Notably, no significant differences in terms of progression-free survival (PFS) or overall survival (OS) were reported between the patients treated with epacadostat plus pembrolizumab versus those receiving placebo plus pembrolizumab, suggesting that the usefulness of IDO1 inhibition as a strategy to enhance anti-PD-1 therapy activity in cancer remains highly controversial [282]. This evidence concerns the gene IDO1 and cancer.