Letter Agreement

September 6, 2023

Arvin Yang

Dear Arvin:

As we discussed, your employment with Mersana Therapeutics, Inc. (the “Company”) will end effective September 29, 2023 (the “Separation Date”). As we also discussed, the Company will provide you with the severance benefits described in paragraph 1 below if you sign and return this letter agreement to me on, but not before, the Separation Date and do not revoke your agreement (as described below).

By signing and returning this letter agreement and not revoking your acceptance, you will be entering into a binding agreement with the Company and will be agreeing to the terms and conditions set forth in the numbered paragraphs below, including the release of claims set forth in paragraph 2. Therefore, you are advised to consult with an attorney before signing this letter agreement and you have been given at least twenty-one (21) days to do so. If you sign this letter agreement, you may change your mind and revoke your agreement during the seven (7) business day period after you have signed it (the “Revocation Period”) by notifying me in writing. If you do not so revoke, this letter agreement will become a binding agreement between you and the Company upon the expiration of the Revocation Period.

Although your receipt of the severance benefits is expressly conditioned on your timely entering into this letter agreement, the following will apply regardless of whether or not you do so:

•As of the Separation Date, all salary payments from the Company will cease and any benefits you had as of the Separation Date under Company-provided benefit plans, programs, or practices will terminate, except as required by federal or state law.

•You will receive on the Separation Date payment for your final wages and any unused vacation time accrued through the Separation Date.

•You may, if eligible and at your own cost, elect to continue receiving group medical insurance pursuant to the “COBRA” law. Please consult the COBRA materials to be provided under separate cover for details regarding these benefits.

•You are obligated to keep confidential and not to use or disclose any and all non-public information concerning the Company that you acquired during the course of your employment with the Company, including any non-public information concerning the Company’s business affairs, business prospects, and financial condition, except as otherwise permitted by paragraph 4(c) below. Further, you remain subject to your continuing obligations to the Company as set forth in the Employee Nondisclosure, Noncompetition and Assignment of Intellectual Property Agreement (the “Nondisclosure Agreement”) you previously executed for the benefit of the Company, which remain in full force and effect.

•You must return to the Company on or before the Separation Date all Company property.

•You will have three (3) months following the Separation Date to exercise any stock options under the Company’s 2017 Stock Incentive Plan or the inducement grant made to you on November 30, 2020 that were vested as of the Separation Date. After that three (3) month period, your stock options will expire and you will no longer have any rights with respect thereto.

If you elect to timely sign and return this letter agreement and do not revoke your acceptance within the Revocation Period, the following terms and conditions will also apply:

1.Severance Benefits –The Company will provide you with the following severance benefits (the “severance benefits”):

a.Severance Pay. The Company will pay to you four hundred and nine thousand, seven hundred forty four dollars ($409,744) less all applicable taxes and withholdings, as severance pay (an amount equivalent to nine (9) months of your current base salary). This severance pay will be paid in installments in accordance with the Company’s regular payroll practices, but in no event shall payments begin earlier than the Company’s first regular payroll date following expiration of the Revocation Period.

b.COBRA Benefits. Should you timely elect and be eligible to continue receiving group health insurance pursuant to the “COBRA” law, the Company will, until the earlier of (x) the date that is nine (9) months following the Separation Date, and (y) the date on which you obtain alternative coverage (as applicable, the “COBRA Contribution Period”), continue to pay the share of the premiums for such coverage to the same extent it was paying such premiums on your behalf immediately prior to the Separation Date. The remaining balance of any premium costs during the COBRA Contribution Period, and all premium costs thereafter, shall be paid by you on a monthly basis for as long as, and to the extent that, you remain eligible for COBRA continuation. You agree that, should you obtain alternative health insurance coverage prior to the date that is nine (9) months following the Separation Date, you will so inform the Company in writing within five (5) business days of obtaining such coverage.

    

You acknowledge and agree that you will not be eligible for, nor shall you have a right to receive, any payments or benefits from the Company following the Separation Date other than as set forth in this paragraph 1.

