PDCD1 and melanoma: The immunological checkpoint inhibitor therapies, the cytotoxic T-lymphocyte protein 4 (CTLA-4) inhibitor, ipilimumab and programmed cell death protein 1 (PD-1) inhibitor, pembrolizumab, have demonstrated marked effects on progression-free survival (PFS) in malignant melanoma, renal cell carcinoma, and cancers with DNA repair deficiencies [6, 7].