X0206 3 2017-06-27 0 0001442836 Mersana Therapeutics, Inc. MRSN 0001237289 SANDELL SCOTT D 1954 GREENSPRING DRIVE SUITE 600 TIMONIUM MD 21093 0 0 1 0 Series A-1 Preferred Stock Common Stock 2647241 I See Note 2 Series B-1 Preferred Stock Common Stock 4000314 I See Note 2 Series C-1 Preferred Stock Common Stock 492583 I See Note 2 Stock Purchase Warrant (right to buy) 0.05 2013-09-27 2023-09-27 Common Stock 70593 I See Note 2 The Series A-1 Convertible Preferred Stock is convertible into shares of common stock at any time at the holder's election and automatically upon the consummation of a public offering of the registrant. There is no expiration date for the Series A-1 Convertible Preferred Stock. The Reporting Person is a director of NEA 14 GP, 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 New Enterprise Associates 14, L.P. ("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. The Series B-1 Convertible Preferred Stock is convertible into shares of common stock at any time at the holder's election and automatically upon the consummation of a public offering of the registrant. There is no expiration date for the Series B-1 Convertible Preferred Stock. The Series C-1 Convertible Preferred Stock is convertible into shares of common stock at any time at the holder's election and automatically upon the consummation of a public offering of the registrant. There is no expiration date for the Series C-1 Convertible Preferred Stock. /s/ Sasha Keough, attorney-in-fact 2017-06-27