Based on preclinical murine data demonstrating synergy between immune checkpoint inhibitors and indoleamine 2,3-dioxygenase 1 (IDO1) enzyme inhibitors [7], this phase 1/2 clinical trial (NCT01604889) was initiated to investigate ipilimumab in combination with epacadostat for the treatment of unresectable or metastatic melanoma. The gene discussed is IDO1; the disease is metastatic melanoma.