Endocrine therapy increases risk of fat necrosis risk after lumpectomy and Intra operative radiation therapy (IORT) in early-stage breast cancer

Abstract Objective The incidence of fat necrosis (FN) is well known (15-35%) with accelerated partial breast irradiation (APBI) techniques such as brachytherapy and external beam radiation therapy. However, specific data related to Intraoperative radiation therapy (IORT) is lacking. Methods This retrospective cohort study was conducted in a single institution with 489 post-menopausal female patients > 45-year-old with early-stage invasive breast cancer (T1-2N0M0) who underwent lumpectomy and IORT between March 2016 and June 2023. The median age was 68 years (range 49-93). WBRT was additionally offered in 36 patients (7.4%) for exhibiting local adverse features. Adjuvant endocrine therapy (consisting of aromatase inhibitors) and chemotherapy were administrated in 384 patients (78.5%) and 12 patients (2.4%) respectively. The incidence and potential predictors of fat necrosis were reviewed. Results Median follow-up was 36 months, the 3-year incidence of FN was 63.1% (95% CI 58.2%-68%). Grade 1, grade 2 and grade 3 FN were present in 278 (57%),10 patients (2%) and 3 patients (0.6%) respectively. The median FN size was 22mm (range: 5-50). Adjuvant endocrine therapy but not whole breast radiation therapy was found to be the only independent predictor associated with significantly increased risk of FN (1.77 (95% CI 1.14-2.76), p = 0.01). Conclusions IORT carries a higher largely asymptomatic FN incidence. Risk increases with aromatase inhibitors, not with WBRT. Endocrine therapy should not be withheld, and asymptomatic FN should not alter routine surveillance. Advances in knowledge Endocrine therapy is associated with increased risk of fat necrosis after lumpectomy and IORT