PDCD1 and melanoma: Meanwhile, immune checkpoint blockade (ICB) therapy that targets programmed cell death-1 and its ligand (PD-1/PD-L1) and cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) has been remarkably successful for the treatment of melanoma and non-small cell lung cancer, which paved the way for immunotherapy for HCC [29, 30].