaims against us, including claims alleging that we infringe their patents or other intellectual property rights. We may
not have sufficient financial or other resources to adequately conduct such litigation or proceedings. Many of our current and
potential competitors have the ability to dedicate substantially greater resources to litigate intellectual property rights than we
can and have more mature and developed intellectual property portfolios. Accordingly, despite our efforts, we may not be
able to prevent third parties from infringing upon or misappropriating our

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intellectual  property.  Even  if  resolved  in  our  favor,  litigation  or  other  intellectual  property  proceedings  could  result  in
substantial costs and diversion of management attention and resources, which could harm our business and financial results.

In addition, in a litigation or other proceeding, a court or administrative judge may decide that a patent owned by or licensed
to  us  is  invalid  or  unenforceable,  or  a  court  may  refuse  to  stop  the  other  party  from  using  the  technology  at  issue  on  the
grounds that our patents do not cover the technology in question. An adverse result in any litigation or other proceeding could
put one or more of our patents at risk of being invalidated, held unenforceable or interpreted narrowly. Furthermore, because
of the substantial amount of discovery required in connection with intellectual property litigation and other proceedings, there
is a risk that some of our confidential information could be compromised by disclosure during this type of litigation. During
the course of any patent or other intellectual property litigation or other proceeding, there could be public announcements of
the  results  of  hearings,  rulings  on  motions  and  other  interim  proceedings  or  developments  and  if  securities  analysts  or
investors  regard  these  announcements  as  negative,  the  perceived  value  of  our  product  candidates,  programs  or  intellectual
property could be diminished. Accordingly, the market price of our common stock may decline. Any of the foregoing could
have a material adverse effect on our business, financial conditions, results of operations and prospects.

Third‑party claims of intellectual property infringement or misappropriation may prevent or delay our development and
commercialization efforts.

Our  commercial  success  depends  in  part  on  our  ability  and  the  ability  of  our  strategic  partners  to  develop,  manufacture,
market  and  sell  product  candidates  and  use  our  proprietary  technologies  without  infringing,  misappropriating  or  otherwise
violating the patents and proprietary rights of third parties. There is a substantial amount of litigation, both within and outside
the United States, involving patent and other intellectual property rights in the biopharmaceutical industries, including patent
infringement  lawsuits,  interferences,  oppositions,  reexamination,  inter  partes  review,  derivation  and  post  grant  review
proceedings  before  the  USPTO  and  corresponding  foreign  patent  offices.  Numerous  U.S.  and  foreign  issued  patents  and
pending  patent  applications  owned  by  third  parties  exist  in  the  fields  in  which  we  are  developing  and  may  develop  our
product  candidates.  As  the  biopharmaceutical  industries  expand  and  more  patents  are  issued,  the  risk  increases  that  our
product candidates may be subject to claims of infringement of the patent rights of third parties.

Third  parties  may  assert  that  we,  our  customers,  licensees  or  parties  indemnified  by  us  are  employing  their  proprietary
technology without authorization or have infringed upon, misappropriated or otherwise violated their intellectual property or
other rights, regardless of their merit. For example, we may be subject to claims that we are infringing the patent, trademark
or  copyright  rights  of  third  parties,  or  that  our  employees  have  misappropriated  or  divulged  their  former  employers’  trade
secrets  or  confidential  information.  There  may  be  third‑party  patents  or  patent  applications  with  claims  to  materials,
formulations, methods of manufacture or methods for treatment related to the use or manufacture of our product candidates,
that we failed to identify. For example, applications filed before November 29, 2000 and certain applications filed after that
date that will not be filed outside the United States remain confidential until issued as patents. Except for certain exceptions,
including the preceding exceptions, patent applications in the United States and elsewhere are generally published only after
a waiting period of approximately 18 months after the earliest filing, and sometimes not at all. Therefore, patent applications
covering  our  platforms  or  our  product  candidates  could  have  been  filed  by  others  without  our  knowledge.  Additionally,
pending patent applications which have been published can, subject to certain limitations, be later amended in a manner that
could cover our platforms, our product candidates or the use or manufacture of our product candidates.

Even if we believe a third party’s claims against us are without merit, a court of competent jurisdiction could hold that such
third party’s patent is valid, enforceable and cover aspects of our product candidates, including the materials, formulations,
methods  of  manufacture,  methods  of  analysis,  or  methods  for  treatment,  in  which  case,  such  third  party  would  be  able  to
block our ability to develop and commercialize the applicable technology or product candidate until such patent expired or
unless we obtain a license and we may be required to pay such third-party monetary damages, which could be substantial.
Such licenses may not be available on acceptable terms, if at all. Even if we were able to obtain a license, the rights may be
nonexclusive, which could result in our competitors gaining access to the same intellectual property and it could require us to
make substantial licensing and royalty payments. Ultimately, we could be prevented

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from  commercializing  a  product,  or  be  forced  to  cease  some  aspect  of  our  business  operations,  if,  as  a  result  of  actual  or
threatened patent infringement claims, we are unable to enter into licenses on acceptable terms.

Parties making claims against us may also obtain injunctive or other equitable relief, which could effectively block our ability
to further develop and commercialize our technologies or one or more of our product candidates. Defending against claims of
patent  infringement,  misappropriation  of  trade  secrets  or  other  violations  of  intellectual  property  could  be  costly  and  time
consuming,  regardless  of  the  outcome.  Thus,  even  if  we  were  to  ultimately  prevail,  or  to  settle  at  an  early  stage,  such
litigation could burden us with substantial unanticipated costs. In addition, litigation or threatened litigation could result in
significant demands on the time and attention of our management team, distracting them from the pursuit of other company
business. In the event of a successful claim of infringement against us, in addition to potential injunctive relief, we may have
to pay substantial damages, including treble damages and attorneys’ fees for willful infringement, pay royalties, redesign our
infringing products or obtain one or more licenses from third parties, which may be impossible or require substantial time
and monetary expenditure.

We may face a claim of misappropriation if a third party believes that we inappropriately obtained and used trade secrets of
such  third  party.  If  we  are  found  to  have  misappropriated  a  third  party’s  trade  secrets,  we  may  be  prevented  from  further
using such trade secrets, limiting our ability to develop our product candidates, we may be required to obtain a license to such
trade secrets which may not be available on commercially reasonable terms or at all and may be non‑exclusive, and we may
be required to pay damages, which could be substantial. Any of the foregoing could have a material adverse effect on our
business, financial condition, results of operations and prospects.

We may not be able to protect our intellectual property and proprietary rights throughout the world.

Filing, prosecuting and defending patents on product candidates in all countries throughout the world where we expect there
to be significant markets for our products could be prohibitively expensive, and the laws of foreign countries may not protect
our rights to the same extent as the laws of the United States. In addition, our intellectual property license agreements may
not  always  include  worldwide  rights.  For  example,  certain  U.S.  and  foreign  issued  patents  and  patent  applications  are
licensed  to  us  by  Recepta  on  a  worldwide  basis,  except  that  Recepta  retains  exclusive  rights  in  such  patents  and  patent
applications  in  Brazil.  Consequently,  we  may  not  be  able  to  prevent  third  parties  from  practicing  our  inventions  in  all
countries outside the United States. Competitors may use our technologies in jurisdictions where we have not obtained patent
protection to develop their own products and, further, may export otherwise infringing products to territories where we have
patent protection or licenses but enforcement is not as strong as that in the United States. These products may compete with
our  products,  and  our  patents  or  other  intellectual  property  rights  may  not  be  effective  or  sufficient  to  prevent  them  from
competing.

Additionally, the laws of some foreign countries do not protect intellectual property rights to the same extent as the laws of
the  United  States,  and  many  companies  have  encountered  significant  problems  in  protecting  and  defending  such  rights  in
foreign  jurisdictions.  The  legal  systems  of  certain  countries,  particularly  certain  developing  countries,  do  not  favor  the
enforcement  of  patents  and  other  intellectual  property  protection,  particularly  those  relating  to  biotechnology,  which  could
make it difficult for us to stop the infringement of our licensed and owned patents or marketing of competing products in
violation  of  our  intellectual  property  and  proprietary  rights  generally.  Proceedings  to  enforce  our  intellectual  property  and
proprietary  rights  in  foreign  jurisdictions  could  result  in  substantial  costs  and  divert  our  efforts  and  attention  from  other
aspects  of  our  business,  could  put  our  patents  at  risk  of  being  invalidated  or  interpreted  narrowly,  could  put  our  patent
applications at risk of not issuing as patents, and could provoke third parties to assert claims against us. We may not prevail
in any lawsuits that we initiate, and the damages or other remedies awarded, if any, may not be commercially meaningful.
Accordingly,  our  efforts  to  enforce  our  intellectual  property  and  proprietary  rights  around  the  world  may  be  inadequate  to
obtain a significant commercial advantage from the intellectual property that we develop or license.

Many  countries  have  compulsory  licensing  laws  under  which  a  patent  owner  may  be  compelled  to  grant  licenses  to  third
parties.  In  addition,  many  countries  limit  the  enforceability  of  patents  against  government  agencies  or  government
contractors. In these countries, the patent owner may have limited remedies, which could materially diminish the value of
such patent. If we or any of our licensors is forced to grant a license to third parties with respect to any patents relevant to our
business, our competitive position may be impaired, and our business, financial condition, results of operations and prospects
may be adversely affected.

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Confidentiality agreements with employees and third parties may not prevent unauthorized disclosure of trade secrets and
other proprietary information.

In addition to the protection afforded by patents, we rely on trade secret protection and confidentiality agreements to protect
proprietary know‑how that is not patentable or that we elect not to patent, processes for which patents are difficult to enforce
and  any  other  elements  of  our  platform  technology  and  discovery  and  development  processes  that  involve  proprietary
know‑how, information or technology that is not covered by patents. However, trade secrets can be difficult to protect. We
seek  to  protect  our  proprietary  technology  and  processes,  in  part,  by  entering  into  confidentiality  agreements  with  our
employees, consultants and outside scientific advisors, contractors and partners. We cannot guarantee that we have entered
into  such  agreement  with  each  party  that  may  have  or  have  had  access  to  our  trade  secrets  or  proprietary  technology  and
processes. Additionally, our confidentiality agreements and other contractual protections may not be adequate to protect our
intellectual property from unauthorized disclosure, third‑party infringement or misappropriation. We may not have adequate
remedies in the case of a breach of any such agreements, and our trade secrets and other proprietary information could be
disclosed  to  our  competitors  or  others  may  independently  develop  substantially  equivalent  or  superior  proprietary
information and techniques or otherwise gain access to our trade secrets or disclose such technologies.

Enforcing a claim that a third party illegally obtained and is using any of our trade secrets is expensive and time consuming,
and the outcome is unpredictable. In addition, some courts outside and within the United States sometimes are less willing to
protect trade secrets. Misappropriation or unauthorized disclosure of our trade secrets could impair our competitive position
and may have a material adverse effect on our business.

We  may  be  subject  to  claims  by  third  parties  asserting  that  our  licensors,  employees,  consultants,  advisors  or  we  have
misappropriated their intellectual property, or claiming ownership of what we regard as our own intellectual property.

Many  of  our  and  our  licensors’  employees,  including  our  senior  management,  consultants  or  advisors  are  currently,  or
previously were, employed at universities or other biotechnology or pharmaceutical companies, including our competitors or
potential competitors. Some of these employees, including members of our senior management, executed proprietary rights,
non‑disclosure  and  non‑competition  agreements,  or  similar  agreements,  in  connection  with  such  previous  employment.
Although we try to ensure that our employees, consultants and advisors do not use the proprietary information or know‑how
of others in their work for us, we may be subject to claims that we or these individuals have used or disclosed intellectual
property,  including  trade  secrets  or  other  proprietary  information,  of  any  such  individual’s  current  or  former  employer.
Litigation  may  be  necessary  to  defend  against  such  claims.  If  we  fail  in  defending  any  such  claims,  in  addition  to  paying
monetary  damages,  we  may  lose  valuable  intellectual  property  rights  or  personnel  or  sustain  damages.  Such  intellectual
property  rights  could  be  awarded  to  a  third  party,  and  we  could  be  required  to  obtain  a  license  from  such  third  party  to
commercialize our technology or products. Such a license may not be available on commercially reasonable terms or at all.
Even if we are successful in defending against such claims, litigation could result in substantial costs and be a distraction to
management.  Any  of  the  foregoing  may  have  a  material  adverse  effect  on  our  business,  financial  condition,  results  of
operations and prospects.

In  addition,  while  it  is  our  policy  to  require  our  employees  and  contractors  who  may  be  involved  in  the  conception  or
development  of  intellectual  property  to  execute  agreements  assigning  such  intellectual  property  to  us,  we  may  be
unsuccessful in executing such an agreement with each party who, in fact, conceives or develops intellectual property that we
regard as our own. The assignment of intellectual property rights may not be self‑executing or the assignment agreements
may be breached, and we may be forced to bring claims against third parties, or defend claims that they may bring against us,
to determine the ownership of what we regard as our intellectual property.

If we do not obtain patent term extension and data exclusivity for any product candidates we may develop, our business
may be materially harmed.

Depending  upon  the  timing,  duration  and  specifics  of  any  FDA  marketing  approval  of  any  product  candidates  we  may
develop, one or more of our owned or in‑licensed U.S. patents may be eligible for limited patent term extension under the
Drug  Price  Competition  and  Patent  Term  Restoration  Act  of  1984,  or  Hatch‑Waxman  Amendments.  The  Hatch‑Waxman
Amendments permit a patent term extension of up to five years as compensation for the patent term lost during the FDA

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regulatory review process. A patent term extension cannot extend the remaining term of a patent beyond a total of 14 years
from  the  date  of  product  approval,  only  one  patent  may  be  extended  and  only  those  claims  covering  the  approved  drug,  a
method  for  using  it  or  a  method  for  manufacturing  it  may  be  extended.  However,  we  may  not  be  granted  an  extension
because  of,  for  example,  failing  to  exercise  due  diligence  during  the  testing  phase  or  regulatory  review  process,  failing  to
apply  within  applicable  deadlines,  failing  to  apply  prior  to  expiration  of  relevant  patents,  or  otherwise  failing  to  satisfy
applicable requirements. Moreover, the applicable time period or the scope of patent protection afforded could be less than
we request. If we are unable to obtain patent term extension or the term of any such extension is less than we request, our
competitors  may  obtain  approval  of  competing  products  following  our  patent  expiration,  and  our  business,  financial
condition, results of operations and prospects could be materially harmed.

Obtaining and maintaining our patent protection depends on compliance with various procedural, document submission,
fee payment, and other requirements imposed by government patent agencies, and our patent protection could be reduced
or eliminated for non‑compliance with these requirements.

Periodic maintenance fees, renewal fees, annuity fees and various other government fees on patents and patent applications
will be due to be paid to the USPTO and various government patent agencies outside of the United States over the lifetime of
our owned or licensed patents and applications. In certain circumstances, we rely on our licensing partners to pay these fees
due to U.S. and non‑U.S. patent agencies. The USPTO and various non‑U.S. government agencies require compliance with
several procedural, documentary, fee payment and other similar provisions during the patent application process. We are also
dependent  on  our  licensors  to  take  the  necessary  action  to  comply  with  these  requirements  with  respect  to  our  licensed
intellectual  property.  In  some  cases,  an  inadvertent  lapse  can  be  cured  by  payment  of  a  late  fee  or  by  other  means  in
accordance with the applicable rules. There are situations, however, in which non‑compliance can result in abandonment or
lapse of the patent or patent application, resulting in a partial or complete loss of patent rights in the relevant jurisdiction. In
such an event, potential competitors might be able to enter the market with similar or identical products or technology, which
could have a material adverse effect on our business, financial condition, results of operations and prospects.

Intellectual property rights do not necessarily address all potential threats.

The degree of future protection afforded by our intellectual property rights is uncertain because intellectual property rights
have  limitations  and  may  not  adequately  protect  our  business  or  permit  us  to  maintain  our  competitive  advantage.  For
example:

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others may be able to make ADC products that are similar to any product candidates we may develop or utilize
similar ADC‑related technology but that are not covered by the claims of the patents that we license or may own in
the future;

we, or our license partners or current or future strategic partners, might not have been the first to make the
inventions covered by the issued patent or pending patent application that we license or may own in the future;

we, or our license partners or current or future strategic partners, might not have been the first to file patent
applications covering certain of our or their inventions;

others may independently develop similar or alternative technologies or duplicate any of our technologies without
infringing our owned or licensed intellectual property rights;

it is possible that our pending licensed patent applications or those that we may own in the future will not lead to
issued patents;

issued patents that we hold rights to may be held invalid or unenforceable, including as a result of legal challenges
by our competitors;

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·

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·

our competitors might conduct research and development activities in countries where we do not have patent rights
and then use the information learned from such activities to develop competitive products for sale in our major
commercial markets;

we may not develop additional proprietary technologies that are patentable;

the patents of others may harm our business; and

we may choose not to file a patent in order to maintain certain trade secrets or know how, and a third party may
subsequently file a patent covering such intellectual property.

Should any of these events occur, they could have a material adverse effect on our business, financial condition, results of
operations and prospects.

Risks related to our business and industry

If we fail to attract and keep senior management and key scientific personnel, we may be unable to successfully develop
our ADC product candidates, conduct our clinical studies and commercialize our ADC product candidates.

Our ability to compete in the highly competitive biotechnology and biopharmaceutical industries depends upon our ability to
attract,  motivate  and  retain  highly  qualified  managerial,  scientific  and  medical  personnel.  We  are  highly  dependent  on
members of our senior management, including Anna Protopapas, our President and Chief Executive Officer. The loss of the
services  of  any  of  our  senior  management  could  impede  the  achievement  of  our  research,  development  and
commercialization objectives. Also, each of these persons may terminate their employment with us at any time. We do not
maintain “key person” insurance for any of our executives or other employees.

Recruiting and retaining qualified scientific, clinical, sales and marketing personnel will also be critical to our success. We
conduct  our  operations  at  our  facility  in  Cambridge,  Massachusetts,  in  a  region  that  is  headquarters  to  many  other
biopharmaceutical companies and many academic and research institutions. Competition for skilled personnel is intense and
the turnover rate can be high, which may limit our ability to hire and retain highly qualified personnel on acceptable terms or
at all. We may not be able to attract and retain these personnel on acceptable terms given the competition among numerous
pharmaceutical  and  biotechnology  companies  for  similar  personnel.  In  addition,  we  rely  on  consultants  and  advisors,
including  scientific  and  clinical  advisors,  to  assist  us  in  formulating  our  research  and  development  and  commercialization
strategy. Our consultants and advisors, may be employed or have commitments under consulting or advisory contracts with
other entities that may limit their availability to us.

We may encounter difficulties in managing our growth and expanding our operations successfully.

As we seek to advance our product candidates through clinical studies and commercialization, we will need to expand our
development,  regulatory,  manufacturing,  marketing  and  sales  capabilities  or  contract  with  third  parties  to  provide  these
capabilities for us. As our operations expand, we expect that we will need to manage additional relationships with various
strategic partners, suppliers and other third parties. Future growth will impose significant added responsibilities on members
of management. Our future financial performance and our ability to commercialize our product candidates and to compete
effectively  will  depend,  in  part,  on  our  ability  to  manage  any  future  growth  effectively.  To  that  end,  we  must  be  able  to
manage  our  development  efforts  and  clinical  studies  effectively  and  hire,  train  and  integrate  additional  management,
administrative  and,  if  necessary,  sales  and  marketing  personnel.  Due  to  our  limited  financial  resources  and  the  limited
experience of our management team in managing a company with such anticipated growth, we may not be able to accomplish
these tasks, and our failure to accomplish any of them could prevent us from successfully growing our company or disrupt
our operations.

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As a pharmaceutical manufacturer, our activities, including our interactions with healthcare providers, third party payors,
patients and government officials, are, and will continue to be, subject to extensive regulation involving health care, anti-
corruption, data privacy and security and consumer protection laws.  Failure to comply with applicable laws could result
in substantial penalties, contractual damages, reputational harm, diminished revenues and curtailment or restructuring of
our operations.

Our activities may now or in the future be directly or indirectly subject to various federal and state laws related to health care,
anti-corruption, data privacy and security consumer protection. If we obtain FDA approval for any of our product candidates
and  begin  commercializing  those  products  in  the  United  States,  our  potential  exposure  under  such  laws  will  increase
significantly, and our costs associated with compliance with such laws are also likely to increase. These laws include, but are
not limited to:

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·

·

·

·

·

federal false claims, false statements and civil monetary penalties laws prohibiting, among other things, any person
from knowingly presenting, or causing to be presented, a false claim for payment of government funds or knowingly
making, or causing to be made, a false statement to get a false claim paid;

the federal anti‑kickback law, which prohibits, among other things, persons from offering, soliciting, receiving or
providing any remuneration, directly or indirectly, to induce, either the referral of an individual, for an item or
service or the purchasing or ordering of a good or service, for which payment may be made under federal health care
programs such as the Medicare and Medicaid;

the federal anti-kickback prohibition known as Eliminating Kickbacks in Recovery Act or EKRA, enacted in 2018,
which  prohibits  certain  payments  related  to  referrals  of  patients  to  certain  providers  (recovery  homes,  clinical
treatment  facilities  and  laboratories)  and  applies  to  services  reimbursed  by  private  health  plans  as  well  as
government health care programs;

the federal law known as HIPAA, which, in addition to privacy protections to healthcare providers and other entities,
prohibits executing a scheme to defraud any healthcare benefit program (which may include private health plans) or
making false statements relating to healthcare matters;

the  FDCA,  which  among  other  things,  strictly  regulates  drug  marketing,  prohibits  manufacturers  from  marketing
such products for off-label use and regulates the distribution of samples;

federal laws that require pharmaceutical manufacturers to report certain calculated product prices to the government
or  provide  certain  discounts  or  rebates  to  government  authorities  or  private  entities,  often  as  a  condition  of
reimbursement under government healthcare programs;

the so-called “federal sunshine” law, which requires pharmaceutical and medical device companies to monitor and
report certain financial interactions with certain healthcare providers to the federal government for re-disclosure to
the public (the scope of which reportable interactions will increase for interactions occurring on or after 2021);

the  privacy,  security  and  breach  provisions  of  HIPAA,  which  impose  obligations  on  certain  “covered  entities”
(healthcare  providers,  health  plans  and  healthcare  clearinghouses)  and  certain  of  their  “business  associate”
contractors  with  respect  to  safeguarding  the  privacy,  security  and  transmission  of  individually  identifiable  health
information;

federal consumer protection and unfair competition laws, which broadly regulate marketplace activities and
activities that potentially harm consumers;

the Foreign Corrupt Practices Act, a United States law which regulates certain financial relationships with foreign
government officials (which could include, for example, certain medical professionals); and

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·

state law analogues of each of the above federal laws, such as anti‑kickback and false claims laws which may apply
to items or services reimbursed by any third‑party payor, including private health plans, state privacy laws, state
consumer protection laws, and state laws regulating interactions between pharmaceutical manufacturers and
healthcare providers, many of which differ from each other in significant ways and often are not preempted by
federal laws, thus complicating compliance efforts.

In addition, the regulatory approval and commercialization of any of our product candidates outside the United States will
also likely subject us to foreign equivalents of the health care laws mentioned above, among other foreign laws.

Efforts to ensure that our business arrangements will comply with applicable health care laws may involve substantial costs.
It is possible that governmental and enforcement authorities will conclude that our business practices may not comply with
current  or  future  statutes,  regulations  or  case  law  interpreting  applicable  fraud  and  abuse  or  other  health  care  laws  and
regulations.  If  our  operations  are  found  to  be  in  violation  of  any  of  the  laws  described  above  or  any  other  governmental
regulations that apply to us, we may be subject to penalties, including, without limitation, civil, criminal and administrative
penalties,  damages,  monetary  fines,  disgorgement,  possible  exclusion  from  participation  in  Medicare,  Medicaid  and  other
federal health care programs, contractual damages, reputational harm, diminished profits and future earnings and curtailment
or restructuring of our operations.

Our  employees  may  engage  in  misconduct  or  other  improper  activities,  including  noncompliance  with  regulatory
standards and requirements and insider trading.

We  are  exposed  to  the  risk  of  employee  fraud  or  other  misconduct.  Misconduct  by  employees  could  include  intentional
failures  to  comply  with  FDA  regulations,  to  provide  accurate  information  to  the  FDA,  to  comply  with  manufacturing
standards we have established, to comply with federal and state health care fraud and abuse laws and regulations, to report
financial  information  or  data  accurately  or  to  disclose  unauthorized  activities  to  us.  In  particular,  sales,  marketing  and
business  arrangements  in  the  health  care  industry  are  subject  to  extensive  laws  and  regulations  intended  to  prevent  fraud,
kickbacks,  self‑dealing  and  other  abusive  practices.  These  laws  and  regulations  may  restrict  or  prohibit  a  wide  range  of
pricing,  discounting,  marketing  and  promotion,  sales  commission,  customer  incentive  programs  and  other  business
arrangements. Employee misconduct could also involve the improper use of information obtained in the course of clinical
studies, which could result in regulatory sanctions and serious harm to our reputation. It is not always possible to identify and
deter employee misconduct, and the precautions we take to detect and prevent this activity may not be effective in controlling
unknown  or  unmanaged  risks  or  losses  or  in  protecting  us  from  governmental  investigations  or  other  actions  or  lawsuits
stemming from a failure to be in compliance with such laws or regulations. If any such actions are instituted against us, and
we  are  not  successful  in  defending  ourselves  or  asserting  our  rights,  those  actions  could  have  a  significant  impact  on  our
business,  including  the  imposition  of  civil,  criminal  and  administrative  penalties,  damages,  monetary  fines,  disgorgement,
possible  exclusion  from  participation  in  Medicare,  Medicaid  and  other  federal  health  care  programs,  contractual  damages,
reputational  harm,  diminished  profits  and  future  earnings  and  curtailment  or  restructuring  of  our  operations,  any  of  which
could adversely affect our ability to operate our business and our results of operations.

If  product  liability  lawsuits  are  brought  against  us,  we  may  incur  substantial  liabilities  and  may  be  required  to  limit
commercialization of our ADC product candidates.

We face an inherent risk of product liability as a result of the clinical testing of our product candidates and will face an even
greater  risk  if  we  commercialize  any  products.  For  example,  we  may  be  sued  if  any  product  we  develop  allegedly  causes
injury  or  is  found  to  be  otherwise  unsuitable  during  product  testing,  manufacturing,  marketing  or  sale.  Any  such  product
liability claims may include allegations of defects in manufacturing, defects in design, a failure to warn of dangers inherent in
the  product,  negligence,  strict  liability  and  a  breach  of  warranties.  Claims  could  also  be  asserted  under  state  consumer
protection  acts.  If  we  cannot  successfully  defend  ourselves  against  product  liability  claims,  we  may  incur  substantial
liabilities  or  be  required  to  limit  commercialization  of  our  product  candidates.  Even  a  successful  defense  would  require
significant financial and management resources. Regardless of the merits or eventual outcome, liability claims may result in:

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injury to our reputation;

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decreased demand for our product candidates or products that we may develop;

withdrawal of clinical study participants;

costs to defend the related litigations;

a diversion of management’s time and our resources;

substantial monetary awards to study participants or patients;

product recalls, withdrawals or labeling, marketing or promotional restrictions;

loss of revenue;

the inability to commercialize our product candidates; and

a decline in our stock price.

Failure  to  obtain  and  retain  sufficient  product  liability  insurance  at  an  acceptable  cost  to  protect  against  potential  product
liability claims could prevent or inhibit the commercialization of products we develop. We currently carry product liability
insurance covering our clinical studies in the amount of $10 million in the aggregate. Although we maintain such insurance,
any claim that may be brought against us could result in a court judgment or settlement in an amount that is not covered, in
whole or in part, by our insurance or that is in excess of the limits of our insurance coverage. Our insurance policies also have
various exclusions, and we may be subject to a product liability claim for which we have no coverage. In such instance, we
might have to pay any amounts awarded by a court or negotiated in a settlement that exceed our coverage limitations or that
are not covered by our insurance, and we may not have, or be able to obtain, sufficient capital to pay such amounts. If we are
unable  to  obtain  or  maintain  sufficient  insurance  coverage  at  an  acceptable  cost  or  to  otherwise  protect  against  potential
product  liability  claims,  it  could  prevent  or  inhibit  the  development  and  commercial  production  and  sale  of  our  product
candidates, which could adversely affect our business, financial condition, results of operations and prospects.

We and our third‑party contract manufacturers must comply with environmental, health and safety laws and regulations,
and failure to comply with these laws and regulations could expose us to significant costs or liabilities.

