What question did this study set out to answer?

This study aims to evaluate whether a preoperative regimen of pembrolizumab combined with subablative radiotherapy can enhance immune responses in triple negative breast cancer.

February 19, 2026Clinical Cancer Research

Abstract PS4-07-15: A single preoperative pembrolizumab dose plus a single subablative radiotherapy fraction (7 Gy) elicits anti-tumor immune response and increases stromal tumor infiltrating lymphocytes in triple negative breast cancer: a phase 1b/2 study

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This study aims to evaluate whether a preoperative regimen of pembrolizumab combined with subablative radiotherapy can enhance immune responses in triple negative breast cancer.
Open-label phase 1b/2 trial with early stage invasive breast cancer participants
Each received a single preoperative dose of pembrolizumab, with or without radiotherapy
Co-primary endpoints included feasibility of the regimen and immune activation measured by changes in stromal tumor infiltrating lymphocytes (sTILs) and circulating T cells.
56% of participants receiving the combined treatment achieved significant tumor size reduction (>30%)
Stromal tumor infiltrating lymphocytes increased from 20% to 50% overall after treatment
Increased proportions of activated T cells were observed post-treatment, indicating enhanced immune response.

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Implication

Phase 1b/2 trial demonstrates improved anti-tumor immune response in triple negative breast cancer, suggesting new treatment strategies.

Cite This Study

Tchou et al. (2026) studied this question.

synapsesocial.com/papers/6996a85cecb39a600b3ef02a https://doi.org/10.1158/1557-3265.sabcs25-ps4-07-15

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Abstract PS4-07-15: A single preoperative pembrolizumab dose plus a single subablative radiotherapy fraction (7 Gy) elicits anti-tumor immune response and increases stromal tumor infiltrating lymphocytes in triple negative breast cancer: a phase 1b/2 study

Key Points

Discussion

Implication

Cite This Study

Abstract PS4-07-15: A single preoperative pembrolizumab dose plus a single subablative radiotherapy fraction (7 Gy) elicits anti-tumor immune response and increases stromal tumor infiltrating lymphocytes in triple negative breast cancer: a phase 1b/2 study

Key Points

Discussion

Implication

Cite This Study

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