The following article features coverage from the 2020 San Antonio Breast Cancer Symposium. Click here to read more of Cancer Therapy Advisor‘s conference coverage.

The addition of pembrolizumab to chemotherapy benefited previously untreated patients with inoperable or metastatic triple-negative breast cancer (TNBC), regardless of chemotherapy regimen, according to an updated analysis of the randomized phase 3 KEYNOTE-355 trial ( Identifier: NCT02819518). The data were presented at the 2020 Virtual San Antonio Breast Cancer Symposium (SABCS).

A total of 847 patients were randomly assigned treatment with pembrolizumab plus chemotherapy or placebo plus chemotherapy. Possible chemotherapy regimens were nab-paclitaxel, paclitaxel, or gemcitabine plus carboplatin.

The updated analysis reported a prespecified exploratory endpoint on the consistency of treatment effect by chemotherapy regimen in the overall study population and among patients with programmed cell death 1 (PD-L1)–positive disease.

Continue Reading

For the overall study population, the addition of pembrolizumab to chemotherapy reduced the risk of disease progression by 18% (hazard ratio [HR], 0.82; 95% CI, 0.69-0.97).

A reduced risk of disease progression for patients who received pembrolizumab was seen regardless of whether they received nab-paclitaxel (HR, 0.69; 95% CI, 0.51-0.93), paclitaxel (HR, 0.57; 95% CI, 0.35-0.93), or gemcitabine plus carboplatin (HR, 0.93; 95% CI, 0.74-1.16). This benefit across chemotherapy regimens was consistent for patients with tumors that had a combined positive score (CPS) equal to or greater than 10 or a CPS equal to or greater than 1.

Further analysis of the trial also revealed that patients with greater PD-L1 expression had a higher response rate and greater disease control.

Specifically, among patients with a CPS or at least 10, the overall response rate was 53.2% for the combination arm and 39.8% for the chemotherapy-alone arm. The disease control rate was 65% for the combination arm and 54.4% for the chemotherapy-alone arm.

“Results for the key secondary endpoints of [overall response rate], [disease control rate], and [duration of response] favored pembrolizumab plus chemotherapy, with the treatment effect increasing with PD-L1 enrichment,” the presenters wrote on their slides. “These data further support a role for the addition of pembrolizumab to standard chemotherapy for the first-line treatment of mTNBC.”

Study discussant Sylvia Adams, MD, professor of medicine and director of the Breast Cancer Center at New York University, commented that the exploratory endpoint finding is “very important” because it is currently unknown what the optimal chemotherapy backbone is.

However, she cautioned that this analysis was exploratory and not powered to show the “winner” as it relates to the best chemotherapy backbone. 

Read more of Cancer Therapy Advisor‘s coverage of the 2020 SABCS meeting by visiting the conference page.


Rugo HS, Schmid P, Cescon DW, et al. Additional efficacy endpoints from the phase 3 KEYNOTE-355 study of pembrolizumab plus chemotherapy vs placebo plus chemotherapy as first-line therapy for locally recurrent inoperable or metastatic triple-negative breast cancer. Presented at: 2020 Virtual San Antonio Breast Cancer Symposium; December 8-11, 2020. Abstract GS3-01.