We  and  our  third‑party  manufacturers  are  subject  to  numerous  environmental,  health  and  safety  laws  and  regulations,
including  those  governing  laboratory  procedures  and  the  use,  generation,  manufacture,  distribution,  storage,  handling,
treatment,  remediation  and  disposal  of  hazardous  materials  and  wastes.  Hazardous  chemicals,  including  flammable  and
biological  materials,  are  involved  in  certain  aspects  of  our  business,  and  we  cannot  eliminate  the  risk  of  injury  or
contamination  from  the  use,  generation,  manufacture,  distribution,  storage,  handling,  treatment  or  disposal  of  hazardous
materials and wastes. In the event of contamination or injury, or failure to comply with environmental, health and safety laws
and  regulations,  we  could  be  held  liable  for  any  resulting  damages  and  any  such  liability  could  exceed  our  assets  and
resources. We could also incur significant costs associated with civil or criminal fines and penalties for failure to comply with
such laws and regulations.

Although we maintain workers’ compensation insurance to cover us for costs and expenses we may incur due to injuries to
our  employees  resulting  from  the  use  of  hazardous  materials,  this  insurance  may  not  provide  adequate  coverage  against
potential liabilities. We do not maintain insurance for environmental liability or toxic tort claims that may be asserted against
us in connection with our storage or disposal of biological, hazardous or radioactive materials.

Environmental, health and safety laws and regulations are becoming increasingly more stringent. We may incur substantial
costs in order to comply with current or future environmental, health and safety laws and regulations. These current or future
laws and regulations may impair our research, development or production efforts. Our failure to comply with these laws and
regulations also may result in substantial fines, penalties or other sanctions.

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Further, with respect to the operations of our third‑party contract manufacturers, it is possible that if they fail to operate in
compliance with applicable environmental, health and safety laws and regulations or properly dispose of wastes associated
with our products, we could be held liable for any resulting damages, suffer reputational harm or experience a disruption in
the manufacture and supply of our product candidates or products.

We may acquire assets or form strategic alliances in the future, and we may not realize the benefits of such acquisitions.

We may acquire additional technologies and assets, form strategic alliances or create joint ventures with third parties that we
believe will complement or augment our existing business. If we acquire assets with promising markets or technologies, we
may  not  be  able  to  realize  the  benefit  of  acquiring  such  assets  if  we  are  unable  to  successfully  integrate  them  with  our
existing  technologies.  We  may  encounter  numerous  difficulties  in  developing,  manufacturing  and  marketing  any  new
products resulting from a strategic alliance or acquisition that delay or prevent us from realizing their expected benefits or
enhancing our business. We cannot be assured that, following any such acquisition, we will achieve the expected synergies to
justify the transaction.

Our  internal  computer  systems,  or  those  of  our  strategic  partners,  third‑party  collaborators  or  other  contractors  or
consultants, may fail or suffer security breaches, which could adversely affect our business, including through  material
disruptions of our programs or business operations.

ransomware,  malware,  unauthorized  access,  natural  disasters, 

Our internal information technology systems and those of our current or future strategic partners, third party collaborators
and  other  contractors  and  consultants  are  vulnerable  to  service  interruptions  or  security  breaches,  including  from  cyber-
terrorism,  war  and
attacks,  computer  viruses, 
telecommunication and electrical failures. If a failure, accident or security breach were to occur and cause interruptions in our
operations  or  the  operations  of  those  third  parties  with  which  we  contract,  it  could  result  in  a  material  disruption  of  our
programs  and  our  business  operations.  We  could  lose  access  to  our  trade  secrets  or  other  proprietary  information  or
experience other disruptions, which could require a substantial expenditure of resources to remedy. For example, the loss of
clinical  study  data  for  our  product  candidates  could  result  in  delays  in  our  regulatory  approval  efforts  and  significantly
increase our costs to recover or reproduce the data.

We  could  also  be  subject  to  risks  caused  by  misappropriation,  misuse,  leakage,  falsification  or  intentional  or  accidental
release  or  loss  of  information  maintained  in  our  information  systems  and  networks,  including  personal  information  of  our
employees  or  others.  Outside  parties  may  attempt  to  penetrate  our  systems  or  those  of  the  third  parties  with  which  we
contract  or  to  coerce  or  fraudulently  induce  our  employees  or  employees  of  such  third  parties  to  disclose  sensitive
information to gain access to our data. The number and complexity of these threats continue to increase over time. Although
we develop and maintain systems and controls designed to prevent these events from occurring, and we have a process to
identify and mitigate threats, such risks cannot be eliminated. Furthermore, there can be no assurance that we, or those third
parties  with  which  we  contract,  will  promptly  detect  any  such  disruption  or  security  breach,  if  at  all.  Additionally,  the
development  and  maintenance  of  these  systems,  controls  and  processes  is  costly  and  requires  ongoing  monitoring  and
updating as technologies change and efforts to overcome security measures become more sophisticated. To the extent that
any  disruption  or  security  breach  results  in  a  loss  of  or  damage  to  our  data  or  applications  or  other  data  or  applications
relating to our technology or product candidates, or inappropriate disclosure of confidential or proprietary information, we
could incur liabilities, our competitive position and the market perception of the effectiveness of our security measures could
be harmed, our credibility could be damaged and the further development of our product candidates could be delayed.

We, or the third parties upon whom we depend, may be adversely affected by serious disasters.

Any  unplanned  event,  such  as  a  flood,  fire,  explosion,  earthquake,  extreme  weather  condition,  medical  epidemic,  power
shortage, telecommunication failure or other natural or human-made accidents or incidents that result in us being unable to
fully use our facilities, or the facilities of third-parties with which we contract, may have a material and adverse effect on our
ability to operate our business and have significant negative consequences on our financial and operating conditions. Loss of
access to these facilities may result in increased costs, delays in the development of our current or future product candidates
or the interruption of our business operations for a substantial period of time.

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There can be no assurance that the amounts of insurance that we maintain will be sufficient to satisfy any damages and losses
in  the  event  a  serious  disaster  or  similar  event  occurs.  If  our  facilities,  or  the  manufacturing  facilities  of  our  third-party
contract  manufacturers,  are  unable  to  operate  because  of  an  accident  or  incident  or  for  any  other  reason,  even  for  a  short
period of time, any or all of our research and development programs and commercialization efforts may be harmed.

Unfavorable global economic conditions could adversely affect our business, financial condition or results of operations.

Our results of operations could be adversely affected by general conditions in the global economy and in the global financial
markets. For example, the global financial crisis caused extreme volatility and disruptions in the capital and credit markets. A
severe or prolonged economic downturn, such as the global financial crisis, could result in a variety of risks to our business,
including, weakened demand for our product candidates and our ability to raise additional capital when needed on acceptable
terms, if at all. A weak or declining economy could also strain our suppliers, possibly resulting in supply disruption. Any of
the foregoing could harm our business and we cannot anticipate all of the ways in which the current economic climate and
financial market conditions could adversely impact our business.

Risks related to our common stock

We are an “emerging growth company,” as defined in the JOBS Act, and we cannot be certain if the reduced disclosure
requirements applicable to emerging growth companies will make our common stock less attractive to investors.

We  are  an  emerging  growth  company,  as  defined  in  the  JOBS  Act.  For  as  long  as  we  continue  to  be  an  emerging  growth
company,  we  may  take  advantage  of  exemptions  from  various  reporting  requirements  that  are  applicable  to  other  public
companies that are not emerging growth companies, including, but not limited to, (1) not being required to comply with the
auditor  attestation  requirements  of  Section  404  of  the  Sarbanes‑Oxley  Act,  (2)  reduced  disclosure  obligations  regarding
executive compensation in our periodic reports and proxy statements and (3) exemptions from the requirements of holding a
non‑binding advisory vote on executive compensation.

We could be an emerging growth company through 2022, although circumstances could cause us to lose that status earlier,
including if the market value of our common stock held by non‑affiliates exceeds $700.0 million as of any June 30 before
that time or if we have total annual gross revenue of $1.07 billion or more during any fiscal year before that time, in which
cases  we  would  no  longer  be  an  emerging  growth  company  as  of  the  following  December  31  or,  if  we  issue  more  than
$1.00  billion  in  non‑convertible  debt  during  any  three‑year  period  before  that  time,  we  would  cease  to  be  an  emerging
growth company immediately. Even after we no longer qualify as an emerging growth company, we may still qualify as a
“smaller  reporting  company”  which  would  allow  us  to  take  advantage  of  many  of  the  same  exemptions  from  disclosure
requirements,  including  not  being  required  to  comply  with  the  auditor  attestation  requirements  of  Section  404  of  the
Sarbanes‑Oxley Act and reduced disclosure obligations regarding executive compensation in our periodic reports and proxy
statements.  We  cannot  predict  if  investors  will  find  our  common  stock  less  attractive  because  we  may  rely  on  these
exemptions. If some investors find our common stock less attractive as a result, there may be a less active trading market for
our  common  stock  and  our  stock  price  may  be  more  volatile.  When  these  exemptions  cease  to  apply,  we  expect  to  incur
additional expenses and devote increased management effort toward ensuring compliance with them, and we cannot predict
or estimate the amount or timing of such additional costs.

Under the JOBS Act, emerging growth companies can also delay adopting new or revised accounting standards until such
time as those standards apply to private companies. We have irrevocably elected not to avail ourselves of this exemption from
new  or  revised  accounting  standards  and,  therefore,  are  subject  to  the  same  new  or  revised  accounting  standards  as  other
public companies that are not emerging growth companies.

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If our stock price is volatile, our stockholders could incur substantial losses.

Our stock price has been and may continue to be volatile. The market price of shares of our common stock could be subject
to  wide  fluctuations  in  response  to  many  risk  factors  listed  in  this  “Risk  Factors”  section,  and  others  beyond  our  control,
including:

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results and timing of preclinical studies and clinical studies of our current or future product candidates, including
XMT‑1536 and XMT-1592;

results of clinical studies of our competitors’ products;

failure to adequately protect our trade secrets;

the terms on which we raise additional capital or our ability to raise it;

commencement or termination of any strategic partnership or licensing arrangement;

regulatory developments, including actions with respect to our products or our competitors’ products;

actual or anticipated fluctuations in our financial condition and operating results;

publication of research reports by securities analysts about us or our competitors or our industry;

our failure or the failure of our competitors to meet analysts’ projections or guidance that we or our competitors may
give to the market;

additions and departures of key personnel;

strategic decisions by us or our competitors, such as acquisitions, divestitures, spin‑offs, joint ventures, strategic
investments or changes in business strategy;

the passage of legislation or other regulatory developments affecting us or our industry;

fluctuations in the valuation of companies perceived by investors to be comparable to us;

sales of our common stock by us (including pursuant to the pre-funded warrants described below), our insiders or
our other stockholders;

speculation in the press or investment community;

announcement or expectation of additional financing efforts;

changes in market conditions for biopharmaceutical stocks; and

changes in general market and economic conditions.

In addition, the stock market has historically experienced significant volatility, particularly with respect to pharmaceutical,
biotechnology and other life sciences company stocks. The volatility of pharmaceutical, biotechnology and other life sciences
company stocks often does not relate to the operating performance of the companies represented by the stock. As a result of
this volatility, stockholders may not be able to sell their common stock at or above the price for which they paid for their
shares.  As  we  operate  in  a  single  industry,  we  are  especially  vulnerable  to  these  factors  to  the  extent  that  they  affect  our
industry or our products, or to a lesser extent our markets. Furthermore, as a result of this volatility, we may not

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be  able  to  maintain  compliance  with  listing  requirements  of  the  Nasdaq  Stock  Market.  In  the  past,  securities  class  action
litigation has often been initiated against companies following periods of volatility in their stock price. This type of litigation
could  result  in  substantial  costs  and  divert  our  management’s  attention  and  resources,  and  could  also  require  us  to  make
substantial payments to satisfy judgments or to settle litigation.

Our principal stockholders and management own a significant percentage of our stock and are able to exercise significant
influence over matters subject to stockholder approval.

As  of  December  31,  2019,  our  executive  officers,  directors  and  stockholders  who  own  more  than  5%  of  our  outstanding
common  stock,  together  with  their  respective  affiliates,  beneficially  owned  a  significant  amount  of  our  common  stock,
including shares subject to outstanding options and warrants that are exercisable within 60 days after such date. Accordingly,
these  stockholders  are  able  to  exert  a  significant  degree  of  influence  over  our  management  and  affairs  and  over  matters
requiring  stockholder  approval,  including  the  election  of  our  board  of  directors  and  approval  of  significant  corporate
transactions.  This  concentration  of  ownership  could  have  the  effect  of  entrenching  our  management  or  board  of  directors,
delaying  or  preventing  a  change  in  our  control  or  otherwise  discouraging  a  potential  acquirer  from  attempting  to  obtain
control of us, which in turn could have a material and adverse effect on the fair market value of our common stock.

We are incurring and will continue to incur significant increased costs as a result of operating as a public company, and
our management is required to devote substantial time to compliance requirements and initiatives.

As a public company, we are incurring and will continue to incur significant legal, insurance, accounting and other expenses
that we did not incur as a private company. In addition, the Sarbanes-Oxley Act and rules of the SEC and The Nasdaq Stock
Market  have  imposed  various  requirements  on  public  companies,  including  requiring  establishment  and  maintenance  of
effective disclosure and financial controls. Our management and other personnel need to devote a substantial amount of time
to these compliance initiatives. Moreover, these rules and regulations have increased and will continue to increase our legal
and financial compliance costs and will make some activities more time-consuming and costly.

We do not expect to pay any cash dividends for the foreseeable future.

We do not anticipate that we will pay any cash dividends to holders of our common stock in the foreseeable future. Instead,
we plan to retain any earnings to maintain and expand our operations. In addition, our credit facility contains terms and any
future debt financing arrangement may contain additional terms prohibiting or limiting the amount of dividends that may be
declared  or  paid  on  our  common  stock.  Accordingly,  investors  must  rely  on  sales  of  their  common  stock  after  price
appreciation, which may never occur, as the only way to realize any return on their investment.

Provisions in our amended and restated certificate of incorporation, our amended and restated by‑laws and Delaware law
may  have  anti‑takeover  effects  that  could  discourage  an  acquisition  of  us  by  others,  even  if  an  acquisition  would  be
beneficial  to  our  stockholders,  and  may  prevent  attempts  by  our  stockholders  to  replace  or  remove  our  current
management.

Our amended and restated certificate of incorporation, amended and restated by‑laws and Delaware law contain provisions
that may have the effect of discouraging, delaying or preventing a change in control of us or changes in our management that
stockholders may consider favorable, including transactions in which our stockholders might otherwise receive a premium
for their shares. Our amended and restated certificate of incorporation and by‑laws include provisions that:

·

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authorize “blank check” preferred stock, which could be issued by our board of directors without stockholder
approval and may contain voting, liquidation, dividend and other rights superior to our common stock;

create a classified board of directors whose members serve staggered three‑year terms;

specify that special meetings of our stockholders can be called only by our board of directors;

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prohibit stockholder action by written consent;

establish an advance notice procedure for stockholder approvals to be brought before an annual meeting of our
stockholders, including proposed nominations of persons for election to our board of directors;

provide that vacancies on our board of directors may be filled only by a majority of directors then in office, even
though less than a quorum;

provide that our directors may be removed only for cause;

specify that no stockholder is permitted to cumulate votes at any election of directors;

expressly authorize our board of directors to have discretion to modify, alter or repeal our amended and restated
by‑laws; and

require supermajority votes of the holders of our common stock to amend specified provisions of our amended and
restated certificate of incorporation and amended and restated by‑laws.

These  provisions,  alone  or  together,  could  delay  or  prevent  hostile  takeovers  and  changes  in  control  or  changes  in  our
management. These provisions could also limit the price that investors might be willing to pay in the future for shares of our
common stock, thereby depressing the market price of our common stock.

In addition, because we are incorporated in the State of Delaware, we are governed by the provisions of Section 203 of the
General Corporation Law of the State of Delaware, or the DGCL, which prohibits a person who owns in excess of 15% of
our outstanding voting stock from merging or combining with us for a period of three years after the date of the transaction in
which the person acquired in excess of 15% of our outstanding voting stock, unless the merger or combination is approved in
a prescribed manner.

Any provision of our amended and restated certificate of incorporation, amended and restated by‑laws or Delaware law that
has  the  effect  of  delaying  or  deterring  a  change  in  control  could  limit  the  opportunity  for  our  stockholders  to  receive  a
premium for their shares of our common stock, and could also affect the price that some investors are willing to pay for our
common stock.

The 2017 Tax Act could adversely affect our business and financial condition.

On  December  22,  2017,  the  U.S.  President  signed  into  law  legislation  commonly  called  the  “Tax  Cuts  and  Jobs  Act”  (the
2017  Tax  Act)  that  significantly  revises  the  Internal  Revenue  Code  of  1986,  as  amended  (the  Code).  The  2017  Tax  Act,
among other things, contains significant changes to corporate taxation, including reduction of the corporate tax rate from a
top marginal rate of 35% to a rate of 21%, limitation of the tax deduction for interest expense to 30% of adjusted earnings
(except  for  certain  small  businesses),  limitation  of  the  deduction  for  net  operating  losses  to  80%  of  current  year  taxable
income  in  respect  of  net  operating  losses  generated  during  or  after  2018  and  elimination  of  net  operating  loss  carrybacks,
immediate deductions for certain new investments instead of deductions for depreciation expense over time, and modifying
or  repealing  many  business  deductions  and  credits.    Notwithstanding  the  reduction  in  the  corporate  income  tax  rate,  the
overall  impact  of  the  2017  Tax  Act  is  uncertain  and  our  business  and  financial  condition  could  be  adversely  affected.   In
addition, it is uncertain if and to what extent various states will conform to the federal tax law.  The impact of this tax reform
on  holders  of  our  common  stock  is  also  uncertain  and  could  be  adverse.  We  urge  you  to  consult  with  your  legal  and  tax
advisors with respect to this legislation and the potential tax consequences of investing in or holding our common stock.

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Our ability to use net operating losses and certain tax credit carryforwards may be subject to certain limitations.

For the years ended December 31, 2019, 2018 and 2017, the Company recorded no income tax benefit for the net operating
losses incurred in each year, due to the uncertainty of realizing a benefit from those items. The Company has incurred net
operating  losses  (NOLs)  since  its  inception.  As  of  December  31,  2019,  the  Company  had  federal  NOLs  of  approximately
$163.5 million and state NOLs of approximately $98.5 million. Of the $163.5 million of federal NOLs, $34.1 million expire
at various dates through 2037. The remaining $129.3 million of federal NOLs do not expire. The state NOLs will expire at
various dates through 2039. As of December 31, 2019, the Company had Federal and State research and development tax
credit  carryforwards  of  approximately  $2.0  million  and  $0.7  million,  respectively,  which  expire  at  various  dates  through
2039. Under the 2017 Tax Act, federal NOLs incurred in 2019 and in future years may be carried forward indefinitely, but the
deductibility of such federal NOLs is limited. It is uncertain if and to what extent various states will conform to the 2017 Tax
Act. In addition, under Section 382 of the Internal Revenue Code, and corresponding provisions of state law, if a corporation
undergoes an “ownership change,” which is generally defined as a greater than 50% change, by value, in its equity ownership
over a three-year period, the corporation’s ability to use its pre-change NOLs and other pre-change tax attributes to offset its
post-change income or taxes may be limited. Our past issuances of stock and other changes in our stock ownership may have
resulted in ownership changes within the meaning of Section 382 of the Code; accordingly, our pre-change NOLs may be
subject  to  limitation  under  Section  382.  If  we  determine  that  we  have  not  undergone  an  ownership  change,  the  Internal
Revenue Service could challenge our analysis, and our ability to use our NOLs to offset taxable income could be limited by
Section 382 of the Code. Future changes in our stock ownership, some of which are outside of our control, could result in
ownership changes under Section 382 of the Code further limiting our ability to utilize our NOLs. Our NOLs may also be
impaired  under  state  law.  Accordingly,  we  may  not  be  able  to  utilize  a  material  portion  of  our  NOLs.  The  Company  has
determined that ownership changes have occurred since our inception and that certain NOLs and research and development
tax  credit  carryforwards  will  be  subject  to  limitation.    We  may  also  have  incurred  subsequent  ownership  changes.
Furthermore,  our  ability  to  utilize  our  NOLs  is  conditioned  upon  our  attaining  profitability  and  generating  U.S.  federal
taxable  income.  We  have  incurred  net  losses  since  our  inception  and  anticipate  that  we  will  continue  to  incur  significant
losses for the foreseeable future; thus, we do not know whether or when we will generate the U.S. federal taxable income
necessary to utilize our NOLs. We have recorded a full valuation allowance related to our NOLs and other deferred tax assets
due to the uncertainty of the ultimate realization of the future benefits of those assets.

Our amended and restated certificate of incorporation designates the state or federal courts within the State of Delaware
as the exclusive forum for certain types of actions and proceedings that may be initiated by our stockholders, which could
limit  our  stockholders’  ability  to  obtain  a  favorable  judicial  forum  for  disputes  with  us  or  our  directors,  officers  or
employees.

Our amended and restated certificate of incorporation provides that, subject to limited exceptions, the state or federal courts
within  the  State  of  Delaware  will  be  exclusive  forums  for  (1)  any  derivative  action  or  proceeding  brought  on  our  behalf,
(2) any action asserting a claim of breach of a fiduciary duty owed by any of our directors, officers or other employees to us
or our stockholders, (3) any action asserting a claim against us arising pursuant to any provision of the DGCL, our amended
and restated certificate of incorporation or our amended and restated by‑laws or (4) any other action asserting a claim against
us that is governed by the internal affairs doctrine. Any person or entity that purchases or otherwise acquires any interest in
shares of our capital stock shall be deemed to have notice of and to have consented to the provisions of our amended and
restated  certificate  of  incorporation  described  above.  This  choice  of  forum  provision  may  limit  a  stockholder’s  ability  to
bring  a  claim  in  a  judicial  forum  that  it  finds  favorable  for  disputes  with  us  or  our  directors,  officers  or  other  employees,
which may discourage such lawsuits against us and our directors, officers and employees. Alternatively, if a court were to
find these provisions of our amended and restated certificate of incorporation inapplicable to, or unenforceable in respect of,
one or more of the specified types of actions or proceedings, we may incur additional costs associated with resolving such
matters in other jurisdictions, which could adversely affect our business and financial condition.

ITEM 1B.           UNRESOLVED STAFF COMMENTS.

None.

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ITEM 2.              PROPERTIES.

Our corporate headquarters are located in Cambridge, Massachusetts. We occupy approximately 34,000 square feet of office
and laboratory space that we lease in a multi-tenant building in which our corporate headquarters are located. We have an
option  to  extend  the  lease  term  for  an  additional  five  years  thereafter.  We  believe  that  this  office  and  laboratory  space  is
sufficient to meet our current needs, and that suitable additional space will be available as and when needed.

ITEM 3.              LEGAL PROCEEDINGS.

From  time  to  time,  we  may  be  subject  to  various  legal  proceedings  and  claims  that  arise  in  the  ordinary  course  of  our
business  activities.  Although  the  results  of  litigation  and  claims  cannot  be  predicted  with  certainty,  as  of  the  date  of  this
Annual Report on Form 10-K, we do not believe we are party to any claim or litigation, the outcome of which, if determined
adversely  to  us,  would  individually  or  in  the  aggregate  be  reasonably  expected  to  have  a  material  adverse  effect  on  our
business. Regardless of the outcome, litigation can have an adverse impact on us because of defense and settlement costs,
diversion of management resources and other factors.

ITEM 4.              MINE SAFETY DISCLOSURES.

Not applicable.

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PART II

ITEM 5.              MARKET FOR REGISTRANT’S COMMON EQUITY, RELATED STOCKHOLDER MATTERS

AND ISSUER PURCHASES OF EQUITY SECURITIES

Certain Information Regarding the Trading of Our Common Stock

Our common stock trades under the symbol “MRSN” on the Nasdaq Global Select Market. As of February 25, 2020, there
were approximately 36 holders of record of shares of our common stock.

Dividend Policy

We  have  never  declared  nor  paid  cash  dividends  on  our  common  stock.  We  currently  intend  to  retain  all  of  our  future
earnings, if any, to finance the growth and development of our business. We do not intend to pay cash dividends in respect of
our common stock in the foreseeable future. Any future determination to pay cash dividends will be made at the discretion of
our board of directors and will depend on restrictions and other factors our board of directors may deem relevant. Investors
should not purchase our common stock with the expectation of receiving cash dividends.

Stock Performance Graph

The following performance graph and related information shall not be deemed to be “soliciting material” or to be “filed” with
the  Securities  and  Exchange  Commission,  or  SEC,  for  purposes  of  Section  18  of  the  Securities  Exchange  Act  of  1934,  as
amended,  or  the  Exchange  Act,  nor  shall  such  information  be  incorporated  by  reference  into  any  future  filing  under  the
Exchange  Act  or  Securities  Act  of  1933,  as  amended,  or  the  Securities  Act,  except  to  the  extent  that  we  specifically
incorporate it by reference into such filing.

The  following  graph  compares  the  performance  of  our  common  stock  to  the  Nasdaq  Composite  Index  and  to  the  Nasdaq
Biotechnology  Index  from  June  28,  2017  (the  first  date  that  shares  of  our  common  stock  were  publicly  traded)  through
December 31, 2019, which was the last trading day of the year. The comparison assumes $100 was invested in our common
stock  and  in  each  of  the  foregoing  indices  after  the  market  closed  on  June  28,  2017,  and  it  assumes  reinvestment  of
dividends,  if  any.  The  stock  price  performance  included  in  this  graph  is  not  necessarily  indicative  of  future  stock  price
performance.

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ITEM 6.              SELECTED FINANCIAL DATA

You should read the following selected financial data together with our financial statements and the related notes appearing
elsewhere  in  this  Annual  Report  on  Form  10-K  and  the  information  under  the  heading  “Management’s  Discussion  and
Analysis of Financial Condition and Results of Operations.” We have derived the statement of operations data for the years
ended December 31, 2019, 2018 and 2017 and the balance sheet data as of December 31, 2019 and 2018 from our audited
financial statements included elsewhere in this Annual Report on Form 10-K. The historical statement of operations data for the
years ended December 31, 2016 and 2015 and the historical balance sheet data as of December 31, 2017, 2016 and 2015 have been
derived from audited financial statements not included in this Annual Report on Form 10-K. All financial information presented has
been consolidated and reflects the operations of Mersana Therapeutics Inc. and its wholly-owned subsidiaries.  Our historical results
are not necessarily indicative of results expected in any future period. The selected historical financial information in this section is
not intended to replace our consolidated financial statements and the related notes thereto.

Statements of Operations Data:
Collaboration revenue
Operating expenses:

Research and development
General and administrative

Total operating expenses
Other income (expense):

Interest income
Interest expense

Total other income (expense), net
Net loss
Net loss attributable to common stockholders —
basic and diluted(1)
Net  loss  per  share  attributable  to  common
stockholders — basic and diluted(1)
Weighted-average  number  of  shares  of  common
stock  used  in  net  loss  per  share  attributable  to
common stockholders — basic and diluted(1)

Balance Sheet Data:
Cash, cash equivalents and marketable securities
Working capital(2)
Total assets
Long-term debt, net of discount
Convertible preferred stock
Total stockholders’ equity (deficit)

2019

2018

Year ended
December 31, 

2017

(in thousands, except
share and per share data)

2016

2015

  $

42,123   $

10,594  $

17,545  $

25,171  $

10,359

55,040  
17,283  
72,323  

59,915   
16,334   
76,249   

46,700   
10,462   
57,162   

32,008   
6,984   
38,992   

21,353
5,347
26,700

2,226  
(234) 
1,992  
(28,208)  $

1,398   
 —   
1,398   
(64,257)  $

910   
 —   
910   
(38,707)  $

121   
 —   
121   
(13,700)  $

 2
(89)
(87)
(16,428)

  $

  $

(28,208)  $

(64,257)  $

(38,707)  $

(13,700)  $

(16,428)

  $

(0.65)  $

(2.79)  $

(3.22)  $

(10.82)  $

(13.43)

  43,492,113  

  23,032,250    12,022,733    1,266,758    1,223,457

2019

2018

Year ended
December 31, 
2017
(in thousands)

2016

2015

  $ 99,790   $ 70,131   $125,216   $100,297   $ 11,534
2,019
  14,409
 —
  36,296
  (42,692)

  73,787  
  105,087  
 —  
  94,450  
  (55,619) 

  77,256  
  107,541  
4,201  
 —  
  78,318  

  85,662  
  130,715  
 —  
 —  
  69,994  

4,880  
  78,502  
 —  
 —  
8,795  

(1)

(2)

See Note 2 to our financial statements appearing elsewhere in this Annual report on Form 10-K for further details on
the calculation of basic and diluted net loss per share applicable to common stockholders.

We define working capital as current assets less current liabilities.

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ITEM  7.                            MANAGEMENT’S  DISCUSSION  AND  ANALYSIS  OF  FINANCIAL  CONDITION  AND

RESULTS OF OPERATIONS

The following discussion and analysis of our financial condition and results of operations should be read in conjunction with
our audited financial statements and related notes appearing elsewhere in this Annual Report on Form 10-K.

