Monoclonal antibodies directed against programmed cell death 1 (PD-1, e.g., nivolumab and pembrolizumab), programmed cell death ligand 1 (PD-L1, e.g., avelumab, atezolizumab, and durvalumab), and cytotoxic T-lymphocyte-associated protein 4 (CTLA-4, e.g., ipilimumab) have been approved for treating multiple solid tumor types, including melanoma, Merkel cell carcinoma, head and neck squamous cell carcinoma, lung cancer, urothelial carcinoma, renal cell carcinoma, and gastrointestinal cancers. This evidence concerns the gene PDCD1 and melanoma.