Intraoperative Tumor Bed Boost With Electrons in Breast Cancer of Clinical Stages I Through III: Updated 10-Year Results.

Purpose: To assess retrospectively the role of an anticipated intraoperative tumor electron radiation therapy (IOERT) as a bed boost during breast-conserving surgery followed by conventional whole breast irradiation (WBI).

Methods And Materials: An unselected cohort of 770 breast cancer patients of all risk types was analyzed in terms of local control (LC) and survival outcome. Patients were treated by breast-conserving surgery, IOERT of 10 Gy, and WBI to total median doses of 54 Gy (range, 1.6-2). Patients were retrospectively analyzed for LC, locoregional control, metastasis-free survival (MFS), overall survival (OS), and breast cancer-specific survival (BCSS).

Results: After a median follow-up of 121 months (range, 4-200), 21 (2.7%) in-breast recurrences (IBRs) were observed, 107 patients (14%) died and 106 (14%) developed metastases. Ten-year rates of LC, locoregional control, MFS, OS, and BCSS amounted to 97.2%, 96.5%, 86%, 85.7%, and 93.2 %, respectively. In multivariate analysis, HER2+ and triple-negative breast cancer subtype (TN) turned out to be significant negative predictors for IBRs (hazard ratios, 15.02 and 12.87, respectively; P < .05). Sorted by subtypes, 10-year LC rates were observed in 98.7% (range, 96.7%-99.5%) (luminal A), 98% (range, 94%-99.3%) (luminal B), 87.9% (range, 66.2%-96%) (HER2+), and 89% (range, 76.9%-94.9%) (TN), respectively.

Conclusions: After 10 years, boost IOERT maintains high LC rates in any risk setting.