ERBB2 and gastric cancer: KEYNOTE-811, a study of pembrolizumab plus trastuzumab plus chemotherapy in previously untreated patients with unresectable or metastatic HER2-positive GC (n = 264) stratified by PD-L1 expression (CPS ≥ 1 or CPS < 1), revealed that 84.1% of patients had tumors with a PD-L1 CPS ≥ 1.