PDCD1 and melanoma: Approvals of novel immunotherapeutic agents such as the cytotoxic T-lymphocyte-associated antigen 4 (CTLA4) inhibitor ipilimumab (IPI) and the anti-programmed cell death-1 (PD1) receptor antibodies pembrolizumab and nivolumab (NIVO) have been regarded as significant breakthroughs in the treatment of advanced melanoma [11–14].