X0306 4 2019-08-28 0 0001442836 Mersana Therapeutics, Inc. MRSN 0001544328 New Enterprise Associates 14, L.P. 1954 GREENSPRING DRIVE SUITE 600 TIMONIUM MD 21093 0 0 1 0 0001559807 Sonsini Peter W. 2855 SAND HILL ROAD MENLO PARK CA 94025 0 0 1 0 0001277631 BASKETT FOREST 1954 GREENSPRING DRIVE SUITE 600 TIMONIUM MD 21093 0 0 1 0 0001559827 Florence Anthony A. Jr. 5425 WISCONSIN AVENUE, SUITE 800 CHEVY CHASE MD 20815 0 0 1 0 0001235112 KERINS PATRICK J 1954 GREENSPRING DRIVE SUITE 600 TIMONIUM MD 21093 0 0 1 0 0001551532 NEA 14 GP, LTD 1954 GREENSPRING DRIVE SUITE 600 TIMONIUM MD 21093 0 0 1 0 0001551531 NEA Partners 14, L.P. 1954 GREENSPRING DRIVE SUITE 600 TIMONIUM MD 21093 0 0 1 0 0001237289 SANDELL SCOTT D 1954 GREENSPRING DRIVE SUITE 600 TIMONIUM MD 21093 0 0 1 0 Common Stock 2019-08-28 4 X 0 70593 0.05 A 11960731 D Common Stock 2019-08-28 4 S 0 1211 2.91 D 11959520 D Stock Purchase Warrant (right to buy) 0.05 2019-08-28 4 X 0 70593 0.00 D 2013-09-27 2023-09-27 Common Stock 70593 0 D The securities are directly held by New Enterprise Associates 14, L.P. ("NEA 14") and are indirectly held by NEA Partners 14, L.P. ("NEA Partners 14"), the sole general partner of NEA 14, NEA 14 GP, LTD ("NEA 14 LTD"), the sole general partner of NEA Partners 14 and each of the individual directors of NEA 14 LTD (NEA Partners 14, NEA 14 LTD and the individual directors of NEA 14 LTD (collectively, the "Directors") together, the "Indirect Reporting Persons"). The Directors of NEA 14 LTD are Forest Baskett, Anthony A. Florence, Jr., Patrick J. Kerins, Scott D. Sandell and Peter Sonsini. The Indirect Reporting Persons disclaim 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 securities in which the Indirect Reporting Persons have no pecuniary interest. On August 28, 2019, NEA 14 exercised a stock purchase warrant to purchase 70,593 shares of the Issuer's common stock for $0.05 per share. NEA 14 paid the exercise price on a cashless exercise basis resulting in the Issuer withholding 1,211 of the warrant shares to pay the exercise price and issuing NEA 14 the remaining 69,382 shares. /s/ Sasha Keough, Attorney-in-Fact 2020-04-13