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Progression-Free Survival Improvements Favour Pembolizumab Plus Chemotherapy Over Chemotherapy in Patients with Advanced TNBC Enrolled in Asia

Patients enrolled from Asia demonstrated consistent findings with those in the overall population of the KEYNOTE-355 study
21 Nov 2020
Breast cancer;  Cancer Immunology and Immunotherapy

Pembrolizumab added to chemotherapy provided improved progression-free survival (PFS) in patients with previously untreated locally recurrent inoperable or metastatic triple negative breast cancer (TNBC) that were enrolled from Asia, investigators reported at the ESMO Asia Virtual Congress 2020, held from 20 to 22 November 2020.

Mastura Md Yusof of the Cancer Centre at Pantai Hospital in Kuala Lumpur, Malaysia, reported findings from the subgroup of patients from Asia participating in the phase III KEYNOTE-355 (NCT02819518) study.

Data from the overall population in this study showed that pembrolizumab plus chemotherapy significantly improved PFS as compared to placebo and chemotherapy in patients with previously untreated locally recurrent inoperable or metastatic TNBC and a PD-L1 combined positive score (CPS) ≥10.

KEYNOTE-355 enrolled patients with de novo or locally recurrent inoperable/metastatic TNBC who demonstrated a disease-free interval of 6 or more months. The patients were randomly assigned 2:1 to receive pembrolizumab plus chemotherapy (physician’s choice of nab-paclitaxel, paclitaxel, or gemcitabine/carboplatin) or placebo plus chemotherapy,  until completion (up to 35 administrations of pembrolizumab/placebo; chemotherapy may be continued at the investigator’s discretion), progression/toxicity, withdrawal of consent, or physician’s decision. Patients were stratified according to the chemotherapy on-study (taxane versus gemcitabine/carboplatin), PD-L1 CPS (≥1 versus <1), and prior (neo)adjuvant treatment with the same class of chemotherapy (yes versus no).

The Asian subgroup which consisted of 160 patients from Hong Kong, Japan, Korea, Malaysia, and Taiwan had similar baseline characteristics between the treatment groups and with the overall study population.

The dual-primary endpoints were PFS per RECIST v1.1 by blinded independent central review (BICR) and overal survival (OS) in the intent-to-treat (ITT) population and in PD-L1–positive patients, which was defined as CPS ≥10 or ≥1. Median PFS was estimated using the Kaplan-Meier method. Hazard ratios (HRs) and associated 95% confidence intervals (CIs) were estimated by using a Cox proportional hazard model.

Among the 113 patients from Asia in the ITT population treated with pembrolizumab plus chemotherapy and 47 receiving placebo plus chemotherapy the median follow-up was 25.7 months.

Pembrolizumab plus chemotherapy improved PFS over placebo plus chemotherapy in the Asia subgroup ITT population and activity was enhanced in patients that expressed higher levels of PD-L1.

In the Asia subgroup ITT population, median PFS with pembrolizumab plus chemotherapy was 8.8 months compared to 6.7 months with placebo plus chemotherapy (HR 0.61; 95% CI 0.41─0.90). With the respective treatments, the cohort with CPS ≥1 demonstrated median PFS of 7.7 months versus 5.6 months (HR 0.56; 95% CI 0.36─0.89) and patients with CPS ≥10 had median PFS of 17.3 months versus 5.6 months (HR 0.45; 95% CI 0.22─0.91).

Regarding the safety analysis, adverse events (AEs) were monitored until 30 days post-treatment and serious AEs were monitored for 90 days after treatment. With pembrolizumab plus chemotherapy, in the Asia subgroup the incidence of grade ≥3 treatment-related AEs was 78% compared to 79% with placebo plus chemotherapy. Rates of grade 3-4 immune-mediated AEs were consistent with the overall study population. No deaths were reported with either treatment.


Based upon the data in the subgroup of patients enrolled in Asia with previously untreated locally recurrent inoperable or metastatic TNBC, the authors concluded that a clinically meaningful improvement in PFS with pembrolizumab plus chemotherapy compared to chemotherapy was consistently demonstrated in the ITT population and in the PD-L1–positive patients.

The pembrolizumab benefit was most pronounced in patients with PD-L1 CPS ≥10.

Treatment with pembrolizumab plus chemotherapy was tolerable in the patients participating in KEYNOTE-355, and the findings support the addition of pembrolizumab to chemotherapy for the first-line treatment of Asian patients with metastatic TNBC with PD-L1 CPS ≥10  according to the authors.

KEYNOTE-355 was funded by Merck Sharp & Dohme Corp., a subsidiary of Merck & Co., Inc., Kenilworth, NJ, USA.


43O – Md Yusof M, Cescon DW, Rugo HS, et al. Phase 3 KEYNOTE-355 Study of Pembrolizumab (Pembro) vs Placebo (Pbo) + Chemotherapy (Chemo) for Previously Untreated Locally Recurrent Inoperable or Metastatic Triple-Negative Breast Cancer (TNBC): Results for Patients (Pts) Enrolled in Asia. ESMO Asia Virtual Congress 2020 (20 to 22 November).

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