Since approval in 1998 for HER2 overexpressing breast cancer and HER2 overexpressing metastatic gastric or GE junction adenocarcinoma, trastuzumab has provided both substantial progression-free and overall survival benefits for patients with HER2 overexpressing breast cancer and is a fundamental part of anti-HER2 treatment [36]. Here, ERBB2 is linked to gastroesophageal junction adenocarcinoma.