Immuno-Oncology Resource Center

Immuno-Oncology Resource Center


Press Release

July 27, 2021
1 min read

Pembrolizumab plus chemotherapy extends OS in breast cancer subset, topline data show


Press Release

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The addition of pembrolizumab to first-line chemotherapy extended OS for certain patients with metastatic triple-negative breast cancer, according to topline data released by the agent’s manufacturer.

Researchers reported a statistically significant and clinically meaningful OS benefit with pembrolizumab (Keytruda, Merck) — an anti-PD-1 therapy — among patients whose tumors expressed PD-L1 with a combined positive score (CPS) of 10 or greater, according to a Merck-issued press release.

Mammogram snapshot of breasts of a female patient on the monitor with undergoing mammography test on the background.
Source: Adobe Stock.

Results of the randomized phase 3 KEYNOTE-355 trial revealed no new safety signals.

“In the fight against triple-negative breast cancer, the subtype with the worst survival prognosis, new options that can extend the lives of patients are urgently needed,” Vicki Goodman, MD, vice president for clinical research at Merck Research Laboratories, said in the press release. “These new overall survival results confirm that Keytruda in combination with chemotherapy represents an important treatment option for certain patients with metastatic [triple-negative breast cancer]. We thank the patients and investigators who have allowed us to evaluate innovative treatment approaches, anchored by Keytruda, across multiple settings and stages of triple-negative breast cancer.”

The second part of the two-part KEYNOTE-355 trial included 847 patients with previously untreated, locally recurrent inoperable or metastatic triple-negative breast cancer.

Researchers randomly assigned patients 2:1 to 200 mg pembrolizumab every 3 weeks plus investigator’s choice of nab-paclitaxel (Abraxane, Celgene), paclitaxel or gemcitabine/carboplatin (n = 566), or placebo plus chemotherapy (n = 281). About 75% of patients in each treatment group had tumor PD-L1 expression with a CPS of at least 1, and about 38% had a CPS of at least 10.

OS and PFS among patients whose tumors expressed PD-L1 and among all participants served as study endpoints.

Results of a prior interim analysis showed the pembrolizumab combination significantly improved PFS vs. chemotherapy alone among patients with a CPS of 10 or higher. The FDA approved the combination for this patient population based on the overall findings of the trial.

The OS results will be submitted to regulatory authorities and presented at a future medical meeting.