Efficacy/safety of epacadostat plus pembrolizumab in triple-negative breast cancer and ovarian cancer: Phase I/II ECHO-202 study.

Abstract

1103 Background: Epacadostat is an oral, potent, and selective inhibitor of indoleamine 2,3-dioxygenase 1, a tryptophan-catabolizing enzyme that induces immune tolerance via T-cell suppression and is associated with poor patient (pt) survival when overexpressed in some cancers. The ongoing, open-label, phase 1/2 (P1/2) ECHO-202/KEYNOTE-037 study is evaluating the efficacy, safety, and tolerability of epacadostat plus PD-1 inhibitor pembrolizumab (E + P) in pts with advanced/recurrent cancers. We report P1/2 study outcomes for triple-negative breast cancer (TNBC) pts and P2 outcomes for ovarian cancer (OVC; no P1) pts as of a 29OCT2016 data cutoff. Methods: Eligible pts were ≥18 years old with no prior checkpoint inhibitor treatment (tx); prior platinum/taxane tx was required for OVC pts. As part of P1 dose escalation, TNBC pts received E (300 mg BID) + P (200 mg Q3W). In P2, TNBC and OVC pts received E (100 mg BID) + P (200 mg Q3W). Response (RECIST v1.1) was assessed in evaluable pts. Safety and tolerability were assessed in pts with ≥1 dose of E + P. Results: A total of 39 pts with TNBC and 37 with OVC were enrolled. The majority of TNBC pts (56%, n = 22) and OVC pts (78%, n = 29) received ≥3 prior lines of tx. For TNBC pts, ORR (CR+PR) was 10% (n = 4; all PR) and DCR (CR+PR+SD) was 36% (n = 14; 10 SD); ORR and DCR for pts with ≤2 prior tx were 12% (n = 2) and 29% (n = 5), respectively, and for ≥3 prior tx were 9% (n = 2) and 41% (n = 9). For OVC pts, ORR was 8% (n = 3; all PR) and DCR was 35% (n = 13; 10 SD); ORR and DCR for pts with ≤2 prior tx were 13% (n = 1) and 25% (n = 2), and for ≥3 prior tx were 7% (n = 2) and 38% (n = 11). The most common TRAEs (≥15% of pts) were rash (18%), fatigue (15%), and nausea (15%) in the 39 TNBC pts, and fatigue (19%) in the 37 OVC pts. Grade ≥3 TRAEs occurred in 13% of TNBC pts (n = 5; none in > 1 pt) and 19% of OVC pts (n = 7; only rash occurred in > 1 pt [n = 3]). TRAEs led to discontinuation in 1 TNBC pt (grade 3 ascites) and 1 OVC pt (grade 2 arthralgia). Conclusions: E + P tx was generally well tolerated and showed antitumor activity consistent with previously reported P monotherapy in pts with advanced TNBC or OVC. Biomarker analysis is ongoing to characterize pt populations enrolled in this study. Clinical trial information: NCT02178722.