Phase 2 study of pembrolizumab (pembro) monotherapy for previously treated metastatic triple-negative breast cancer (mTNBC): KEYNOTE-086 cohort A.

Abstract

1008 Background: In KEYNOTE-012, pembro showed durable activity and manageable safety in patients (pts) with PD-L1+ mTNBC. Cohort A of KEYNOTE-086 (NCT02447003) examined the efficacy/safety of pembro in previously treated mTNBC, regardless of PD-L1 expression. Methods: Pts with centrally confirmed mTNBC, ≥1 prior chemotherapy for metastatic disease, and ECOG PS 0-1 had pembro 200 mg Q3W for up to 24 mo; imaging q 9 wk for the first 12 mo, then q 12 wk. Clinically stable pts with PD could remain on pembro until PD confirmed on next assessment. Primary endpoints: ORR (RECIST v1.1, central review) in all pts and pts with PD-L1+ tumors, and safety. Secondary endpoints: DOR, disease control rate (DCR; CR + PR + SD ≥24 wk), PFS, and OS. Planned enrollment was 160 pts; analysis based on data as of Nov 10, 2016. Results: 60% of screened PD-L1-evaluable pts had PD-L1+ tumors (combined positive score ≥1%). Of 170 pts enrolled (100% women; median age 54 y), 44% had ≥3 prior lines of therapy, 51% had elevated LDH, 74% had visceral mets and 62% had PD-L1+ tumors. After a median follow-up of 10.9 mo, 9 (5%) pts remained on pembro. Treatment-related AEs (TRAEs) of any grade and grade 3-4 occurred in 60% and 12% of pts, respectively; 4% discontinued due to TRAEs. There were no deaths due to AE. Overall ORR was 5% regardless of PD-L1 expression (Table). Best overall response was 0.6% CR, 4% PR, 21% SD; not evaluable (3%). DCR was 8% (95% CI 4-13). Median DOR was 6.3 mo (range 1.2+ to 10.3+); 5 (63%) responders w/o PD at data cutoff. Median PFS and OS were 2.0 mo (95% CI 1.9-2.0) and 8.9 mo (95% CI 7.2-11.2), with 6-mo rates of 12% and 69%, respectively. ORR was numerically lower in pts with poor prognostic factors (e.g., high LDH, liver/visceral mets; Table). Conclusions: In KEYNOTE-086 Cohort A, pembro monotherapy showed manageable safety and durable responses in a subset of pts with heavily pretreated mTNBC. Randomized studies of monotherapy and combination therapy are ongoing. Clinical trial information: NCT02447003. [Table: see text]