PDCD1 and melanoma: The effect of anti-PD-1 or anti-PD-L1 (PD-L1: programmed death-ligand 1), sometimes combined with anti-CTLA-4, has been investigated in most solid malignancies and has gained FDA approval for use in, for instance, melanoma, non-small cell lung cancer (NSCLC), urothelial cancer, Hodgkin lymphoma and high microsatellite instability cancer.