Sec Form 4 Filing - SANDELL SCOTT D @ Mersana Therapeutics, Inc. - 2020-09-14

FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person SANDELL SCOTT D 2. Issuer Name and Ticker or Trading Symbol Mersana Therapeutics, Inc. [ MRSN] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director X __ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) 1954 GREENSPRING DRIVE, SUITE 600 3. Date of Earliest Transaction (MM/DD/YY) 09/14/2020 (Street) TIMONIUM, MD21093 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) __ X __ Form filed by One Reporting Person _____ Form filed by More than One Reporting Person (City) (State) (Zip)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned 1.Title of Security (Instr. 3) 2. Transaction Date (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price Common Stock 09/14/2020 J( 1 ) 2,000,000 D $ 0 5,959,520 I See Note 2 ( 2 ) Common Stock 09/14/2020 J( 3 ) 20,000 A $ 0 20,000 I See Note 4 ( 4 ) Common Stock 09/14/2020 J( 5 ) 20,000 D $ 0 0 I See Note 4 ( 4 ) Common Stock 09/14/2020 J( 6 ) 10,000 A $ 0 10,000 I See Note 7 ( 7 ) Common Stock 09/14/2020 J( 8 ) 10,000 D $ 0 0 I See Note 7 ( 7 ) Common Stock 09/14/2020 J( 9 ) 39 A $ 0 39 I See Note 10 ( 10 ) Common Stock 09/14/2020 J( 11 ) 5,830 A $ 0 5,869 I See Note 10 ( 10 ) Common Stock 09/14/2020 J( 12 ) 4,391 A $ 0 10,260 I See Note 10 ( 10 ) Common Stock 09/14/2020 J( 13 ) 138 A $ 0 138 I See Note 14 ( 14 ) Common Stock 09/14/2020 J( 15 ) 138 A $ 0 138 I See Note 16 ( 16 ) Common Stock 09/14/2020 J( 17 ) 486 A $ 0 486 I See Note 18 ( 18 ) Common Stock 09/14/2020 J( 19 ) 343 A $ 0 829 I See Note 18 ( 18 )

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned ( e.g. , puts, calls, warrants, options, convertible securities) 1. Title of Derivative Security (Instr. 3) 2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 4. Transaction Code (Instr. 8) 5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5) 6. Date Exercisable and Expiration Date (MM/DD/YY) 7. Title and Amount of Underlying Securities (Instr. 3 and 4) 8. Price of Derivative Security (Instr. 5) 9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4) 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4) 11. Nature of Indirect Beneficial Ownership (Instr. 4) Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other SANDELL SCOTT D 1954 GREENSPRING DRIVE SUITE 600 TIMONIUM, MD21093 X Signatures /s/ Sasha Keough, attorney-in-fact 09/16/2020 Signature of Reporting Person Date

Explanation of Responses:

