PDCD1 and melanoma: Ipilimumab, a CTLA‐4 antibody, has been shown to improve overall survival and the 5 year rate of recurrence‐free survival in patients with advanced melanoma and was the first monoclonal antibody approved by FDA in 2011.24, 25 Another commonly targeted immune checkpoint is the PD‐1/PD‐L1 receptor/ligand pair.23, 26, 27, 28 The PD‐L1 ligand is expressed on many tissues to limit autoimmunity, but it is overexpressed on tumors and recognized as a major immune resistance mechanism in the tumor microenvironment.