CStone Pharmaceuticals announced that the results from a pivotal phase III clinical trial (GEMSTONE-303), evaluating sugemalimab in combination with chemotherapy as a first-line treatment for locally advanced or metastatic gastric or gastroesophageal junction (G/GEJ) adenocarcinoma, has been accepted as a late-breaking abstract (LBA) and showcased in an oral session at the European Society for Medical Oncology (ESMO) Congress 2023. In the GEMSTONE-303 study, sugemalimab in combined with chemotherapy as a first- line treatment of locally advanced or metastatic gastrics or gastroesophageal intersection (G/GEJ) Adenocarcinoma has demonstrated statistically significant and clinically meaningful improvement in progression-free survival (PFS) and overall survival (OS).ugemalimab would become the world's first PD -L1 monoclonal antibody for this indication, if approved. CStone plan to consult with global regulatory agencies on regulatory pathways to bring sugemalimab to patients with G/GEJ adenocarcinoma.

The GEMSTONE-303 trial is a multi-center, randomized, double-blinded, placebo-controlled phase III 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 co-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).

The GEMSTONE- 303 data shows that sugemalimab in partnership with chemotherapy has significantly prolonged PFS and OS of patients with G/GE J adenocarcinoma while maintaining a good safety profile. The data presented at the ESMO Congress 2023 is based on the final analyses of PFS as of August 6, 2022, and OS as of July 9, 2023. The results show that the GEMSTONE- 303 study has met its pre-specified co-specified co-primary endpoints.

In patients with PD-L1 expression5%, sugemalIMab in combination with chemotherapy has demonstrated statistically significant and clinically significant and clinically meaningful improvement in PFS and OS, compared with placebo plus chemotherapy. Key findings are as follows: The investigator-assessed median PFS was 7.6 months in the sugemalimab treatment group compared with 6.1 months in the placebo group, with a hazard ratio (HR) of 0.66 (95% CI, 0.54-0.81), P<0.0001. Median OS was 15.6 months in the su gemalimab treatment group versus 12.6 months in the placebo group, With an HR of 0.75 (95% CI, 0.61-0.92), P=0.0060.

Subgroup analyses has demonstrated clinical benefits across all pre-defined subgroups, including PD- L1 expression status. Sugemalimab treatment resulted in an investigator-assessed ORR of 68.6% compared with 52.7% in the placebo group, with a median DoR of 6.9 months versus 4.6 months. Sugemalimab in combination with chemotherapy appears safe and tolerable, with no new safety signal identified.