PDCD1 and melanoma: While immunotherapies such as anti-CTLA4, anti-PD1, and anti-PD-L1 show efficacy in a large number of melanoma patients, a significant proportion do not respond to this treatment (Brahmer et al., 2012, Hamid et al., 2013, Hodi et al., 2010, Topalian et al., 2012).