( 1 )New Enterprise Associates 14, L.P. ("NEA 14") made a pro rata distribution for no consideration of an aggregate of 2,000,000 shares of Common Stock of the Issuer to its general partner and its limited partners on September 14, 2020. ( 2 )The Reporting Person is a director of NEA 14 GP, LTD ("NEA 14 LTD"), which is the sole general partner of NEA Partners 14, L.P. ("NEA Partners 14"). NEA Partners 14 is the sole general partner of NEA 14, which is the direct beneficial owner of the securities. The Reporting Person disclaims beneficial ownership, within the meaning of Section 16 of the Securities Exchange Act of 1934, as amended, or otherwise of such portion of the NEA 14 shares in which the Reporting Person has no pecuniary interest. ( 3 )NEA Partners 14 received 20,000 shares of Common Stock of the Issuer in the distribution by NEA 14 on September 14, 2020. ( 4 )The Reporting Person is a director of NEA 14 LTD, which is the sole general partner of NEA Partners 14, the direct beneficial owner of the securities. The Reporting Person disclaims beneficial ownership, within the meaning of Section 16 of the Securities Exchange Act of 1934, as amended, or otherwise of such portion of the NEA Partners 14 shares in which the Reporting Person has no pecuniary interest. ( 5 )NEA Partners 14 made a pro rata distribution for no consideration of an aggregate of 20,000 shares of Common Stock of the Issuer to its limited partners on September 14, 2020. ( 6 )NEA 14 Manager Fund, L.P. ("NEA 14 Manager Fund") received 10,000 shares of Common Stock of the Issuer in the distribution by NEA 14 on September 14, 2020. ( 7 )The Reporting Person is a director of NEA 14 LTD, which is the sole general partner of NEA 14 Manager Fund. The Reporting Person disclaims beneficial ownership within the meaning of Section 16 of the Securities Exchange Act of 1934, as amended, or otherwise of such portion of the securities of the Issuer held by NEA 14 Manager Fund in which the Reporting Person has no pecuniary interest. ( 8 )NEA 14 Manager Fund made a pro rata distribution for no consideration of an aggregate of 10,000 shares of Common Stock of the Issuer to its limited partners on September 14, 2020. ( 9 )New Enterprise Associates, LLC ("NEA LLC") received 39 shares of Common Stock of the Issuer in the distribution by NEA 14 on September 14, 2020. ( 10 )The Reporting Person is a member of the Board of Directors of NEA LLC, which is the direct beneficial owner of the shares. The Reporting Person disclaims beneficial ownership within the meaning of Section 16 of the Securities Exchange Act of 1934, as amended, or otherwise of such portion of the shares of the Issuer held by NEA LLC in which the Reporting Person has no pecuniary interest. ( 11 )NEA LLC received 5,830 shares of Common Stock of the Issuer in the distribution by NEA Partners 14 on September 14, 2020. ( 12 )NEA LLC received 4,391 shares of Common Stock of the Issuer in the distribution by NEA 14 Manager Fund on September 14, 2020. ( 13 )Genevieve P. Hardigg, as trustee of the Jennifer Ayer Sandell Rising River Trust, dated December 20, 2012 (the "Jennifer Sandell Rising River Trust"), received 138 shares of Common Stock of the Issuer in the distribution by NEA Partners 14 on September 14, 2020. ( 14 )The securities are held directly by the Jennifer Sandell Rising R iver Trust. The Reporting Person disclaims beneficial ownership within the meaning of Section 16 of the 1934 Act, as amended, of such portion of the shares of Common Stock of the Issuer held by the Jennifer Sandell Rising River Trust in which the Reporting Person has no pecuniary interest. ( 15 )Genevieve P. Hardigg, as trustee of the Scott Sandell Rising River Trust, dated December 20, 2012 (the "Scott Sandell Rising River Trust"), received 138 shares of Common Stock of the Issuer in the distribution by NEA Partners 14 on September 14, 2020. ( 16 )The securities are held directly by the Scott Sandell Rising River Trust. The Reporting Person disclaims beneficial ownership within the meaning of Section 16 of the 1934 Act, as amended, of such portion of the shares of Common Stock of the Issuer held by the Scott Sandell Rising River Trust in which the Reporting Person has no pecuniary interest. ( 17 )Scott D. Sandell, as trustee of the Blue Mountain Trust, dated April 29, 2019 (the "Blue Mountain Trust") received 486 shares of Common Stock of the Issuer in the distribution by NEA Partners 14 on September 14, 2020. ( 18 )The securities are held directly by the Blue Mountain Trust. The Reporting Person disclaims beneficial ownership within the meaning of Section 16 of the 1934 Act, as amended, of such portion of the shares of Common Stock of the Issuer held by the Blue Mountain Trust in which the Reporting Person has no pecuniary interest. ( 19 )The Blue Mountain Trust received 343 shares of Common Stock of the Issuer in the distribution by NEA 14 Manager Fund on September 14, 2020.

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* If the form is filed by more than one reporting person, see Instruction 4(b)(v).

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