2.Release of Claims – In consideration of the severance benefits, which you acknowledge you would not otherwise be entitled to receive, you hereby fully, forever, irrevocably and unconditionally release, remise and discharge the Company, its past and present affiliates, subsidiaries, parent companies, predecessors, and successors, and all of their respective past and present officers, directors, stockholders, partners, members, employees, agents, representatives, plan administrators, attorneys, insurers and fiduciaries (each in their individual and corporate capacities) (collectively, the “Released Parties”) from any and all claims, charges, complaints, demands, actions, causes of action, suits, rights, debts, sums of money, costs, accounts, reckonings, covenants, contracts, agreements, promises, doings, omissions, damages, executions, obligations, liabilities, and expenses (including attorneys’ fees and costs), of every kind and nature that you ever had or now have against any or all of the Released Parties, whether known or unknown, including, but not limited to, any and all claims arising out of or relating to your employment with and/or separation from the Company, including, but not limited to, all claims under Title VII of the Civil Rights Act of 1964, 42 U.S.C. § 2000e et seq., the Americans With Disabilities Act of 1990, 42 U.S.C. § 12101 et seq., the Age Discrimination in Employment Act, 29 U.S.C. § 621 et seq., the Genetic Information Nondiscrimination Act of 2008, 42 U.S.C. § 2000ff et seq., the Family and Medical Leave Act, 29 U.S.C. § 2601 et seq., the Worker Adjustment and Retraining Notification Act (“WARN”), 29 U.S.C. § 2101 et seq., the Rehabilitation Act of 1973, 29 U.S.C. § 701 et seq., Executive Order 11246, Executive Order 11141, the Fair Credit Reporting Act, 15 U.S.C. § 1681 et seq., and the Employee Retirement Income Security Act of 1974 (“ERISA”), 29 U.S.C. § 1001 et seq., all as amended; all claims arising out of the Massachusetts Fair Employment Practices Act, Mass. Gen. Laws ch. 151B, § 1 et seq., the Massachusetts Civil Rights Act, Mass. Gen. Laws ch. 12, §§ 11H and 11I, the Massachusetts Equal Rights Act, Mass. Gen. Laws. Ch. 93, § 102, Mass. Gen. Laws ch. 214, § 1C (Massachusetts right to be free from sexual harassment law), the Massachusetts Labor and Industries Act, Mass. Gen. Laws ch. 149, § 1 et seq., Mass. Gen. Laws ch. 214, § 1B (Massachusetts right of privacy law), the Massachusetts Parental Leave Act, Mass. Gen. Laws ch.

149, § 105D, the Massachusetts Paid Family and Medical Leave Act, Mass. Gen. Laws ch. 175m, § 1, et seq., the Massachusetts Earned Sick Time Law, Mass. Gen. Laws ch. 149, § 148c, and the Massachusetts Small Necessities Leave Act, Mass. Gen. Laws ch. 149, § 52D, all as amended; all rights and claims under the Massachusetts Wage Act, Mass. Gen. Laws ch. 149, § 148 et seq., as amended (Massachusetts law regarding payment of wages and overtime), including any rights or claims thereunder to unpaid wages, including overtime, bonuses, commissions, and accrued, unused vacation time; all common law claims including, but not limited to, actions in defamation, intentional infliction of emotional distress, misrepresentation, fraud, wrongful discharge, and breach of contract (including, without limitation, any claims arising out of or related to the November 5, 2020 employment offer letter between you and the Company); all claims to any non-vested ownership interest in the Company or any of its affiliates, contractual or otherwise; all state and federal whistleblower claims to the maximum extent permitted by law; and any claim or damage arising out of your employment with and/or separation from the Company (including a claim for retaliation) under any common law theory or any federal, state or local statute or ordinance not expressly referenced above; provided, however, that this release of claims does not prevent you from filing a charge with, cooperating with, or participating in any investigation or proceeding before, the Equal Employment Opportunity Commission or a state fair employment practices agency (except that you acknowledge that you may not recover any monetary benefits in connection with any such charge, investigation, or proceeding, and you further waive any rights or claims to any payment, benefit, attorneys’ fees or other remedial relief in connection with any such charge, investigation or proceeding).

