PDCD1 and melanoma: Blockade of cytotoxic T lymphocyte–associated protein 4 (CTLA-4) by a specific antibody resulted in survival benefits for 20% of patients with melanoma, and blockade of the T cell checkpoint receptor or ligand, like programmed cell death 1 (PD-1) and programmed death ligand 1 (PD-L1), achieved responses as high as 30%–40% in several solid tumors (1).