CStone Announces China NMPA New Drug Approval of Precision Therapy AYVAKIT® (avapritinib) for the Treatment of Adults with Unresectable or Metastatic PDGFRA Exon 18 Mutant Gastrointestinal Stromal Tumor

SUZHOU,China,March 31,2021 -- CStone Pharmaceuticals (CStone,HKEX: 2616),a leading biopharmaceutical company focused on developing and commercializing innovative immuno-oncology therapies and precision medicines,today announces that the National Medical Products Administration (NMPA) of China has approved AYVAKIT (avapritinib) tablets for the treatment of adults with unresectable or metastatic gastrointestinal stromal tumor (GIST) harboring a PDGFRA exon 18 mutation,including PDGFRA D842V mutations. Discovered by CStone's partner Blueprint Medicines,AYVAKIT is China's first approved therapy for patients with PDGFRA exon 18 mutant GIST specifically designed to target the underlying molecular driver of their disease.

"AYVAKIT is the second approved therapy in the same month for CStone and it is a first-in-class therapy for patients with PDGFRA exon 18 mutant GIST," Dr. Frank Jiang,Chairman and CEO of CStone,noted. "The approval of AYVAKIT in China reflects the collective efforts and accomplishments of the CStone team. We would like to thank all the patients and investigators involved in the clinical study and the NMPA for their support during the priority review. Together,we are aiming to solve Chinese cancer patients' urgent unmet medical needs. With our first two approvals,CStone will strive to bring more first-in-class and best-in-class innovative precision medicines and immuno-oncology therapies to patients."

"Historically,there has been a lack of treatment options for patients with GIST harboring PDGFRA exon 18 mutations. AYVAKIT has shown effective anti-tumor activity and a generally well-tolerated safety profile in Chinese patients with advanced PDGFRA exon 18 mutant GIST," said Dr. Lin Shen,Vice President of Peking University Cancer Hospital and Institute,"We believe the approval of AYVAKIT in China may bring important clinical benefit to Chinese patients with advanced PDGFRA exon 18 mutant GIST."

The NMPA approval of AYVAKIT for the treatment of adults with unresectable or metastatic PDGFRA exon 18 mutant GIST was based on an open-label,multicenter phase I/II bridging study,designed to evaluate the safety,pharmacokinetics,and anti-tumor activity of AYVAKIT in Chinese patients with advanced unresectable or metastatic GIST.Study results demonstrated effective anti-tumor activity,with evidence of tumor regression in target lesions among all eight evaluable Chinese patients with PDGFRA D842V mutant GIST who received 300 mg once daily (QD) doses of AYVAKIT,and the overall response rate (ORR) was 62.5%. AYVAKIT was generally well tolerated. Most treatment-related adverse events (AEs) were Grade 1-2.

About Gastrointestinal Stromal Tumor (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.

About AYVAKIT (avapritinib)

AYVAKIT (avapritinib) is a kinase inhibitor approved by the China NMPA for the treatment of adults with unresectable or metastatic GIST harboring the PDGFRA exon 18 mutation.

The U.S. Food and Drug Administration (FDA) has approved AYVAKITTM for the treatment of adults with unresectable or metastatic gastrointestinal stromal tumor harboring a PDGFRA exon 18 mutation,including PDGFRA D842V mutations. This medicine is approved by the European Commission under the brand name AYVAKYT®for the treatment of adults with unresectable or metastatic GIST harboring the PDGFRA D842V mutation.

AYVAKIT/AYVAKYT is not approved for the treatment of any other indication in China by the NMPA,in the U.S. by the FDA or in Europe by the European Commission,or for any indication in any other jurisdiction by any other health authority.

CStone and Blueprint Medicines have an exclusive collaboration and license agreement 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.

Blueprint Medicines is developing avapritinib globally for the treatment of advanced and indolent systemic mastocytosis (SM). The 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,and for the treatment of moderate to severe indolent SM.

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 14 drug candidates with a strategic emphasis on immuno-oncology combination therapies. Currently,two products have been approved by the China NMPA and multiple late-stage candidates are at pivotal trials or registration stages. CStone's vision is to become globally recognized as a world-renowned biopharmaceutical company by bringing innovative oncology therapies to cancer patients worldwide.

For more information about CStone,please visit: www.cstonepharma.com

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