X0306 4 2020-01-29 0 0001290149 Sierra Oncology, Inc. SRRA 0001794070 Ashiya Mona C/O SIERRA ONCOLOGY, INC. 2150 - 885 WEST GEORGIA STREET VANCOUVER A1 V6C 3E8 BRITISH COLUMBIA, CANADA 1 0 1 0 Common Stock 2020-01-29 4 C 0 1477320 0.00 A 1477320 I See footnotes Series A Convertible Voting Preferred Stock 2020-01-29 4 C 0 19500 D Common Stock 1477320 0 I See footnotes On January 22, 2020, a 1-for-40 reverse split of the Issuer's Common Stock (the "Reverse Split") was effected. These securities reflect the Reverse Split. Each share of Series A Convertible Voting Preferred Stock (the "Series A Preferred Stock") converted into 75.76 shares of the Issuer's Common Stock, as adjusted for the Reverse Split, automatically upon the 5th trading date following the Issuer's announcement of receiving stockholder approval for the first reverse stock split of the Issuer following November 13, 2019. The Series A Preferred Stock has no expiration date. Consists of 1,136,400 shares of Common Stock held of record by OrbiMed Private Investments VII, LP ("OPI VII"), 170,460 shares of Common Stock held of record by OrbiMed Partners Master Fund Limited ("OPM") and 170,460 shares of Common Stock held of record by OrbiMed Genesis Master Fund, L.P. ("Genesis"), as adjusted for the Reverse Split. OrbiMed Capital GP VII LLC ("GP VII") is the general partner of OPI VII. OrbiMed Advisors is the managing member of GP VII. OrbiMed Global Healthcare GP LLC ("Healthcare GP") is the general partner of Genesis and OrbiMed Advisors is the managing member of Healthcare GP. OrbiMed Capital LLC ("OrbiMed Capital") is the investment manager of OPM and OrbiMed Capital is a relying advisor of OrbiMed Advisors. (Continued in footnote 4) GP VII and OrbiMed Advisors may be deemed to have voting and investment power with respect to the securities held by OPI VII and as a result may be deemed to have beneficial ownership of such securities; Healthcare GP and OrbiMed Advisors may be deemed to have voting power and investment power over the securities held by Genesis and as a result, may be deemed to have beneficial ownership over such securities; and OrbiMed Capital may be deemed to have voting power and investment power over the securities held by OPM and as a result, may be deemed to have beneficial ownership over such securities. Each of GP VII, Healthcare GP, OrbiMed Advisors, OrbiMed Capital and the Reporting Person disclaims beneficial ownership of the shares held by OPI VII, Genesis or OPM, as applicable, except to the extent of its or her pecuniary interest therein, if any. The Reporting Person is an employee of OrbiMed Advisors. Consists of 19,500 shares of Series A Preferred Stock which are convertible into an aggregate of 1,477,320 shares of Common Stock, as adjusted for the Reverse Split. Of the shares reported, 15,000 shares of Series A Preferred Stock are held of record by OPI VII, 2,250 shares of Series A Preferred Stock are held of record by Genesis, and 2,250 shares of Series A Preferred Stock are held of record by OPM. /s/ Sukhi Jagpal as attorney-in-fact for Mona Ashiya 2020-01-31