3. Continuing Obligations – You acknowledge and reaffirm your confidentiality and non-disclosure obligations discussed above in this letter agreement, as well as all of the ongoing obligations set forth in the Nondisclosure Agreement, which survive your separation from employment with the Company. In addition, as an express condition of your receipt of the severance benefits, you agree that, for a period of twelve (12) months following the Separation Date, you shall not, on your own behalf, or as an owner, manager, stockholder, consultant, director, officer, or employee of any business entity (except as a holder of not more than one (1%) percent of the stock of a publicly held company), in any geographic areas in which you provided services or had a material presence or influence at any time during your last two (2) years of employment (which, given your responsibilities as the Company’s Chief Medical Officer, includes anywhere that the Company does business), participate, directly or indirectly, in any capacity involving any of the services that you provided to the Company at any time during the last two (2) years of your employment, in any business that is a Competitive Business. For purposes hereof, “Competitive Business” shall mean any biopharmaceutical business that is engaged in the research, development and/or commercialization of antibody drug conjugates for oncology or immunotherapy. Notwithstanding the foregoing, you shall not be precluded from becoming an employee of, or from otherwise providing services to, a separate division or operating unit of a multi-divisional business or enterprise (a “Division”) if: (i) the Division by which you are employed, or to which you provide services, is not a Competitive Business, (ii) you do not provide services, directly or indirectly, to any other division or operating unit of such multi-divisional business or enterprise which is a Competitive Business (individually, a ”Competitive Division” and collectively, the “Competitive Divisions”), and (iii) the Competitive Divisions, in the aggregate, accounted for less than one-third of the multi-divisional business’s or enterprise’s consolidated revenues for the fiscal year, and each subsequent quarterly period, prior to your commencement of employment with the Division. If any restriction set forth in the foregoing sentence is found by any court of competent jurisdiction to be unenforceable because it extends for too long a period of time or over too great a range of activities or in too broad a geographic area, it shall be interpreted to extend only over the maximum period of time, range of activities or geographic area as to which it may be enforceable. If you violate the non-competition provisions set forth in this paragraph, you shall continue to be bound by the restrictions set forth in such paragraph until a period of one year has expired without any violation of such provisions.

4.Disclosures –

a.  Non-Disparagement – Except as otherwise permitted by paragraph 4(c) below and applicable law, you agree not to, in public or private, make any false, disparaging, derogatory or defamatory statements, online (including, without limitation, on any social media, networking, or employer review site) or otherwise, to any person or entity, including, but not limited to, any media outlet, industry group, financial institution or current or former employee, board member, consultant, client, or customer of the Company, regarding the Company or any of the other Released Parties, or regarding the business affairs, business prospects, or financial condition of the Company or any of the other Released Parties.

b.  Confidentiality – Except as otherwise permitted by paragraph 4(c) below and applicable law, you agree to maintain as confidential and not to disclose the terms and contents of this letter agreement, and the contents of the negotiations and discussions resulting in this letter agreement.

c.  Permitted Disclosures – Nothing in this letter agreement or elsewhere prohibits you from (a) communicating with government agencies about possible violations of federal, state, or local laws or otherwise providing information to government agencies, filing a complaint with government agencies, or participating in government agency investigations or proceedings, or (b) making disclosures or communications to engage in protected, concerted activity or to otherwise exercise rights under Section 7 of the National Labor Relations Act.  You are not required to notify the Company of any such communications; provided, however, that nothing herein authorizes the disclosure of information you obtained through a communication that was subject to the attorney-client privilege.  Further, notwithstanding your confidentiality and nondisclosure obligations, you are hereby advised as follows pursuant to the Defend Trade Secrets Act: “An individual shall not be held criminally or civilly liable under any Federal or State trade secret law for the disclosure of a trade secret that (A) is made (i) in confidence to a Federal, State, or local government official, either directly or indirectly, or to an attorney; and (ii) solely for the purpose of reporting or investigating a suspected violation of law; or (B) is made in a complaint or other document filed in a lawsuit or other proceeding, if such filing is made under seal.  An individual who files a lawsuit for retaliation by an employer for reporting a suspected violation of law may disclose the trade secret to the attorney of the individual and use the trade secret information in the court proceeding, if the individual (A) files any document containing the trade secret under seal; and (B) does not disclose the trade secret, except pursuant to court order.

