PDCD1 and neoplasm: Among them, ICIs are the most widely used tumor immunotherapy methods at present, and FDA has approved antibodies against programmed cell death-1 (PD-1), programmed death ligand-1 (PD-L1), and cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4) for various solid tumors, which proved the effectiveness and prospects of immunotherapy as an anticancer approach.