S307
Clinical - Breast
ESTRO 2026
to establish the role of hypo-fractionated RT and the safety aspects, especially in resource constrained settings with large patient loads and with advanced disease. References: 1. Veronesi U, Arnone P, Veronesi P, et al. The value of radiotherapy on metastatic internal mammary nodes in breast cancer. Results on a large series. Ann Oncol. 2008;19(9):1553-1560.2. Kim J, Chang JS, Choi SH, et al. Radiotherapy for initial clinically positive internal mammary nodes in breast cancer. Radiat Oncol J. 2019;37(2):91-100. Keywords: IM Node, Breast cancer, hypofractionation Management and outcomes of locally recurrent breast cancer: A population-based analysis in Ontario, Canada Danielle Rodin 1,2 , Rinku Sutradhar 3,4 , Ezra Hahn 1,2 , Katarzyna J Jerzak 5 , Lena Nguyen 3 , Lawrence Paszat 3,2 , Eileen Rakovitch 2,6 1 Radiation Medicine Program, Princess Margaret Cancer Centre, Toronto, Canada. 2 Department of Radiation Oncology, University of Toronto, Toronto, Canada. 3 Cancer Research Program, Institute for Clinical Evaluative Sciences, Toronto, Canada. 4 Institute of Health Policy, Management and Evaluation, Dalla Lana School of Public Health, University of Toronto, Toronto, Canada. 5 Department of Medical Oncology, Sunnybrook Health Sciences Centre, Toronto, Canada. 6 Department of Radiation Oncology, Sunnybrook Health Sciences Centre, Toronto, Canada Purpose/Objective: Ipsilateral breast recurrence (IBR) remains an ongoing risk following initial treatment for localized breast cancer with breast-conserving surgery (BCS) and radiation (RT). We conducted a population-based study to describe the incidence, treatment patterns, and oncologic outcomes associated with IBR in patients previously treated with BCS+RT, with a focus on the frequency and outcomes of repeat BCS followed by reirradiation (rRT). Material/Methods: A population-based cohort of women who were Mini-Oral 3622 diagnosed with non-metastatic invasive breast cancer or ductal carcinoma in situ (DCIS) between April 1, 2005 and December 31, 2023 who were treated with BCS+RT and subsequently developed IBR that was surgically excised. The index date was defined as the time of first IBR. The primary outcome was time to second IBR (IBR2). Fine and Gray competing risk regression models were used to evaluate factors associated with the risk of IBR2 and cumulative incidence functions were used to estimate time to
recurrence or death was seen in a total of 36(24.5 %) patients. The estimated Disease-Free Survival and Overall Survival at 3 years are 74.7% and 97.9%, respectively. There has not been any documented clinically evident cardiac or pulmonary toxicity, in this study cohort.
Conclusion: Hypo-fractionated RT is feasible and results in satisfactory outcomes in the treatment of patients of breast cancer with IMN nodes. Further long term follow up and randomized clinical trials are necessary
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