—Topline data expected by February 2022—

—Prithviraj Bose, MD, to join Sierra Oncology Leadership to discuss importance of treating anemia in myelofibrosis patients—

Sierra Oncology, Inc. (NASDAQ: SRRA), a late-stage biopharmaceutical company on a mission to deliver targeted therapies that treat rare forms of cancer, today announced it will host an analyst and investor event on Thursday, December 16, 2021, at 12:00 pm ET. The event will feature a presentation by Prithviraj Bose, MD, Department of Leukemia, MD Anderson Cancer Center, on the importance of treating anemia in myelofibrosis patients. Dr. Bose will also review momelotinib data from the Phase 3 SIMPLIFY studies. Sierra management will discuss the MOMENTUM trial design as well as highlight registration and commercialization preparations currently underway. An open question & answer session with all presenters will conclude the event.

Analyst & Investor Event Webcast Information

Date and Time: Thursday, December 16, 2021, 12:00 pm ET

To register, please click here.

The presentation will be webcast live, and an archive of the presentation will be accessible for approximately 30 days after the event through the Sierra Oncology website: www.SierraOncology.com.

About Momelotinib

Momelotinib is a selective and orally bioavailable JAK1, JAK2 and ACVR1/ALK2 inhibitor currently under investigation for the treatment of myelofibrosis. Myelofibrosis results from dysregulated JAK-STAT signaling and is characterized by constitutional symptoms, splenomegaly (enlarged spleen) and progressive anemia.

Sierra Oncology is currently awaiting topline results of the MOMENTUM clinical trial, a global, randomized, double-blind Phase 3 study evaluating momelotinib for the treatment of symptomatic and anemic myelofibrosis patients. Top-line data are anticipated by February 2022. Assuming positive data, the company plans to file a New Drug Application with the US Food & Drug Administration (FDA) in the second quarter of 2022. The FDA has granted Fast Track designation for momelotinib.

About Sierra Oncology

Sierra Oncology is a late-stage biopharmaceutical company on a quest to deliver targeted therapies that treat rare forms of cancer. We harness our deep scientific expertise to identify compounds that target the root cause of disease to advance targeted therapies with assets on the leading edge of cancer biology. Our team takes an evidence-based approach to understand the limitations of current treatments and explore new ways to change the cancer treatment paradigm. Together we are transforming promise into patient impact.

For more information, visit www.SierraOncology.com.

Cautionary Note on Forward-Looking Statements

This press release contains forward-looking statements within the meaning of the "safe harbor" provisions of the Private Securities Litigation Reform Act of 1995, including, but not limited to, statements regarding the expected timing for top-line data in the MOMENTUM clinical trial and the timing of filing a New Drug Application with the US Food & Drug Administration (FDA). All statements other than statements of historical fact are statements that could be deemed forward-looking statements. These statements are based on management's current expectations and beliefs and are subject to a number of risks, uncertainties and assumptions that could cause actual results to differ materially from those described in the forward-looking statements. Such forward-looking statements are subject to risks and uncertainties, including, among others, the risk that Sierra Oncology may not be able to successfully develop, obtain regulatory approval for and commercialize momelotinib or experience significant delays in doing so, Sierra Oncology may not be able to demonstrate acceptable safety and efficacy of momelotinib, the risk that disruptions and impacts of COVID-19 will be significant and lengthy, Sierra Oncology’s ability to continue as a going concern, Sierra Oncology's cash resources may be insufficient to fund its current operating plans and it may be unable to raise additional capital when needed, Sierra Oncology may be unable to acquire additional assets to build a pipeline of additional product candidates, Sierra Oncology's third-party manufacturers may cause its supply of materials to become limited or interrupted or fail to be of satisfactory quantity or quality, Sierra Oncology may be unable to obtain and enforce intellectual property protection for its technologies and momelotinib and the other factors described under the heading "Risk Factors" set forth in Sierra Oncology's filings with the Securities and Exchange Commission from time to time. Sierra Oncology undertakes no obligation to update the forward-looking statements contained herein or to reflect events or circumstances occurring after the date hereof, other than as may be required by applicable law.

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