Our  actual  results  and  timing  of  certain  events  may  differ  materially  from  the  results  discussed,  projected,  anticipated,  or
indicated  in  any  forward-looking  statements.  We  caution  you  that  forward-looking  statements  are  not  guarantees  of  future
performance and that our actual results of operations, financial condition and liquidity, and the development of the industry
in which we operate may differ materially from the forward-looking statements contained in this Annual Report. In addition,
even if our results of operations, financial condition and liquidity, and the development of the industry in which we operate
are consistent with the forward-looking statements contained in this Annual Report, they may not be predictive of results or
developments in future periods. 

The following information and any forward-looking statements should be considered in light of factors discussed elsewhere
in the Annual Report on Form 10-K, including those risks identified under Part II, Item 1A. Risk Factors.

We caution readers not to place undue reliance on any forward-looking statements made by us, which speak only as of the
date they are made. We disclaim any obligation, except as specifically required by law and the rules of the SEC, to publicly
update or revise any such statements to reflect any change in our expectations or in events, conditions or circumstances on
which any such statements may be based, or that may affect the likelihood that actual results will differ from those set forth in
the forward-looking statements.

Overview

We are a clinical-stage biopharmaceutical company focused on developing antibody drug conjugates, or ADCs, that offer a
clinically  meaningful  benefit  for  cancer  patients  with  significant  unmet  need.  We  have  leveraged  20  years  of  industry
learning in the ADC field to develop proprietary and differentiated technology platforms that enable us to design ADCs to
have improved efficacy, safety and tolerability relative to existing ADC therapies.

We believe that our innovative platforms which include Dolaflexin and Dolasynthen, delivering our DolaLock payload, as
well  as  Immunosynthen,  delivering  a  novel  stimulator  of  interferon  genes,  or  STING,  agonist,  compose  a  highly  efficient
product  engine  that  has  enabled  a  robust  discovery  pipeline  for  us  and  our  partners.  Our  ADCs  in  preclinical  and  clinical
studies  are  first-in-class  molecules  that  target  multiple  tumor  types  with  high  unmet  medical  need  and  have  exhibited
improved safety and efficacy compared to ADCs developed using first-generation technology.

Our  goal  is  to  become  a  leading  oncology  company  by  leveraging  the  potential  of  our  innovative  and  differentiated  ADC
technologies and the experience and competencies of our management team to identify, acquire and develop promising ADC
product candidates and to commercialize cancer therapeutics that are improvements over existing treatments.

XMT-1536, a first-in-class ADC targeting the sodium-dependent phosphate transport protein NaPi2b, utilizes the Dolaflexin
platform to deliver an average of 10-12 DolaLock payload molecules per antibody. The NaPi2b antigen is broadly expressed
in  NSCLC  adenocarcinoma  and  ovarian  cancer  with  limited  expression  in  normal  tissue.    We  are  actively  recruiting  and
dosing patients with ovarian cancer and NSCLC adenocarcinoma, where a majority of patients express NaPi2b in a Phase 1
clinical trial.

We have selected our next clinical product candidate, XMT-1592. XMT-1592 uses one of our new platforms, Dolasynthen,
and  also  targets  NaPi2b.    XMT-1592  comprises  the  same  proprietary  NaPi2b  antibody  and  potent  auristatin  DolaLock
payload  with  controlled  bystander  effect  as  XMT-1536,  with  the  additional  features  of  homogeneous,  site-specific
bioconjugation and precise DAR.

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Our early stage programs include a potentially first-in-class B7-H4-targeted DolaLock ADC addressing areas of high unmet
medical need. Our objective is to rapidly progress through IND-enabling studies and scale up manufacturing activities with
third parties. B7-H4 provides significant opportunities for development in areas of high unmet need such as breast cancer,
NSCLC and ovarian cancer.

In addition, we have established strategic research and development partnerships with Merck KGaA and Asana Biosciences
for  the  development  and  commercialization  of  additional  ADC  product  candidates  against  a  limited  number  of  targets
selected by our partners based on our Fleximer platform. We believe the potential of our ADC technologies, supported by our
world class management team and protected by our robust intellectual property portfolio, will allow us to develop targeted
and highly tailored therapies to help cancer patients become cancer survivors.

Since inception, our operations have focused on building our platforms, identifying potential product candidates, producing
drug  substance  and  drug  product  material  for  use  in  preclinical  studies,  conducting  preclinical  and  toxicology  studies,
manufacturing  clinical  study  material  and  conducting  clinical  studies,  establishing  and  protecting  our  intellectual  property,
staffing our company and raising capital. We do not have any products approved for sale and have not generated any revenue
from product sales. We have funded our operations primarily through our strategic partnerships, private placements of our
convertible preferred stock and public offerings of our common stock.

Since inception, we have incurred significant cumulative operating losses. Our net losses were $28.2 million, $64.3 million
and $38.7 million for the years ended December 31, 2019, 2018 and 2017, respectively. As of December 31, 2019, we had an
accumulated deficit of $192.4 million. We expect to continue to incur significant expenses and operating losses over the next
several years. We anticipate that our expenses will increase significantly in connection with our ongoing activities, as we:

·

·

·

·

continue clinical development activities for our lead product candidate XMT-1536 and anticipate initiating clinical
development activities for XMT-1592;

initiate first-in-human studies for our next clinical candidate XMT-1592;

develop a research assay and companion diagnostic for the NaPi2b biomarker;

continue activities to discover, validate and develop additional product candidates; 

· maintain, expand and protect our intellectual property portfolio; and

·

hire additional research, development and general and administrative personnel. 

Financial Operations Overview

Revenue

To date, we have not generated any revenue from the sale of products. All of our revenue has been generated from strategic
partnerships.

In June 2014, we entered into an agreement with Merck KGaA for the development and commercialization of ADC product
candidates utilizing Fleximer for up to six target antigens. Merck KGaA is responsible for generating antibodies against the
target  antigens  and  we  are  responsible  for  generating  Fleximer  and  our  proprietary  payloads  and  conjugating  this  to  the
antibody  to  create  the  ADC  product  candidates.  Merck  KGaA  has  the  exclusive  right  to  and  is  responsible  for  the  further
development  and  commercialization  of  these  ADC  product  candidates.  In  May  2018,  we  entered  into  a  supply  agreement
with Merck KGaA for the supply of materials that could be used for IND-enabling studies and clinical trials.

For  the  years  ended  December  31,  2019,  2018  and  2017,  we  recognized  revenue  of  $2.1  million,  $2.4  million  and  $3.6
million, respectively, related to the Merck KGaA agreements.

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In January 2016, we entered into collaboration agreements with Takeda for the development and commercialization of XMT-
1522,  a  HER2-targeted  ADC,  and  up  to  seven  ADC  product  candidates  utilizing  Fleximer.  The  Company’s  collaboration
agreements with Takeda were terminated during the first quarter of 2019.

We recognized the remaining deferred revenue of $40.0 million related to the termination of the Takeda agreements in the
first quarter of 2019. We do not expect to have any further revenue related to these agreements.

We  have  provided  limited  services  to  Asana  BioSciences.  For  the  years  ended  December  31,  2019,  2018  and  2017,  we
recorded  an  immaterial  amount  of  revenue  and  revenue  of  $0.8  million  and  $0.1  million,  respectively,  related  to  those
services. In addition, we recognized revenue of $1.5 million related to a milestone achieved during the third quarter of 2018.

For the foreseeable future, we expect substantially all of our revenue to be generated from our collaboration agreements with
Merck  KGaA  and  Asana  BioSciences.  Given  the  uncertain  nature  and  timing  of  clinical  development,  we  cannot  predict
when or whether we will receive further milestone payments or any royalty payments under these collaborations.

For  information  about  our  revenue  recognition  policy,  see  the  notes  to  consolidated  financial  statements  included  in  this
Annual Report on Form 10-K.

Expenses

Research and Development Expenses

Research  and  development  expenses  consist  primarily  of  costs  incurred  for  our  research  and  development  activities,
including our drug discovery efforts, and the development of our product candidates, which include:

·

·

·

·

·

employee-related expenses, including salaries, benefits, and stock-based compensation expense; 

costs of funding research and development performed by third parties that conduct research, preclinical activities,
manufacturing and clinical studies on our behalf; 

 laboratory supplies; 

 facility costs, including rent, depreciation and maintenance expenses; and 

 upfront and milestone payments under our third-party licensing agreements.

Research and development costs are expensed as incurred. Costs of certain activities, such as manufacturing, preclinical and
clinical studies, are generally recognized based on an evaluation of the progress to completion of specific tasks. Costs for
certain development activities, such as clinical studies, are recognized based on an evaluation of the progress to completion
of specific tasks using data such as patient enrollment, clinical site activations and information provided to us by the third
parties with whom we contract.

Research  and  development  activities  are  central  to  our  business  model.    Product  candidates  in  later  stages  of  clinical
development generally have higher development costs than those in earlier stages of clinical development, primarily due to
the increased size and duration of later-stage clinical trials and manufacturing costs. We expect that our total future research
and development costs will continue to increase over current levels, depending on the progress of our clinical development
programs.  There  are  numerous  factors  associated  with  the  successful  development  and  commercialization  of  any  of  our
product candidates, including future trial design and various regulatory requirements, many of which cannot be determined
with accuracy at our current stage of development. Additionally, future commercial and regulatory factors beyond our control
may impact our clinical development programs and plans.

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A  significant  portion  of  our  research  and  development  costs  have  been  external  costs,  which  we  track  on  a  program-by-
program basis following nomination as a product candidate. We have not historically tracked all of our internal research and
development expenses on a program-by-program basis as they are deployed across multiple projects under development. The
following  table  summarizes  our  external  research  and  development  expenses,  by  program,  following  nomination  as  a
development  candidate  for  the  years  ended  December  31,  2019,  2018  and  2017.  All  external  research  and  development
expenses  not  attributable  to  the  XMT-1536  and  XMT-1522  programs  are  captured  within  preclinical  and  discovery  costs.
These costs relate to our next ADC clinical candidate, XMT-1592, as well as additional earlier discovery stage programs and
certain unallocated costs. We terminated the development of XMT-1522 in the first quarter of 2019. Our internal research and
development  costs  are  primarily  personnel-related  costs,  stock-based  compensation  costs,  facility  costs,  including
depreciation,  and  lab  consumables.  Pre-development  candidate  expenses,  unallocated  costs  and  internal  research  and
development costs have been stated separately.

(in thousands)
XMT-1536 external costs
XMT-1522 external costs
Preclinical and discovery costs
Internal research and development costs
Total research and development costs

2019

9,461
1,936
16,980
26,663
55,040

  $

  $

 $

Year ended
December 31, 
2018
15,922   $
15,562  
4,517  
23,914  
59,915   $

 $

2017

8,647
14,661
3,093
20,299
46,700

The successful development of our product candidates is highly uncertain. As such, we cannot reasonably estimate or know
the nature, timing and estimated costs of the efforts that will be necessary to complete the remainder of the development of
our  product  candidates.  We  are  also  unable  to  predict  when,  if  ever,  material  net  cash  inflows  will  commence  from  the
development efforts associated with our product candidates. This is due to the numerous risks and uncertainties associated
with developing drugs, including the uncertainty of:

·

·

·

·

·

·

·

successful completion of preclinical studies and IND-enabling studies;

successful enrollment in and completion of clinical studies;

receipt of marketing approvals from applicable regulatory authorities;

establishing commercial manufacturing capabilities or making arrangements with third-party manufacturers;

obtaining and maintaining patent and trade secret protection and regulatory exclusivity for our product candidates;

commercializing the product candidates, if and when approved, whether alone or in collaboration with others; and

continued acceptable safety profile of the drugs following approval.

A change in the outcome of any of these variables with respect to the development, manufacture or commercialization of any
of our product candidates would significantly change the costs, timing and viability associated with the development of that
product candidate.

General and Administrative Expenses

General  and  administrative  expenses  consist  primarily  of  salaries  and  other  employee-related  costs,  including  stock-based
compensation,  for  personnel  in  executive,  finance,  accounting,  business  development,  legal  operations,  information
technology and human resources functions. Other significant costs include facility costs not otherwise included in research

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and  development  expenses,  legal  fees  relating  to  patent  and  corporate  matters,  and  fees  for  accounting  and  consulting
services.

We  anticipate  that  our  general  and  administrative  expenses  will  increase  in  the  future  to  support  continued  research  and
development activities, including increased costs related to the hiring of additional personnel, fees to outside consultants and
patent costs, among other expenses.

Other Income (Expense)

Other income (expense) consists primarily of interest income earned on cash equivalents and marketable securities. Interest
expense is related to the credit facility that we entered into on May 9, 2019, with Silicon Valley Bank. It bears a floating per
annum rate interest, as well as a final payment of 5% of the amounts drawn, that is being recorded as interest expense over
the term through the maturity date using the effective-interest method. Also included in interest expense is the amortization
of the deferred financing costs and the accretion of debt discount relating to the credit facility.

Results of Operations

Comparison of Years Ended December 31, 2019 and 2018

The following table summarizes our results of operations for the years ended December 31, 2019 and 2018, together with the
changes in those items:

(in thousands)
Collaboration revenue
Operating expenses:

Research and development
General and administrative

Total operating expenses
Other income (expense):

Interest income
Interest expense

Total other income (expense), net
Net loss

Collaboration Revenue

Year ended
December 31, 

2019
42,123   $

2018
10,594   $

     Dollar Change
31,529

  $

55,040  
17,283  
72,323  

2,226  
(234) 
1,992  

59,915  
16,334  
76,249  

1,398  
 —  
1,398  

  $ (28,208)  $ (64,257)  $

(4,875)
949
(3,926)

828
(234)
594
36,049

Collaboration revenue was $42.1 million during the year ended December 31, 2019, compared to $10.6 million during
the year ended December 31, 2018, an increase of $31.5 million, primarily as a result of the termination of the Takeda
agreements and the recognition of the remaining deferred revenue of $40.0 million in early 2019. Additionally, revenue of
$2.1 million was recognized in connection with the Merck KGaA Agreement and Merck KGaA Supply Agreement in the
year ended December 31, 2019. This compares to the revenue recognized during the year ended December 31, 2018 for
support of partner programs with Takeda, Merck KGaA and Asana BioSciences of $9.1 million and recognition of a
milestone of $1.5 million achieved upon completion of a GLP toxicology study by Asana BioSciences.

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Research and Development Expense

Research and development expense was $55.0 million for the year ended December 31, 2019, compared to $59.9 million for
the year ended December 31, 2018. The overall decrease of $4.9 million was primarily attributable to the following:

·

·

decrease of $13.5 million related to the development and manufacturing activities for XMT-1522; and

decrease of $9.0 million related to manufacturing activities for XMT-1536.

These decreased costs were partially offset by the following:

·

·

·

·

·

·

increase  of  approximately  $8.3  million  related  to  preclinical  development  and  manufacturing  activities  for  XMT-
1592;

increase of approximately $3.0 million related to XMT-1536 clinical and regulatory expenses;

increase  of  approximately  $3.0  million  related  to  research  efforts  to  further  platform  development  and  evaluate
potential product candidates;

increase of $1.8 million related to employee compensation, including stock-based compensation expense;

increase  of  $0.8  million  related  to  advancement  of  companion  diagnostic  development  efforts  for  the  NaPi2B
biomarker; and

increase of $0.6 million related to a milestone paid upon dosing of the first patient in the expansion cohort of the
XMT-1536 clinical trial.

We expect our research and development expenses to increase as we continue our clinical development XMT-1536 and
XMT-1592 and continue to advance our preclinical product candidate pipeline and invest in improvements in our ADC
technologies.

General and Administrative Expense

General and administrative expense was $17.3 million for the year ended December 31, 2019, compared to $16.3 million for
the year ended December 31, 2018. The overall increase of $0.9 million was primarily attributable to the increase in stock-
based compensation expense.

We  expect  that  our  general  and  administrative  expense  will  increase  in  the  future  to  support  continued  research  and
development activities. These increases will likely include legal, auditing and filing fees, additional insurance premiums and
general compliance and consulting expenses. 

Total Other Income (Expense), Net

Total  other  income  (expense),  net  was  $2.0  million  and  $1.4  million  for  the  years  ended  December  31,  2019  and  2018,
respectively.  Other  income  consists  primarily  of  interest  income  on  cash  equivalents  and  short-term  marketable  securities,
which increased $0.8 million due to higher investable balances for the year ended December 31, 2019. Interest expense of
$0.2 million was related to our outstanding borrowings under the credit facility.

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Comparison of Years Ended December 31, 2018 and 2017

The following table summarizes our results of operations for the years ended December 31, 2018 and 2017, together with the
changes in those items:

(in thousands)
Collaboration revenue
Operating expenses:

Research and development
General and administrative

Total operating expenses
Other income (expense):

Interest income
Interest expense

Total other income (expense), net
Net loss

Collaboration Revenue

Year ended
December 31, 

2018
10,594   $

2017
17,545   $

     Dollar Change
(6,951)

  $

59,915  
16,334  
76,249  

1,398  
 —  
1,398  

46,700  
10,462  
57,162  

910  
 —  
910  

  $ (64,257)  $ (38,707)  $

13,215
5,872
19,087

488
 —
488
(25,550)

The decrease in collaboration revenue from $17.5 million during the year ended December 31, 2017 to $10.6 million for the
year ended December 31, 2018 was primarily the result of a decrease in efforts to support partner programs and a third
quarter 2018 increase in total projected efforts associated with longer anticipated timelines, as a result of partial clinical hold,
used to recognize XMT-1522 revenue. In addition, the year ended December 31, 2017 included a $4.0 million increase in
revenue relating to changes in estimates of the costs to complete services under the Takeda agreements.

Research and Development Expense

Research and development expense increased by $13.2 million from $46.7 million for the year ended December 31, 2017 to
$59.9 million for the year ended December 31, 2018, an increase of 28%.

The increase in research and development expense was primarily attributable to the following:

·

·

·

·

·

approximately $2.3 million in increased employee compensation and $0.7 million in increased lab consumables both
primarily due to an increase in headcount as our programs progressed in clinical and preclinical studies;

approximately  $9.3  million  in  increased  external  research  and  development  expenses  for  manufacturing  activities
for XMT-1536 and XMT-1522, as well as research efforts to further platform development and evaluate potential
product candidates;

approximately  $2.9  million  in  increased  external  clinical  and  regulatory  expenses  due  primarily  to  the
commencement of our first in-human trials for XMT-1536; and

approximately $1.5 million in increased lab consumables and facilities costs;

partially offset by a reduction of  approximately $2.8 million related to milestone payments in 2017 in connection
with the XMT-1522 and XMT-1536 clinical trials, which were non-recurring events.

We expect our research and development expenses to increase as we continue our clinical development of XMT-1536 and
continue to advance our preclinical product candidate pipeline and invest in improvements in our ADC technologies.

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General and Administrative Expense

General and administrative expense increased by $5.9 million from $10.5 million during the year ended December 31, 2017
to $16.3 million for the year ended December 31, 2018, an increase of 56%.

The increase in general and administrative expense was primarily attributable to the following:

·

·

·

approximately  $3.0  million  in  increased  personnel  costs  primarily  due  to  additional  headcount  as  we  built  the
infrastructure to support the growth of the research and development organization;

approximately $1.7 million in increased professional fees, including external legal fees, corporate communications
and public relations costs to support operations as a growing public company; and

approximately $1.0 million in increased other costs, including insurance, software and franchise taxes.

We expect that our general and administrative expense will increase in future periods as we expand our operations and incur
additional costs in connection with being a public company. These increases will likely include legal, auditing and filing fees,
additional insurance premiums and general compliance and consulting expenses.

Other Income

Other income increased by $0.5 million from $0.9 million for the year ended December 31, 2017 to $1.4 million for the year
ended  December  31,  2018.  The  change  in  other  income  was  primarily  due  to  increased  interest  income  in  the  year  ended
December 31, 2018.

Liquidity and Capital Resources

Sources of Liquidity

Since the closing of our initial public offering in July 2017, we have financed our operations primarily with the proceeds
from that offering and our 2019 follow-on public offering. The follow-on public offering was completed on March 5, 2019
and resulted in net proceeds of $92.2 million. On May 8, 2019, the Company entered into a term-loan agreement for up to
$20.0 million, of which $5.0 million was funded in connection with the execution of the agreement. No additional amounts
have been drawn since the initial $5.0 million. As of December 31, 2019, we had cash, cash equivalents and short-term
marketable securities of $99.8 million.

On July 2, 2018, we established an ATM pursuant to which we are able to offer and sell up to $75.0 million of our common
stock from time to time at prevailing market prices. As of December 31, 2019, we had not sold any shares under the ATM
and had $75.0 million of potential availability under the program.

Cash Flows

The following table provides information regarding our cash flows for the years ended December 31, 2019, 2018 and 2017:

(in thousands)
Net cash used in operating activities
Net cash provided by (used in) investing activities
Net cash provided by financing activities
Increase (decrease) in cash, cash equivalents and restricted cash

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2019

Year ended
December 31, 
2018
  $ (67,744)  $ (55,216)  $ (42,679)
(99,624)
87,195  
1,064  
68,597
33,043   $ (73,706)

(27,293) 
97,704  
2,667   $

  $

2017

 
 
 
 
 
 
 
 
 
 
 
 
 
 
    
    
    
 
 
 
 
 
 
 
 
 
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Net Cash Used in Operating Activities

Net cash used in operating activities was $67.7 million for the year ended December 31, 2019 and primarily consisted of a
net loss of $28.2 million adjusted for non-cash items including stock-based compensation of $4.9 million and depreciation of
$1.2 million, as well as change in our net working capital and the decrease in deferred revenue of $41.4 million primarily
related to Takeda agreements. Net cash used in operating activities was $55.2 million for the year ended December 31, 2018
and primarily consisted of a net loss of $64.3 million adjusted for non-cash items including stock-based compensation of $3.9
million and depreciation of $1.3 million, as well as change in our net working capital and the decrease in deferred revenue of
$6.2 million. Net cash used in operating activities was $42.7 million for the year ended December 31, 2017 and primarily
consisted of a net loss of $38.7 million adjusted for non-cash items including stock-based compensation of $1.4 million and
depreciation  of  $0.9  million,  as  well  as  change  in  our  net  working  capital  and  the  decrease  in  deferred  revenue  of  $9.9
million.

Net Cash Provided by (Used in) Investing Activities

Net  cash  used  in  investing  activities  was  $27.3  million  during  the  year  ended  December  31,  2019  compared  to  net  cash
provided  by  investing  activities  of  $87.2    million  during  the  year  ended  December  31,  2018.  Net  cash  used  in  investing
activities for the year ended December 31, 2019 consisted primarily of purchases of marketable securities, partially offset by
maturities of marketable securities. Net cash provided by investing activities for the year ended December 31, 2018 consisted
primarily of maturities of marketable securities. Net cash used in investing activities for the year ended December 31, 2017
consisted primarily of purchases of marketable securities offset by maturities of marketable securities. 

Net Cash Provided by Financing Activities

Net cash provided by financing activities was $97.7 million during the year ended December 31, 2019 compared to net cash
provided by financing activities of $1.1 million during the year ended December 31, 2018. During the year ended December
31, 2019 cash provided by financing activities consisted primarily of the proceeds from our follow-on public offering of our
common  stock  and  issuance  of  debt.  During  the  year  ended  December  31,  2018  cash  provided  by  financing  activities
consisted  primarily  of  the  proceeds  from  the  exercise  of  stock  options.  During  the  year  ended  December  31,  2017  cash
provided by financing activities consisted primarily of the proceeds from our initial public offering.

Funding Requirements

We  expect  our  cash  expenditures  to  increase  in  connection  with  our  ongoing  activities,  particularly  as  we  continue  the
research and development of, initiate clinical studies of, and seek marketing approval for our product candidates. In addition,
if we obtain marketing approval for any of our product candidates, we expect to incur significant commercialization expenses
related to drug sales, marketing, manufacturing and distribution to the extent that such sales, marketing and distribution are
not the responsibility of potential collaborators.

Our future capital requirements will depend on many factors, including:

·

·

·

·

·

the scope, progress, results and costs of drug discovery, preclinical development, laboratory testing and clinical
studies for our product candidates;

the scope, prioritization and number of our research and development programs;

the costs, timing and outcome of regulatory review of our product candidates;

our ability to establish and maintain collaborations on favorable terms, if at all;

the achievement of milestones or occurrence of other developments that trigger payments under any collaboration
agreements we obtain;

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·

·

·

·

·

the extent to which we are obligated to reimburse, or entitled to reimbursement of, clinical study costs under future
collaboration agreements, if any;

the costs of preparing, filing and prosecuting patent applications, maintaining and enforcing our intellectual property
rights and defending intellectual property‑related claims;

the extent to which we acquire or in‑license other product candidates and technologies;

the costs of securing manufacturing arrangements for clinical and commercial production; and

the costs of establishing or contracting for sales and marketing capabilities if we obtain regulatory approvals to
market our product candidates.

We  plan  to  raise  funds  from  collaborations,  licensing  agreements  or  other  strategic  partnerships  or  raise  additional  capital
through  the  issuance  and  sale  of  our  common  stock.  There  is  inherent  uncertainty  associated  with  these  fundraising
activities.  In the absence of such funding, we plan to strategically manage uncommitted spend to execute our priorities and
implement  cost-saving  measures  to  reduce  research  and  development  and  general  and  administrative  expenditures  which
could include limiting or delaying or terminating preclinical studies or other development activities for one or more of our
ADC product candidates. Therefore, we estimate that our cash, cash equivalents and marketable securities are sufficient to
fund our operating plan through at least the next twelve months following the filing of our Annual Report on Form 10-K,
including our Phase 1 clinical study for XMT-1536 and our planned dose escalation study for XMT-1592.

Identifying  potential  product  candidates  and  conducting  preclinical  testing  and  clinical  studies  is  a  time‑consuming,
expensive and uncertain process that takes many years to complete, and we may never generate the necessary data or results
required  to  obtain  marketing  approval  and  achieve  drug  sales.  In  addition,  our  product  candidates,  if  approved,  may  not
achieve commercial success. Our commercial revenues, if any, will be derived from sales of drugs that we do not expect to be
commercially  available  for  many  years,  if  at  all.  Accordingly,  we  will  need  to  continue  to  rely  on  additional  financing  to
achieve our business objectives. Adequate additional financing may not be available to us on acceptable terms, or at all.

Until  such  time,  if  ever,  as  we  can  generate  substantial  product  revenues,  we  expect  to  finance  our  cash  needs  through  a
combination  of  equity  offerings,  debt  financings,  strategic  partnerships  and  licensing  arrangements.  To  the  extent  that  we
raise  additional  capital  through  the  sale  of  equity  or  convertible  debt  securities,  the  ownership  interests  of  our  common
stockholders  will  be  diluted,  and  the  terms  of  these  securities  may  include  liquidation  or  other  preferences  that  adversely
affect the rights of our common stockholders. We have access to an additional line of credit of $15.0 million under the Credit
Facility  along  with  funds  to  be  earned  in  connection  with  our  agreements  with  Merck  KGaA  and  Asana  BioSciences,  if
development  activities  are  successful  under  those  agreements.  Future  additional  debt  financing,  if  available,  may  involve
agreements that include covenants limiting or restricting our ability to take specific actions, such as incurring additional debt,
making capital expenditures or declaring dividends.

If  we  raise  funds  through  additional  strategic  partnerships  or  licensing  arrangements  with  third  parties,  we  may  have  to
relinquish valuable rights to our technologies, future revenue streams, research programs or product candidates or to grant
licenses on terms that may not be favorable to us. If we are unable to raise additional funds through equity or debt financings
when  needed,  we  may  be  required  to  delay,  limit,  reduce  or  terminate  our  drug  development  or  future  commercialization
efforts  or  grant  rights  to  develop  and  market  product  candidates  that  we  would  otherwise  prefer  to  develop  and  market
ourselves.

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The following table summarizes our significant contractual obligations as of payment due date by period at December 31,
2019:

Contractual Obligations

(in thousands)
Lease commitments(1)
Long-term debt obligations(2)
Total

Total

  Less than  
1 Year

1 to 3
     Years

3 to 5
     Years

  $ 3,489   $ 2,510   $

887   $

  5,648  

867  

  4,196  

  $ 9,137   $ 3,377   $ 5,083   $

  More than
     5 years
 —
 —
 —

92   $
585  
677   $

(1) Represents  future  minimum  lease  payments  under  our  non‑cancelable  operating  and  finance  leases,  which  expire
through  February  2024.  The  minimum  lease  payments  above  do  not  include  any  related  common  area  maintenance
charges or real estate taxes.

(2) Represents  future  debt  principal  plus  interest  and  final  payments  under  our  term-loan,  which  is  payable  in  full  on

February 1, 2023. Refer to footnote 8 in the Notes to the Consolidated Financial Statements.

