First-line standard of care in patients with human epidermal growth factor receptor 2-negative (HER2−), unresectable, or recurrent G/GEJ cancer includes a two-drug combination of platinum-based agents and fluoropyrimidines, e.g., cisplatin, oxaliplatin, S-1, capecitabine, or 5-fluorouracil. This evidence concerns the gene ERBB2 and cancer.