Specifically, the use of ICIs that block cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4), programmed cell death 1 (PD-1) protein, and programmed cell death 1 ligand 1 (PD-L1) has resulted in unprecedented durable responses and long-term survival rates in cancer patients with different tumor types (1). The gene discussed is PDCD1; the disease is cancer.