We  enter  into  agreements  in  the  normal  course  of  business  with  contract  research  organizations,  contract  manufacturing
organizations and institutions to license intellectual property. We have not included these payments in the table of contractual
obligations above since the contracts are cancelable at any time by us, generally upon 30 days prior written notice.

In July 2015, we entered into a license agreement with Recepta Biopharma S.A., or Recepta, as amended, for the NaPi2b
antibody. Under this agreement, we paid Recepta an upfront payment of $1.0 million and are obligated to pay Recepta up to
$65.5 million in development, regulatory and commercial milestones and tiered royalties in the low‑single digit percentages
on net sales of products outside of Brazil until the expiration of the royalty term. Upon the expiration of each royalty term in
each  country  for  each  applicable  product,  the  exclusive  licenses  granted  to  each  party  under  the  agreement  will  become
fully‑paid up and royalty‑free. We have made $1.9 million in development milestone payments to date.

In  January  2019,  we  entered  into  a  license  agreement  with  Synaffix  B.V.,  or  Synaffix,  to  develop,  manufacture  and
commercialize  ADC  targets  using  Synaffix’s  proprietary  technology  for  a  total  of  six  targets.  At  contract  inception  we
designated the first target and paid an upfront, non-refundable license fee of $0.8 million. We are required to make milestone
payments to Synaffix of up to an aggregate of $24.8 million in development and regulatory milestones, up to $20.0 million in
one-time  sales  milestones  based  on  the  achievement  of  annual  sales  objectives  for  the  first  target.  In  addition,  upon
designation  of  additional  targets,  we  will  be  obligated  to  pay  in  the  range  of  $44.8  million  to  $62.8  million  for  issuance,
development,  regulatory  and  one  time  sales  milestones.  Finally,  pursuant  to  the  terms  this  license  agreement,  upon
commencement of commercial sales of a product, if any, we are required to pay to Synaffix tiered royalties in the low‑single
digit percentages on net sales of the respective products. We have not made any milestone payments to Synaffix to date.

We did not have, during the periods presented, and we do not currently have, any off‑balance sheet arrangements, as defined
under applicable Securities and Exchange Commission rules.

Off‑Balance Sheet Arrangements

JOBS Act

In April 2012, the Jumpstart Our Business Startups Act of 2012, or the JOBS Act, was enacted. Section 107 of the JOBS Act
provides that an “emerging growth company,” or an EGC, can take advantage of the extended transition period provided in
Section  7(a)(2)(B)  of  the  Securities  Act  of  1933,  as  amended,  or  the  Securities  Act,  for  complying  with  new  or  revised
accounting  standards.  Thus,  an  EGC  can  delay  the  adoption  of  certain  accounting  standards  until  those  standards  would
otherwise apply to private companies. We have irrevocably elected not to avail ourselves of this extended transition

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period and, as a result, we will adopt new or revised accounting standards on the relevant dates on which adoption of such
standards is required for other public companies.

We continue to evaluate the benefits of relying on other exemptions and reduced reporting requirements under the JOBS Act.
Subject  to  certain  conditions,  as  an  EGC,  we  intend  to  rely  on  certain  of  these  exemptions,  including  without  limitation,
(i)  providing  an  auditor’s  attestation  report  on  our  system  of  internal  controls  over  financial  reporting  pursuant  to
Section  404(b)  of  the  Sarbanes‑Oxley  Act  and  (ii)  complying  with  any  requirement  that  may  be  adopted  by  the  Public
Company Accounting Oversight Board, or PCAOB, regarding mandatory audit firm rotation or a supplement to the auditor’s
report  providing  additional  information  about  the  audit  and  the  financial  statements,  known  as  the  auditor  discussion  and
analysis. We will remain an EGC until the earlier of (i) the last day of the fiscal year in which we have total annual gross
revenues  of  $1.07  billion  or  more;  (ii)  the  last  day  of  the  fiscal  year  following  the  fifth  anniversary  of  the  date  of  the
completion  of  our  IPO;  (iii)  the  date  on  which  we  have  issued  more  than  $1  billion  in  nonconvertible  debt  during  the
previous three years; or (iv) the date on which we are deemed to be a large accelerated filer under the rules of the Securities
and Exchange Commission.

Critical Accounting Policies and Significant Judgements and Estimates

Our  management's  discussion  and  analysis  of  our  financial  condition  and  results  of  operations  are  based  on  our  financial
statements, which have been prepared in accordance with U.S. generally accepted accounting principles. The preparation of
these financial statements requires us to make judgments and estimates that affect the reported amounts of assets, liabilities,
revenues,  and  expenses  and  the  disclosure  of  contingent  assets  and  liabilities  in  our  financial  statements.  We  base  our
estimates  on  historical  experience,  known  trends  and  events,  and  various  other  factors  that  are  believed  to  be  reasonable
under  the  circumstances.  Actual  results  may  differ  from  these  estimates  under  different  assumptions  or  conditions.  On  an
ongoing  basis,  we  evaluate  our  judgments  and  estimates  in  light  of  changes  in  circumstances,  facts  and  experience.  The
effects of material revisions in estimates, if any, will be reflected in the financial statements prospectively from the date of
change in estimates.

We  believe  that  our  most  critical  accounting  policies  are  those  relating  to  revenue  recognition,  accrued  research  and
development expenses as discussed in the notes to consolidated financial statements included in this Annual Report on Form
10-K.

Revenue Recognition

We enter into collaboration agreements which are within the scope of Accounting Standards Update 2014-09, Revenue from
Contracts  with  Customers,  or  Topic  606,  under  which  we  license  rights  to  our  technology  and  certain  of  our  product
candidates  and  perform  research  and  development  services  for  third  parties.    The  terms  of  these  arrangements  typically
include payment of one or more of the following: non-refundable, up-front fees; reimbursement of research and development
costs; development, regulatory and commercial milestone payments; and royalties on net sales of licensed products.  

Under  Topic  606,  an  entity  recognizes  revenue  when  its  customer  obtains  control  of  promised  goods  or  services,  in  an
amount  that  reflects  the  consideration  which  the  entity  expects  to  receive  in  exchange  for  those  goods  or  services.    To
determine the appropriate amount of revenue to be recognized for arrangements determined to be within the scope of Topic
606,  we  perform  the  following  five  steps:  (i)  identification  of  the  promised  goods  or  services  in  the  contract;  (ii)
determination of whether the promised goods or services are performance obligations; (iii) measurement of the transaction
price,  including  the  constraint  on  variable  consideration;  (iv)  allocation  of  the  transaction  price  to  the  performance
obligations; and (v) recognition of revenue when (or as) we satisfy each performance obligation.   We only apply the five-
step model to contracts when it is probable that the entity will collect consideration it is entitled to in exchange for the goods
or services it transfers to the customer.

The promised good or services in our arrangement typically consist of license rights to our intellectual property and research
and development services.  We also have optional additional items in contracts, which are considered marketing offers and
are accounted for as separate contracts with the customer if such option is elected by the customer, unless the option provides
a material right which would not be provided without entering into the contract.  Performance obligations

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are promised goods or services in a contract to transfer a distinct good or service to the customer.  Promised goods or services
are considered distinct when (i) the customer can benefit from the good or service on its own or together with other readily
available  resources  or  (ii)  the  promised  good  or  service  is  separately  identifiable  from  other  promises  in  the  contract.    In
assessing  whether  promised  good  or  services  are  distinct,  we  consider  factors  such  as  the  stage  of  development  of  the
underlying intellectual property, the capabilities of the customer to develop the intellectual property on their own or whether
the required expertise is readily available.

We  estimate  the  transaction  price  based  on  the  amount  expected  to  be  received  for  transferring  the  promised  goods  or
services in the contract.  The consideration may include both fixed consideration or variable consideration.  At the inception
of each arrangement that includes variable consideration and at each reporting period, we evaluate the amount of potential
payment and the likelihood that the payments will be received.  We utilize either the most likely amount method or expected
amount method to estimate the amount expected to be received based on which method better predicts the amount expected
to be received.  If it is probable that a significant revenue reversal would not occur, the variable consideration is included in
the transaction price.

Our  contracts  often  include  development  and  regulatory  milestone  payments.  At  contract  inception  and  at  each  reporting
period, we evaluate whether the milestones are considered probable of being reached and estimates the amount to be included
in the transaction price using the most likely amount method.  If it is not probable that a significant revenue reversal would
not  occur,  the  associated  milestone  value  is  included  in  the  transaction  price.    Milestone  payments  that  are  not  within  our
control or the licensee’s control, such as regulatory approvals, are not included in the transaction price.  At the end of each
subsequent reporting period, we re-evaluate the probability of achievement of such development milestones and any related
constraint, and if necessary, adjust our estimate of the overall transaction price.  

For arrangements that include sales-based royalties, including milestone payments based on the level of sales, and the license
is deemed to be the predominant item to which the royalties relate, we recognize revenue at the later of (i) when the related
sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied
(or partially satisfied). 

We allocate the transaction price based on the estimated standalone selling price of the underlying performance obligations or
in  the  case  of  certain  variable  consideration  to  one  or  more  performance  obligations.    We  must  develop  assumptions  that
require judgment to determine the stand-alone selling price for each performance obligation identified in the contract.  We
utilize key assumptions to determine the stand-alone selling price, which may include other comparable transactions, pricing
considered in negotiating the transaction and the estimated costs to complete the respective performance obligation.  Certain
variable consideration is allocated specifically to one or more performance obligations in a contract when the terms of the
variable  consideration  relate  to  the  satisfaction  of  the  performance  obligation  and  the  resulting  amounts  allocated  to  each
performance obligation are consistent with the amounts we would expect to receive for each performance obligation.   

For  performance  obligations  consisting  of  licenses  and  other  promises,  we  utilize  judgment  to  assess  the  nature  of  the
combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a
point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue from non-
refundable, up-front fees.  We evaluate the measure of progress each reporting period and, if necessary, adjusts the measure
of performance and related revenue recognition.  If the license to our intellectual property is determined to be distinct from
the  other  performance  obligations  identified  in  the  arrangement,  we  will  recognize  revenue  from  non-refundable,  up-front
fees allocated to the license when the license is transferred to the customer and the customer is able to use and benefit from
the license.

Collaborative Arrangements

We  record  the  elements  of  our  collaboration  agreements  that  represent  joint  operating  activities  in  accordance  with  ASC
Topic 808, Collaborative Arrangements (ASC 808). Accordingly, the elements of the collaboration agreements that represent
activities  in  which  both  parties  are  active  participants  and  to  which  both  parties  are  exposed  to  the  significant  risks  and
rewards  that  are  dependent  on  the  commercial  success  of  the  activities,  are  recorded  as  collaborative  arrangements.  We
consider the guidance in ASC Topic 606 in determining the appropriate treatment for the transactions

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between us and our collaborative partners and the transactions between us and third parties. Generally, the classification of
transactions under the collaborative arrangements is determined based on the nature and contractual terms of the arrangement
along with the nature of the operations of the participants. To the extent revenue is generated from a collaboration, we will
recognize our share of the net sales on a gross basis if we are deemed to be the principal in the transactions with customers,
or on a net basis if we are instead deemed to be the agent in the transactions with customers, consistent with the guidance in
Topic 606.

Accrued Research and Development Expenses

As  part  of  the  process  of  preparing  our  financial  statements,  we  are  required  to  estimate  our  accrued  expenses  as  of  each
balance sheet date. This process involves reviewing open contracts and purchase orders, communicating with our personnel
to identify services that have been performed on our behalf and estimating the level of service performed and the associated
cost incurred for the service when we have not yet been invoiced or otherwise notified of the actual cost. The majority of our
service  providers  invoice  us  monthly  in  arrears  for  services  performed  or  when  contractual  milestones  are  met.  We  make
estimates of our accrued expenses as of each balance sheet date based on facts and circumstances known to us at that time.
We  periodically  confirm  the  accuracy  of  our  estimates  with  the  service  providers  and  make  adjustments  if  necessary.  The
significant estimates in our accrued research and development expenses include the costs incurred for services performed by
our vendors in connection with research and development activities for which we have not yet been invoiced.

We record our expenses related to research and development activities based upon our estimates of the services received and
efforts expended pursuant to quotes and contracts with vendors that conduct research and development on our behalf. The
financial  terms  of  these  agreements  are  subject  to  negotiation,  vary  from  contract  to  contract  and  may  result  in  uneven
payment flows. There may be instances in which payments made to our vendors will exceed the level of services provided
and result in a prepayment of the research and development expense. In accruing service fees, we estimate the time period
over  which  services  will  be  performed,  enrollment  of  subjects,  number  of  sites  activated  and  the  level  of  effort  to  be
expended in each period.  If the actual timing of the performance of services or the level of effort varies from our estimate,
we  adjust  the  accrued  or  prepaid  expense  balance  accordingly.   Although  we  do  not  expect  our  estimates  to  be  materially
different from amounts actually incurred, if our estimates of the status and timing of services performed differ from the actual
status and timing of services performed, we may report amounts that are too high or too low in any particular period.  To
date, there have been no material differences from our estimates to the amounts actually incurred. Significant judgement is, at
times, involved in making the above estimates.

Recent accounting pronouncements

See Note 2, Recently Issued Accounting Pronouncements, in the Notes to Consolidated Financial Statements for a description
of recent accounting pronouncements applicable to our business.

ITEM 7A.           QUANTITATIVE AND QUALITATIVE DISCLOSURES ABOUT MARKET RISK

We  are  exposed  to  market  risk-related  to  changes  in  interest  rates.  Our  primary  exposure  to  market  risk  is  interest  rate
sensitivity,  which  is  affected  by  changes  in  the  general  level  of  U.S.  interest  rates,  particularly  because  our  investments,
including  cash  equivalents  and  marketable  securities  are  invested  in  U.S.  Treasury  obligations,  commercial  paper  and
corporate bonds. However, we believe that due to the short-term duration of our investment portfolio and low-risk profile of
our investments, an immediate 100 basis points change in interest rates would not have a material effect on the fair market
value of our investments portfolio.

We are currently not exposed to market risk related to changes in foreign currency exchange rates, but we may contract with
vendors that are located Asia and Europe and may be subject to fluctuations in foreign currency rates at that time.

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ITEM 8.              FINANCIAL STATEMENTS AND SUPPLEMENTARY DATA

Mersana Therapeutics, Inc.

Index to Consolidated Financial Statements

Report of Independent Registered Public Accounting Firm 
Consolidated Balance Sheets 
Consolidated Statements of Operations and Comprehensive Loss 
Consolidated Statements of Convertible Preferred Stock and Stockholders’ Equity (Deficit) 
Consolidated Statements of Cash Flows 
Notes to Consolidated Financial Statements 

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Report of Independent Registered Public Accounting Firm

To the Shareholders and the Board of Directors of Mersana Therapeutics, Inc.

Opinion on the Financial Statements

We  have  audited  the  accompanying  consolidated  balance  sheets  of  Mersana  Therapeutics,  Inc.  (the  Company)  as  of
December  31,  2019  and  2018,  the  related  consolidated  statements  of  operations  and  comprehensive  loss,  convertible
preferred stock and stockholders' equity (deficit) and cash flows for each of the three years in the period ended December 31,
2019,  and  the  related  notes  (collectively  referred  to  as  the  “consolidated  financial  statements”).  In  our  opinion,  the
consolidated financial statements present fairly, in all material respects, the financial position of the Company at December
31,  2019  and  2018,  and  the  results  of  its  operations  and  its  cash  flows  for  each  of  the  three  years  in  the  period  ended
December 31, 2019, in conformity with U.S. generally accepted accounting principles.

Adoption of ASU No. 2016-02, “Leases”

As discussed in Note 2 to the consolidated financial statements, the Company changed its method of accounting for leases in
2019  due  to  the  adoption  of  Accounting  Standards  Update  (ASU)  No.  2016-02,  Leases  (Topic  842),  and  the  related
amendments.

Basis for Opinion

These financial statements are the responsibility of the Company's management. Our responsibility is to express an opinion
on  the  Company’s  financial  statements  based  on  our  audits.  We  are  a  public  accounting  firm  registered  with  the  Public
Company  Accounting  Oversight  Board  (United  States)  (PCAOB)  and  are  required  to  be  independent  with  respect  to  the
Company in accordance with the U.S. federal securities laws and the applicable rules and regulations of the Securities and
Exchange Commission and the PCAOB.

We conducted our audits in accordance with the standards of the PCAOB. Those standards require that we plan and perform
the  audit  to  obtain  reasonable  assurance  about  whether  the  financial  statements  are  free  of  material  misstatement,  whether
due to error or fraud. The Company is not required to have, nor were we engaged to perform, an audit of its internal control
over financial reporting. As part of our audits we are required to obtain an understanding of internal control over financial
reporting  but  not  for  the  purpose  of  expressing  an  opinion  on  the  effectiveness  of  the  Company's  internal  control  over
financial reporting. Accordingly, we express no such opinion.

Our audits included performing procedures to assess the risks of material misstatement of the financial statements, whether
due to error or fraud, and performing procedures that respond to those risks. Such procedures included examining, on a test
basis,  evidence  regarding  the  amounts  and  disclosures  in  the  financial  statements.  Our  audits  also  included  evaluating  the
accounting principles used and significant estimates made by management, as well as evaluating the overall presentation of
the financial statements. We believe that our audits provide a reasonable basis for our opinion.

/s/ Ernst & Young LLP 

We have served as the Company’s auditor since 2013.
Boston, Massachusetts
February 28, 2020

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Mersana Therapeutics, Inc.

Consolidated Balance Sheets

(in thousands, except share and per share data)

Assets
Current assets:

Cash and cash equivalents
Short-term marketable securities
Accounts receivable
Prepaid expenses and other current assets

Total current assets
Property and equipment, net
Operating lease right-of-use assets
Other assets
Total assets
Liabilities and stockholders’ equity
Current liabilities:
Accounts payable
Accrued expenses
Deferred revenue
Operating lease liabilities
Short-term debt
Other liabilities

Total current liabilities
Operating lease liabilities
Long-term debt, net
Other liabilities
Total liabilities
Commitments (Note 15)
Stockholders' equity
Preferred  stock,  $0.0001  par  value;  25,000,000  shares  authorized;  0  shares  issued  and
outstanding at December 31, 2019 and December 31, 2018, respectively
Common  stock,  $0.0001  par  value;  175,000,000  shares  authorized;  45,388,023  and
23,234,472 shares issued and outstanding at December 31, 2019 and December 31, 2018,
respectively
Additional paid-in capital
Accumulated other comprehensive income (loss)
Accumulated deficit
Total stockholders’ equity
Total liabilities and stockholders’ equity

December 31,   

December 31, 

2019

2018

$

$

$

62,351   $
37,439  
 —  
1,536  
101,326  
2,164  
2,598  
1,453  
107,541   $

7,296   $
8,986  
4,815  
2,219  
667  
87  
24,070  
677  
4,201  
275  
29,223  

59,634
10,497
459
3,715
74,305
2,694
 —
1,503
78,502

10,727
12,375
46,196
 —
 —
127
69,425
 —
 —
282
69,707

 —  

 —

 5  
270,662  
25  
(192,374) 
78,318  
107,541   $

 3
172,966
(8)
(164,166)
8,795
78,502

$

The accompanying notes are an integral part of these consolidated financial statements.

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Mersana Therapeutics, Inc.

Consolidated Statements of Operations and Comprehensive Loss

(in thousands, except share and per share data)

Collaboration revenue
Operating expenses:

Research and development
General and administrative

Total operating expenses
Other income (expense):

Interest income
Interest expense

Total other income (expense), net
Net loss
Other comprehensive loss:

Unrealized gain (loss) on marketable securities

Comprehensive loss
Net loss attributable to common stockholders — basic and diluted
Net loss per share attributable to common stockholders — basic and diluted
Weighted-average  number  of  shares  of  common  stock  used  in  net  loss  per
share attributable to common stockholders — basic and diluted

Year ended
December 31, 
2018

2017

2019

  $

42,123   $

10,594   $

17,545

55,040  
17,283  
72,323  

59,915  
16,334  
76,249  

2,226  
(234) 
1,992  
(28,208)  $

33  
(28,175)  $
(28,208)  $
(0.65)  $

1,398  
 —  
1,398  
(64,257)  $

141  
(64,116)  $
(64,257)  $
(2.79)  $

46,700
10,462
57,162

910
 —
910
(38,707)

(149)
(38,856)
(38,707)
(3.22)

  $

  $
  $
  $

    43,492,113  

  23,032,250  

  12,022,733

The accompanying notes are an integral part of these consolidated financial statements.

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Mersana Therapeutics, Inc.

Consolidated Statements of Convertible Preferred Stock and Stockholders’ Equity (Deficit)

(in thousands, except share and per share data)

Series A-1
Convertible

Series B-1
Convertible

Series C-1
Convertible

  Additional   Accumulated  

Other

Preferred Stock

Preferred Stock

Preferred Stock

Shares

     Amount

Shares

     Amount

Shares

     Amount

Common Stock
Shares

Paid-in
    Amount     Capital

Comprehensive  Accumulated   Stockholders’
Deficit
  Income (Loss)     

Equity

Balance 
December 31, 2016  25,085,153   $ 26,336   32,936,919   $ 35,232   14,674,062   $ 32,882    1,294,352   $

at

 1   $

3,551  $

 —   $ (59,171)  $ (55,619)

of
stock
partial
of

of
Issuance 
stock
common 
under 
initial
public  offering,
net  of 
issuance
costs of $7,580
Issuance 
common 
under 
exercise 
overallotment
option,  net  of
issuance  costs  of
$55
Conversion 
preferred 
into 
stock
Exercise of stock
options 
and
warrants
Stock-based
compensation
expense
Other
comprehensive
loss
Net loss

of
stock
common

Balance 
at
December 31, 2017 

of
stock

Cumulative
effect  adjustment
for  adoption  of
ASC 606
Exercise of stock
options
Purchase 
common 
under ESPP
Stock-based
compensation
expense
Other
comprehensive
gain
Net loss

of
stock

Balance 
at
December 31, 2018 
of
Issuance 
stock
common 
under 
public
offering,  net  of
issuance  costs  of
$5,587
Exercise of stock
options 
and
warrants
Purchase 
common 
under ESPP
Retirement 
of
common stock in
exchange 
for
common 
stock
warrant
Issuance 
common 
warrant 
exchange 
retirement 
common stock
Stock-based
compensation
expense
Other
comprehensive
income
Net loss

of
stock
in
for
of

Balance 
at
December 31, 2019 

 —  

 —  

 —  

 —  

 —  

 —    5,000,000  

 —  

  67,420   

 —  

 —  

67,420

 —  

 —  

 —  

 —  

 —  

 —   

51,977  

 —  

725   

 —  

 —  

725

  (25,085,153) 

  (26,336)  (32,936,919) 

  (35,232)  (14,674,062) 

  (32,882)    16,154,671  

 2  

  94,448   

 —  

 —  

94,450

 —  

 —  

 —  

 —  

 —  

 —   

264,017  

 —  

452   

 —  

 —  

452

 —  

 —  

 —  

 —  

 —  

 —   

 —  

 —  

1,422   

 —  

 —  

1,422

 —  
 —  

 —  

 —  

 —  

 —  
 —  

 —  

 —  

 —  

 —  
 —  

 —  

 —  

 —  

 —  
 —  

 —  

 —  

 —  

 —  
 —  

 —  

 —  

 —  

 —   
 —   

 —  
 —  

 —  
 —  

 —   
 —   

(149) 
 —  

 —  
(38,707) 

(149)
(38,707)

 —    22,765,017   $

 3   $168,018  $

(149)  $ (97,878)  $ 69,994

 —   

 —  

 —  

 —   

427,269  

 —  

 —   

918   

 —  

 —  

(2,031) 

(2,031)

 —  

918

42,186  

 —  

146   

 —  

 —  

146

 —  

 —  

 —  

 —  

 —  

 —   

 —  

 —  

3,884   

 —  

 —  

3,884

 —  
 —  

 —  

 —  
 —  

 —  

 —  
 —  

 —  

 —  
 —  

 —  

 —  
 —  

 —  

 —   
 —   

 —  
 —  

 —  
 —  

 —   
 —   

141  
 —  

 —  
(64,257) 

141
(64,257)

 —    23,234,472   $

 3   $172,966  $

(8)  $(164,166)  $

8,795

 —  

 —  

 —  

 —  

 —  

 —    24,437,500  

 2  

  92,160   

 —  

 —  

92,162

 —  

 —  

 —  

 —  

 —  

 —   

150,978  

 —  

175   

 —  

 —  

175

 —  

 —  

 —  

 —  

 —  

 —   

140,073  

 —  

489   

 —  

 —  

489

 —  

 —  

 —  

 —  

 —  

 —    (2,575,000) 

 —  

(8,986)  

 —  

 —  

(8,986)

 —  

 —  

 —  

 —  

 —  

 —   

 —  

 —  

8,986   

 —  

 —  

8,986

 —  

 —  

 —  

 —  

 —  

 —   

 —  

 —  

4,872   

 —  

 —  

4,872

 —  
 —  

 —   $

 —  
 —  

 —  

 —  
 —  

 —   $

 —  
 —  

 —  

 —  
 —  

 —   
 —   

 —  
 —  

 —  
 —  

 —   
 —   

33  
 —  

 —  
(28,208) 

33
(28,208)

 —   $

 —    45,388,023   $

 5   $270,662  $

25   $(192,374)  $ 78,318

The accompanying notes are an integral part of these consolidated financial statements.

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Mersana Therapeutics, Inc.

Consolidated Statements of Cash Flows

(in thousands)

Cash flows from operating activities

Net loss
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation
Loss on disposal of fixed assets
Net amortization of premiums and discounts on investments
Stock-based compensation
Change in deferred rent
Other non-cash items
Changes in operating assets and liabilities:

Accounts receivable
Prepaid expenses and other current assets
Other assets
Accounts payable
Accrued expenses
Operating lease assets
Operating lease liabilities
Deferred revenue

Net cash used in operating activities

Cash flows from investing activities
Maturities of marketable securities
Purchase of marketable securities
Purchase of property and equipment
Net cash provided by (used in) investing activities

Cash flows from financing activities

Net proceeds from public offering of common stock
Net proceeds from initial public offering
Net proceeds from issuance of common stock upon partial exercise of overallotment
Proceeds from exercise of stock options
Proceeds from purchases of common stock under ESPP
Proceeds from issuance of debt, net of issuance costs
Payments under capital lease obligations
Net cash provided by financing activities

Increase (decrease) in cash, cash equivalents and restricted cash
Cash, cash equivalents and restricted cash, beginning of period
Cash, cash equivalents and restricted cash, end of period

Supplemental disclosures of non-cash activities:
Fair value of common stock retired in exchange for issuance of common stock warrant
Conversion of preferred stock to common stock upon closing of initial public offering
Purchases of property and equipment in accounts payable and accrued expenses
Debt financing costs in accrued expenses
Cash paid for interest
Right-of-use assets obtained in exchange for operating lease liabilities
Right-of-use assets obtained in exchange for financing lease liabilities
Adjustment to accumulated deficit and deferred revenue upon adoption of Topic 606

$

$
$
$
$
$
$
$
$

Year ended
December 31, 
2018

2017

2019

$

(28,208) 

$

(64,257) 

$

(38,707)

1,245  
 —  
(222) 
4,872  
 —  
103  

459  
2,179  
 —  
(3,110) 
(3,569) 
1,771  
(1,883) 
(41,381) 
(67,744) 

27,000  
(53,688) 
(605) 
(27,293) 

92,162  
 —  
 —  
175  
489  
4,965  
(87) 
97,704  

2,667  
60,005  
62,672  

8,986  
 —  
 —  
180  
132  
4,369  
429  
 —  

$

$
$
$
$
$
$
$
$

1,257  
20  
(296) 
3,884  
110  
 —  

325  
(1,690) 
(1,132) 
7,375  
5,431  
 —  
 —  
(6,243) 
(55,216) 

88,565  
 —  
(1,370) 
87,195  

 —  
 —  
 —  
918  
146  
 —  
 —  
1,064  

33,043  
26,962  
60,005  

 —  
 —  
317  
 —  
 —  
 —  
 —  
2,031  

$

$
$
$
$
$
$
$
$

928
 —
(293)
1,422
(159)
 —

267
(1,200)
60
1,335
3,562
 —
 —
(9,894)
(42,679)

47,220
(145,701)
(1,143)
(99,624)

 —
67,420
725
452
 —
 —
 —
68,597

(73,706)
100,668
26,962

 —
94,450
35
 —
 —
 —
 —
 —

The accompanying notes are an integral part of these consolidated financial statements.

