X0306 4 2022-07-01 1 0001290149 Sierra Oncology, Inc. SRRA 0001819688 Turner William D. C/O SIERRA ONCOLOGY, INC. 1820 GATEWAY DR., SUITE 110 SAN MATEO CA 94404 0 1 0 0 Chief Reg & Tech Ops Officer Stock Option (right to buy) 12.05 2022-07-01 4 D 0 75000 0.00 D 2030-08-04 Common Stock 75000 0 D Stock Option (right to buy) 12.15 2022-07-01 4 D 0 49000 0.00 D 2030-08-12 Common Stock 49000 0 D Stock Option (right to buy) 16.73 2022-07-01 4 D 0 12300 0.00 D 2031-03-15 Common Stock 12300 0 D Stock Option (right to buy) 31.54 2022-07-01 4 D 0 35000 0.00 D 2032-03-14 Common Stock 35000 0 D The option vested as to 25% of the total shares on August 4, 2021, and then the remaining shares vest in equal monthly installments over the following 36 months, with 100% of the total shares vested on August 4, 2024, subject to the Reporting Person's provision of service to the Issuer on each vesting date. Pursuant to the terms of the merger agreement between issuer, GlaxoSmithKline plc ("GSK") and a subsidiary of GSK, this option was cancelled on the effective date of the merger in exchange for a cash payment equal to, on a per share basis, the offer price of $55.00 less the exercise price. On August 12, 2020, the reporting person was granted an option to purchase 49,000 shares of common stock. The option vests based on the satisfaction by Issuer of certain performance criteria. The option vested as to 25% of the total shares subject to the option on March 15, 2022, and then 2.0833% of the shares subject to the option vest monthly thereafter, with 100% of the total shares subject to the option vested on March 15, 2025, subject to Reporting Person's provision of service to the Issuer on each vesting date. The option vests as to 25% of the total shares subject to the option on March 14, 2023, and then 2.0833% of the shares subject to the option vest monthly thereafter, with 100% of the total shares subject to the option vested on March 14, 2026, subject to Reporting Person's provision of service to the Issuer on each vesting date. /s/ Mary Christina Thomson, Attorney-In-Fact for William D. Turner 2022-07-01