A phase II study of epacadostat and pembrolizumab in patients with advanced sarcoma.

11049 Background: Tumors express IDO1, an intracellular enzyme involved in the degradation of tryptophan to kynurenine, in order to evade immunosurveillance. Epacadostat inhibits IDO1 and shifts the tumor microenvironment from an immunosuppressive state to an immune-stimulated state. Pembrolizumab previously demonstrated activity in select sarcoma subtypes. We performed an open-label, single-center, phase II study of epacadostat and pembrolizumab in patients with advanced sarcoma. Methods: Patients received the recommended phase II dose of oral epacadostat (100mg) twice per day and intravenous pembrolizumab (200mg/dose) every 3 weeks. The primary endpoint was best objective response rate (ORR) (complete response and partial response [PR]) at 24 weeks by RECIST 1.1. Secondary endpoints included adverse events (AEs), ORR by irRECIST, progression free survival (PFS) and overall survival (OS). Correlative studies performed on pre/on-treatment biopsy specimens included PD-L1, IDO1, and kynurenine expression and characterization of tumor infiltrating lymphocytes by IHC, whole exome and RNA sequencing. Results: Twenty-nine patients were enrolled [median age 53 years (range, 24-78), 57% male, ECOG PS 0 83%]. Histological subtypes included leiomyosarcoma (17%), UPS (17%), myxofibrosarcoma (7%), liposarcoma (10.5%), EHE (10.5%), angiosarcoma (3%), “other” sarcoma subtype (35%). Patients were refractory to 0 (21%), 1 (38%), 2 (24%) and ≥ 3 (17%) prior lines of therapy. The most common ( > 20% of pts) grade (G)1 or 2 treatment related AEs (TRAEs) observed included fatigue (31%), rash (31%) and ALT elevation (24%). G3 TRAEs included AST elevation (10%), ALT elevation, anemia, hypophosphatemia and increased lipase each occurred in 3% of pts. Three patients discontinued therapy due to G3 immune mediated hepatitis. Among the 29 evaluable patients 1 (3%) confirmed PR (leiomyosarcoma), 13 stable diseases (45%) and 15 progressions (52%) were observed by RECIST 1.1. The median PFS was 8.0 weeks (two-sided 95% CI: 6.9 ~ 26.7) and the PFS rate at 24 weeks was 27.9% (two-sided 95% CI: 15.0% ~ 52.2%). The median OS was not estimable (two-sided 95% CI: 40.9 weeks ~ NE). The OS at 24 weeks was 85.2% (95% CI: 72.8%, 99.7%). Conclusions: Epacadostat in combination with pembrolizumab was generally well tolerated. Limited anti-tumor activity was observed among advanced sarcoma patients. Correlative analyses including determination of adequacy of IDO1 inhibition will be reported. Clinical trial information: NCT03414229.