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Table of Contents

Mersana Therapeutics, Inc.
Notes to consolidated financial statements

1. Nature of Business and Basis of Presentation

Mersana Therapeutics, Inc. is a clinical-stage biopharmaceutical company focused on developing antibody drug conjugates
(ADCs) that offer a clinically meaningful benefit for cancer patients with significant unmet need. The Company leveraged
20 years of industry learning in the ADC field to develop proprietary and differentiated technology platforms that enable it to
design  ADCs  to  have  improved  efficacy,  safety  and  tolerability  relative  to  existing  ADC  therapies.  The  Company’s
innovative  platforms  which  include  Dolaflexin  and  Dolasynthen,  delivering  its  DolaLock  payload,  as  well  as
Immunosynthen,  delivering  a  novel  stimulator  of  interferon  genes  (STING)  agonist,  compose  a  highly  efficient  product
engine  that  has  enabled  a  robust  discovery  pipeline  for  the  Company  and  its  partners.  The  Company’s  product  candidates
include XMT‑1536 and XMT-1592. XMT-1536, an ADC utilizing the Company’s Dolaflexin platform and targeting NaPi2b,
an antigen broadly expressed in ovarian cancer and non-small cell lung cancer (NSCLC) adenocarcinoma is currently in a
Phase  1  study  including  both  a  dose  escalation  cohort  and  two  expansion  cohorts  in  ovarian  cancer  and  NSCLC
adenocarcinoma. XMT-1592 uses one of the Company’s new platforms, Dolasynthen, and also targets NaPi2b. The Company
expects to file an Investigational New Drug (IND) application and initiate a Phase 1 dose escalation study of XMT-1592 in
patients with tumors likely to express NaPi2b in the first half of 2020.

The Company is subject to risks common to companies in the biotechnology industry, including but not limited to, the need
for  additional  capital,  risks  of  failure  of  preclinical  and  clinical  studies,  the  need  to  obtain  marketing  approval  and
reimbursement for any drug product candidate that it may identify and develop, the need to successfully commercialize and
gain  market  acceptance  of  its  product  candidates,  dependence  on  key  personnel,  protection  of  proprietary  technology,
compliance with government regulations, development of technological innovations by competitors, reliance on third party
manufacturers and the ability to transition from pilot-scale production to large-scale manufacturing of products.

The Company has incurred net losses since inception. The Company’s net loss was $28,208, $64,257 and $38,707 for the
years ended December 31, 2019, 2018 and 2017, respectively. The Company expects to continue to incur operating losses for
at least the next several years.  As of December 31, 2019, the Company had an accumulated deficit of $192,374. The future
success  of  the  Company  is  dependent  on  its  ability  to  identify  and  develop  its  product  candidates,  and  ultimately  upon  its
ability  to  attain  profitable  operations.  The  Company  has  devoted  substantially  all  of  its  financial  resources  and  efforts  to
research and development and general and administrative expense to support such research and development. Net losses and
negative  cash  flows  have  had,  and  will  continue  to  have,  an  adverse  effect  on  the  Company’s  stockholders’  equity  and
working capital, and accordingly, its ability to execute its future operating plans.

The  Company  plans  to  obtain  funding  from  collaborations,  licensing  agreements  or  other  strategic  partnerships  or  raise
additional  capital  through  the  issuance  and  sale  of  its  common  stock.  There  is  inherent  uncertainty  associated  with  these
fundraising  activities  and  they  are  not  considered  probable.  In  the  absence  of  such  funding,  the  Company  plans  to
strategically manage its uncommitted spend to execute its priorities and implement cost saving measures to reduce research
and  development  and  general  and  administrative  expenditures  which  could  include  limiting  or  delaying  or  terminating
preclinical  studies  or  other  development  activities  for  one  or  more  of  the  Company’s  ADC  product  candidates.  It  is
considered probable that the Company can successfully implement efforts to manage uncommitted spending and carry out
necessary  cost  saving  measures.  Therefore,  the  Company  expects  its  plans  will  enable  its  cash,  cash  equivalents  and
marketable securities as of the filing of its Annual Report on Form 10-K to be sufficient to fund its projected operating plan
through at least the next twelve months, including the Phase 1 clinical study for XMT-1536 and the planned dose escalation
study for XMT-1592.

The  funding  requirements  of  the  Company’s  operating  plan,  however,  are  based  on  estimates  that  are  subject  to  risks  and
uncertainties and may change as a result of many factors currently unknown. Although management continues to pursue the
plans described above, there is no assurance that the Company will be successful in obtaining sufficient funding on terms
acceptable to the Company to fund continuing operations, if at all. Until such time as the Company can generate substantial
product revenues, if ever, the Company expects to finance its cash needs through a combination of equity

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Mersana Therapeutics, Inc.
Notes to consolidated financial statements
(continued)

offerings,  debt  financings,  strategic  partnerships  and  licensing  arrangements.  The  terms  of  any  future  financing  may
adversely affect the holdings or the rights of the Company’s existing stockholders.

The accompanying consolidated financial statements have been prepared in accordance with accounting principles generally
accepted in the United States (U.S. GAAP) and the rules and regulations of the Securities and Exchange Commission (SEC).
Any  reference  in  these  notes  to  applicable  guidance  is  meant  to  refer  to  the  authoritative  U.S.  GAAP  as  found  in  the
Accounting Standards Codification (ASC) and Accounting Standards Updates (ASU) of the Financial Accounting Standards
Board  (FASB).  All  dollar  amounts,  except  per  share  data  in  the  text  and  tables  herein,  are  stated  in  thousands  unless
otherwise indicated.

2. Summary of Significant Accounting Policies

Principles of Consolidation

The  accompanying  consolidated  financial  statements  include  those  of  the  Company  and  its  wholly-owned  subsidiary,
Mersana Securities Corp. All intercompany balances and transactions have been eliminated.

Use of Estimates

The preparation of the Company's consolidated financial statements in conformity with U.S. GAAP requires management to
make estimates and assumptions that affect the reported amounts of assets, liabilities, equity, revenue, expenses and related
disclosure  of  contingent  assets  and  liabilities  at  the  date  of  the  financial  statements  and  reported  amounts  of  revenue  and
expenses  during  the  reporting  period.  On  an  ongoing  basis,  the  Company's  management  evaluates  its  estimates  which
include, but are not limited to, management's judgments with respect to the separate units of accounting and best estimate of
selling price of those units of accounting within its revenue arrangements, accrued expenses, valuation of stock-based awards
and income taxes. Actual results could differ from those estimates.

Segment Information

Operating  segments  are  defined  as  components  of  an  enterprise  about  which  separate  discrete  information  is  available  for
evaluation by the chief operating decision-maker, or decision making group, in deciding how to allocate resources and assess
performance. The Company views its operations and manage its business as a single operating segment, which is the business
of discovering and developing ADCs.

Research and Development

Research and development costs are expensed as incurred and include:

·

·

·

·

employee-related expenses, including salaries, bonuses, benefits, travel and stock-based compensation expense;

fees  and  expenses  incurred  under  agreements  with  contract  research  organizations,  investigative  sites  and  other
entities in connection with the conduct of preclinical and clinical studies and related services;

the  cost  of  acquiring,  developing  and  manufacturing  ADC  product  candidates,  clinical  study  materials  and  other
research and development materials;

fees and costs related to regulatory filings and activities;

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Mersana Therapeutics, Inc.
Notes to consolidated financial statements
(continued)

·

·

·

costs  associated  with  collaboration  agreements  and  license  fees  and  milestone  payments  related  to  license
agreements;

facilities,  depreciation  and  other  expenses,  which  include  direct  and  allocated  expenses  for  rent,  utilities,
maintenance of facilities, insurance and other supplies; and

other costs associated with clinical, preclinical, discovery and other research activities.

Costs for certain development activities, such as clinical studies and manufacturing development activities, are recognized
based  on  an  evaluation  of  the  progress  to  completion  of  specific  tasks  using  data  such  as  patient  enrollment,  clinical  site
activations,  and  information  provided  to  the  Company  by  its  vendors  on  their  actual  costs  incurred  or  level  of  effort
expended.  Payments for these activities are based on the terms of the individual arrangements, which may differ from the
pattern of costs incurred, and are reflected on the consolidated balance sheets as prepaid or accrued research and development
expenses.  

Revenue Recognition

The Company enters into collaboration agreements which are within the scope of Accounting Standards Update (ASU) No.
2014-09, Revenue from Contracts with Customers (Topic 606), under which the Company licenses rights to its technology
and  certain  of  the  Company’s  product  candidates  and  performs  research  and  development  services  for  third  parties.    The
terms  of  these  arrangements  typically  include  payment  of  one  or  more  of  the  following:  non-refundable,  up-front  fees;
reimbursement  of  research  and  development  costs;  development,  regulatory  and  commercial  milestone  payments;  and
royalties on net sales of licensed products.  

Under  Topic  606,  an  entity  recognizes  revenue  when  its  customer  obtains  control  of  promised  goods  or  services,  in  an
amount  that  reflects  the  consideration  which  the  entity  expects  to  receive  in  exchange  for  those  goods  or  services.    To
determine the appropriate amount of revenue to be recognized for arrangements determined to be within the scope of Topic
606, the Company performs the following five steps: (i) identification of the promised goods or services in the contract; (ii)
determination of whether the promised goods or services are performance obligations; (iii) measurement of the transaction
price,  including  the  constraint  on  variable  consideration;  (iv)  allocation  of  the  transaction  price  to  the  performance
obligations; and (v) recognition of revenue when (or as) the Company satisfies each performance obligation.   The Company
only applies the five-step model to contracts when it is probable that the entity will collect consideration it is entitled to in
exchange for the goods or services it transfers to the customer.

The promised good or services in the Company’s arrangement typically consist of license rights to the Company’s intellectual
property  and  research  and  development  services.   The  Company  also  has  optional  additional  items  in  contracts,  which  are
considered marketing offers and are accounted for as separate contracts with the customer if such option is elected by the
customer,  unless  the  option  provides  a  material  right  which  would  not  be  provided  without  entering  into  the
contract.  Performance obligations are promised goods or services in a contract to transfer a distinct good or service to the
customer.  Promised goods or services are considered distinct when (i) the customer can benefit from the good or service on
its own or together with other readily available resources or (ii) the promised good or service is separately identifiable from
other promises in the contract.  In assessing whether promised goods or services are distinct, the Company considers factors
such  as  the  stage  of  development  of  the  underlying  intellectual  property,  the  capabilities  of  the  customer  to  develop  the
intellectual property on their own or whether the required expertise is readily available.

The  Company  estimates  the  transaction  price  based  on  the  amount  expected  to  be  received  for  transferring  the  promised
goods or services in the contract.  The consideration may include both fixed consideration and variable consideration.  At the
inception of each arrangement that includes variable consideration and at each reporting period, the Company evaluates the
amount of potential payment and the likelihood that the payments will be received.  The Company utilizes either the

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Notes to consolidated financial statements
(continued)

most  likely  amount  method  or  expected  amount  method  to  estimate  the  amount  expected  to  be  received  based  on  which
method  better  predicts  the  amount  expected  to  be  received.    If  it  is  probable  that  a  significant  revenue  reversal  would  not
occur,  the  variable  consideration  is  included  in  the  transaction  price.  We  assessed  each  of  our  revenue  generating
arrangements  in  order  to  determine  whether  a  significant  financing  component  exists  and  concluded  that  a  significant
financing  component  does  not  exist  in  any  of  our  arrangements  because:  (a)  the  promised  consideration  approximates  the
cash  selling  price  of  the  promised  goods  and  services;  and  (b)  timing  of  payment  approximates  the  transfer  of  goods  and
services and performance is over a relatively short period of time within the context of the entire term of the contract.

The Company’s contracts often include development and regulatory milestone payments. At contract inception and at each
reporting period, the Company evaluates whether the milestones are considered probable of being reached and estimates the
amount  to  be  included  in  the  transaction  price  using  the  most  likely  amount  method.    If  it  is  probable  that  a  significant
revenue reversal would not occur, the associated milestone value is included in the transaction price.  Milestone payments
that  are  not  within  the  Company’s  control  or  the  licensee’s  control,  such  as  regulatory  approvals,  are  not  included  in  the
transaction price.  At the end of each subsequent reporting period, the Company re-evaluates the probability of achievement
of  such  development  milestones  and  any  related  constraint,  and  if  necessary,  adjusts  its  estimate  of  the  overall  transaction
price.  Any such adjustments are recorded on a cumulative catch-up basis, which would affect license, collaboration and other
revenues and earnings in the period of adjustment.

For arrangements that include sales-based royalties, including milestone payments based on the level of sales, and the license
is deemed to be the predominant item to which the royalties relate, the Company recognizes revenue at the later of (i) when
the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has
been satisfied (or partially satisfied).  To date, the Company has not recognized any royalty revenue resulting from any of the
Company’s collaboration arrangements.

The Company allocates the transaction price based on the estimated standalone selling price of the underlying performance
obligations  or  in  the  case  of  certain  variable  consideration  to  one  or  more  performance  obligations.    The  Company  must
develop  assumptions  that  require  judgment  to  determine  the  stand-alone  selling  price  for  each  performance  obligation
identified  in  the  contract.    The  Company  utilizes  key  assumptions  to  determine  the  stand-alone  selling  price,  which  may
include other comparable transactions, pricing considered in negotiating the transaction and the estimated costs to complete
the respective performance obligation.  Certain variable consideration is allocated specifically to one or more performance
obligations in a contract when the terms of the variable consideration relate to the satisfaction of the performance obligation
and  the  resulting  amounts  allocated  to  each  performance  obligation  are  consistent  with  the  amounts  the  Company  would
expect to receive for each performance obligation.   

For performance obligations consisting of licenses and other promises, the Company utilizes judgment to assess the nature of
the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a
point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue from non-
refundable, up-front fees.  The Company evaluates the measure of progress each reporting period and, if necessary, adjusts
the  measure  of  performance  and  related  revenue  recognition.    If  the  license  to  the  Company’s  intellectual  property  is
determined to be distinct from the other performance obligations identified in the arrangement, the Company will recognize
revenue from non-refundable, up-front fees allocated to the license when the license is transferred to the customer and the
customer is able to use and benefit from the license.

The Company receives payments from its customers based on billing schedules established in each contract. Such billings
generally have 30-day terms. Up-front payments and fees are recorded as deferred revenue upon receipt or when due until the
Company performs its obligations under these arrangements. Amounts are recorded as accounts receivable when the right to
consideration is unconditional.

Effective  January  1,  2018,  the  Company  adopted  the  provisions  of  Topic  606,  using  the  modified  retrospective  transition
method.  Under this method, the Company recorded the cumulative effect of initially applying the new standard to all

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contracts in process as of the date of adoption.  This standard applied to all contracts with customers, except for contracts that
are within the scope of other standards, such as leases, insurance, collaboration arrangements and financial instruments. The
adoption of the new revenue recognition guidance resulted in increases of $2,031 in deferred revenue and accumulated deficit
as of January 1, 2018. For the years ended December 31, 2019 and 2018, revenue was not materially impacted as compared
to the Company’s prior revenue recognition methodology under ASC 605 Revenue Recognition.

Collaborative Arrangements

The Company records the elements of its collaboration agreements that represent joint operating activities in accordance with
ASC  Topic  808,  Collaborative Arrangements  (ASC  808).  Accordingly,  the  elements  of  the  collaboration  agreements  that
represent activities in which both parties are active participants and to which both parties are exposed to the significant risks
and rewards that are dependent on the commercial success of the activities, are recorded as collaborative arrangements. The
Company considers the guidance in ASC Topic 606 in determining the appropriate treatment for the transactions between the
Company  and  its  collaborative  partners  and  the  transactions  between  the  Company  and  third  parties.  Generally,  the
classification of transactions under the collaborative arrangements is determined based on the nature and contractual terms of
the  arrangement  along  with  the  nature  of  the  operations  of  the  participants.  To  the  extent  revenue  is  generated  from  a
collaboration, the Company will recognize its share of the net sales on a gross basis if it is deemed to be the principal in the
transactions  with  customers,  or  on  a  net  basis  if  it  is  instead  deemed  to  be  the  agent  in  the  transactions  with  customers,
consistent with the guidance in Topic 606.

Fair Value Measurements

Fair value is defined as the price that would be received upon sale of an asset or paid to transfer a liability between market
participants at measurement dates. ASC Topic 820 Fair Value Measurement (ASC 820), establishes a three-level valuation
hierarchy for instruments measured at fair value. The hierarchy is based on the transparency of inputs to the valuation of an
asset or liability as of the measurement date. The three levels are defined as follows:

Level  1—Inputs  to  the  valuation  methodology  are  quoted  prices  (unadjusted)  for  identical  assets  or  liabilities  in  active
markets.

Level 2—Inputs to the valuation methodology include quoted prices for similar assets and liabilities in active markets, and
inputs that are observable for the asset or liability, either directly or indirectly, for substantially the full term of the financial
instrument.

Level 3—Inputs to the valuation methodology are unobservable and significant to the fair value measurement.

Cash and Cash Equivalents

The  Company  considers  all  highly  liquid  investments  with  an  original  maturity,  or  a  remaining  maturity  at  the  time  of
purchase, of three months or less to be cash equivalents. The Company invests excess cash primarily in money market funds,
commercial paper and government agency securities, which are highly liquid and have strong credit ratings. These

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investments are subject to minimal credit and market risks. Cash and cash equivalents are stated at cost, which approximates
market value.

Cash and cash equivalents
Restricted cash included in other assets, noncurrent
Total  cash,  cash  equivalents  and  restricted  cash  per  statement  of
cash flows

$

$

59,634  
371  

60,005  

$

$

62,351   $
321  

26,591  
371  

62,672   $

26,962  

$

$

59,634
371

60,005

Year ended

Year ended

December 31, 2019

December 31, 2018

Beginning
of period

End
of period

Beginning
of period

End
of period

Marketable Securities

Short-term marketable securities consist of investments in debt securities with maturities greater than three months and less
than  one  year  from  the  balance  sheet  date.  The  Company  classifies  all  of  its  marketable  securities  as  available-for-sale.
Accordingly,  these  investments  are  recorded  at  fair  value.  Amortization  and  accretion  of  discounts  and  premiums  are
recorded as interest income within other income. Unrealized gains and losses on available-for-sale securities are included in
other accumulated comprehensive loss as a component of stockholders’ equity (deficit) until realized.

Other Assets

The Company recorded other assets of $1,453 and $1,503 as of December 31, 2019 and 2018, respectively. The December
31, 2019 and 2018 amounts are comprised of restricted cash of $321 and $371, respectively, held as security deposit for a
standby letter of credit related to a facility lease and $1,132 held by a service provider.

Accounting for Stock-based Compensation

The  Company  accounts  for  its  stock-based  compensation  in  accordance  with  ASC  Topic  718  Compensation—Stock
Compensation  (ASC  718).  ASC  718  requires  all  stock-based  payments  to  employees,  directors  and  non-employees  to  be
recognized as expense in the statements of operations based on their grant date fair values. The Company estimates the fair
value  of  options  granted  using  the  Black-Scholes  option  pricing  model.  The  Black-Scholes  option  pricing  model  requires
inputs  based  on  certain  subjective  assumptions,  including  (a)  the  expected  stock  price  volatility,  (b)  the  calculation  of
expected term of the award, (c) the risk-free interest rate and (d) expected dividends. Due to the lack of a public market for
the Company's common stock prior to completion of the initial public offering and a lack of company-specific historical and
implied  volatility  data,  the  Company  has  based  its  estimate  of  expected  volatility  on  the  historical  volatility  of  a  group  of
similar  companies  that  are  publicly  traded.  The  historical  volatility  is  calculated  based  on  a  period  of  time  commensurate
with the expected term assumption.  The historical volatility is calculated based on a period of time commensurate with the
expected  term  assumption.  The  computation  of  expected  volatility  is  based  on  the  historical  volatility  of  a  representative
group  of  companies  with  similar  characteristics  to  the  Company,  including  stage  of  product  development  and  life  science
industry  focus.  The  Company  uses  the  simplified  method  as  prescribed  by  the  SEC  Staff  Accounting  Bulletin  No.  107,
Share-Based Payment, to calculate the expected term for options granted to employees as it does not have sufficient historical
exercise data to provide a reasonable basis upon which to estimate the expected term. For options granted to non-employees,
the Company utilizes the contractual term of the arrangement as the basis for the expected term assumption. The risk-free
interest  rate  is  based  on  a  treasury  instrument  whose  term  is  consistent  with  the  expected  term  of  the  stock  options.  The
expected dividend yield is assumed to be zero as the Company has never paid dividends and has no current plans to do so.

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The Company determines the fair value of each restricted stock unit, or RSU, at its grant date based on the closing market
price  of  the  Company’s  common  stock  on  that  date.  For  stock-based  compensation  subject  to  service-based  vesting
conditions,  the  Company  recognizes  stock-based  compensation  expense  equal  to  the  grant  date  fair  value  of  stock-based
compensation on a straight-line basis over the requisite service period.

The Company records forfeitures as a cumulative adjustment in the period in which they occur.

Net Loss per Share

Basic net loss per common share is calculated by dividing the net loss attributable to common stockholders by the weighted-
average  number  of  common  shares  outstanding  and  2,575,000  Exchange  Warrants  (as  defined  in  footnote  10)  outstanding
during the period, without further consideration for potentially dilutive securities. In accordance with Accounting Standards
Codification Topic 260, Earnings Per Share,  the  Exchange  Warrants  are  included  in  the  computation  of  basic  net  loss  per
share because the exercise price is negligible and they are fully vested and exercisable at any time after the original issuance
date. Diluted net loss per share is computed by dividing the net loss attributable to common stockholders by the weighted-
average number of common shares and potentially dilutive securities outstanding for the period determined using the treasury
stock method.

For purposes of the diluted net loss per share calculation, stock options, unvested restricted stock units (RSUs) and warrants
to purchase common stock and options to purchase common stock are considered to be potentially dilutive securities, but are
excluded from the calculation of diluted net loss per share because their effect would be anti-dilutive and therefore, basic and
diluted net loss per share were the same for all periods presented.

The following table sets forth the outstanding potentially dilutive securities that have been excluded from the calculation of
diluted net loss per share because to include them would be anti-dilutive (in common stock equivalent shares):

Stock options
Unvested restricted stock units
Warrants

Property and Equipment

2019

Year ended
December 31, 
2018
4,720,772   3,746,567   3,205,485
 —
110,365
5,207,582   3,856,932   3,315,850

447,336  
39,474  

 —  
110,365  

2017

Property  and  equipment  is  stated  at  cost,  less  accumulated  depreciation.  Depreciation  is  computed  using  the  straight-line
method over the estimated useful life of each asset as follows:

Computer equipment, office equipment and software
Laboratory equipment
Leasehold improvements

3 years
5 years

  Shorter of useful life or life of lease

Upon retirement or sale, the cost of the assets disposed of and the related accumulated depreciation are eliminated from the
balance sheet and related gains or losses are reflected in the statement of operations. There were no material sales of assets
during the years ended December 31, 2019, 2018 and 2017.

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The Company reviews its long-lived assets for impairment whenever events or changes in business circumstances indicate
that the carrying amount of the assets may not be fully recoverable. If an impairment review is performed to evaluate an asset
for recoverability, the Company compares forecasts of undiscounted cash flows expected to result from the use and eventual
disposition of the asset to its carrying value. If the carrying amount of the asset exceeds its estimated undiscounted future net
cash  flows,  an  impairment  charge  is  recognized  in  the  amount  by  which  the  carrying  amount  of  the  asset  exceeds  the  fair
value of the asset. The Company did not recognize impairment charges during the years ended December 31, 2019, 2018 and
2017.

Leases

Consistent with ASC 842, the Company determines if an arrangement is a lease at inception. Operating leases are included in
right-of-use lease assets (ROU assets), current portion of lease obligations and long-term lease obligations on the Company’s
consolidated balance sheets. Assets subject to finance leases are included in property and equipment, and the related lease
obligation is included in other current liabilities and other long-term liabilities on the Company’s consolidated balance sheets.
Lease  assets  are  tested  for  impairment  in  the  same  manner  as  long-lived  assets  used  in  operations.  Lease  expense  for
operating leases is recognized on a straight-line basis over the lease term as an operating expense while expense for financing
leases  is  recognized  as  depreciation  expense  and  interest  expense  using  the  effective  interest  method.  The  Company  has
elected the short-term lease recognition exemption for short-term leases, which allows the Company not to recognize lease
liabilities and ROU assets on the consolidated balance sheets for leases with an original term of twelve months or less.

ROU assets represent the Company’s right to use an underlying asset for the lease term, and lease obligations represent the
Company’s obligation to make lease payments arising from the lease. Operating lease liabilities and their corresponding ROU
assets  are  initially  recorded  based  on  the  present  value  of  lease  payments  over  the  expected  remaining  lease  term.  When
determining the lease term, the Company includes options to extend or terminate the lease when it is reasonably certain that
the option will be exercised. Certain adjustments to the ROU asset may be required for items such as incentives received. The
interest rate implicit in lease contracts is typically not readily determinable. As a result, the Company utilizes its incremental
borrowing  rate  to  discount  lease  payments.  The  incremental  borrowing  rate  reflects  the  fixed  rate  at  which  the  Company
could borrow, on a collateralized basis, the amount of the lease payments in the same currency, for a similar term, in a similar
economic  environment.    Prospectively,  the  Company  will  adjust  the  ROU  assets  for  straight-line  rent  expense,  or  any
incentives received and remeasure the lease liability at the net present value using the same incremental borrowing rate that
was in effect as of the lease commencement or transition date.

The Company has lease agreements with lease and non-lease components, which are generally accounted for separately.

Patent Costs

The  Company  expenses  patent  application  and  related  legal  costs  as  incurred  and  classifies  such  costs  as  general  and
administrative expenses in the accompanying consolidated statements of operations.

Income Taxes

The Company accounts for income taxes in accordance with ASC Topic 740, Accounting for Income Taxes, which provides
for deferred taxes using an asset and liability approach.  The Company recognizes deferred tax assets and liabilities for the
expected future tax consequences of events that have been included in the financial statements or tax returns.  The Company
determines its deferred tax assets and liabilities based on differences between financial reporting and tax bases of assets and
liabilities, which are measured using the enacted tax rates and laws that will be in effect when the differences are expected to
reverse. Valuation  allowances  are  provided  if,  based  upon  the  weight  of  available  evidence,  it  is  more  likely  than  not  that
some or all of the deferred tax assets will not be realized.

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The Company recognizes the effect of income tax positions only if those positions are more likely than not to be sustained.
Recognized income tax positions are measured at the largest amount that is more likely than not to be realized. Changes in
recognition or measurement are reflected in the period in which the change in judgment occurs.

Comprehensive Income (Loss)

Comprehensive  income  (loss)  comprises  net  loss  and  other  comprehensive  loss.  For  the  years  ended  December  31,  2019,
2018 and 2017, other comprehensive income (loss) consisted of unrealized income and loss on marketable securities.

Concentration of Credit Risk and Off-balance Sheet Risk

The Company has no financial instruments with off-balance sheet risk, such as foreign exchange contracts, option contracts,
or other foreign hedging arrangements. Financial instruments that potentially subject the Company to concentrations of credit
risk  primarily  consist  of  cash  equivalents  and  marketable  securities.  Under  its  investment  policy,  the  Company  limits
amounts invested in such securities by credit rating, maturity, industry group, investment type and issuer, except for securities
issued  by  the  U.S.  government.  The  Company  is  not  exposed  to  any  significant  concentrations  of  credit  risk  from  these
financial instruments.

Recently Issued Accounting Pronouncements

In February 2016, the FASB issued ASU No. 2016-02, Leases (ASC 842), which replaced the guidance in ASC 840, Leases.
The updated standard aims to increase transparency and comparability among organizations by requiring lessees to recognize
lease assets and lease liabilities on the balance sheet and requiring disclosure of key information about leasing arrangements.
This standard became effective for fiscal years beginning after December 15, 2018. The Company adopted the new standard
effective  January  1,  2019  using  the  modified  retrospective  method  as  of  the  beginning  of  the  period  of  adoption.  The
Company has elected the package of practical expedients permitted in ASC Topic 842. Accordingly, the Company accounted
for  its  existing  operating  leases  as  operating  leases  under  the  new  guidance,  without  reassessing  (a)  whether  the  contracts
contain a lease under ASC Topic 842, (b) whether classification of the operating leases would be different in accordance with
ASC  Topic  842,  or  (c)  whether  the  unamortized  initial  direct  costs  would  have  met  the  definition  of  initial  direct  costs  in
ASC  Topic  842  at  lease  commencement.  The  Company  also  elected  not  to  include  leases  with  an  initial  term  of  twelve
months  or  less  in  the  recognized  ROU  asset  and  lease  liabilities.  As  a  result  of  the  adoption  of  the  new  lease  accounting
guidance, the Company recognized on January 1, 2019 (a) an operating lease liability of $4,778, and (b) an operating ROU
asset of $4,369 which represents the lease liability of $4,778 adjusted for deferred rent of $409. This standard had a material
impact  on  the  Company’s  balance  sheets  but  had  no  impact  on  the  Company’s  results  of  operations  and  cash  flows  from
operations. The most significant impact was the recognition of ROU assets, lease obligations, and disclosures regarding the
amount, timing, and uncertainty of cash flows arising from leases.

