Abstract P3-12-02: Intraoperative radiotherapy outcomes in early-stage breast cancer: A study in elderly Canadian women

Objective. Breast-conserving therapy with external beam radiotherapy (EBRT) is currently the standard of care for women with early breast cancer. Our aim was to determine if early-stage breast cancers treated with lumpectomy and primary intraoperative radiotherapy (IORT) have comparable local recurrence rates. This is the first study examining the Canadian experience with IORT. Methods. Patients who underwent breast-conserving therapy with pre-pathology IORT between 2007- 2017 were retrospectively identified. The primary outcome measure was ipsilateral breast tumor recurrence (IBRT). A time to event analysis was performed; Kaplan-Meier estimates report the fraction of patients living free of recurrence. Secondary outcomes included acute and chronic wound complications. Results. 106 patients with a median age of 70 (IQR 65-75) were included. Median follow-up was 33 months. The majority of patients had screen-detected (94.3%), estrogen-receptor positive (96.2%), HER2neu negative (93.4%), invasive ductal carcinomas (92.5%). Only 50 (47.6%) were prescribed adjuvant endocrine blockade. IBTR occurred in 5 (4.7%) patients. Five and ten-year local recurrence-free rates were 0.95 and 0.81, respectively. The superficial skin infection rate was 9.4%. Acute symptomatic seromas occurred in 23 (21.7%), while only 10 (9.4%) persisted chronically. Conclusion. In this cohort of Canadian post-menopausal women treated with breast-conserving surgery and IORT, the IBTR approached 5%. Despite selection of low-risk patients, the local recurrence rate is higher than what is reported in the literature with EBRT. The low rates of prescribed adjuvant systemic therapy may have contributed to this outcome. Citation Format: Elmi M, Tigert A, Escallon J, Zagorski B, Leong W, Vranic M, Fyles A, Vitkin A, Cil T, McCready D. Intraoperative radiotherapy outcomes in early-stage breast cancer: A study in elderly Canadian women [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P3-12-02.