Momelotinib Review Article Published in Journal of Hematology & Oncology Highlights Importance of Anemia Benefit for Myelofibrosis Patients

Sierra Oncology, Inc. (NASDAQ: SRRA), a late-stage biopharmaceutical company dedicated to delivering targeted therapies for rare cancers, today announced the publication of a review article in the Journal of Hematology & Oncology that outlines the potential ability of momelotinib—a novel JAK1, JAK2 and ACVR1 / ALK2 inhibitor—to address the critical unmet need of anemia for myelofibrosis patients. Srdan Verstovsek, MD, PhD, Chief, Section for Myeloproliferative Neoplasms, Department of Leukemia, Division of Cancer Medicine at The University of Texas MD Anderson Cancer Center and co-Primary Investigator of the pivotal Phase 3 MOMENTUM study, co-authored the article.

“We are delighted to see this publication that reinforces momelotinib as the potential JAK inhibitor of choice for myelofibrosis patients with anemia—a need that is currently not met with approved JAK inhibitors. We look forward to sharing MOMENTUM topline data the end of January 2022,” said Stephen Dilly, MBBS, PhD, President and Chief Executive Officer at Sierra Oncology.

Myelofibrosis is characterized by constitutional symptoms, including fatigue, body and bone pain and excessive sweating or fever; splenomegaly (enlarged spleen); and anemia. Moderate-to-severe anemia afflicts 40-60% of myelofibrosis patients at the time of diagnosis and increases to up-to 90% of patients over time.¹ Anemia is a predictor of reduced overall survival and is associated with a nearly four-fold increase in the risk of death compared to no anemia, with a median survival of just 2.1 years.^2,3

While JAK inhibitors are the mainstay of treatment options for myelofibrosis patients, currently approved JAK inhibitors cause myelosuppression, worsening anemia and creating poorer outcomes for patients. This profile creates a critical gap in the myelofibrosis treatment landscape and the need for a therapy that can address all three hallmarks of disease.

The authors noted in the publication, “Momelotinib’s mechanism of action uniquely positions it amongst approved and late-stage JAK inhibitors to be able to significantly alleviate the inflammation-driven, iron-restricted anemia of MF [ myelofibrosis] and eliminate/prevent RBC [red blood cell] transfusion dependence in a significant portion of MF patients besides treating the other two cardinal features of MF (splenomegaly and constitutional symptoms).”

To read the full article, titled “Momelotinib: an emerging treatment for myelofibrosis patients with anemia,” please visit the Journal of Hematology & Oncology website.

About Momelotinib

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

Momelotinib is currently under investigation in the MOMENTUM clinical trial, a global, randomized, double-blind Phase 3 study for symptomatic and anemic myelofibrosis patients. The study enrolled 195 patients based on a planned 180 patients across 21 countries. Topline data are anticipated by the end of January 2022, and assuming positive results, the company intends to file an NDA with the FDA in the second quarter of 2022.

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 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 potential for momelotinib to serve as a critical unmet need for myelofibrosis patients. 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.

¹ Constitutional or non-specific symptoms. Sierra Qualitative Market Research.

² Gupta V, Harrison C, Hexner EO, Al-Ali HK, Foltz L, Montgomery M, Sun W, Gopalakrishna P, Kantarjian H, Verstovsek S. The impact of anemia on overall survival in patients with myelofibrosis treated with ruxolitinib in the COMFORT studies. Haematologica. 2016 Dec;101(12):e482. Tefferi A, Lasho TL, Jimma T, Finke CM, Gangat N, Vaidya R, Begna KH, Al-Kali A, Ketterling RP, Hanson CA, Pardanani A. One thousand patients with primary myelofibrosis: the mayo clinic experience. InMayo Clinic Proceedings 2012 Jan 1 (Vol. 87, No. 1, pp. 25-33). Elsevier.

³ Nicolosi M, Mudireddy M, Lasho TL, et al. Sex and degree of severity influence the prognostic impact of anemia in primary myelofibrosis: analysis based on 1109 consecutive patients. Leukemia. 2018 May;32(5):1254-1258.

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