In June 2018, the FASB issued ASU No. 2018-07, Improvements  to  Nonemployee  Share-Based  Payment  Accounting. This
guidance simplifies the accounting for share-based payments to non-employees by aligning it with the accounting for share-
based  payments  to  employees,  with  certain  exceptions.  This  guidance  became  effective  for  annual  reporting  periods
beginning after December 15, 2018, including interim periods within those annual reporting periods, and early adoption is
permitted. The guidance per ASU 2018-07 is to be adopted by using a modified retrospective approach with the cumulative
effect  of  initially  applying  the  new  standard  at  the  date  of  initial  application.  The  Company  adopted  the  new  standard
effective  January  1,  2019.  The  adoption  of  this  standard  did  not  have  a  material  impact  on  the  Company’s  consolidated
financial statements.

In November 2018, the FASB issued ASU No. 2018-18, Collaborative Arrangements (Topic 808): Clarifying the Interaction
between  Topic  808  and  Topic  606.  The  main  provisions  of  ASU  2018-18  include:  (i)  clarifying  that  certain  transactions
between collaborative arrangement participants should be accounted for as revenue when the collaborative

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arrangement participant is a customer in the context of a unit of account and (ii) precluding the presentation of transactions
with collaborative arrangement participants that are not directly related to sales to third parties together with revenue. This
guidance will be effective for annual reporting periods beginning after December 15, 2019, including interim periods within
those  annual  reporting  periods,  and  early  adoption  is  permitted.  The  guidance  per  ASU  2018-18  is  to  be  adopted
retrospectively  to  the  date  of  initial  application  of  Topic  606.  The  Company  does  not  anticipate  a  material  impact  to  the
consolidated financial statements as a result of the adoption of this guidance.

In  June  2016,  the  FASB  issued  ASU  2016-13,  Financial  Instruments-Credit  Losses  (Topic  326):  Measurement  of  Credit
Losses  on  Financial  Instruments,  which  requires  that  financial  assets  measured  at  amortized  cost  be  presented  at  the  net
amount expected to be collected. Currently, U.S. GAAP delays recognition of the full amount of credit losses until the loss is
probable of occurring. Under this ASU, the income statement will reflect an entity’s current estimate of all expected credit
losses.  The  measurement  of  expected  credit  losses  will  be  based  upon  historical  experience,  current  conditions,  and
reasonable and supportable forecasts that affect the collectability of the reported amount. Credit losses relating to available-
for-sale  debt  securities  will  be  recorded  through  an  allowance  for  credit  losses  rather  than  as  a  direct  write-down  of  the
security. This ASU is effective for annual periods beginning after December 15, 2019, including interim periods within those
annual reporting periods, and early adoption is permitted. The Company is currently evaluating the potential impact that ASU
2016-13 may have on its financial position and results of operations.

3. Collaboration Agreements

Merck KGaA

In June 2014, the Company entered into a Collaboration and Commercial License Agreement with Merck KGaA (the Merck
KGaA Agreement). Upon the execution of the Merck KGaA Agreement, Merck KGaA paid the Company a nonrefundable
technology access fee of $12,000 for the right to develop ADCs directed to six exclusive targets over a specified period of
time. No additional fees are due when a target is designated and the commercial license to the target is granted. Merck KGaA
will  be  responsible  for  the  product  development  and  marketing  of  any  products  resulting  from  this  collaboration.  All  six
targets were designated prior to 2018.

Under the terms of the Merck KGaA Agreement, the Company and Merck KGaA develop research plans to evaluate Merck
KGaA's antibodies as ADCs incorporating the Company's technology. The Company receives reimbursement for its efforts
under the research plans. The goal of the research plans is to provide Merck KGaA with sufficient information to formally
nominate a development candidate and begin IND-enabling studies or cease development on the designated target.

In  addition  to  the  payments  received  for  research  and  development  activities  performed  on  behalf  of  Merck  KGaA,  the
Company is also eligible to receive up to a total of $780,000 in future milestones related to all targets under the Merck KGaA
Agreement,  plus  low  to  mid  single  digit  royalties  on  the  commercial  sales  of  any  resulting  products  during  the  applicable
royalty  term.  The  total  milestones  are  categorized  as  follows:  development  milestones  $84,000;  regulatory  milestones
$264,000;  and  sales  milestones  $432,000.  There  are  six  individual  development  milestones  per  target,  payable  upon  the
completion of various activities from the delivery of ADCs meeting defined specifications, through the dosing in a Phase 3
clinical trial. There are five regulatory milestones, which are payable upon regulatory approvals for a first indication in each
of the U.S., European Union and Japanese markets and regulatory approvals for both a second and a third indication in the
United States. There are three individual commercial milestones, which are payable upon the attainment of certain defined
thresholds for annual net sales.

Prior  to  2018,  the  Company  had  received  $3,000  related  to  development  milestones  under  the  Merck  KGaA  Agreement.
There  have  been  no  additional  milestone  payments  in  the  years  ended  December  31,  2018  or  2019.  The  next  potential
milestone payment the Company will be eligible to receive will be a development milestone of $500 on Merck KGaA's

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(continued)

designation  of  a  preclinical  development  candidate  for  any  target.  Revenue  will  be  recognized  when  achievement  of  the
milestone is considered probable.

Unless earlier terminated, the Merck KGaA Agreement will expire upon the expiration of the last royalty term for a product
under the Merck KGaA Agreement, after which time, Merck KGaA will have a perpetual, royalty-free license, or if Merck
KGaA  does  not  designate  any  ADC  product  candidates  produced  by  the  Company  under  the  Merck  KGaA  Agreement  as
preclinical development candidates, upon the expiration of the last to expire research program. Merck KGaA may terminate
the Merck KGaA Agreement in its entirety or with respect to any target for convenience upon 60 days' prior written notice.
Each party may terminate the Merck KGaA Agreement in its entirety upon bankruptcy or similar proceedings of the other
party or upon an uncured material breach of the Merck KGaA Agreement by the other party. However, if such breach only
relates to one target, the agreement may only be terminated with respect to such target.

In  May  2018,  the  Company  entered  into  a  Supply  Agreement  with  Merck  KGaA  (the  Merck  KGaA  Supply  Agreement).
Under the terms of the Merck KGaA Supply Agreement, the Company will provide Merck KGaA preclinical non-GMP ADC
Drug Substance and clinical GMP Drug Substance for use in clinical trials associated with one of the antibodies designated
under the Merck KGaA Agreement. The Company receives fees for its efforts under the Merck KGaA Supply Agreement
and reimbursement equal to the supply cost. The Company may also enter into future supply agreements to provide clinical
supply material should Merck KGaA pursue clinical development of any other candidates nominated under the Merck KGaA
Agreement.

Accounting Analysis

The Company identified the following performance obligations under the Merck KGaA Agreement: (i) exclusive license and
research services for six designated targets, (ii) rights to future technological improvements and (iii) participation of project
team leaders and providing joint research committee services.

The  Company  has  concluded  that  each  license  for  a  designated  target  is  not  distinct  from  the  research  services  performed
related  to  the  designated  target  as  Merck  KGaA  cannot  obtain  the  benefit  of  the  license  without  the  related  research
services.    Each  license  for  a  designated  target  and  the  related  services  performance  obligation  is  considered  distinct  from
every  other  license  for  a  designated  target  and  related  services  performance  obligation  as  each  research  plan  is  pursued
independent of every other research plans for other designated targets. 

The Company utilizes the expected value approach to estimate the amount of consideration related to the payment of fees
associated with development and research services.  The Company utilizes the most likely amount approach to estimate any
development and regulatory milestone payments to be received.  As of the date of initial application of Topic 606, there were
no  milestones  payments  that  had  not  already  been  received,  included  in  the  estimated  transaction  price.    The  Company
considered the stage of development and the remaining risks associated with the remaining development required to achieve
the  milestone,  as  well  as  whether  the  achievement  of  the  milestone  is  outside  the  control  of  the  Company  or  Merck
KGaA.  The milestone payment amounts were fully constrained, as a result of the uncertainty whether any of the associated
milestones would be achieved.  The Company has determined that any commercial milestones and sales based royalties will
be  recognized  when  the  related  sales  occur  as  they  were  determined  to  relate  predominantly  to  the  license  granted  and
therefore have also been excluded from the transaction price. 

The transaction price was allocated to the performance obligations based on the relative estimated standalone selling prices of
each performance obligation or in the case of certain variable consideration to one or more performance obligations.  The
estimated standalone selling prices for performance obligations, that include a license and research services, were developed
using the estimated selling price of the license and an estimate of the overall effort to perform the research service and an
estimated market rate for research services. The estimated standalone selling price of the licenses was established based on
comparable transactions.  The estimated standalone selling price for the rights to future technological

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(continued)

improvements was developed based on the estimated selling prices of a license or rights received, as well as considering the
probability  that  additional  technology  would  be  made  available  or  the  probability  the  counterpart  would  utilize  the
technology. The estimated standalone selling price for the joint research committee services was developed using an estimate
of the time and costs incurred to participate in the committees.

The  Company  re-evaluates  the  transaction  price  in  each  reporting  period  and  as  uncertain  events  are  resolved  or  other
changes in circumstances occur. As of December 31, 2018, the total transaction price for the Merck KGaA Agreement was
$22,070. In the third quarter of 2019, the Company revised its estimate for fees associated with research and development
activities under the Merck KGaA Agreement to $6,500, a decrease of $570. The revised total transaction price for the Merck
KGaA  Agreement  is  $21,500.  The  transaction  price  of  $21,500  was  allocated  to  the  performance  obligations  as  follows:
approximately $3,941 for each of the license and corresponding research and development services units of account for the
first and second designated targets; $3,439 for each of the license and corresponding research and development services units
of  account  for  the  third  and  sixth  designated  target;  $3,152  for  the  license  and  corresponding  research  and  development
services unit of account for the fourth designated target; $2,921 for the license and corresponding research and development
services unit of account for the fifth designated target; $425 for rights to future technological improvements; and $242 for
joint research committee services.

The  Company  is  recognizing  revenue  related  to  the  exclusive  license  and  research  and  development  services  performance
obligation over the estimated period of the research and development services using a proportional performance model.  The
Company  measures  proportional  performance  based  on  the  costs  incurred  relative  to  the  total  costs  expected  to  be
incurred.  To the extent that the Company receives fees for the research services as they are preformed, these amounts are
recorded as deferred revenue. Revenue related to future technological improvements and joint research committee services
will  be  recognized  ratably  over  the  performance  period  (which  in  the  case  of  the  joint  research  committee  services
approximate the time and cost incurred each period), which are 10 and 5 years, respectively.  The Company is continuing to
reassess the estimated remaining term at each subsequent reporting period.

During the years ended December 31, 2019, 2018 and 2017, the Company recorded collaboration revenue of $853, $2,444
and $3,636, respectively, related to its efforts under the Merck KGaA Agreement. During the year ended December 31, 2019,
the Company recognized collaboration revenue and corresponding research and development expense of $1,280 related to the
Merck KGaA Supply Agreement. There were no amounts recognized during the years ended December 31, 2018 and 2017
related to the Merck KGaA Supply Agreement.  Included in accounts receivable as of December 31, 2019 and 2018 was $0
and $450, respectively, related to the Merck KGaA Agreement and Merck KGaA Supply Agreement.

As of December 31, 2019 and 2018, the Company had recorded $4,815 and $5,462, respectively, in deferred revenue related
to the Merck KGaA Agreement and Merck KGaA Supply Agreement that will be recognized over the remaining performance
period.

Takeda XMT-1522 Strategic Partnership

In January 2016, the Company entered into a Development Collaboration and Commercial License Agreement with Takeda’s
wholly owned subsidiary, Millennium Pharmaceuticals, Inc. for the development and commercialization of XMT-1522 (the
XMT-1522 Agreement). Under the XMT-1522 Agreement, Takeda was granted the exclusive right to commercialize XMT-
1522  outside  of  the  United  States  and  Canada.  Under  the  XMT-1522  Agreement,  the  Company  was  responsible  for
conducting  certain  Phase  1  development  activities  for  XMT-1522,  including  the  ongoing  Phase  1  clinical  trial,  at  its  own
expense.  The  parties  agreed  to  collaborate  on  the  further  development  of  XMT-1522  in  accordance  with  a  global
development plan (Post-Phase 1 Development). On January 2, 2019, the Company received notice from Takeda stating that
Takeda was exercising its right to terminate the XMT-1522 Agreement upon 30 days’ prior written notice. The XMT-1522
Agreement terminated in accordance with its provisions, and the Company and Takeda wound down activities related to the
XMT-1522 Agreement as of March 31, 2019. Under the XMT-1522 Agreement, the Company and Takeda

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(continued)

shared equally all agreed Post-Phase 1 Development costs through the date of termination and for a period of 30 days after
the effective termination date.

Takeda Strategic Research and Development Partnership

In  March  2014,  the  Company  entered  into  a  Research  Collaboration  and  Commercial  License  Agreement  with  Takeda’s
wholly  owned  subsidiary,  Millennium  Pharmaceuticals,  Inc.  (the  2014  Agreement).  The  2014  Agreement  was  amended  in
January 2015 and amended and restated in January 2016 (the 2016 Restated Agreement). The agreements provided Takeda
with the right to develop ADCs directed to a total of seven exclusive targets, designated by Takeda, over a specified period of
time. On January 2, 2019, the Company received notice from Takeda stating that Takeda was exercising its right to terminate
the 2016 Restated Agreement upon 45 days’ prior written notice. The 2016 Restated Agreement terminated in accordance
with its provisions, and the Company and Takeda wound down activities related to the 2016 Restated Agreement as of March
31, 2019.

Accounting Analysis

The Company’s collaboration agreements with Takeda were terminated following receipt of written notices during the first
quarter of 2019. As there are no further performance obligation, the Company recognized the remaining deferred revenue of
$39,965 related to the termination of the Takeda agreements in the first quarter of 2019.

Prior to the termination of the agreements, the Company had identified 14 performance obligations in the agreements. The
Company  concluded  that  the  license  related  to  each  of  the  designated  targets  was  not  distinct  from  the  research  services
performed  related  to  each  of  the  designated  targets  as  Takeda  could  not  have  obtain  the  benefit  of  the  license  without  the
related research services. Each license to a designated target and the related service performance obligation was considered
distinct from every other license to a designated target and related services performance obligation as each research plan was
pursued independent of the any other research plans for other designated targets. Further, the material rights provided were
determined  to  be  distinct  from  the  other  performance  obligations  in  the  arrangement  as  they  were  options  in  the  contract
Takeda  agreements  and  not  required  for  Takeda  to  obtain  the  benefit  of  the  other  promised  goods  or  services  in  the
arrangement.  Similarly,  the  Company  concluded  that  the  XMT-1522  license  and  the  related  research  and  development
services,  including  the  Phase  1  development  and  the  transfer  of  certain  materials  and  know-how  related  to  the  Company's
manufacturing  processes,  were  one  performance  obligation.  The  license  to  the  Company's  intellectual  property  was  not
determined to be distinct from the research and related development services that the Company was obligated to perform. For
the years ended December 31, 2019, 2018 and 2017, the Company recorded total revenue of $39,965, $5,868 and $13,784,
respectively, related to its efforts under the 2016 Restated Agreement and the XMT-1522 Agreement. Included in accounts
payable as of December 31, 2019 and 2018 was $2,310 and $2,749, respectively, related to the Takeda agreements. As  of
December  31,  2019  and  2018,  the  Company  had  $0  and  $39,965,  respectively,  of  deferred  revenue  related  to  the  Takeda
agreements.

The  Company  concluded  that  the  Post-Phase  1  Development  activities  under  the  XMT-1522  Agreement  represented  joint
operating activities in which both parties were active participants and of which both parties were exposed to significant risks
and  rewards  that  are  dependent  on  the  commercial  success  of  the  activities.  Accordingly,  the  Company  accounted  for  the
Post-Phase 1 Development activities in accordance with ASC 808. For the years ended December 31, 2019, 2018 and 2017,
the  Company  was  billed  approximately  $200,  $8,046  and  $3,408,  respectively,  from  Takeda  representing  Post-Phase  1
Development  costs  incurred  by  Takeda.  These  amounts  have  been  reflected  as  research  and  development  costs  in  the
consolidated statement of operations. The Company did not perform any Post-Phase 1 Development activities or incur any
associated costs prior to January 1, 2018. During the years ended December 31, 2019, 2018 and 2017, the Company billed
Takeda $195, $3,746 and $0, respectively, related to ASC 808 costs.

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Summary of Contract Assets and Liabilities

The following table presents changes in the balances of our contract assets and liabilities during the years ended December
31, 2019 and December 31, 2018:

Balance at
Beginning  
of Period

     Additions      Deductions     End of Period

Balance at

Year ended December 31, 2019
Contract assets
Contract liabilities:
Deferred revenue

Year ended December 31, 2018
Contract assets
Contract liabilities:
Deferred revenue

  $

 —   $

 —   $

 —   $

 —

  $

46,196   $

210   $ 41,591   $

4,815

Balance at

Beginning  

Balance at

of Period

     Additions      Deductions     End of Period

  $

 —   $

 —   $

 —   $

 —

  $

52,439   $

2,851   $ 9,094   $

46,196

During  the  year  ended  December  31,  2019,  the  Company  recognized  the  following  revenues  as  a  result  of  changes  in  the
contract asset and the contract liability balances in the respective periods.

Revenue recognized in the period from:
Amounts included in the contract liability at the beginning of the period
Performance obligations satisfied in previous periods

Other Revenue

Year ended
December 31, 

2019

2018

  $
  $

41,591   $
 —   $

8,704
 —

The Company has provided limited services for a collaboration partner, Asana BioSciences. For the years ended December
31, 2019, 2018 and 2017, the Company recorded revenue of $25, $782 and $125, respectively, related to these services. In
addition,  during  the  year  ended  December  31,  2018,  the  Company  recognized  revenue  of  $1,500  related  to  a  milestone
achieved upon the completion of a GLP toxicology study by Asana BioSciences. The next potential milestone the Company
is  eligible  to  receive  is  $2,500  upon  dosing  the  fifth  patient  in  a  Phase  1  clinical  study  by  Asana  BioSciences.  As  of
December 31, 2019, the Company considered this next milestone to be fully constrained as there is considerable judgment
involved in determining whether it is probable that a significant revenue reversal would occur. As part of its evaluation of the
constraint,  the  Company  considered  numerous  factors,  including  the  fact  that  achievement  of  the  milestone  is  outside  the
control of the Company and there is a high level of uncertainty in achieving this milestone, as this would require initiation of
clinical trials by the collaboration partner. The Company reevaluates the probability of achievement of a milestone subject to
constraint at each reporting period and as uncertain events are resolved or other changes in circumstances occur.

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4. Fair Value Measurements

The following table presents information about the Company’s assets and liabilities regularly measured and carried at a fair
value and indicates the level within fair value hierarchy of the valuation techniques utilized to determine such value as of
December 31, 2019 and 2018:

  Quoted Prices 
in Active
Markets
(Level 1)

  Significant  
Other

Significant

  Observable  Unobservable

Inputs
(Level 2)     

Inputs
(Level 3)

Fair
     Value

December 31, 2019
Marketable securities:
Commercial paper
Corporate bonds
U.S. Treasuries

December 31, 2018
Marketable securities:

U.S. Treasuries

  $ 11,940   $
  12,010  
  13,489  
  $ 37,439   $

 —   $ 11,940   $
 —  
13,489  
13,489   $ 23,950   $

  12,010  
 —  

 —
 —
 —
 —

  Quoted Prices 
in Active
Markets
(Level 1)

  Significant  
Other

Significant

  Observable  Unobservable

Inputs
(Level 2)     

Inputs
(Level 3)

Fair
     Value

  $ 10,497   $
  $ 10,497   $

10,497   $
10,497   $

 —   $
 —   $

 —
 —

There were no changes in valuation techniques or transfers between fair value measurement levels during the years ended
December 31, 2019 and 2018.

The  carrying  amounts  reflected  in  the  consolidated  balance  sheets  for  prepaid  expenses  and  other  current  assets,  accounts
payable and accrued expenses approximate their fair values due to their short-term nature.

As  of  December  31,  2019,  the  carrying  value  of  the  Company’s  outstanding  borrowing  under  the  Credit  Facility
approximated fair value (a Level 2 fair value measurement), reflecting interest rates currently available to the Company. The
Credit Facility is discussed more detail in Note 8, “Debt”.

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5. Marketable Securities

The following table summarizes marketable securities held at December 31, 2019 and 2018.

Gross
  Amortized   Unrealized  Unrealized 

Gross

Cost

     Gains

     Losses

Fair
     Value

December 31, 2019
Commercial paper
Corporate bonds
U.S. Treasuries

December 31, 2018
U.S. Treasuries

  $ 11,940   $
  11,990  
  13,484  
  $ 37,414   $

 —   $
20  
 5  
25   $

 —   $ 11,940
  12,010
 —  
 —  
  13,489
 —   $ 37,439

Gross
  Amortized   Unrealized  Unrealized 

Gross

Cost

     Gains

     Losses

Fair
     Value

  $ 10,505   $
  $ 10,505   $

 —   $
 —   $

(8)  $ 10,497
(8)  $ 10,497

As of December 31, 2019, the Company did not hold any securities that were in an unrealized loss position. As of December
31, 2018, the Company held three securities that were in an unrealized loss position. The aggregate fair value of securities
held by the Company in an unrealized loss position at December 31, 2018 was $10,497. These securities were held by the
Company  in  an  unrealized  loss  position  for  more  than  12  months.  The  Company  determined  that  there  was  no  material
change in the credit risk of these securities. As a result, the Company determined it did not hold any investments with an
other-than-temporary impairment as of December 31, 2019 and 2018. 

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6. Property and Equipment

Property and equipment consists of the following as of December 31, 2019 and 2018:

Laboratory equipment
Computer equipment and office equipment
Leasehold improvements
Total property and equipment at cost
Less: Accumulated depreciation

     December 31,    December 31, 

2019

2018

  $

  $

6,419   $
1,068  
1,886  
9,373  
(7,209) 
2,164   $

6,134
1,035
1,886
9,055
(6,361)
2,694

The  Company  recorded  assets  under  finance  leases  of  $429  as  laboratory  equipment  during  the  year  ended  December  31,
2019.  Financing  leases  are  discussed  in  more  detail  in  Note  12  “Leases”.  Depreciation  expense  for  the  years  ended
December 31, 2019, 2018 and 2017 was $1,245, $1,257 and $928, respectively.

7. Accrued Expenses

Accrued expenses consist of the following as of December 31, 2019 and 2018:

Accrued payroll and related expenses
Accrued preclinical, manufacturing and clinical expenses
Accrued professional fees
Accrued other

    December 31,   December 31, 

2019

2018

  $

  $

4,037  $
4,230   
675   
44   
8,986  $

3,042
8,314
567
452
12,375

8. Debt

On  May  8,  2019,  the  Company  entered  into  a  loan  and  security  agreement  (the  Credit  Facility)  with  Silicon  Valley  Bank
(SVB) pursuant to which the Company can borrow, at its option, up to $20,000, in up to four principal advances of at least
$5,000 each (each, a Term Loan or collectively, the Term Loans) through August 31, 2020. The Company drew $5,000 on the
Term Loan upon execution of the Credit Facility.

The Term Loans bear interest at a floating per annum rate equal to the greater of (i) 4.0% and (ii) 1.50% below the Prime
Rate,  as  defined.    The  Company  is  obligated  to  make  monthly  interest  only  payments  on  each  outstanding  Term  Loan
commencing on the first calendar day of the month following the funding date of such Term Loan and continuing on the first
calendar day of each month thereafter through August 31, 2020. Commencing on September 1, 2020 and continuing on the
first calendar day of each month thereafter, the Company is obligated to make 30 consecutive equal payments of principal,
together with applicable interest in arrears to SVB.

All  outstanding  principal  and  accrued  and  unpaid  interest  with  respect  to  the  Term  Loans  are  due  and  payable  in  full  on
February 1, 2023. Upon repayment of the Term Loans, the Company is also required to make a final payment to SVB equal
to 5.0% of the principal amount of the Term Loans then extended to the Company. This final payment is accreted under the
effective interest method over the life of each loan. The Term Loans are secured by substantially all of the

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Company’s  assets,  except  for  its  intellectual  property  which  is  subject  to  a  negative  pledge,  and  certain  other  customary
exclusions.

At the Company’s option, it may prepay the outstanding principal balance of any Term Loans in whole but not in part, subject
to a prepayment fee of: (a) 3.0% of the Term Loans then extended to the Company if the prepayment occurs on or prior to
May 8, 2020, (b) 2.0% of the Term Loans then extended to the Company if the prepayment occurs after May 8, 2020 but on
or prior to May 8, 2021, or (c) 1.0% of the Term Loans then extended to the Company if the prepayment occurs after May 8,
2021 but before February 1, 2023. In the event the Company has not borrowed a total of $20,000 upon the earlier of August
21, 2020, acceleration of the Company’s payment obligations or Company’s prepayment of the then extended Term Loans,
the Company is required to pay an additional fee equal to 3.0% of any unborrowed portion of the committed funding (the
Unused Term Loan Commitment Fee).

financial,  and 

includes  customary  affirmative, 

the
The  Credit  Facility 
Company.    Affirmative  covenants  include,  among  others,  covenants  requiring  the  Company  to  maintain  its  corporate
existence  and  governmental  approvals,  deliver  certain  financial  reports,  maintain  insurance  coverage  and  satisfy  certain
requirements regarding deposit accounts. Financial covenants include maintaining a liquidity ratio (as defined in the Credit
Facility) of 1.50 to 1.00. The restrictive covenants include, among others, requirements relating to the Company’s ability to
transfer  collateral,  incur  additional  indebtedness,  engage  in  mergers  or  acquisitions,  pay  dividends  or  make  other
distributions,  make  investments,  create  liens,  sell  assets  and  agree  to  a  change  in  control,  in  each  case  subject  to  certain
customary exceptions.

restrictive  covenants  applicable 

to 

The Company’s payment obligations under the Credit Facility are subject to acceleration upon the occurrence of specified
events  of  default,  which  include,  but  are  not  limited  to,  the  occurrence  of  a  material  adverse  change  in  the  Company’s
business,  operations,  or  financial  or  other  condition.  Amounts  outstanding  upon  the  occurrence  of  an  event  of  default  are
payable  upon  SVB’s  demand  and  shall  accrue  interest  at  an  additional  rate  of  5.0%  per  annum  of  the  past  due  amount
outstanding.  As  of  December  31,  2019,  the  Company  was  in  compliance  with  all  covenants  under  the  Credit  Facility.  As
such, as of December 31, 2019, the classification of the loan balance as stated on the balance sheet was based on the timing
of defined future payment obligations.

The Company incurred $215 of debt issuance costs related to external legal and transaction fees. The Company recorded the
debt issuance costs as a direct deduction from the carrying value of the Term Loans which are amortized as interest expense
using the effective-interest method over the term of the Term Loans.

As of December 31, 2019, the Company had drawn a Term Loan of $5,000.

As of December 31, 2019, Debt consisted of the following:

Total debt
Less: Current portion of long-term-debt
Total debt, net of current portion
Debt financing costs, net of accretion
Accretion related to final payment
Long-term debt, net

104

December 31, 

2019

5,000
(667)
4,333
(177)
45
4,201

$

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Mersana Therapeutics, Inc.
Notes to consolidated financial statements
(continued)

As of December 31, 2019, the estimated future principal payments due are as follows:

2020
2021
2022
2023
Total debt

$

$

667
2,000
2,000
333
5,000

During the year ended December 31, 2019 the Company recognized $214 of interest expense related to the Credit Facility.

9. Preferred Stock

As of December 31, 2019, the Company has 25,000,000 shares of authorized preferred stock. No shares of preferred stock
have been issued.

10. Stockholders’ Equity (Deficit)

Common Stock

The  holders  of  the  common  stock  are  entitled  to  one  vote  for  each  share  held.  Common  stockholders  are  not  entitled  to
receive dividends, unless declared by the Board of Directors (the Board).

As of December 31, 2019 and 2018 there were 7,782,582 and 3,856,932, respectively, shares of common stock reserved for
the exercise of outstanding stock options and warrants. 

Stock options
Restricted stock units
Exchange warrants
Warrants

Warrants

  December 31,    December 31, 

2019

4,720,772  
447,336  
2,575,000  
39,474  
7,782,582  

2018
3,746,567
 —
 —
110,365
3,856,932

In  connection  with  a  2013  Series  A‑1  Preferred  Stock  issuance,  the  Company  granted  to  certain  investors  warrants  to
purchase  129,491  shares  of  common  stock.  The  warrants  have  a  $0.05  per  share  exercise  price  and  a  contractual  life  of
10 years. The fair value of these warrants was recorded as a component of equity at the time of issuance. As of December 31,
2018,  there  were  warrants  to  purchase  110,365  shares  of  common  stock.  During  the  year  ended  December  31,  2019,  the
Company issued 69,680 shares of common stock upon the exercise of warrants.

