Although epacadostat exhibits over a 1000-fold selectivity for IDO-1 over IDO-2/TDO, the phase III trial of epacadostat combined with the PD-1 inhibitor pembrolizumab did not show a clinical benefit when compared with pembrolizumab monotherapy in patients with advanced malignant melanoma—this negative study elicited a general dampening of excitement regarding the therapeutic utility of IDO-1 inhibitors in cancer [38]. This evidence concerns the gene IDO1 and cancer.