PDCD1 and hepatocellular carcinoma: Like other types of cancer, HCC escapes the cancer-immune system by expressing several immune checkpoint molecules such as PD-1/PD-L1, CTLA-4, T cell immunoglobulin and mucin-containing molecule 3 (TIM-3), and lymphocyte-activation gene 3, and immunotherapy targeting these molecules could be a promising approach [109].