PDCD1 and melanoma: Pembrolizumab and nivolumab, two therapeutic monoclonal antibodies that block the programmed cell death protein 1 (PD-1, CD279) immune checkpoint receptor, improve survival in patients with advanced melanoma when compared to the cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4, CD152) immune checkpoint inhibitor (ICI) ipilimumab or dacarbazine chemotherapy and have become a preferred treatment option [1,2,3].