Nowadays, patients with ERBB2-positive metastasized gastric or esophagogastric adenocarcinoma qualify for a combination of chemotherapy and the monoclonal cytotoxic ERBB2 antibody trastuzumab, improving the patients’ survival compared to chemotherapeutic treatment alone [71]. The gene discussed is ERBB2; the disease is gastroesophageal junction adenocarcinoma.