Intraoperative radiation therapy (IORT) in Taiwanese breast cancer patients: factors influencing local relapse risk and disease-free survival.

Background: Intraoperative radiation therapy (IORT) delivered during breast-conserving surgery may streamline treatment and enhance cosmetic outcomes. However, optimal patient selection criteria remain uncertain, especially in Asian populations, where international guidelines may not be fully applicable. This study aimed to evaluate local recurrence rates, identify key prognostic factors, and assess the impact of supplemental external beam radiation therapy (EBRT) in Taiwanese patients receiving IORT. Materials and methods: This retrospective analysis included 1,306 Taiwanese patients who underwent IORT between June 2014 and December 2021. Patients were stratified into low-risk and high-risk groups based on institutional criteria. Low-risk patients were those meeting all of the following: age ≥ 45 years, tumor size ≤ 3.5 cm, negative nodal involvement, Ki-67 ≤ 30%, hormone receptor (HR) positivity, and HER2 negativity. Patients who did not meet one or more of these criteria were classified as high-risk and were recommended to receive supplemental external beam radiation therapy (EBRT) following IORT. Results: In our cohort of 1,306 patients, the 3-year disease-free survival rate was 93.11% [95% confidence interval (CI): 91.6-94.4%], with 87 patients (6.89%) experiencing recurrence. The median age was 52 years, and the median follow-up duration was 30.5 months. The overall local recurrence rate was 9.3%, which declined to 1.78% after excluding patients who did not receive indicated adjuvant therapies. Multivariable analysis identified Ki-67 > 30%, omission of hormone therapy, and omission of recommended EBRT as significant predictors of local recurrence, whereas age < 45 was not independently associated with increased risk. Among high-risk patients, the addition of EBRT was associated with a 48.8% reduction in recurrence, achieving outcomes comparable to those of low-risk patients. Conclusions: Age alone should not determine IORT eligibility. A multifaceted approach, including tumour biology and adherence to recommended therapies, is essential. Supplemental EBRT improves outcomes in high-risk patients, and adapting guidelines may enhance patient selection in Asian populations.