ESMO 2023: Focus on Pathologic Complete Response in KEYNOTE-756 Breast Cancer Trial

By: Celeste L. Dixon
Posted: Friday, November 3, 2023

Adding pembrolizumab to chemotherapy significantly increased the pathologic complete response rate in patients with early-stage, high-risk, estrogen receptor (ER)-positive, HER2-negative breast cancer who participated in the global phase III KEYNOTE-756 trial. Fatima Cardoso, MD, of Champalimaud Clinical Center, Lisbon, and colleagues presented the results of this 1,286-patient study at the European Society for Medical Oncology (ESMO) Congress 2023 (Abstract LBA21). Also, they reported, safety was consistent with the known profiles of each regimen. Along with pathologic complete response, the trial’s other primary endpoint is event-free survival, for which results remain immature.

The patients were randomly assigned on a 1:1 basis to receive chemotherapy plus pembrolizumab (n = 635) or placebo (n = 643). At the final pathologic complete response analysis (first interim analysis data cutoff of May 2023), the median follow-up was 33.2 months. In the intention-to-treat population, 24.3% of the pembrolizumab arm had a statistically significant improvement in pathologic complete response vs 15.6% of the placebo arm (P = .00005).

Eligible patients had T1c–2 (≥ 2 cm) cN1–2 or T3–4 cN0–2, centrally confirmed, grade 3, invasive ductal ER-positive, HER2-negative breast cancer. Neoadjuvant treatment was either pembrolizumab at 200 mg every 3 weeks or placebo, both given with paclitaxel once weekly for 12 weeks, then four cycles of doxorubicin or epirubicin plus cyclophosphamide. Following definitive surgery, with or without radiation therapy, patients received pembrolizumab or placebo for nine cycles plus standard endocrine therapy. Stratification factors included region (Eastern Europe, China, or other), tumor PD-L1 status (combined positive score ≥ 1 [positive] vs < 1 [negative]), nodal involvement (positive vs negative), ER positivity (≥ 10% vs < 10%), and anthracycline schedule (every 3 vs every 2 weeks).

Disclosure: The study authors’ disclosure information can be found at cslide.ctimeetingtech.com.

ESMO Congress 2023