CStone Pharmaceuticals announced that the Phase 3 GEMSTONE-303 study of sugemalimab in combination with chemotherapy as a first-line treatment for unresectable locally advanced or metastatic gastric or gastroesophageal junction (G/GEJ) adenocarcinoma with PD-L1 expression 5%, met its primary endpoint of overall survival (OS). Sugemalimab in combination with chemotherapy demonstrated a statistically significant and clinically meaningful improvement in OS, compared with placebo plus chemotherapy . The safety profile was consistent with previous reports of sugemalimab studies, and no new safety signals were identified.

Key Highlights: In the GEMSTONE-303 study, sugemalimab in combination with chemotherapy as a first-line treatment of locally advanced or metastatic gastric or gastroesophageal junction (G/GEJ) adenocarcinoma has demonstrated a statistically significant and clinically meaningful improvement in overall survival (OS). The GEMSTONE-303 study has met both pre-specified primary endpoints of progression-free survival (PFS) and OS and key secondary endpoints: BICR-PFS and ORR. The National Medical Products Administration (NMPA) of China has accepted the supplemental biologics license application (sBLA) for sugemalimab in combination with chemotherapy as a first- line treatment for locally advanced or metastatic G/GEJ adenocarcinoma.

The application is currently under review. 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). 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 <0.0001. In February 2023, the NMPA of China accepted the sBLA for sugemalimab in combination with chemotherapy as the first-line treatment of unresectable locally advanced or metastatic G/GEJ adenocarcinoma, which is currently under review. The GEMSTONE-303 study results will be presented at an upcoming international academic conference.