In the ToGA trial, where the effect of add-on trastuzumab plus chemotherapy as first-line therapy was examined in HER2-positive patients, the proportion of patients with gastric adenocarcinoma and esophagogastric junction adenocarcinoma was 80%–83% and 17%–20%, respectively [121]. Here, ERBB2 is linked to gastroesophageal junction adenocarcinoma.