Title: Pembrolizumab Monotherapy for Previously Untreated, PD-L1–Positive, Metastatic Triple-Negative Breast Cancer: Cohort B of the Phase 2 KEYNOTE-086 Study

Abstract

Background

Standard first-line treatment for metastatic triple-negative breast cancer (mTNBC) is chemotherapy. However, outcomes are poor, and new treatment options are needed. In cohort B of the phase 2 KEYNOTE-086 study, we evaluated pembrolizumab as first-line therapy for patients with PD-L1–positive mTNBC.

Patients and methods

Eligible patients had centrally confirmed mTNBC, no prior systemic anticancer therapy for metastatic disease, measurable disease at baseline per RECIST v1.1 by central review, no radiographic evidence of central nervous system metastases, and a tumor PD-L1 combined positive score ≥1. Patients received pembrolizumab 200 mg intravenously every 3 weeks for up to 2 years. The primary endpoint was safety. Secondary end points included objective response rate (ORR), disease control rate (DCR; percentage of patients with complete or partial response or stable disease for ≥24 weeks), duration of response, progression-free survival (PFS) and overall survival (OS).

Results

All 84 patients enrolled were women, and 73 (86.9%) received prior (neo)adjuvant therapy. Fifty-three (63.1%) patients had treatment-related adverse events (AEs), including 8 patients (9.5%) with grade 3 severity; no patients experienced grade 4 AEs or died because of treatment-related AEs. Four patients had a complete response and 14 had a partial response, for an ORR of 21.4% (95% CI, 13.9-31.4). Of the 13 patients with stable disease, 2 had stable disease lasting ≥24 weeks, for a DCR of 23.8% (95% CI, 15.9-34.0). At data cutoff, 8 of 18 (44.4%) responses were ongoing, and median duration of response was 10.4 months (range, 4.2-19.2+). Median PFS was 2.1 months (95% CI, 2.0-2.2) and median OS was 18.0 months (95% CI, 12.9-23.0).

Conclusions

Pembrolizumab monotherapy had a manageable safety profile and showed durable antitumor activity as first-line therapy for patients with PD-L1–positive mTNBC.

Clinical trial registration

ClinicalTrials.gov, NCT02447003

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