Exchange Warrants

On November 26, 2019, the Company entered into an exchange agreement with entities affiliated with Biotechnology Value
Fund,  L.P.  (the  “Exchanging  Stockholders”),  pursuant  to  which  the  Exchanging  Stockholders  exchanged  an  aggregate  of
2,575,000 shares of common stock for pre-funded warrants (the “Exchange Warrants”) to purchase an aggregate of 2,575,000
shares of common stock (subject to adjustment in the event of any stock dividends and splits, reverse stock split, merger or
consolidation, change of control, reorganization or similar transaction, as described in the

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Mersana Therapeutics, Inc.
Notes to consolidated financial statements
(continued)

Exchange Warrants), with an exercise price of $0.0001 per share. The Exchange Warrants will expire ten years from the date
of issuance. The Exchange Warrants are exercisable at any time prior to expiration except that the Exchange Warrants cannot
be exercised by the Exchanging Stockholders if, after giving effect thereto, the Exchanging Stockholders would beneficially
own more than 9.99% of the Company’s common stock, subject to certain exceptions.

In  accordance  with  Accounting  Standards  Codification  Topic  505,  Equity,  the  Company  recorded  the  retirement  of  the
common  stock  exchanged  as  a  reduction  of  common  shares  outstanding  and  a  corresponding  debit  to  additional  paid-in-
capital at the fair value of the Exchange Warrants on the issuance date. The Exchange Warrants are classified as equity in
accordance with Accounting Standards Codification Topic 480, Distinguishing Liabilities from Equity, and fair value of the
Exchange Warrants was recorded as a credit to additional paid-in capital and is not subject to remeasurement. The Company
determined that the fair value of the Exchange Warrants is substantially similar to the fair value of the retired shares on the
issuance  date  due  to  the  negligible  exercise  price  for  the  Exchange  Warrants.  As  of  December  31,  2019,  none  of  the
Exchange Warrants had been exercised.

11. Stock Options

Stock option plans

As of June 30, 2017, there were 3,141,625 options outstanding under the Company’s 2007 Stock Incentive Plan.  The 2007
Plan expired in June 2017. Any cancellations under the 2007 Stock Incentive Plan will increase the options available under
the 2017 Stock Incentive Plan as described below.

In June 2017 the Company’s shareholders approved the 2017 Stock Incentive Plan (the 2017 Plan or the Plan).  Under the
2017 Plan initially, up to 2,255,000 shares of common stock may be granted to the Company's employees, officers, directors,
consultants and advisors in the form of options, restricted stock units (RSUs) or other stock-based awards. The number of
shares of common stock issuable under the Plan will be cumulatively increased annually by 4% of the outstanding shares or
such lesser amount specified by the Board. The terms of the awards are determined by the Board, subject to the provisions of
the  Plan.  As  of  December  31,  2019  there  were  1,511,587  shares  available  for  future  issuance  under  the  Plan,  including
929,378 shares automatically added to the plan on January 1, 2019.

With respect to incentive stock options, the exercise price per share will equal the fair market value of the common stock on
the date of grant, as determined by the Board, and the vesting period is generally four years. Nonqualified stock options will
be granted at an exercise price established by the Board at its sole discretion (which has not been less than fair market value
on the date of grant) and the vesting periods may vary. Options granted under the Plan expire no later than 10 years from the
date  of  grant.  The  Board  may  accelerate  vesting  or  extend  the  expiration  of  granted  options  in  the  case  of  a  merger,
consolidation, dissolution, or liquidation of the Company.

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Mersana Therapeutics, Inc.
Notes to consolidated financial statements
(continued)

Stock option activity

A summary of the activity under the Plan is as follows:

Number
     of Shares

  Weighted-
Average

  Weighted Average  
Remaining
    Exercise Price     Contractual Term      Intrinsic Value

Aggregate

Outstanding at January 1, 2019
Granted
Exercised
Cancelled
Outstanding at December 31, 2019

  3,746,567   $
  1,698,383  
(81,298) 
(642,880) 
  4,720,772   $

6.58  
3.74  
2.15  
9.42  
5.24  

7.6   $

3,897

7.3   $

9,836

Exercisable at December 31, 2019

  2,684,095   $

4.49  

6.3   $

7,064

The weighted-average grant date fair value of options granted during the years ended December 31, 2019, 2018 and 2017,
was $2.47, $8.78 and $5.53 per share, respectively.

Cash received from the exercise of stock options was $175, $918 and $452 for the years ended December 31, 2019, 2018 and
2017, respectively.

Restricted stock units

In July 2019, the Company issued RSUs with service conditions to employees. Vesting of these awards is contingent on the
fulfillment of the service conditions during the vesting term. The awards cliff-vest two years after the grant date.

Number

     of Shares

  Weighted-Average  
Remaining
  Contractual Term  

  Weighted-Average

Aggregate

Grant Date

Intrinsic Value  

Fair Value

 —  
449,331  
 —  
(1,995) 
447,336  

 —   $
 —  
 —  
 —  
1.5   $

 —   $

2,564   $

 —
4.00
 —
4.00
4.00

Unvested at January 1, 2019
Granted
Vested
Forfeited
Unvested at December 31, 2019

Stock-based compensation expense

The Company uses the provisions of ASC 718, Stock Compensation, to account for all stock-based awards to employees and
nonemployees.

The measurement date for employee awards is generally the date of grant. Stock-based compensation expense is recognized
over the requisite service period, which is generally the vesting period, using the straight-line method.

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Mersana Therapeutics, Inc.
Notes to consolidated financial statements
(continued)

The following table presents stock-based compensation expense by award type included within the Company’s consolidated
statement of operations and comprehensive loss:

Stock options
Restricted stock units
Employee stock purchase plan
Stock-based compensation expense included in Total operating expenses   $

  $

Year ended

December 31, 

2019

2018

2017

4,230   $
410  
232  
4,872   $

3,754   $
 —  
130  
3,884   $

1,422
 —
 —
1,422

The  following  table  presents  stock-based  compensation  expense  as  reflected  in  the  Company’s  consolidated  statements  of
operations and comprehensive loss:

Research and development
General and administrative
Stock-based compensation expense included in Total operating expenses   $

  $

Year ended

December 31, 

2019

2018

2017

2,245   $
2,627  
4,872   $

1,788   $
2,096  
3,884   $

770
652
1,422

As  of  December  31,  2019,  there  was  $7,450  and  $1,379  of  unrecognized  compensation  expense  related  to  unvested  stock
options and unvested RSUs, respectively, that is expected to be recognized over a weighted average period of 2.5 and 1.5
years.

The fair value of each option award is estimated on the date of grant using the Black–Scholes option pricing model with the
following weighted average assumptions:

Risk-free interest rate
Expected dividend yield
Expected term (years)
Expected stock price volatility

December 31, 
2018  

2019     

2017  

2.3 %  
 — %  
5.99  

2.7 % 2.2 %
 — %  — %
6.07  

6.21  

74 %  

73 % 67 %

Expected  volatility  for  the  Company’s  common  stock  was  determined  based  on  the  historical  volatility  of  comparable
publicly  traded  companies.  The  risk-free  interest  rate  is  based  on  the  yield  of  U.S.  Treasury  securities  consistent  with  the
expected term of the option. No dividend yield was assumed as the Company has not historically and does not expect to pay
dividends on its common stock. The expected term of the options granted is based on the use of the simplified method, in
which the expected term is presumed to be the mid-point between the vesting date and the end of the contractual term.

Prior to the Company’s initial public offering in June 2017, the fair value of the common stock had been determined by the
Board at each date of grant based on the variety of factors, including the Company’s financial position and historical

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Mersana Therapeutics, Inc.
Notes to consolidated financial statements
(continued)

financial  performance,  the  status  of  developments  within  the  Company’s  research  and  development  activities,  the
composition  and  ability  of  the  current  research  and  management  team,  an  evaluation  of  the  Company’s  competition,  the
current climate in the marketplace, the illiquid nature of the common stock, the effect of the rights and preferences of the
preferred shareholders, and the prospects of the liquidity event, among others.

The fair value of RSUs is determined based on the closing price of the Company’s common stock on the date of grant.

Employee Stock Purchase Plan

During the year ended December 31, 2017, the Board adopted and the Company's stockholders approved the 2017 employee
stock purchase plan (the 2017 ESPP). The Company initially reserved 225,000 shares of common stock for issuance under
the  2017  ESPP.  During  the  years  ended  December  31,  2019  and  2018  the  Company  issued  140,073  and  42,186  shares,
respectively, under the 2017 ESPP. As of December 31, 2019, there were 275,085 available for issuance, including 232,344
shares automatically added to the 2017 ESPP on January 1, 2019.

12. Leases

The Company has an operating lease for its facility and operating and finance leases for certain equipment. The Company
leases office space in Cambridge, MA under an operating lease, which was last amended in January 2018, and is effective
through  March  2021.  The  Company  has  an  option  to  extend  the  lease  term  for  an  additional  five  years.  The  Company’s
exercise of this option was not considered reasonably certain as of December 31, 2019. The Company has remaining lease
terms of three years to five years for certain equipment, some of which may include options to purchase at fair value.

In connection with the office lease, the Company had a letter of credit agreement for the benefit of its landlord in the amount
of $321 as of each December 31, 2019 and 2018, collateralized by a money market account.

During the first quarter of 2019, the Company entered into finance leases for certain equipment. The Company recorded
assets under finance leases of $429 as property and equipment.

The components of lease expense were as follows:

Operating lease cost

Finance lease cost:

Amortization of right-of-use assets
Interest on lease liabilities

109

Year ended

December 31, 2019
2,160

$

  $

  $

75
20
95

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Table of Contents

Mersana Therapeutics, Inc.
Notes to consolidated financial statements
(continued)

Supplemental balance sheet information related to leases was as follows:

Operating leases:

Operating lease right-of-use assets
Operating lease liabilities, current
Operating lease liabilities

Finance leases:

Property and equipment, gross
Property and equipment, accumulated depreciation
Other liabilities, current
Other liabilities

Weighted-average remaining lease term:

Operating leases
Finance leases

Weighted-average discount rate:

Operating leases
Finance leases

Supplemental cash flow information related to leases was as follows:

Cash paid for amounts included in the measurement of lease liabilities:

Operating cash flows from operating leases
Operating cash flows from finance leases
Financing cash flows from finance leases

110

Year ended

December 31, 2019

2,598
2,219
677

429
(75)
87
275

1.3 years
3.7 years

10.3%
6.9%

Year ended

December 31, 2019

2,271
20
87

$

$

$

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Table of Contents

Mersana Therapeutics, Inc.
Notes to consolidated financial statements
(continued)

Rent expense was $2,160, $1,994 and $1,834 for the years ended December 31, 2019, 2018 and 2017, respectively.

Future minimum lease payments under non-cancellable leases as of December 31, 2019 were as follows:

2020
2021
2022
2023
2024
Total lease payments
Present value adjustment
Present value of lease liabilities

13. Income Taxes

Operating leases  

Finance leases

  $

  $

2,394   $
687  
 —  
 —  
 —  
3,081  
(186) 
2,895   $

116
116
84
74
18
408
(46)
362

For the years ended December 31, 2019, 2018 and 2017, the Company recorded no income tax benefit for the net operating
losses incurred in each year, due to its uncertainty of realizing a benefit from those items.

A  reconciliation  of  income  taxes  computed  using  the  U.S.  federal  statutory  rate  to  that  reflected  in  operations  as  of
December 31, 2019, 2018 and 2017 are as follows:

Income tax computed at federal statutory tax rate
State taxes, net of federal benefit
Permanent differences
Research and development expenditures
General business credits
Impact of tax reform
Impact of ownership shift
Change in valuation allowance

111

     2019     

2017  

2018  
21.0 %   21.0 % 34.0 %
5.1 %
6.5 %
6.1 %  
0.6 % (0.8)%
(2.0)%  
(2.3)%  
 — %  
 — %  
4.2 %
10.3 %  
8.2 %
 — % (27.3)%
 — %  
 — %
 — %
(53.3)%  
17.9 %   (32.3)% (16.9)%
 — %
 — %
 — %  

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Table of Contents

Mersana Therapeutics, Inc.
Notes to consolidated financial statements
(continued)

Deferred  income  taxes  reflect  the  net  tax  effects  of  temporary  differences  between  the  carrying  amounts  of  assets  and
liabilities  for  financial  reporting  purposes  and  the  amounts  used  for  income  tax  purposes.  Significant  components  of  the
Company’s net deferred tax assets as of December 31, 2019 and 2018 are as follows:

Deferred tax assets:

Net operating losses
Accrued expenses
Tax credit carryforwards
Licensed technology
Deferred revenue
Lease liabilities
Depreciation
Deferred expenses
Other

Total gross deferred tax assets
Valuation allowance
Net deferred tax assets less valuation allowance
Deferred tax liabilities
Right-of-use assets

Total gross deferred tax liabilities
Net deferred taxes

2019

2018

  $ 40,554   $ 27,916
1,585
  10,178
1,160
  12,410
 —
405
112
174
  53,940
  (53,940)
 —

2,520  
2,448  
1,402  
1,315  
791  
492  
 —  
77  
49,599  
(48,889) 
710  

(710) 
(710) 

  $

 —   $

 —
 —
 —

The Company has incurred net operating losses (NOL) since inception. At December 31, 2019, the Company had Federal and
State net operating loss carryforwards of approximately $163,465 and $98,517, respectively. Of the $163,465 of Federal net
operating loss carryforwards, $34,149 expire at various dates through 2037. The remaining $129,316 of Federal net operating
loss  carryforwards  do  not  expire.  The  State  net  operating  loss  carryforwards  expire  at  various  dates  through  2039.  At
December 31, 2019, the Company had Federal and State research and development tax credit carryforwards of approximately
$1,989 and $687, respectively, which expire at various dates through 2039.

As required by ASC 740, management of the Company has evaluated the evidence bearing upon the reliability of its deferred
tax assets. Based on the weight of available evidence, both positive and negative, management has determined that it is more
likely  than  not  that  the  Company  will  not  realize  the  benefits  of  all  of  these  assets.  Accordingly,  the  Company  recorded  a
valuation  allowance  of  $48,889  and  $53,940  at  December  31,  2019  and  December  31,  2018,  respectively.  The  valuation
allowance  decreased  by  $5,051  and  increased  $21,338  during  the  years  ended  December  31,  2019  and  2018,  respectively,
primarily as a result of the Company’s 382 limitation and net operating losses generated during the periods, respectively.

Utilization  of  the  NOLs  and  research  and  development  tax  credit  carryforwards  may  be  subject  to  a  substantial  annual
limitation under Section 382 due to ownership change limitations that have occurred previously or that could occur in the
future in accordance with Section 382, as well as similar state provisions. These ownership changes may limit the amount of
NOLs and research and development tax credit carryforwards that can be utilized annually to offset future taxable income
and  tax,  respectively.  If  a  change  in  control  as  defined  by  Section  382  has  occurred  at  any  time  since  the  Company’s
formation,  utilization  of  its  NOLs  or  research  and  development  tax  credit  carryforwards  would  be  subject  to  an  annual
limitation under Section 382, which is determined by first multiplying the value of the Company’s stock at the time of the
ownership  change  by  the  applicable  long-term  tax-exempt  rate,  which  could  then  be  subject  to  additional  adjustments,  as
required. Any limitation may result in expiration of a portion of the NOLs or research and development tax carryforwards
before their utilization. The Company has determined that ownership changes have occurred through November 4, 2019 and
that certain NOLs and research and development tax credit carryforwards will be subject to limitation. The amounts

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Mersana Therapeutics, Inc.
Notes to consolidated financial statements
(continued)

presented  do  not  include  NOLs  or  research  and  development  tax  credit  carryforwards  that  will  expire  unused  due  to
ownership changes.

The  Company  applies  the  accounting  guidance  in  ASC  740  related  to  accounting  for  uncertainty  in  income  taxes.  The
Company’s reserves related to taxes are based on a determination of whether, and how much of, a tax benefit taken by the
Company  in  its  tax  filings  or  positions  is  more  likely  than  not  to  be  realized  following  resolution  of  any  potential
contingencies present related to the tax benefit. As of December 31, 2019 and 2018, the Company had no unrecognized tax
benefits.

The Company has not conducted a study of its research and development credit carryforwards. This study may result in an
adjustment  to  research  and  development  credit  carryforwards;  however,  until  a  study  is  completed  and  any  adjustment  is
known, no amounts are being presented as an uncertain tax position. A full valuation allowance has been provided against the
Company’s  research  and  development  credits  and,  if  an  adjustment  is  required,  this  adjustment  would  be  offset  by  an
adjustment to the valuation allowance. Thus, there would be no impact to the balance sheets or statements of operations if an
adjustment were required.

Interest  and  penalties  related  to  uncertain  tax  positions  would  be  classified  as  income  tax  expense  in  the  accompanying
statements of operations. As of December 31, 2019 and 2018, the Company had no accrued interest or penalties related to
uncertain tax positions.

The Company files income tax returns in the United States federal tax jurisdiction and one state jurisdiction. The Company
did not have any foreign operations during the years ended December 31, 2019, 2018 and 2017. The statute of limitations for
assessment  by  the  Internal  Revenue  Service  and  state  tax  authorities  is  closed  for  tax  years  prior  to  2016,  although
carryforward  attributes  that  were  generated  prior  to  tax  year  2015  may  still  be  adjusted  upon  examination  to  the  extent
utilized in a future period. There are no federal or state audits currently in progress.

14. Employee Benefit Plan

The Company has a defined contribution plan established under Section 401(k) of the Internal Revenue Code (401(k) Plan),
which  covers  substantially  all  employees.  Employees  who  have  attained  the  age  of  21  are  eligible  to  participate  in  the
401(k) Plan with no service requirement. Employees may contribute up to 75% of eligible pay on a pre–tax basis up to the
federal annual limits. For the years ended December 31, 2018 and 2017 and the period from January 1, 2019 to July 31, 2019,
the Company matched the employees’ contributions at 50% on the first 6% up to $6. For the period from August 1, 2019 to
December  31,  2019,  the  Company  matched  the  employees’  contributions  at  100%  on  the  first  4%  up  to  $7.  For  the  years
ended December 31, 2019, 2018 and 2017, the Company recorded expense of $404, $332 and $273, respectively, related to
its contribution to its 401(k) Plan.

15. Commitments

License Agreements

Through  December  31,  2019  the  Company  has  licensed  intellectual  property  from  two  biotechnology  companies.  The
consideration  included  upfront  payments  and  a  commitment  to  pay  annual  license  fees,  milestone  payments,  and,  upon
product  commercialization,  royalties  on  revenue  generated  from  the  sale  of  products  covered  by  the  licenses.  During  the
years ended December 31, 2019, 2018 and 2017, the Company recorded expense related to milestone payments of $600, $0
and $2,750, respectively, related to these agreements.

See Note 12 for the Company’s future obligations related to leases as of December 31, 2019.

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Mersana Therapeutics, Inc.
Notes to consolidated financial statements
(continued)

16. Related Party Transactions

Included  in  Series  C‑1  financing  and  the  Company’s  initial  public  offering  were  investments  of  $10,000  and  $10,000,
respectively, by Takeda.

17. Subsequent Events

The Company considered the events or transactions occurring after the balance sheet date, but prior to the issuance of the
consolidated  financial  statements,  for  potential  recognition  or  disclosure  in  its  consolidated  financial  statements.  All
significant subsequent events have been properly disclosed in the consolidated financial statements.

18. Selected Quarterly Financial Data (unaudited)

The  following  table  contains  selected  quarterly  financial  information  for  2019  and  2018.  The  Company  believes  that  the
following  information  reflects  all  normal  recurring  adjustments  necessary  for  a  fair  statement  of  the  information  for  the
periods presented. The operating results for any quarter are not necessarily indicative of results for any future period.

Three months ended

Collaboration revenue
Operating expenses:

Research and development
General and administrative

Total operating expenses
Other income:

Interest income
Interest expense

to  common

share  attributable 

share  attributable 

Total other income (expense), net
Net loss
Net 
loss  per 
stockholders — basic
loss  per 
Net 
stockholders — diluted
Weighted-average number of common shares used in
net loss per share attributable to common stockholders
— basic
Weighted-average number of common shares used in
net loss per share attributable to common stockholders
— diluted

to  common

     March 31, 2019      June 30, 2019      September 30, 2019      December 31, 2019
42
  $

41,035   $

844   $

202   $

15,143  
4,443  
19,586  

13,766  
4,192  
17,958  

452  
 —  
452  
21,901   $

725  
(40) 
685  
(17,071)  $

13,701  
4,436  
18,137  

608   
(107)   
501   
(16,792)  $

0.72   $

(0.36)  $

(0.35)  $

0.70   $

(0.36)  $

(0.35)  $

12,430
4,212
16,642

441
(87)
354
(16,246)

(0.34)

(0.34)

  $

  $

  $

  30,299,650  

  47,708,085  

47,833,607  

47,886,144

  31,461,696  

  47,708,085  

47,833,607  

47,886,144

114

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
   
 
   
 
 
 
 
 
 
 
 
 
  
 
  
 
  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
  
 
  
 
  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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Collaboration revenue
Operating expenses:

Research and development
General and administrative

Total operating expenses
Other income:

loss  per 

Interest income
Total other income
Net loss
Net 
stockholders — basic and diluted
Weighted-average number of common shares used in
net loss per share attributable to common stockholders
— basic and diluted

share  attributable 

to  common

Mersana Therapeutics, Inc.
Notes to consolidated financial statements
(continued)

Three months ended

     March 31, 2018      June 30, 2018      September 30, 2018      December 31, 2018
1,188
  $

3,064   $

2,151   $

4,191   $

12,256  
3,571  
15,827  

12,663  
4,231  
16,894  

15,180  
4,380  
19,560  

360  
360  
(12,403)  $

349  
349  
(12,354)  $

340   
340   
(17,069)  $

19,816
4,152
23,968

349
349
(22,431)

(0.54)  $

(0.54)  $

(0.74)  $

(0.97)

  $

  $

  22,816,521  

  22,966,314  

23,152,019  

23,184,459

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ITEM  9.                            CHANGES  IN  AND  DISAGREEMENTS  WITH  ACCOUNTANTS  ON  ACCOUNTING  AND

FINANCIAL DISCLOSURE

None.

ITEM 9A.           CONTROLS AND PROCEDURES

Management’s Evaluation of our Disclosure Controls and Procedures

We  maintain  “disclosure  controls  and  procedures,”  as  defined  in  Rules  13a-15(e)  and  15d-15(e)  under  the  Securities
Exchange  Act  of  1934,  as  amended,  or  the  Exchange  Act,  that  are  designed  to  ensure  that  information  required  to  be
disclosed in the reports that we file or submit under the Exchange Act is (1) recorded, processed, summarized and reported
within  the  time  periods  specified  in  the  Securities  and  Exchange  Commission’s  rules  and  forms  and  (2)  accumulated  and
communicated to our management, including our principal executive and principal financial officer, as appropriate to allow
timely decisions regarding required disclosure. Our management recognizes that any controls and procedures, no matter how
well  designed  and  operated,  can  provide  only  reasonable  assurance  of  achieving  their  objectives  and  our  management
necessarily  applies  its  judgment  in  evaluating  the  cost-benefit  relationship  of  possible  controls  and  procedures.  Our
disclosure controls and procedures are designed to provide reasonable assurance of achieving their control objectives.

Our management, with the participation of our principal executive officer and principal financial officer, has evaluated the
effectiveness  of  our  disclosure  controls  and  procedures  as  of  December  31,  2019,  the  end  of  the  period  covered  by  this
Annual  Report  on  Form  10-K.  Based  upon  such  evaluation,  our  principal  executive  officer  and  principal  financial  officer
have concluded that our disclosure controls and procedures were effective at the reasonable assurance level as of such date.

Internal Control Over Financial Reporting

Management’s Report on Internal Control Over Financial Reporting

Our  management  is  responsible  for  establishing  and  maintaining  adequate  internal  control  over  our  financial  reporting.
Internal control over financial reporting is defined in Rules 13a-15(f) and 15d-15(f) promulgated under the Exchange Act as
a process designed by, or under the supervision of, our principal executive and principal financial officers and effected by our
board  of  directors,  management  and  other  personnel  to  provide  reasonable  assurance  regarding  the  reliability  of  financial
reporting  and  the  preparation  of  financial  statements  for  external  purposes  in  accordance  with  U.S.  GAAP.  Our  internal
control over financial reporting includes those policies and procedures that:

·

·

·

pertain  to  the  maintenance  of  records  that,  in  reasonable  detail,  accurately  and  fairly  reflect  our  transactions  and
dispositions of our assets;

provide  reasonable  assurance  that  transactions  are  recorded  as  necessary  to  permit  preparation  of  financial
statements  in  accordance  with  U.S.  GAAP,  and  that  our  receipts  and  expenditures  are  being  made  only  in
accordance with authorizations of our management and directors; and

provide  reasonable  assurance  regarding  prevention  or  timely  detection  of  unauthorized  acquisition,  use  or
disposition of our assets that could have a material effect on our financial statements.

Because  of  its  inherent  limitations,  internal  control  over  financial  reporting  may  not  prevent  or  detect  misstatements.
Projections of any evaluation of effectiveness to future periods are subject to the risk that controls may become inadequate
because of changes in conditions, or that the degree of compliance with the policies or procedures may deteriorate.

Our  management  assessed  the  effectiveness  of  our  internal  control  over  financial  reporting  as  of  December  31,  2019.  In
making  this  assessment,  management  used  the  criteria  set  forth  by  the  Committee  of  Sponsoring  Organizations  of  the
Treadway Commission (COSO) in its 2013 Internal Control — Integrated Framework. Based on our assessment, our

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management has concluded that, as of December 31, 2019, our internal control over financial reporting is effective based on
those criteria.

This Annual Report on Form 10-K does not include an attestation report of our independent registered public accounting firm
regarding internal control over financial reporting due to an exemption established by the Jumpstart Our Business Startups
Act of 2012 for “emerging growth companies.”

Changes in Internal Control over Financial Reporting

No change in our internal control over financial reporting (as defined in Rules 13a-15(f) and 15d-15(f) under the Exchange
Act)  occurred  during  the  three  months  ended  December  31,  2019  that  has  materially  affected,  or  is  reasonably  likely  to
materially affect, our internal control over financial reporting.

ITEM 9B.           OTHER INFORMATION

None.

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PART III

ITEM 10.            DIRECTORS, EXECUTIVE OFFICERS AND CORPORATE GOVERNANCE

The information required by this Item 10 will be included in our definitive proxy statement to be filed with the SEC with
respect to our 2020 Annual Meeting of Stockholders and is incorporated herein by reference.

ITEM 11.            EXECUTIVE COMPENSATION

The information required by this Item 11 will be included in our definitive proxy statement to be filed with the SEC with
respect to our 2020 Annual Meeting of Stockholders and is incorporated here by reference.

ITEM 12.            SECURITY OWNERSHIP OF CERTAIN BENEFICIAL OWNERS AND MANAGEMENT AND

RELATED STOCKHOLDER MATTERS

The information required by this Item 12 will be included in our definitive proxy statement to be filed with the SEC with
respect to our 2020 Annual Meeting of Stockholders and is incorporated herein by reference.

ITEM  13.                        CERTAIN  RELATIONSHIPS  AND  RELATED  TRANSACTIONS,  AND  DIRECTOR

INDEPENDENCE

The information required by this Item 13 will be included in our definitive proxy statement to be filed with the SEC with
respect to our 2020 Annual Meeting of Stockholders and is incorporated herein by reference.

ITEM 14.            PRINCIPAL ACCOUNTING FEES AND SERVICES

The information required by this Item 14 will be included in our definitive proxy statement to be filed with the SEC with
respect to our 2020 Annual Meeting of Stockholders and is incorporated herein by reference.

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ITEM 15.            EXHIBITS, FINANCIAL STATEMENT SCHEDULES

Financial Statements

PART IV

For a list of the consolidated financial statements included herein, see Index to the Consolidated Financial Statements in this
Annual Report on Form 10-K, which is incorporated into this Item by reference.

Financial Statement Schedules

No  financial  statement  schedules  have  been  submitted  because  they  are  not  required  or  are  not  applicable  or  because  the
information required is included in the consolidated financial statements or the notes thereto.

Exhibits

See the Exhibit Index immediately before the signature page of this Annual Report on Form 10-K. The exhibits listed in the
Exhibit Index are filed or incorporated by reference as part of this Annual Report on Form 10-K.

ITEM 16.            FORM 10-K SUMMARY

None.

