This trial was a randomized, double-blind, placebo-controlled, phase III study, which investigated the role of pembrolizumab, in combination with trastuzumab, an anti-HER2 mAb, in GC or gastro-esophageal junction adenocarcinomas, with HER2 amplification or overexpression, which occur in around 20% of advanced cancers. This evidence concerns the gene ERBB2 and gastric cancer.