Fluorouracil plus platinum-based chemotherapy is the most commonly used first-line therapy for unresectable advanced or metastatic human epidermal growth factor receptor 2 (HER2)-negative gastric and gastroesophageal junction adenocarcinoma, with a median overall survival rate (OS) less than 1 year [22–24]. The gene discussed is ERBB2; the disease is gastroesophageal junction adenocarcinoma.