PDCD1 and melanoma: Combinations of PD-1/PD-L1 axis inhibitors with inhibitors of cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) have also been studied, and are now widely used for melanoma, renal cell carcinoma (RCC), and non-small cell lung cancer [3,4,5,6,7,8,9,10].