Mitchell TC, et al. - In this open-label phase I/II ECHO-202/KEYNOTE-037 trial, researchers assessed epacadostat (a potent and highly selective IDO1 enzyme inhibitor) plus pembrolizumab, a programmed death protein 1 inhibitor, in patients with advanced solid tumors. Patients received twice daily increased doses of oral epacadostat (25, 50, 100, or 300 mg) plus intravenous pembrolizumab 2 mg/kg or 200 mg every 3 weeks. Patients received epacadostat (50, 100 or 300 mg) twice daily plus pembrolizumab 200 mg every 3 weeks during the expansion of safety. Participants were 62 patients and received one or more doses of study treatment. Fifty-two patients experienced treatment-related adverse events (TRAEs), with fatigue, rash, arthralgia, pruritus, and nausea occurring in ≥ 20%. Epacadostat was generally well tolerated in combination with pembrolizumab and encouraged antitumor activity in multiple advanced solid tumors.