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Clin Cancer Res. 2018 Jun 15;24(12):2804-2811. doi: 10.1158/1078-0432.CCR-17-3452. Epub 2018 Mar 20.

Safety and Antitumor Activity of Pembrolizumab in Patients with Estrogen Receptor-Positive/Human Epidermal Growth Factor Receptor 2-Negative Advanced Breast Cancer.

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Helen Diller Family Comprehensive Cancer Center, University of California San Francisco, San Francisco, California.
Department of Medical Oncology, Institut Claudius Regaud, Oncolpole-Toulouse, France.
Department of Internal Medicine, Seoul National University Hospital, Cancer Research Institute, Seoul National University College of Medicine, Seoul, Republic of Korea.
Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, Massachusetts.
Department of Investigational Cancer Therapeutics, The University of Texas MD Anderson Cancer Center, Houston, Texas.
Division of Medical Oncology, UHN Princess Margaret Cancer Centre, Toronto, ON, Canada.
Breast and GYN Early Trials Program, Scottsdale Healthcare Shea Medical Center, Scottsdale, Arizona.
Department of Drug Development and Innovation, Institut Curie, Paris & Saint-Cloud, France, INSERM U900 Research Unit, Saint-Cloud France, and Versailles-Saint-Quentin-en-Yvelines University, Montigny-le-Bretonneux, France.
Department of Clinical Pharmacology, Netherlands Cancer Institute, Amsterdam, the Netherlands.
Drug Development Department, Gustave Roussy, Villejuif, France.
Peter MacCallum Cancer Centre, University of Melbourne, Melbourne, Victoria, Australia.
Department of Clinical Oncology, Merck & Co., Inc., Kenilworth, New Jersey.
Division of Medical Oncology, Department of Medicine, Rutgers Cancer Institute of New Jersey, New Brunswick, New Jersey.


Purpose: We investigated the safety and antitumor activity of the anti-programmed death 1 monoclonal antibody pembrolizumab in patients with estrogen receptor-positive (ER+)/human epidermal growth factor receptor 2-negative (HER2-) advanced breast cancer with programmed death ligand 1-positive (PD-L1-positive) tumors in the phase Ib open-label, multicohort KEYNOTE-028 (NCT02054806) study.Patients and Methods: Patients with ER+/HER2- advanced breast cancer with PD-L1-positive tumors (combined positive score ≥1) received pembrolizumab (10 mg/kg every 2 weeks) up to 2 years or until confirmed progression/intolerable toxicity. Primary endpoints were safety and overall response rate (ORR), based on Response Evaluation Criteria in Solid Tumors, version 1 (RECIST v1.1) as assessed by investigator review.Results: Between April 2014 and January 2015, 25 patients were enrolled. Median number of prior therapies for breast cancer, including endocrine agents, was 9 (range, 3-15). Median follow-up was 9.7 months (range, 0.7-31.8 months). Three patients experienced partial response (PR) and none experienced complete response (CR), resulting in an ORR of 12.0% (95% CI, 2.5%-31.2%); 16% of patients had stable disease (SD) and clinical benefit rate (CR + PR + [SD for ≥24 weeks]) was 20% (95% CI, 7-41). Median duration of response was 12.0 months (range, 7.4-15.9 months). The incidence of treatment-related adverse events was 64%; nausea (20%) and fatigue (12%) were most common and were predominantly grade 1/2. No treatment-related discontinuations or deaths occurred.Conclusions: Pembrolizumab was well tolerated with modest but durable overall response in certain patients with previously treated, advanced, PD-L1-positive, ER+/HER2- breast cancer. Clin Cancer Res; 24(12); 2804-11. ©2018 AACR.

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