CStone Pharmaceuticals announced that two key phase 3 registrational clinical trials of sugemalimab, a fully human, full-length anti-PD-L1 antibody developed in-house, have completed patient enrollment. The two trials are GEMSTONE-303, where sugemalimab in combination with standard of care chemotherapy is used as first-line treatment of unresectable locally advanced or metastatic gastric adenocarcinoma (GC)/gastro-esophageal junction (GEJ) adenocarcinoma, and GEMSTONE-304, where sugemalimab in combination with standard of care chemotherapy is used as first-line treatment of unresectable locally advanced, recurrent, or metastatic esophageal squamous cell carcinoma (ESCC). Gastric/esophageal cancer is one of the most common cancers globally.

According to the GLOBOCAN 2020 data, there were more than 1 million new cases of gastric cancer worldwide and 769,000 deaths in 2020. The incidence and mortality of gastric cancer ranked 5th and 4th respectively among all common cancers worldwide. There were more than 600,000 new cases of esophageal cancer, and 544,000 deaths in 2020, with the incidence and mortality ranking 8th and 6th, respectively, globally.

The incidence of gastric adenocarcinoma accounted for more than 90% of gastric malignancies, and the incidence of GEJ adenocarcinoma has been on the rise in recent years. Epidemiological data indicated that around 90% of all esophageal cancer cases in China are ESCC, and ESCC cases were commonly locally advanced or metastatic at the time of diagnosis and miss the opportunities of curative treatments. The GEMSTONE-303 study is a multi-center, placebo-controlled phase 3 registrational clinical trial designed to evaluate the efficacy and safety of sugemalimab plus capecitabine and oxaliplatin (CAPOX) as the first-line treatment in patients with unresectable locally advanced or metastatic gastric adenocarcinoma or GEJ adenocarcinoma.

In a phase Ib study in this patient population, sugemalimab in combination with CAPOX demonstrated an objective response rate (ORR) of 62.1% (18/29), and a disease control rate (DCR) of 82.8%, with durable responses in patients. The GEMSTONE-304 study is a multi-center, placebo-controlled phase 3 registrational clinical trial designed to evaluate the efficacy and safety of sugemalimab in combination with 5-fluorouracil plus cisplatin (FP) as first-line treatment in patients with unresectable locally advanced, recurrent, or metastatic ESCC. In a phase Ib trial in this population, sugemalimab in combination with FP achieved an ORR of 67.6% (25/37) and a DCR of 89.2%, along with durable responses in first-line ESCC patients.