IDO1 and cancer: Most importantly, despite the initial experimental and clinical indications about the efficacy of IDO1 inhibitors in cancer immunotherapy (16), in the recently Incyte’s phase III clinical trial, the addition of the IDO1 inhibitor epacadostat in a therapy with the programmed death 1 immune checkpoint inhibitor pembrolizumab, made no difference for the patients with metastatic melanoma receiving both drugs.