Background
Indoleamine 2,3-dioxygenase 1 (IDO1) is a tryptophan-catabolizing enzyme that is expressed in many cancers and induces immune tolerance by suppressing T cell responses. Epacadostat is a potent, selective oral inhibitor of IDO1. A dose-escalation study of epacadostat with ipilimumab in patients with advanced melanoma showed favorable ORR, disease control rate (DCR), and PFS in immunotherapy-naïve patients [1]. Preliminary data of epacadostat with pembrolizumab in patients with selected advanced cancers are reported.