ASO Visual Abstract: Recurrence and Survival Rates for 1400 Early Breast Tumors Treated with Intraoperative Radiation Therapy (IORT)

Introduction: Intraoperative radiotherapy (IORT) permits accurate delivery of radiation therapy directly to the tumor bed. We report local, regional, and distant recurrence data along with overall and breast cancer-specific survival for 1400 tumors treated with x-ray IORT. Methods: A total of 1367 patients with 1400 distinct tumors were enrolled in a registry trial. All received breast conservation surgery and low-energy 50 kV x-ray IORT. To be eligible for excision plus IORT as the only local treatment, histopathology had to confirm tumor size ≤30 mm, margins ≥2 mm, negative lymph nodes, and no extensive lymphovascular invasion. Patients who failed any parameters were referred for additional surgery and/or whole breast radiation therapy (WBRT). Results: There were 64 ipsilateral local recurrences, 60 were in the IORT only group, 7 axillary recurrences, and 7 distant recurrences. Forty-one local recurrences were within the same quadrant as the index cancer. Twenty-three were in different quadrants. With 62 months of median follow-up, the 5-year Kaplan–Meier probability of any event for all 1400 tumors was 5.27%. For 1175 patients who received IORT only, it was 5.98%. For favorable subtypes, it ranged from 2.41 to 4.31%. Multivariate analysis revealed that biologic subtype luminal A and the addition of WBRT significantly reduced the risk of local recurrence. Conclusions: The local, regional, and distant recurrence rates observed were comparable to those reported in the literature for IORT but higher than those reported for standard forms of WBRT, hypofractionated treatment, or APBI. IORT benefits include convenience, decreased exposure to medical environments, and low complication rates. © 2022, The Author(s).