In the KEYNOTE-811 trial, in which the effect of add-on pembrolizumab to combined chemotherapy plus trastuzumab therapy was verified in HER2-positive patients, the proportion of patients with gastric adenocarcinoma and esophagogastric junction adenocarcinoma was 65.4%–72.2% and 27.8%–34.6%, respectively [119]. This evidence concerns the gene ERBB2 and gastroesophageal junction adenocarcinoma.