Perioperative tislelizumab plus chemotherapy for locally advanced gastric cancer: A randomized, prospective phase 2 trial

In patients whose tumours expressed tsMHC-II, adding tislelizumab to perioperative chemotherapy raised the major pathological response rate from 26.5% to 61.8% (p=0.003), meeting the prespecified primary endpoint — but this is a phase 2 trial in 136 patients, and the endpoint measured response in the resected specimen, not survival. No benefit was seen in the tsMHC-II-negative subgroup. Within the combination arm, tsMHC-II-positive patients also had a higher pathological complete response rate than tsMHC-II-negative patients (32.4% vs 5.9%; p=0.006). The Mountain-02 investigators treat tsMHC-II as a promising predictive biomarker requiring validation in larger studies, not as a ready tool for selecting treatment.