PDCD1 and hepatocellular carcinoma: Currently, the FDA has approved four immune checkpoint inhibitors for single or combined use as first-line or second-line treatment for HCC: atilizumab (targeting programmed death ligand 1 (PD-L1)) in combination with bevacizumab (targeting vascular endothelial growth factor (VEGF)), ipilimumab (targeting cytotoxic T lymphocyte-associated antigen 4 (CTLA-4)) in combination with nivolumab (targeting programmed cell death protein 1 (PD1)), and pembrolizumab (PD1) or nivolumab alone.