Sierra Oncology Provides Update to Momelotinib Development Timeline and Closes on $34 Million in Additional Funding

Sierra Oncology, Inc. (NASDAQ: SRRA), a late-stage biopharmaceutical company on a mission to deliver targeted therapies that treat rare forms of cancer, today updated guidance on the development timeline for its lead product candidate, momelotinib. The company now expects topline data from the Phase 3 registration-enabling MOMENTUM study by February 2022, and assuming positive results, the company plans to file a New Drug Application with the U.S. Food & Drug Administration in Q2 2022.

Sierra also announced it has raised $34 million in gross proceeds thus far in Q3 2021 through the use of its at-the-market (ATM) offering. These funds are in addition to the $90.7 million in cash and cash equivalents on hand at the close of the second quarter of 2021, further bolstering the company’s cash balance as it prepares for momelotinib commercialization. The company also has the potential to obtain up to $33.3 million in cash from Series B warrants that must be exercised within 75 days of the announcement of MOMENTUM topline data.

Stephen Dilly, MBBS, PhD, President and Chief Executive Officer of Sierra Oncology noted, “The continued excellent execution of the MOMENTUM study and further acceleration of the timeline, combined with the additional funding secured over the last few weeks, puts us in a very strong position as we approach topline data.”

About Sierra Oncology

Sierra Oncology is a late-stage biopharmaceutical company on a mission 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. 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, the expected timing of the NDA filing for momelotinib and the potential to obtain addition cash from the exercise of Series B warrants. 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 and momelotinib in combination with AZD5153, 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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