PDCD1 and melanoma: Metastatic lung cancer, melanoma and renal cancer are good examples, as the routine therapeutic strategies now include ICI, such as anti-cytotoxic T-lymphocyte antigen4 (CTLA-4), or anti-programmed cell death 1 (PD1) or its ligand (PDL1) [2,3,4,5,6,7,8,9,10].