PDCD1 and melanoma: Ipilimumab (anti-CTLA-4 monoclonal antibody) is currently used to treat a variety of cancers, such as melanoma, colorectal cancer (CRC), hepatocellular carcinoma (HCC), non-small cell lung cancer (NSCLC), and renal cell carcinoma (RCC), either by itself or in combination with nivolumab (anti-PD-1 monoclonal antibody) (103).