Gastric cancer (GC) is a molecularly heterogeneous disease where monoclonal antibodies against human epidermal growth factor receptor 2 (HER2), vascular endothelial growth factor (VEGF), and programmed cell death 1 (PD-1) combined with systemic chemotherapy have improved survival in patients with unresectable or metastatic GC. The gene discussed is PDCD1; the disease is gastric cancer.