Preoperative Chemotherapy, Pembrolizumab and Low or High Dose RADiation in an Expansion Cohort of Node(+), Triple Negative Breast Cancer

This is a prospective radiation dose-finding, phase 2 expansion study of the Triple Negative (TN) cohort of the multicenter randomized study P-RAD (A Randomized Study of Preoperative Chemotherapy, Pembrolizumab and No, Low or High Dose RADiation in Node-Positive, HER2-Negative Breast Cancer; NCT04443348) that seeks to establish the optimal dose of radiation therapy (RT) to elicit an immune response when combined with immune checkpoint inhibitor (ICI) in breast cancer patients. Eligible subjects include women or men with operable, lymph node-positive, triple negative (TN) breast cancer who are candidates for standard of care neoadjuvant chemo-immunotherapy (NAC) based on the KEYNOTE-522 clinical trial. Thirty-two (n=32) patients will be randomized 1:1 to receive either low RT boost (9Gy total) or high RT boost (24Gy total). All RT will be delivered to the intact breast tumor in 3 daily fractions over 3 days. In the Neoadjuvant Phase, the first cycle (C1) of pembrolizumab (200 mg i.v.) will be administered within 0-2 days of initiating RT. Participation in this study requires availability of residual diagnostic tissue biopsies of the primary tumor and metastatic lymph node for research use. If this tissue is not available, baseline research biopsies will be performed. Additionally, a research biopsy of the breast tumor and lymph node is required on Day 10-14 of C1 of pembrolizumab. After completion of the research biopsy in Week 2, the participants can commence standard-of-care neoadjuvant chemotherapy and pembrolizumab at the discretion of their medical oncology provider. After completing NAC, participants will undergo standard of care surgical resection of the breast and axillary lymph nodes, at the discretion of their surgical oncology provider. In the Adjuvant Phase, participants will receive standard of care adjuvant systemic therapy and standard of care adjuvant radiotherapy (if indicated), although recognizing that the breast tumor boost portion of this treatment has already been administered preoperatively. Except for late radiation adverse reactions of special interest, which will be followed yearly for up to 5 years, follow-up will occur every 6 months for 3 years.