X0306 4 2017-07-03 0 0001442836 Mersana Therapeutics, Inc. MRSN 0001237289 SANDELL SCOTT D 1954 GREENSPRING DRIVE SUITE 600 TIMONIUM MD 21093 0 0 1 0 Common Stock 2017-07-03 4 C 0 7140138 A 7140138 I See Note 3 Common Stock 2017-07-03 4 P 0 1000000 15.00 A 8140138 I See Note 3 Series A-1 Preferred Stock 2017-07-03 4 C 0 11931173 0.00 D Common Stock 2647241 0 I See Note 3 Series B-1 Preferred Stock 2017-07-03 4 C 0 18001419 0.00 D Common Stock 4000314 0 I See Note 3 Series C-1 Preferred Stock 2017-07-03 4 C 0 2216626 0.00 D Common Stock 492583 0 I See Note 3 The total represents shares received upon conversion of Series A-1, Series B-1 and Series C-1 Convertible Preferred Stock. Upon closing of the Issuer's initial public offering, each share of Series A-1, Series B-1 and Series C-1 Convertible Preferred Stock automatically converted into .22222 shares of Common Stock without payment of further consideration. There was no expiration date for the Series A-1, Series B-1 or Series C-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. /s/ Sasha Keough, attorney-in-fact 2017-07-06