PDCD1 and neoplasm: ICIs are monoclonal antibodies that target and regulate two key signaling pathways in T lymphocyte activation and exhaustion by binding to and inhibiting cytotoxic T lymphocyte antigen 4 or programmed cell death 1 (PD-1) and its ligand PD-L1, which can increase anti-tumor immune effect of T lymphocyte (Page et al. 2014; Topalian et al. 2016; Wright et al. 2021).