Widespread use of immune checkpoint inhibitors (ICI) against cytotoxic T-lymphocyte antigen 4 (anti-CTLA-4) and programmed cell death 1 (anti-PD-1) or its ligand (anti-PD-L1) for a range of advanced cancers in recent years has resulted in a dramatic increase in incidence (1–4). The gene discussed is PDCD1; the disease is cancer.