Tumor-Infiltrating Lymphocytes and Preoperative Partial Breast Irradiation in Early-Stage Breast Cancer: Insights From the Prospective PAPBI Cohort

Gunster, JLB; Groen, EJ; Salgado, R; Marijnen, CAM; Scholten, AN

Author(s): Gunster, JLB; Groen, EJ; Salgado, R; Marijnen, CAM; Scholten, AN;
Details: Publication Year 2026-02-01,Volume 124,Issue #2,Page 387-394
Journal Title: International Journal of Radiation Oncology, Biology, Physics
Publication Type: Research article
Abstract: PURPOSE: Current understanding of the interaction between radiation therapy (RT) and tumor-infiltrating lymphocytes (TILs) is limited. We investigated the impact of preoperative accelerated partial breast irradiation (PAPBI) on TILs in early-stage breast cancer patients. In addition, we evaluated whether baseline TILs were associated with pathologic response to RT. METHODS AND MATERIALS: In the prospective PAPBI trial, early-stage breast cancer patients received preoperative RT (10 × 4 or 5 × 6 Gy), followed by a wide local excision after 6 weeks. Matched control patients who underwent postoperative RT were retrospectively collected for validation. Stromal TILs (sTILs) were manually scored on hematoxylin- and eosin-stained slides from diagnostic biopsy and resection specimens, following established guidelines. Baseline differences in sTILs between patients with and without a pathologic complete response (pCR) were analyzed using the Mann-Whitney U test, and longitudinal changes in sTILs were evaluated with a linear mixed model. RESULTS: A total of 72 PAPBI patients and 68 matched controls were included. In the PAPBI cohort, baseline sTILs were generally low, with a median of 2% (IQR, 1%-2%). Eight patients (11%) achieved a pCR, and these patients had significantly higher baseline sTILs compared with patients without a pCR (P = .021). Among the 64 PAPBI patients with evaluable preirradiation and postirradiation samples, a minimal, nonsignificant increase in sTILs was observed following RT. Control patients had similarly low baseline sTILs (median, 2%; IQR, 1%-2%), with no significant changes over time. CONCLUSIONS: In this cohort of early-stage breast cancer patients receiving preoperative partial breast irradiation, longitudinal assessment showed minimal changes in sTILs after RT. In patients who achieved a pCR, we observed significantly higher baseline sTILs compared with those without a pCR.
Publisher: Elsevier
Keywords: Humans; Female; *Breast Neoplasms/pathology/radiotherapy/surgery/immunology; *Lymphocytes, Tumor-Infiltrating/radiation effects; Middle Aged; Prospective Studies; Aged; Adult; Neoplasm Staging; Case-Control Studies
Department(s): Laboratory Research
Publisher's Version: https://doi.org/10.1016/j.ijrobp.2025.08.058
Open Access at Publisher's Site: https://doi.org/10.1016/j.ijrobp.2025.08.058
Terms of Use/Rights Notice: Refer to copyright notice on published article.

Creation Date: 2025-10-21 02:34:15

Last Modified: 2026-01-20 05:38:39