The Food and Drug Administration (FDA) has granted accelerated approval to Keytruda® (pembrolizumab; Merck) in combination with chemotherapy for patients with locally recurrent unresectable or metastatic triple-negative breast cancer (TNBC) whose tumors express PD-L1 (combined positive score [CPS] ≥10), as determined by an FDA approved test.

The approval was based on data from the double-blind, placebo-controlled phase 3 KEYNOTE-355 trial that evaluated the efficacy and safety of pembrolizumab plus chemotherapy in adults with locally recurrent inoperable or metastatic TNBC, who had not been previously treated with chemotherapy in the metastatic setting. Patients were randomized 2:1 to receive either pembrolizumab 200mg on day 1 every 3 weeks or placebo in combination with chemotherapy. The primary end point of the study was progression free survival (PFS); additional efficacy measures were overall survival, objective response rate (ORR) and duration of response (DoR).

Among patients who were PD-L1 positive with a CPS greater than or equal to 10, results showed that treatment with pembrolizumab plus chemotherapy significantly reduced the risk of disease progression or death by 35% (hazard ratio [HR] 0.65; 95% CI, 0.49-0.86; =.0012), with a median PFS of 9.7 months (95% CI, 7.6-11.3) compared with 5.6 months (95% CI, 5.3-7.5) for placebo plus chemotherapy. Additionally, the ORR and DoR in the pembrolizumab arm were 53% (95% CI, 46-60) and 19.3 months (95% CI, 9.9-29.8), respectively, vs 40% (95% CI, 30-50) and 7.3 months (95% CI, 5.3-15.8) for placebo.

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“Approximately 15-20% of patients with breast cancer are diagnosed with triple-negative breast cancer, which is a difficult-to-treat and aggressive cancer,” said Dr Hope Rugo, director of Breast Oncology and Clinical Trials Education, University of California San Francisco (UCSF) Helen Diller Family Comprehensive Cancer Center. “Notably, in KEYNOTE-355, Keytruda was combined with 3 different chemotherapy regimens: paclitaxel, nab-paclitaxel or gemcitabine and carboplatin.

As for safety, the most common adverse reactions (incidence of greater than or equal to 20%) for pembrolizumab plus chemotherapy were fatigue, nausea, diarrhea, constipation, vomiting, alopecia, rash, cough, decreased appetite, and headache.

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The PD-L1 IHC 22C3 pharmDx (Dako North America, Inc) was also approved as a companion diagnostic for selecting patients with TNBC for treatment with pembrolizumab.

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1.    FDA grants accelerated approval to pembrolizumab for locally recurrent unresectable or metastatic triple negative breast cancer. [press release]. US Food and Drug Administration; November 13, 2020. 

2.    FDA approves Merck’s Keytruda® (pembrolizumab) in combination with chemotherapy for patients with locally recurrent unresectable or metastatic triple‑negative breast cancer whose tumors express PD-L1 (CPS ≥10). [press release]. Kenilworth, NJ: Merck; November 13, 2020.

This article originally appeared on MPR