Since the first Food and Drug Administration (FDA) approval of the Cytotoxic T-lymphocyte Antigen-4 (CTLA-4) antibody ipilimumab for metastatic melanoma a decade ago, dozens of approvals for antibodies targeting programmed cell death protein 1 (PD-1) or programmed death ligand 1 (PD-L1) alone or in combination with ipilimumab and/or chemotherapy have followed. The gene discussed is PDCD1; the disease is metastatic melanoma.