X0306 4 2019-11-29 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 Stock Option (Right to Buy) 0.3467 2019-11-29 4 A 0 60000 0.00 A 2029-11-29 Common Stock 60000 60000 D Stock options were granted on November 29, 2019 in connection with the Reporting Person's appointment to the Issuer's Board of Directors on November 22, 2019. The option vests as to 8.333% of the total shares monthly, beginning on December 29, 2019, with 100% of the total shares vested and exercisable on November 29, 2020, subject to the Reporting Person's provision of service to the Issuer on each vesting date. The Reporting Person is an employee of OrbiMed Advisors LLC ("OrbiMed Advisors") and is obligated to transfer any shares issued pursuant to any equity grants made to her by the Issuer, or the economic benefits thereof, to OrbiMed Advisors and certain of its related entities. As such, the Reporting Person disclaims beneficial ownership of the securities reported herein for purposes of Rule 16a-1(a) under the Securities Exchange Act of 1934, as amended (the "Exchange Act"), except to the extent of her pecuniary interest therein, if any. This report shall not be deemed an admission that the Reporting Person is a beneficial owner for the purpose of Section 16 of the Exchange Act, or for any other purpose. /s/ Sukhi Jagpal as attorney-in-fact for Mona Ashiya 2019-12-03