PDCD1 and neoplasm: Immune checkpoint inhibitors (ICIs), which target co-inhibitory pathways such as cytotoxic T lymphocyte antigen 4 (CTLA4) and programmed cell death 1 (PD-1) on T cells, as well as programmed death ligand 1 (PD-L1) on tumor and immune cells, can restore T-cell function and enhance antitumor immunity (10).