PDCD1 and hepatocellular carcinoma: Immune-checkpoint inhibitors, targeting programmed cell death-1 (PD-1), programmed cell death ligand-1 (PD-L1), or cytotoxic T-lymphocyte protein 4 (CTLA-4), can specifically block the corresponding immunosuppressive signals and exhibit potential efficacy on malignant tumor including advanced HCC (35, 36).