5.Return of Company Property – You confirm that you have returned to the Company all keys, files, records (and copies thereof), equipment (including, but not limited to, computer hardware, software, printers, flash drives and other storage devices, wireless handheld devices, cellular phones, tablets, etc.), Company identification, and any other Company owned property in your possession or control, and that you have left intact all, and have otherwise not destroyed, deleted, or made inaccessible to the Company any, electronic Company documents, including, but not limited to, those that you developed or helped to develop during your employment, and that you have not (a) retained any copies in any form or media; (b) maintained access to any copies in any form, media, or location; (c) stored any copies in any physical or electronic locations that are not readily accessible or known to the Company or that remain accessible to you; or (d) sent, given, or made accessible any copies to any persons or entities that the Company has not authorized to receive such electronic or hard copies. You further confirm that you have cancelled all accounts for your benefit, if any, in the Company’s name, including but not limited to, credit cards, telephone charge cards, cellular phone accounts, and computer accounts.

6.Business Expenses and Final Compensation – You acknowledge that you have been reimbursed by the Company for all business expenses incurred in conjunction with the performance of your employment and that no other reimbursements are owed to you. You further acknowledge that you have received payment in full for all services rendered in conjunction with your employment by the Company, including payment for all wages, bonuses, commissions, and accrued, unused vacation time, and that no other compensation is owed to you except as explicitly provided in this letter agreement.

7.Cooperation – You agree that, to the extent permitted by law, and in addition to your cooperation obligations pursuant to the Nondisclosure Agreement, you shall cooperate fully with the Company in: (i) any internal investigation; (ii) any investigation, defense or prosecution of any claims or actions which already have been brought, are currently pending, or which may be brought in the future against the Company by a third party or by or on behalf of the Company against any third party, whether before a state or federal court, any state or federal government agency, or a mediator or arbitrator; and/or (iii) any other administrative, regulatory, or judicial inquiry, investigation, proceeding or arbitration.  Your full cooperation hereunder shall include, but not be limited to, making yourself available to the Company upon reasonable notice for interviews and factual investigations; appearing at the Company’s request to give testimony without requiring service of a subpoena or other legal process; volunteering to the Company pertinent information; and turning over all relevant documents which are in or may come into your possession.  The term “cooperation” does not mean that you must provide information that is favorable to the Company; it means only that you will provide truthful information within your knowledge and possession upon request of the Company.  The Company will reimburse you for all reasonable and documented out-of-pocket expenses that you incur at the Company’s request to comply with this paragraph. You further agree that, to the extent permitted by law, you will notify the Company promptly in the event that you are served with a subpoena (other than a subpoena issued by a government agency), or in the event that you are asked to provide a third party (other than a government agency) with information concerning any actual or potential complaint or claim against the Company.

8.Amendment and Waiver – This letter agreement shall be binding upon the parties and may not be modified in any manner, except by an instrument in writing of concurrent or subsequent date signed by duly authorized representatives of the parties hereto. This letter agreement is binding upon and shall inure to the benefit of the parties and their respective agents, assigns, heirs, executors, successors and administrators. No delay or omission by the Company in exercising any right under this letter agreement shall operate as a waiver of that or any other right. A waiver or consent given by the Company on any one occasion shall be effective only in that instance and shall not be construed as a bar to or waiver of any right on any other occasion.

