Adding pembrolizumab to chemotherapy can significantly improve overall survival (OS) in patients with triple-negative breast cancer (TNBC) and high PD-L1 expression, according to final results from the KEYNOTE-355 study.

Patients with a PD-L1 combined positive score (CPS) of 10 or higher had a significant improvement in OS with pembrolizumab. These results were published in The New England Journal of Medicine.

The KEYNOTE-355 trial (ClinicalTrials.gov Identifier: NCT02819518) enrolled 847 patients with previously untreated, locally recurrent inoperable or metastatic TNBC. 


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Patients were randomly assigned 2:1 to pembrolizumab plus investigator’s choice of chemotherapy (n=566) or placebo plus investigator’s choice of chemotherapy (n=281). The chemotherapy options were nab-paclitaxel, paclitaxel, or gemcitabine plus carboplatin. 

A total of 636 patients had a PD-L1 CPS of 1 or higher—425 in the pembrolizumab arm and 211 in the placebo arm. There were 323 patients who had a CPS of 10 or higher—220 in the pembrolizumab arm and 103 in the placebo arm.

Among patients with a PD-L1 CPS of 1 or higher, there was no significant difference in OS between the treatment arms. The median OS was 17.6 months with pembrolizumab and 16.0 months with chemotherapy alone (hazard ratio [HR], 0.89; 95% CI, 0.76-1.05; P =.1125). The 18-month OS rate was 48.4% and 41.4%, respectively.

However, there was a significant improvement in OS with pembrolizumab among patients who had a PD-L1 CPS of 10 or higher. The median OS was 23.0 months in the pembrolizumab arm and 16.1 months in the chemotherapy-alone arm (HR, 0.73; 95% CI, 0.55-0.95; P =.0185). The 18-month OS rate was 58.3% and 44.7%, respectively. 

The researchers noted that a prior analysis from this trial showed that patients with a PD-L1 CPS of 10 or higher had a significant improvement in progression-free survival with pembrolizumab. 

Therefore, the current analysis “provides further support that a CPS of 10 or more is an appropriate criterion to define the population of patients with advanced triple-negative breast cancer who would be expected to derive benefit from pembrolizumab plus chemotherapy,” the researchers concluded. 

Disclosures: This research was supported by Merck Sharp and Dohme. Some study authors declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of disclosures.

Reference

Cortes J, Rugo HS, Cescon DW, et al. Pembrolizumab plus chemotherapy in advanced triple-negative breast cancer. N Engl J Med. Published online July 21, 2022. doi:10.1056/NEJMoa2202809.

This article originally appeared on Cancer Therapy Advisor