PDCD1 and melanoma: Currently, the FDA has approved five anti-PD-1 or anti-PD-L1 antibodies (pembrolizumab, nivolumab, atezolizumab, durvalumab, and avelumab) for the treatment of 11 types of cancer, including refractory melanoma, advanced non-small cell lung cancer, Merkel cell carcinoma, Hodgkin’s lymphoma, highly microsatellite instability (MSI-h) tumors, head and neck cancer, bladder cancer, urothelial carcinoma, gastric esophageal cancer, hepatocellular carcinoma, and renal cell carcinoma (69).