ESTRO 2025 - Abstract Book

S621

Clinical - Breast

ESTRO 2025

Material/Methods: This was a Prospective observational study conducted between 2016-2023. 151 Patients with histopathologically proven infiltrating ductal carcinoma breast, were included in the study. Based on the indications patients also received regional-nodal irradiation. Patients were treated with 50 Gray in 25 fractions with additional 10-16 Gray boost in 5-8 fractions in BCS patients by Conventional Field border-based plans on LINAC machine. Patients who developed local or regional recurrences were studied and mapped for patterns of recurrences and compared with the RTOG Guidelines of CTV delineation. Patient characteristics are enumerated in Table-1.

Results: Median follow-up was 60 months. 15 patients (9.93%) developed loco-regional recurrences. When compared to the index population 40% of patients were triple negative in the recurrence group vs 35.1% in the index group, and 27% were HER2-positive in the recurrence group vs 17% in the index group. 5-year locoregional recurrence-free survival, distant metastasis-free survival, and overall survival were 90.07%, 82.79%, and 89.41% respectively. Most of the patients with recurrences had aggressive biological features with IDC grade-III tumors in 10/15 patients (66.67%) with >4 node-positive disease in 15/15 patients (100%), and triple-negative tumors in 6/15 (40%), HER2Neu 3+ in 4/15 patients (26.67%). Lymphovascular invasion was observed in 10/15 cases (66.67%). In 10 cases locoregional recurrences were diagnosed simultaneously as metastatic disease whereas 5 patients presented with distant metastases secondarily. Chest wall recurrences occurred in 12 cases (80%) that too marginal failure i.e. at the posterior border of RTOG volumes. 13 regional recurrences were observed in 11 patients, out of these 7 recurrences occurred in the SCF region (3 recurrences were outside RTOG CTV and 4 at the posterolateral border of SCF), 4 recurrences occurred inside RTOG level-III axilla, and 2 recurrences occurred inside RTOG volume in IMN region. Only 3 regional recurrences occurred outside RTOG CTV, while 10 recurrences occurred inside RTOG volumes. (Image-1,2)