9.Validity – Should any provision of this letter agreement be declared or be determined by any court of competent jurisdiction to be illegal or invalid, the validity of the remaining parts, terms or provisions shall not be affected thereby and said illegal or invalid part, term or provision shall be deemed not to be a part of this letter agreement.

10.Nature of Agreement – You understand and agree that this letter agreement is a severance agreement and does not constitute an admission of liability or wrongdoing on the part of the Company or any of the other Released Parties.

11.Acknowledgments – You acknowledge that you have been given at least twenty-one (21) days to consider this letter agreement, and that the Company is hereby advising you to consult with an attorney of your own choosing prior to signing this letter agreement. You understand that you may revoke this letter agreement for a period of seven (7) business days after you sign this letter agreement by notifying me in writing, and the letter agreement shall not be effective or enforceable until the expiration of this seven (7) day business revocation period. You understand and agree that by entering into this letter agreement, you are waiving any and all rights or claims you might have under the Age Discrimination in Employment Act, as amended by the Older Workers Benefit Protection Act, and that you have received consideration beyond that to which you were previously entitled.

12.Voluntary Assent – You affirm that no other promises or agreements of any kind have been made to or with you by any person or entity whatsoever to cause you to sign this letter agreement, and that you fully understand the meaning and intent of this letter agreement. You further state and represent that you have carefully read this letter agreement, understand the contents herein, freely and voluntarily assent to all of the terms and conditions hereof, and sign your name of your own free act.

13.Applicable Law; Forum – This letter agreement shall be interpreted and construed by the laws of the Commonwealth of Massachusetts, without regard to conflict of laws provisions. You hereby irrevocably submit to and acknowledge and recognize the jurisdiction of the courts of the Commonwealth of Massachusetts, or if appropriate, a federal court located in the Commonwealth of Massachusetts (which courts, for purposes of this letter agreement, are the only courts of competent jurisdiction), over any suit, action or other proceeding arising out of, under or in connection with this letter agreement or the subject matter hereof. You further hereby irrevocably waive any right to a trial by jury in any action, suit or other legal proceeding arising under or relating to any provision of this letter agreement. Further, you acknowledge that the restrictions referenced and contained in paragraph 3 of this Agreement are necessary for the protection of the business and goodwill of the Company and are considered by you to be reasonable for such purpose. You agree that any breach or threatened breach of such provisions is likely to cause the Company substantial and irrevocable damage which is difficult to measure. Therefore, in the event of any such breach or threatened breach, you agree that the Company, in addition to such other remedies which may be available, shall have the right to obtain an injunction from a court restraining such a breach or threatened breach without posting a bond and the right to specific performance of such provisions and you hereby waive the adequacy of a remedy at law as a defense to such relief.

14.Entire Agreement – This letter agreement contains and constitutes the entire understanding and agreement between the parties hereto with respect to your severance benefits and the settlement of claims against the Company and the other Released Parties and cancels all previous oral and written negotiations, agreements, and commitments in connection therewith.

15.Tax Acknowledgement – In connection with the severance benefits provided to you pursuant to this letter agreement, the Company shall withhold and remit to the tax authorities the amounts required under applicable law, and you shall be responsible for all applicable taxes with respect to such severance benefits under applicable law. You acknowledge that you are not relying upon the advice or representation of the Company with respect to the tax treatment of any of the severance benefits set forth in paragraph 1 of this letter agreement.

If you have any questions about the matters covered in this letter agreement, please call me.

Very truly yours,

By: /s/ Alejandra Carvajal________________________

    Alejandra Carvajal

    SVP, Chief Legal Officer & Secretary

I hereby agree to the terms and conditions set forth above. I have been given at least twenty-one (21) days to consider this letter agreement, and I have chosen to execute this on the date below. I intend that this letter agreement will become a binding agreement between me and the Company if I do not revoke my acceptance in seven (7) business days.

/s/Arvin Yang____________________        9/29/2023_____________________

Arvin Yang                    Date

To be returned in a timely manner as set forth on the first page of this letter agreement.