PDCD1 and neoplasm: ICBs, which restore host anti-tumor and immune effects by blocking immune checkpoints (e.g., cytotoxic T-lymphocyte associated protein 4 [CTLA-4], programmed cell death protein 1 [PD-1]/programmed death-ligand 1 [PD-L1]), have achieved breakthroughs in multiple clinical practices and are gradually redefining the treatment paradigm for tumors [10, 11].