Exhibit
Number
3.1

3.2

4.1

4.2

  Description of Exhibit

EXHIBIT INDEX

  Fifth  Amended  and  Restated  Certificate  of  Incorporation  (incorporated  by  reference  to  Exhibit  3.1  to  the

Company’s Form 8-K, File No. 001-38129, filed on July 10, 2017).

  Amended and Restated Bylaws (incorporated by reference to Exhibit 3.2 to the Company’s Form 8-K, File

No. 001-38129, filed on July 10, 2017).

  Form of Common Stock Warrant (incorporated by reference to Exhibit 4.1 to the Company’s Form S-1, File

No. 333-218412, filed on June 1, 2017).

  Third Amended and Restated Investor Rights Agreement, dated as of June 15, 2016, by and among Mersana
Therapeutics,  Inc.  and  the  Stockholders  listed  therein  (incorporated  by  reference  to  Exhibit  4.2  to  the
Company’s Form S-1, File No. 333-218412, filed on June 1, 2017).

4.3

  Form of Exchange Warrant (incorporated by reference to Exhibit 4.1 to the Company’s Form 8-K, File No.

001-38129, filed on November 27, 2019).

4.4*

  Description of Registrant’s Common Stock.

10.1†

  Form of Indemnification Agreement (incorporated by reference to Exhibit 10.1 to the Company’s Form S-

1/A, File No. 333-218412, filed on June 16, 2017).

10.2

  Commercial Lease, dated February 24, 2009, between Mersana Therapeutics, Inc. and Rivertech Associates
II, LLC (incorporated by reference to Exhibit 10.2 to the Company’s Form S-1, File No. 333-218412, filed
on June 1, 2017).

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10.3

10.4+

10.5+

10.6+

10.7+

10.8

10.9+

10.10

10.11+

10.12+

10.13+

10.14+

10.15

  Sixth  Lease  Extension  and  Modification  Agreement,  dated  January  17,  2018,  by  and  between  Mersana
Therapeutics,  Inc.  and  Rivertech  Associates  II  LLC  (incorporated  by  reference  to  Exhibit  10.1  to  the
Company’s Form 10-Q, File No. 001-38129, filed on May 15, 2018).

  Collaboration  and  Commercial  License  Agreement,  dated  June  23,  2014,  by  and  between  Mersana
Therapeutics, Inc. and Merck KGaA (incorporated by reference to Exhibit 10.4 to the Company’s Form S-1,
File No. 333-218412, filed on June 1, 2017).

  Amendment 1 to the Collaboration and Commercial License Agreement, dated June 1, 2016, by and between
Mersana Therapeutics, Inc. and Merck KGaA (incorporated by reference to Exhibit 10.5 to the Company’s
Form S-1, File No. 333-218412, filed on June 1, 2017).

  Amendment  2  to  the  Collaboration  and  Commercial  License  Agreement,  dated  August  12,  2016,  by  and
between  Mersana  Therapeutics,  Inc.  and  Merck  KGaA  (incorporated  by  reference  to  Exhibit  10.6  to  the
Company’s Form S-1, File No. 333-218412, filed on June 1, 2017).

  Amendment  3  to  the  Collaboration  and  Commercial  License  Agreement,  dated  February  28,  2017,  by  and
between  Mersana  Therapeutics,  Inc.  and  Merck  KGaA  (incorporated  by  reference  to  Exhibit  10.7  to  the
Company’s Form S-1, File No. 333-218412, filed on June 1, 2017).

  Amendment 4 to Collaboration and Commercial License Agreement dated May 15, 2018, by and between
Mersana Therapeutics, Inc. and Merck KGaA (incorporated by reference to Exhibit 10.1 to the Company’s
Form 10-Q, File No. 001-38129, filed on August 14, 2018).

  License,  Development  and  Commercialization  Agreement,  dated  July  9,  2015,  by  and  between  Mersana
Therapeutics, Inc. and Recepta Biopharma S.A. (incorporated by reference to Exhibit 10.8 to the Company’s
Form S-1, File No. 333-218412, filed on June 1, 2017).

  First Amendment to the License, Development and Commercialization Agreement, dated August 19, 2019,
by  and  between  Mersana  Therapeutics,  Inc.  and  Recepta  Biopharma  S.A.  (incorporated  by  reference  to
Exhibit 10.1 to the Company’s Form 10-Q, File No. 001-38129, filed on November 6, 2019).

  Agreement  Regarding  LICR  Technology,  dated  July  9,  2015,  by  and  between  Ludwig  Institute  for  Cancer
Research,  Recepta  Biopharma  S.A.  and  Mersana  Therapeutics,  Inc.  (incorporated  by  reference  to  Exhibit
10.9 to the Company’s Form S-1, File No. 333-218412, filed on June 1, 2017).

  Collaboration  Agreement,  dated  as  of  July  25,  2012,  by  and  between  Adimab,  LLC  and  Mersana
Therapeutics,  Inc.  (incorporated  by  reference  to  Exhibit  10.10  to  the  Company’s  Form  S-1,  File  No.  333-
218412, filed on June 1, 2017).

  Amendment  Number  One  to  the  Collaboration  Agreement,  dated  February  21,  2013,  by  and  between
Adimab, LLC and Mersana Therapeutics, Inc. (incorporated by reference to Exhibit 10.11 to the Company’s
Form S-1, File No. 333-218412, filed on June 1, 2017).

  Amendment  Number  One,  to  the  Collaboration  Agreement  dated  June  17,  2014,  by  and  between  Adimab,
LLC and Mersana Therapeutics, Inc. (incorporated by reference to Exhibit 10.12 to the Company’s Form S-
1, File No. 333-218412, filed on June 1, 2017).

  Second Amendment to Amended and Restated Research Collaboration and Commercial License Agreement,
as  amended,  dated  August  2,  2017  by  and  between  Mersana  Therapeutics,  Inc.  and  Millennium
Pharmaceuticals, Inc. (incorporated by reference to Exhibit 10.1 to the Company’s Form 10-Q, File No. 001-
38129, filed on August 11, 2017).

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10.16

10.17

10.18

10.19

10.20†

10.21†

10.22†

  Third  Amendment  to  the  Amended  and  Restated  Research  Collaboration  and  Commercial  License
Agreement,  as  amended,  dated  October  30,  2017  by  and  between  Mersana  Therapeutics,  Inc.  and
Millennium Pharmaceuticals, Inc. (incorporated by reference to Exhibit 10.1 to the Company’s Form 10-Q,
file No. 001-38129, filed on November 13.2017).

  Exchange  Agreement,  dated  November  26,  2019,  by  and  between  Biotechnology  Value  Fund,  L.P.,
Biotechnology Value Fund II, L.P., Biotechnology Value Trading Fund OS, L.P. and Mersana Therapeutics,
Inc.  (incorporated  by  reference  to  Exhibit  10.1  to  the  Company’s  Form  8-K,  File  No.  001-38129,  filed  on
November 27, 2019).

  Loan  and  Security  Agreement,  dated  May  8,  2019,  by  and  between  Silicon  Valley  Bank  and  Mersana
Therapeutics,  Inc.  (incorporated  by  reference  to  Exhibit  10.2  to  the  Company’s  Form  10-Q,  File  No.  001-
38129, filed on May 9, 2019).

  First Amendment to the Loan and Security Agreement, dated June 21, 2019 by and between Silicon Valley
Bank and Mersana Therapeutics, Inc. (incorporated by reference to Exhibit 10.2 to the Company’s Form 10-
Q, File No. 001-38129, filed on August 8, 2019).

  Amended and Restated Offer Letter, by and between Mersana Therapeutics, Inc. and Anna Protopapas, dated
March  17,  2017  (incorporated  by  reference  to  Exhibit  10.16  to  the  Company's  Form  S-1,  File  No.  333-
218412, filed on June 1, 2017).

  Amended and Restated-Offer-Letter, by and between Mersana Therapeutics, Inc. and Timothy B. Lowinger,
dated March 8, 2017 (incorporated by reference to Exhibit 10.18 to the Company's Form S-1, File No. 333-
218412, filed on June 1, 2017).

  Offer  Letter,  by  and  between  Mersana  Therapeutics,  Inc.  and  David  Spellman,  dated  December  18,  2017
(incorporated by reference to Exhibit 10.1 to the Company’s Form 10-Q, File No. 001-38129, filed on May
9, 2019).

10.23†

  2007 Stock Incentive Plan, as amended (incorporated by reference to Exhibit 10.19 to the Company’s Form

S-1, File No. 333-218412, filed on June 1, 2017).

10.24†

  Form of Incentive Stock Option under the 2007 Stock Incentive Plan (incorporated by reference to Exhibit

10.20 to the Company’s Form S-1, File No. 333-218412, filed on June 1, 2017).

10.25†

  Form  of  Nonqualified  Stock  Option  under  the  2007  Stock  Incentive  Plan  (incorporated  by  reference  to

Exhibit 10.21 to the Company’s Form S-1, File No. 333-218412, filed on June 1, 2017).

10.26†

  2017 Stock Incentive Plan (incorporated by reference to Exhibit 10.22 to the Company’s Form S-1/A, File

No. 333-218412, filed on June 16, 2017).

10.27†

  Form of Incentive Stock Option under the 2017 Stock Incentive Plan (incorporated by reference to Exhibit

10.23 to the Company’s Form S-1/A, File No. 333-218412, filed on June 16, 2017).

10.28†

  Form  of  Nonqualified  Stock  Option  under  the  2017  Stock  Incentive  Plan  (incorporated  by  reference  to

Exhibit 10.24 to the Company’s Form S-1/A, File No. 333-218412, filed on June 16, 2017).

10.29†

  2017 Employee Stock Purchase Plan (incorporated by reference to Exhibit 10.25 to the Company’s Form S-

1/A, File No. 333-218412, filed on June 16, 2017).

10.30†

  2017 Cash Bonus Plan (incorporated by reference to Exhibit 10.26 to the Company’s Form S-1/A, File No.

333-218412, filed on June 16, 2017).

121

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Table of Contents

21.1*

23.1*

31.1*

31.2*

  Subsidiaries of Mersana Therapeutics, Inc. 

  Consent of Ernst & Young LLP.

  Certification pursuant to Section 302 of Sarbanes Oxley Act of 2002 by Chief Executive Officer.

  Certification pursuant to Section 302 of Sarbanes Oxley Act of 2002 by Principal Financial Officer.

32.1**

  Certification  of  periodic  financial  report  pursuant  to  Section  906  of  Sarbanes  Oxley  Act  of  2002  by  Chief

Executive Officer and Principal Financial Officer.

101. *
INS
101. *
SCH
101. *
CAL
101. *
DEF
101. *
LAB
101. *
PRE

*
**
†
+

  XBRL Instance Document.

  XBRL Taxonomy Extension Schema.

  XBRL Taxonomy Extension Calculation Linkbase.

  XBRL Taxonomy Extension Definition Linkbase.

  XBRL Taxonomy Extension Label Linkbase.

  XBRL Taxonomy Extension Presentation Linkbase.

Filed herewith.

Furnished herewith.

Indicates a management contract or compensatory plan.

Portions of this exhibit (indicated by asterisks) have been omitted pursuant to a request for confidential treatment
and this exhibit has been submitted separately to the Securities and Exchange Commission.

122

 
 
 
 
 
 
 
 
 
 
Table of Contents

Pursuant to the requirements of Section 13 or 15(d) of the Securities Exchange Act of 1934, the Company has duly caused
this report to be signed on its behalf by the undersigned, thereunto duly authorized.

SIGNATURES

Dated: February 28, 2020

Mersana Therapeutics, Inc.

/s/ Anna Protopapas
Anna Protopapas
President and Chief Executive Officer

Pursuant  to  the  requirements  of  the  Securities  Exchange  Act  of  1934,  this  report  has  been  signed  below  by  the  following
persons on behalf of the registrant and in the capacities and on dates indicated.

Signature

Title

Date

/s/ ANNA PROTOPAPAS

Anna Protopapas

(Principal Executive Officer)

  President,  Chief  Executive  Officer  and  Director

February 28, 2020

/s/ BRIAN DESCHUYTNER

Brian DeSchuytner

/s/ ASHISH MANDELIA

Ashish Mandelia

/s/ DAVID MOTT

David Mott

/s/ KRISTEN HEGE

Kristen Hege, M.D.

/s/ ANDREW A. F. HACK

Andrew A. F. Hack, M.D., Ph.D.

/s/ LAWRENCE M. ALLEVA

Lawrence M. Alleva

/s/ WILLARD H. DERE, M.D.

Willard H. Dere, M.D.

  Senior  Vice  President,  Finance  &  Product  Strategy

(Principal Financial Officer)

February 28, 2020

  Vice  President,  Controller  (Principal  Accounting

Officer)

February 28, 2020

  Chairman of the Board

February 28, 2020

  Director

  Director

  Director

  Director

123

February 28, 2020

February 28, 2020

February 28, 2020

February 28, 2020

 
 
 
 
 
 
 
 
 
 
 
    
    
 
 
 
 
 
 
 
 
 
 
 
 
 
 
DESCRIPTION OF THE REGISTRANT’S SECURITIES

Exhibit 4.4

The following summary description of the Common Stock (as defined below) of Mersana Therapeutics, Inc., or

the Corporation, is based on the provisions of our fifth amended and restated certificate of incorporation, or the Restated
Certificate, our amended and restated bylaws, or Bylaws, and the applicable provisions of the General Corporation Law
of the State of Delaware, or DGCL. This information may not be complete in all respects and is qualified entirely by
reference to the provisions of the Restated Certificate, the Bylaws, and the DGCL. The Restated Certificate and Bylaws
are filed as exhibits to the Annual Report on Form 10-K to which this Description of Securities is an exhibit.

General

Our Restated Certificate authorizes us to issue 175,000,000 shares of common stock (“Common Stock”), par value

$0.0001 per share, and 25,000,000 shares of preferred stock, par value $0.0001 per share. Our Common Stock is
registered under Section 12 of the Securities Exchange Act of 1934, as amended, and listed on the Nasdaq Global Select
Market under the symbol “MRSN.”

Common Stock

Each holder of our Common Stock shall be entitled to one vote for each share of Common Stock held of record by

such holder on all matters on which stockholders generally are entitled to vote and does not have cumulative voting
rights. A contested election of directors by our stockholders shall be determined by a plurality of the votes cast by the
stockholders entitled to vote on the election; otherwise, a nominee is elected if the votes properly cast for such nominee
exceed the votes properly cast against such nominee.

Dividends of cash or property may be declared and paid on the Common Stock from funds lawfully available
therefor as and when determined by our board of directors and subject to any preferential dividend rights of any then
outstanding preferred stock. The holders of the Common Stock shall have no preemptive rights to subscribe for any
shares of any class of stock of the Corporation whether now or hereafter authorized. The Common Stock shall not be
convertible into, or exchangeable for, shares of any other class or classes or of any other series of the same class of the
Corporation’s capital stock. Upon the dissolution, liquidation or winding up of the affairs of the Corporation, whether
voluntary or involuntary, after payment or provision for payment of the debts and liabilities of the Corporation and of the
preferential and other amounts, if any, to which the holders of preferred stock shall be entitled, holders of Common
Stock shall be entitled to receive all assets of the Corporation available for distribution to its stockholders, ratably in
proportion to the number of shares held by each such stockholder. 

Additional shares of authorized common stock may be issued, as authorized by our board of directors from time to

time, without stockholder approval, except as may be required by applicable stock exchange requirements.

Anti-Takeover Effects of our Restated Certificate, Bylaws and the DGCL

Authorized but Unissued Shares.

Our authorized but unissued shares of Common Stock and preferred stock are available for future issuance without

stockholder approval. Our board of directors, has the authority under our Restated Certificate to issue preferred stock
with rights superior to the rights of the holders of Common Stock. As a result, the issuance of preferred stock may have
the effect of delaying, deferring or preventing a change of control of the Corporation without further action by the
stockholders and may adversely affect the voting and other rights of the holders of Common Stock.

 
 
 
 
 
 
 
 
 
 
 
 
 
 
Exhibit 4.4

Classified Board

Our Restated Certificate provides for our board of directors to be divided into three classes, with staggered three-

year terms. As a result, only one class of directors is elected at each annual meeting of stockholders, with the other
classes continuing for the remainder of their respective three-year terms. Our Restated Certificate also provides that,
subject to any rights of holders of preferred stock to elect additional directors under specified circumstances, the number
of directors will be fixed exclusively pursuant to a resolution adopted by our board of directors.

Removal of Directors

Our Restated Certificate provides that our directors may be removed only for cause by the affirmative vote of at

least 75% of the voting power of our outstanding shares of capital stock, voting together as a single class. This
requirement of a supermajority vote to remove directors could enable a minority of our stockholders to prevent a change
in the composition of our board of directors.

Action by Written Consent; Special Meeting of Stockholders

Our Restated Certificate also requires that any action required or permitted to be taken by our stockholders must
be effected at a duly called annual or special meeting of the stockholders and cannot be taken by written consent in lieu
of a meeting. A special meeting of the stockholders may be called only by or at the direction of our board of directors
pursuant to a written resolution adopted by a majority of the total number of directors which the Corporation would have
if there were no vacancies. These provisions may have the effect of delaying, deferring or preventing a change in control
and may also delay or prevent changes in management of the Corporation.

Advance Notice Procedures

Our Bylaws establish an advance notice procedure for stockholder proposals to be brought before an annual

meeting of our stockholders, including proposed nominations of persons for election to the board of directors.
Stockholders at an annual meeting are only able to consider proposals or nominations specified in the notice of meeting
or brought before the meeting by or at the direction of the board of directors or by a stockholder who was a stockholder
of record on the record date for the meeting, who is entitled to vote at the meeting and who has given our Secretary
timely written notice, in proper form, of the stockholder’s intention to bring that business before the meeting. Although
our Bylaws do not give the board of directors the power to approve or disapprove stockholder nominations of candidates
or proposals regarding other business to be conducted at a special or annual meeting, our Bylaws may have the effect of
precluding the conduct of certain business at a meeting if the proper procedures are not followed or may discourage or
deter a potential acquirer from conducting a solicitation of proxies to elect its own slate of directors or otherwise
attempting to obtain control of us.

Super Majority Approval Requirements

Our Restated Certificate and Bylaws provide that the affirmative vote of holders of at least 75% of the total votes

eligible to be cast in the election of directors is required to amend, alter, change or repeal specified provisions. This
requirement of a supermajority vote to approve amendments to our Restated Certificate and Bylaws could enable a
minority of our stockholders to exercise veto power over any such amendments.

Exclusive Forum

Our Restated Certificate requires, to the fullest extent permitted by law, that derivative actions brought in the name

of the Corporation, actions against directors, officers and employees for breach of a fiduciary duty and other similar
actions may be brought only in specified courts in the State of Delaware. Although we believe this provision benefits us
by providing increased consistency in the application of Delaware law in the types of lawsuits to which it applies, the
provision may have the effect of discouraging lawsuits against our directors and officers.

 
 
 
 
 
 
 
 
 
 
 
 
Exhibit 4.4

These and other provisions are intended to enhance the likelihood of continued stability in the composition of our

board of directors and to discourage certain types of transactions that may involve an actual or threatened change of
control. However, such provisions could have the effect of discouraging others from making tender offers for our shares
and, as a consequence, such provisions also may inhibit fluctuations in the market price of our shares that could result
from actual or rumored takeover attempts.

Section 203 of the General Corporation Law of the State of Delaware

We are subject to Section 203 of the DGCL which regulates acquisitions of some Delaware corporations. In
general, Section 203 prohibits, with some exceptions, a publicly held Delaware corporation such as us from engaging in
a “business combination” with an “interested stockholder” for a period of three years following the time that the
stockholder became an interested stockholder, unless the business combination is approved in a prescribed manner. A
“business combination” includes, among other things, a merger, asset or stock sale or other transaction resulting in a
financial benefit to the interested stockholder. An "interested stockholder" is a person who, together with affiliates and
associates, owns, or did own within three years prior to the determination of interested stockholder status, 15% or more
of the corporation's voting stock.

Under Section 203, a business combination between a corporation and an interested stockholder is prohibited

unless it satisfies one of the following conditions: before the stockholder became interested, the board of directors
approved either the business combination or the transaction which resulted in the stockholder becoming an interested
stockholder; upon consummation of the transaction which resulted in the stockholder becoming an interested
stockholder, the interested stockholder owned at least 85% of the voting stock of the corporation outstanding at the time
the transaction commenced, excluding for purposes of determining the voting stock outstanding, shares owned by
persons who are directors and also officers, and employee stock plans, in some instances; or at or after the time the
stockholder became interested, the business combination was approved by the board of directors of the corporation and
authorized at an annual or special meeting of the stockholders by the affirmative vote of at least two-thirds of the
outstanding voting stock which is not owned by the interested stockholder.

        A Delaware corporation may "opt out" of these provisions with an express provision in its original certificate of
incorporation or an express provision in its certificate of incorporation or by-laws resulting from a stockholders'
amendment approved by at least a majority of the outstanding voting shares. We have not opted out of these provisions.
As a result, mergers or other takeover or change in control attempts of us may be discouraged or prevented.

 
 
Exhibit 21.1

Subsidiaries of the Registrant 

Entity

State of Incorporation or Organization

Mersana Securities Corp.

Massachusetts

 
 
 
 
 
 
   
 
Consent of Independent Registered Public Accounting Firm

We consent to the incorporation by reference in the following Registration Statements:

Exhibit 23.1 

(1) Registration  Statement  (Form  S-3  No.  333-226055)  of  Mersana  Therapeutics,  Inc.  and  in  the  related

(2) Registration  Statement  (Form  S-8  No.  333-230159)  pertaining  to  the  Mersana  Therapeutics,  Inc.  2017  Stock

Incentive Plan and the Mersana Therapeutics, Inc. 2017 Employee Stock Purchase Plan,

(3) Registration  Statement  (Form  S-8  No.  333-222845)  pertaining  to  the  Mersana  Therapeutics,  Inc.  2017  Stock

Prospectus,

Incentive Plan, and

(4) Registration  Statement  (Form  S-8  No.  333-219388)  pertaining  to  the  Mersana  Therapeutics,  Inc.  2007  Stock
Incentive  Plan,  as  amended,  the  Mersana  Therapeutics,  Inc.  2017  Stock  Incentive  Plan  and  the  Mersana
Therapeutics, Inc. 2017 Employee Stock Purchase Plan;

of  our  report  dated  February  28,  2020,  with  respect  to  the  consolidated  financial  statements  of  Mersana
Therapeutics,  Inc.  included  in  this  Annual  Report  (Form  10-K)  of  Mersana  Therapeutics,  Inc.  for  the  year  ended
December 31, 2019.

Boston, Massachusetts
February 28, 2020

/s/ Ernst & Young LLP

 
 
 
 
CERTIFICATIONS

Exhibit 31.1

I, Anna Protopapas, certify that:  

1.       I have reviewed this Annual Report on Form 10-K of Mersana Therapeutics, Inc.;

2.       Based on my knowledge, this report does not contain any untrue statement of a material fact or omit to state a

material fact necessary to make the statements made, in light of the circumstances under which such statements
were made, not misleading with respect to the period covered by this report;

3.      Based on my knowledge, the financial statements, and other financial information included in this report, fairly

present in all material respects the financial condition, results of operations and cash flows of the registrant as of,
and for, the periods presented in this report;

4.      The registrant’s other certifying officer and I are responsible for establishing and maintaining disclosure controls
and procedures (as defined in Exchange Act Rules 13a-15(e) and 15d-15(e)) and internal control over financial
reporting (as defined in Exchange Act Rules 13a-15(f) and 15d-15(f)) for the registrant and have:

a)      Designed such disclosure controls and procedures, or caused such disclosure controls and procedures to be
designed under our supervision, to ensure that material information relating to the registrant, including its
consolidated subsidiaries, is made known to us by others within those entities, particularly during the period
in which this report is being prepared;

b)  

Designed such internal control over financial reporting, or caused such internal control over financial
reporting to be designed under our supervision, to provide reasonable assurance regarding the reliability of
financial reporting and the preparation of financial statements for external purposes in accordance with
generally accepted accounting principles;

c)      Evaluated the effectiveness of the registrant’s disclosure controls and procedures and presented in this report
our conclusions about the effectiveness of the disclosure controls and procedures, as of the end of the period
covered by this report based on such evaluation; and

d)      Disclosed in this report any change in the registrant’s internal control over financial reporting that occurred

during the registrant’s most recent fiscal quarter (the registrant’s fourth fiscal quarter in the case of an annual
report), that has materially affected, or is reasonably likely to materially affect, the registrant’s internal
control over financial reporting; and

5.      The registrant's other certifying officer and I have disclosed, based on our most recent evaluation of internal control

over financial reporting, to the registrant's auditors and the audit committee of the registrant's board of directors
(or persons performing the equivalent functions):

a)      All significant deficiencies and material weaknesses in the design or operation of internal control over

financial reporting which are reasonably likely to adversely affect the registrant's ability to record, process,
summarize and report financial information; and

b)      Any fraud, whether or not material, that involves management or other employees who have a significant

role in the registrant's internal control over financial reporting.

 Date: February 28, 2020

By:

 /s/ Anna Protopapas
Anna Protopapas
President and Chief Executive Officer
(Principal Executive Officer)

 
 
 
 
 
 
 
 
CERTIFICATIONS

Exhibit 31.2

I, Brian DeSchuytner, certify that:

1.       I have reviewed this Annual Report on Form 10-K of Mersana Therapeutics, Inc.;

2.       Based on my knowledge, this report does not contain any untrue statement of a material fact or omit to state a

material fact necessary to make the statements made, in light of the circumstances under which such statements
were made, not misleading with respect to the period covered by this report;

3.       Based on my knowledge, the financial statements, and other financial information included in this report, fairly

present in all material respects the financial condition, results of operations and cash flows of the registrant as of,
and for, the periods presented in this report;

4.       The registrant’s other certifying officer and I are responsible for establishing and maintaining disclosure controls

and procedures (as defined in Exchange Act Rules 13a-15(e) and 15d-15(e)) and internal control over financial
reporting (as defined in Exchange Act Rules 13a-15(f) and 15d-15(f)) for the registrant and have:

a)      Designed such disclosure controls and procedures, or caused such disclosure controls and procedures to be
designed under our supervision, to ensure that material information relating to the registrant, including its
consolidated subsidiaries, is made known to us by others within those entities, particularly during the period
in which this report is being prepared; 

b)  

Designed such internal control over financial reporting, or caused such internal control over financial
reporting to be designed under our supervision, to provide reasonable assurance regarding the reliability of
financial reporting and the preparation of financial statements for external purposes in accordance with
generally accepted accounting principles;

c)       Evaluated the effectiveness of the registrant’s disclosure controls and procedures and presented in this report
our conclusions about the effectiveness of the disclosure controls and procedures, as of the end of the period
covered by this report based on such evaluation; and

d)      Disclosed in this report any change in the registrant’s internal control over financial reporting that occurred

during the registrant’s most recent fiscal quarter (the registrant’s fourth fiscal quarter in the case of an annual
report), that has materially affected, or is reasonably likely to materially affect, the registrant’s internal
control over financial reporting; and

5. The registrant's other certifying officer and I have disclosed, based on our most recent evaluation of internal control
over financial reporting, to the registrant's auditors and the audit committee of the registrant's board of directors
(or persons performing the equivalent functions):

(a)

(b)

All significant deficiencies and material weaknesses in the design or operation of internal control over
financial reporting which are reasonably likely to adversely affect the registrant's ability to record, process,
summarize and report financial information; and

Any fraud, whether or not material, that involves management or other employees who have a significant
role in the registrant's internal control over financial reporting.

 Date: February 28, 2020

By:

 /s/ Brian DeSchuytner
Brian DeSchuytner
Senior Vice President, Finance & Product Strategy
(Principal Financial Officer)

 
 
 
 
 
 
 
 
 
Exhibit 32.1

CERTIFICATIONS OF CEO AND CFO PURSUANT TO 18 U.S.C. SECTION 1350, AS ADOPTED
PURSUANT
TO SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002

In connection with this Annual Report on Form 10-K of Mersana Therapeutics, Inc. (the “Company”) for the year ended
December 31, 2019 as filed with the Securities and Exchange Commission on the date hereof (the “Report”), each of the
undersigned officers of the company, hereby certifies, pursuant to Section 1350 of Chapter 63 of Title 18, United States
Code, that to the best of her or his knowledge:

(1)     the Report fully complies with the requirements of Section 13(a) or 15(d) of the Securities Exchange Act

of 1934; and

(2)     the information contained in the Report fairly presents, in all material respects, the financial condition and

results of operations of the Company.

Date: February 28, 2020

Date: February 28, 2020

By:   

/s/ Anna Protopapas
Anna Protopapas
President and Chief Executive Officer
(Principal Executive Officer)

By:    

/s/ Brian DeSchuytner
Brian DeSchuytner
Senior Vice President, Finance & Product Strategy
(Principal Financial Officer)