The following article features coverage from the European Society for Medical Oncology (ESMO) 2019 meeting. Click here to read more of Cancer Therapy Advisor‘s conference coverage.

Pembrolizumab monotherapy does not improve overall survival (OS) compared with single-agent chemotherapy among women with metastatic triple negative breast cancer (mTNBC), according to authors of the randomized, open-label, phase 3 KEYNOTE-119 trial ( Identifier: NCT02555657). The finding was presented at the European Society of Medical Oncology (ESMO) Congress 2019 in Barcelona, Spain.

“Pembro monotherapy did not significantly improve OS as 2/3L [second- or third-line] treatment for mTNBC versus chemo, although the pembro treatment effect increased as PD-L1 enrichment increased,” wrote study authors led by Javier Cortés, MD, PhD, of the IOB Institute of Oncology, Quironsalud Group, Madrid and Barcelona, and VHIO Vall d’Hebrón Institut d’Oncologia, in Barcelona, Spain. They added, “Pembrolizumab was generally well tolerated and had less high-grade toxicity than chemo.”

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Pembrolizumab had previously shown promising activity against mTNBC in the KEYNOTE-012 and KEYNOTE-086 clinical trials. The study authors enrolled 

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patients with centrally confirmed TNBC who had received 1 or 2 prior systemic therapies for metastatic disease that had progressed after most recent therapy and a prior anthracycline or taxane. Patients were randomly assigned in a 1:1 ratio to receive pembrolizumab (200 mg every 3 weeks; 312 patients) or doctor’s choice of chemotherapy with capecitabine, eribulin, gemcitabine, or vinorelbine (310 individuals). Patients were stratified by programmed cell death ligand 1 protein (PD-L1) positivity or negativity and prior adjuvant or neoadjuvant therapy versus mTNBC at diagnosis.

At a median follow-up of 9.9 months for patients receiving pembrolizumab and 10.9 months for those on chemotherapy, there was no significant improvement in OS among patients on pembrolizumab with a PD-L1 combined positivity score (CPS) of at least 10 (P =.057, n.s.) or at least CPS of 1 (P =.0728). Nor did pembrolizumab improve progression-free survival (PFS), safety, or ORR.

Grade 3 to grade 5 treatment-related adverse event rates were 14% for pembrolizumab (including 1 patient death) compared with 36% with chemo (including 2 deaths). Rates of grade 3/4 immune-mediated adverse events (irAEs) and infusion reactions were 3.2% and 1.0%, respectively.

However, pembrolizumab-associated OS appeared to improve as PD-L1 CPS increased, the research team wrote. 

“In an exploratory analysis of patients with CPS ≥20, median OS was 14.9 [months] with pembro versus 12.5 [months] with chemo (hazard ratio [HR], 0.58; 95% CI, 0.38-0.88),” the team reported.

Disclosure: The study was funded by Merck Sharp & Dohme Corp., a subsidiary of Merck & Co., Inc. For a full list of disclosures, please refer to the abstract.

Read more of Cancer Therapy Advisor‘s coverage of the ESMO annual meeting by visiting the conference page.


Cortés J, Lipatov O, Im S-A, et al. KEYNOTE-119: Phase III study of pembrolizumab (pembro) versus single-agent chemotherapy (chemo) for metastatic triple negative breast cancer (mTNBC). Presented at: European Society of Medical Oncology (ESMO) Congress 2019; September 27-October 1, 2019: Barcelona, Spain. Abstract LBA21.