Suzhou - CStone Pharmaceuticals ('CStone', HKEX: 2616), a leading biopharmaceutical company focused on the research, development, and commercialization of innovative immuno-oncology therapies and precision medicines, today announced that the Phase 3 GEMSTONE-303 study met its primary endpoint of overall survival (OS).

Sugemalimab in combination with chemotherapy demonstrated statistically significant and clinically meaningful improvement in OS, compared with placebo plus chemotherapy, as a first-line treatment for unresectable locally advanced or metastatic gastric or gastroesophageal junction (G/GEJ) adenocarcinoma with PD-L1 expression 5%. The safety profile was consistent with previous reports of sugemalimab studies, and no new safety signals were identified.

The GEMSTONE-303 study is a multi-center, randomized, placebo-controlled Phase 3 registrational clinical trial, designed to evaluate the efficacy and safety of sugemalimab plus capecitabine and oxaliplatin (CAPOX) as a first-line treatment in patients with unresectable locally advanced or metastatic G/GEJ adenocarcinoma with PD-L1 expression 5%. The dual primary endpoints were investigator-assessed PFS and OS. Secondary endpoints include blinded independent central review (BICR)-assessed PFS, investigator-assessed objective response rate (ORR), and duration of response (DoR).

Dr. Jason Yang, Chief Executive Officer of CStone, said, 'We are excited that sugemalimab demonstrated remarkable clinical efficacy as the first-line treatment for gastric cancer after achieving successes in stage III and IV NSCLC, esophagus cancer and R/R-ENKTL. With this achievement, all registrational trials for sugemalimab have been successfully completed. The NMPA of China is currently reviewing the sugemalimab sBLA for the first-line G/GEJ adenocarcinoma, positioning sugemalimab to potentially become the world's first anti-PD-L1 monoclonal antibody approved in the first-line setting of this indication. We also plan to communicate with the United States Food and Drug Administration (FDA) and the European Medicines Agency (EMA) to explore the global registrational pathway to bring this innovative therapy to patients with gastric cancer worldwide.'

Professor Lin Shen, Peking University Cancer Hospital, the principal investigator of the GEMSTONE-303 study said, 'Clinically, most patients are already at a late stage when diagnosed with gastric adenocarcinoma, and those with unresectable or metastatic gastric cancer usually had poor prognosis and huge unmet medical needs. Today, we are pleased to see the positive OS results from the GEMSTONE-303 study. Sugemalimab in combination with chemotherapy can significantly prolong the OS and PFS of patients with G/GEJ adenocarcinoma and combination was well tolerated, and we believe that sugemalimab will provide an attractive treatment option to this patient population.'

In November 2022, the GEMSTONE-303 study met the primary endpoint of PFS and also showed a clear trend toward benefit for OS. Sugemalimab in combination with chemotherapy demonstrated statistically significant and clinically meaningful improvement in investigator-assessed PFS, compared with placebo plus chemotherapy, HR=0.66 (95% CI: 0.54, 0.81), p-value

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