– European Commission decision anticipated by the end of September 2020 –

SUZHOU, China Aug. 5^th, 2020 – The partner of CStone Pharmaceuticals (“CStone”, HKEX: 2616),Blueprint Medicines , announced on July 24^th that the European Medicines Agency's Committee for Medicinal Products for Human Use (CHMP) has adopted a positive opinion, recommending conditional marketing authorization for avapritinib as a monotherapy for the treatment of adult patients with unresectable or metastatic gastrointestinal stromal tumors (GIST) harboring the PDGFRA D842V mutation.

The CHMP opinion will now be reviewed by the European Commission, which has the authority to grant marketing authorization for medicinal products in the European Union (EU). A final decision on the marketing authorization application for avapritinib is anticipated by the end of September 2020. If approved by the European Commission, avapritinib would be the first treatment in the EU indicated for patients with PDGFRA D842V mutant GIST and would be commercialized under the brand name AYVAKYT^®.

The CHMP based its opinion on efficacy results from the Phase 1 NAVIGATOR trial as well as combined safety results from the NAVIGATOR and Phase 3 VOYAGER trials. Treatment with avapritinib showed deep and durable clinical responses and was well-tolerated in patients with PDGFRA D842V mutant GIST. Data in this patient population were published in The Lancet Oncology on June 29, 2020.

About Avapritinib

Avapritinib is a kinase inhibitor approved by the U.S. Food and Drug Administration (FDA) under the brand name AYVAKIT^™ for the treatment of adults with unresectable or metastatic GIST harboring a PDGFRA exon 18 mutation, including PDGFRA D842V mutations. The U.S. FDA granted breakthrough therapy designation to avapritinib for the treatment of unresectable or metastatic GIST harboring the PDGFRA D842V mutation.

Avapritinib is not approved for the treatment of any other indication in the U.S. by the FDA or for any indication in any other jurisdiction by any other health authority.

The European Commission granted orphan medicinal product designation for avapritinib for the treatment of GIST and macrocytosis. Blueprint Medicines is developing avapritinib globally for patients with advanced and indolent systemic mastocytosis (SM). The U.S. FDA granted breakthrough therapy designation to avapritinib for the treatment of advanced SM, including the subtypes of aggressive SM, SM with an associated hematologic neoplasm and mast cell leukemia.

Blueprint Medicines has an exclusive collaboration and license agreement with CStone Pharmaceuticals for the development and commercialization of avapritinib and certain other drug candidates in Mainland China, Hong Kong, Macau and Taiwan. Blueprint Medicines retains development and commercial rights for avapritinib in the rest of the world.

About GIST

GIST is a sarcoma, or tumor of bone or connective tissue, of the GI tract. Tumors arise from cells in the wall of the GI tract and occur most often in the stomach or small intestine. Most patients are diagnosed between the ages of 50 to 80, and diagnosis is typically triggered by GI bleeding, incidental findings during surgery or imaging and, in rare cases, tumor rupture or GI obstruction.

About 5 to 6 percent of primary GIST cases are caused by a PDGFRA D842V mutation, the most common PDGFRA exon 18 mutation. Prior to the FDA approval of AYVAKIT, there were no highly effective treatments for PDGFRA D842V mutant GIST in the U.S. Published data have shown poor outcomes in patients with PDGFRA D842V mutant GIST treated with imatinib and other approved therapies, including a median overall survival of 15 months, a median progression-free survival of 3 months and an overall response rate of 0 percent.¹

About CStone

CStone Pharmaceuticals (HKEX: 2616) is a biopharmaceutical company focused on developing and commercializing innovative immuno-oncology and precision medicines to address the unmet medical needs of cancer patients in China and worldwide. Established in 2015, CStone has assembled a world-class management team with extensive experience in innovative drug development, clinical research, and commercialization. The company has built an oncology-focused pipeline of 15 drug candidates with a strategic emphasis on immuno-oncology combination therapies. Currently, 5 late-stage candidates are at pivotal trials. With an experienced team, a rich pipeline, a robust clinical development-driven business model and substantial funding, CStone’s vision is to become globally recognized as a leading Chinese biopharmaceutical company by bringing innovative oncology therapies to cancer patients worldwide.

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Reference

1 Cassier PA, Fumagalli E, Rutkowski P., et al. Outcome of patients with platelet-derived growth factor receptor alpha-mutated gastrointestinal stromal tumors in the tyrosine kinase inhibitor era. Clin Cancer Res. 2012;18(16):4458-4464.