Given advancements in cancer therapy, development of immune checkpoint inhibitors employing antibodies targeting programmed cell death 1 (PD-1), PD-1 ligand (PD-L1), or monoclonal antibodies against cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4) in patients with various types of cancer has steadily increased. The gene discussed is PDCD1; the disease is cancer.