PDCD1 and neoplasm: Immune checkpoint inhibitors (ICIs), including anti-programmed death receptor-1 (PD-1)/programmed death ligand-1 (PD-L1) and anti-cytotoxic T lymphocyte associated antigen-4 (CTLA-4) monoclonal antibodies, reinvigorate antitumor immune responses by blocking key pathways that tumor cells utilize to evade immune surveillance.