PDCD1 and neoplasm: ICIs target checkpoint receptors or ligands such as programmed cell death receptor 1 (PD-1), programmed cell death ligand 1 (PD-L1), or cytotoxic T lymphocyte-associated antigen-4 (CTLA-4, also known as CD152), blocking tumor immune suppression signals and thereby restoring the body's antitumor immune response.