PDCD1 and melanoma: Combination immune checkpoint inhibition (cICI) with cytotoxic T-lymphocyte associated protein 4 (CTLA-4) and programmed cell death protein 1 (PD-1) or its ligand (PD-L1) inhibition is approved for use in patients with advanced melanoma and other malignancies including renal cell carcinoma and non-small cell lung cancer [1,2,3,4].