ESTRO 2024 - Abstract Book

S642

Clinical - Breast

ESTRO 2024

2380

Digital Poster

PMRT improves Disease-Free Survival after Total Mastectomy with 1-3 Positive Sentinel Nodes

Miranda Addie 1 , Tomás Y. T. De Souza 2 , Alexandre-Darius Miron 3 , Ericka Iny 4 , Basmah Alhassan 2 , Amina Ferroum 4 , Stephanie Wong 4,5 , Ipshita Prakash 4,5 , Sarkis Meterissian 1,4,6 , Tarek Hijal 2,7 1 McGill University, Department of Surgical and Interventional Sciences, Montréal, Canada. 2 McGill University, Department of Oncology, Montréal, Canada. 3 Université de Montréal, Faculty of Pharmacy, Montréal, Canada. 4 McGill University, Medical School, Montréal, Canada. 5 Lady Davis Institute for Medical Research, Sir Mortimer B. Davis Jewish General Hospital, Montréal, Canada. 6 McGill University Health Centre, Department of Surgery, Montréal, Canada. 7 McGill University Health Centre, Division of Radiation Oncology, Montréal, Canada

Purpose/Objective:

The randomized, multicentre, open-label, phase 3 non-inferiority EORTC 10981-22023 AMAROS trial confirmed the safety and efficacy of axillary radiation in patients with breast cancer and positive lymph nodes treated by breast conserving surgery or mastectomy and sentinel node biopsy (SLNB) without completion axillary dissection (cALND). The objectives of this study were to assess the outcomes of patients treated by mastectomy and sentinel node biopsy (SLNB) with or without completion axillary dissection (cALND), and to investigate the impact of post mastectomy radiotherapy (PMRT) on these patients.

Material/Methods:

A multicenter retrospective cohort study was conducted of all stage I and II breast cancer patients with clinically negative axillae that underwent mastectomy and had 1-3 positive lymph nodes (SLN+) at two academic institutions. Clinicopathological and radiological features, adjuvant management and outcomes were obtained for the patient population. Radiation data were collected for the whole cohort, while regional nodal irradiation (RNI) volumes were collected from one of the two institutions. Kaplan-Meier survival curves were used to estimate overall survival (OS), disease-free-survival (DFS) and locoregional recurrence (LRR). Multiple logistic regression was used to compare whether performing a cALND altered adjuvant treatment.

Results:

This cohort was comprised of 139 patients, with a median follow up of 5.2 years. Median age was 54 years (IQR: 47 68). Most patients had clinical T1 disease (48%), while 29% had cT2 and 23% had cT3 disease. Pathologic stage was pN1 in 91% of patients, with 6.5% having pN2 disease and 2.9% having pN3 disease. 34 patients (25%) underwent cALND, while 111 patients (79.8%) received PMRT. Patients who received PMRT were more likely to have macrometastases (77% vs. 54%, p=0.01) and larger nodal metastatic deposits (5.0 mm vs. 2.1 mm, p=0.017). Radiation dose consisted of 40.05 Gy in 15 fractions in 48% of patients, 50-50.4 Gy in 25-28 fractions in 40% of patients and ultrahypofractionated RT in 10 % of patients. 32% of patients received a chest wall boost, with 10 Gy in 4 or 5 fractions being the most common dose (78% of patients). Use of PMRT was the same whether patients underwent cALND or SNLB (79% vs. 82%, p=0.68). Radiation volumes were available for all patients treated in one of