IDO1 and cancer: Several clinical trials are ongoing to overcome these limitations and to evaluate in unresectable or advanced melanoma the effect of immune checkpoint inhibitors in combinatorial regimes with targeted therapy (NCT01767454), other immune modulators such as interleukin-2 (ClinicalTrials.gov Identifier: NCT0456212) and IDO (ClinicalTrials.gov Identifier: NCT02073123), therapeutic cancer vaccine (ClinicalTrials.gov Identifiers: NCT04382664, NCT04697576) or stereotactic body radiation therapy (ClinicalTrials.gov Identifier: NCT03693014).