Breast Cancer Coverage from Every Angle

KEYNOTE-355 Update on Pembrolizumab in Triple-Negative Breast Cancer

By: Julia Fiederlein
Posted: Thursday, April 1, 2021

In the KEYNOTE-355 trial, patients with metastatic triple-negative breast cancer who expressed PD-L1 with a Combined Positive Score (CPS) of at least 10 seemed to derive a progression-free survival benefit from first-line treatment with pembrolizumab plus chemotherapy versus chemotherapy alone. Using the data from this phase III study, Hope S. Rugo, MD, of the University of California San Francisco Comprehensive Cancer Center, and colleagues conducted additional efficacy analyses. Their findings, which were presented during the virtual edition of the 2021 PER’s Miami Breast Cancer Conference (Abstract 22), further support pembrolizumab's addition to standard chemotherapy in this patient population.

A total of 847 patients with a locally recurrent inoperable or metastatic disease were enrolled in the intention-to-treat (ITT) population; they were randomly assigned in a 2:1 ratio to receive chemotherapy in combination with pembrolizumab (n = 566) or a placebo (n = 281). The chemotherapy regimens included nab-paclitaxel, paclitaxel, and gemcitabine plus carboplatin. Patients were stratified by chemotherapy regimen, PD-L1 status, and whether they received prior treatment with the same class of chemotherapy in the neoadjuvant or adjuvant setting.

In patient groups with a CPS of at least 10 (9.7 vs. 5.6 months; hazard ratio = 0.65; P = .0012), at least 1 (7.6 vs. 5.6 months; hazard ratio = 0.74; P = .0014), and in the ITT population (7.5 vs. 5.6 months; hazard ratio = 0.82), the median duration of progression-free survival was longer with pembrolizumab than with the placebo. Based on the subgroup analyses results, pembrolizumab seemed to improve progression-free survival compared with the placebo; progression-free survival benefits were observed regardless of the chemotherapy regimen. The objective response rate, disease control rate, and response duration also appeared to favor pembrolizumab versus the placebo; the treatment effect seemed to improve with increasing PD-L1 enrichment.

Disclosure: No information regarding conflicts of interest was provided.

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