ESTRO 2024 - Abstract Book

S463

Clinical - Breast

ESTRO 2024

In this single-center retrospective study, we included breast cancer patients from 2008-2018 with positive lymph nodes which received RNI using arc technique. Patients with less than 1 year follow up and those presented with distant metastasis before radiation were excluded. Our study endpoints include disease free survival (DFS), overall survival (OS), failure patterns and radiation-related adverse events.

Results:

A total of 188 patients treated with volumetric modulated arc therapy (VMAT) or helical tomotherapy (HT) were analyzed; 83 patients received IMNI while the other 105 patients received RNI without IMNI. The median follow-up time was 6.2 years. Nearly all received adjuvant chemotherapy and 72.9% received hormone therapy in both groups. No significant difference in age, laterality, BMI, comorbidities, histological grade and T stage were noted. The IMNI group had higher clinical staging at diagnosis with more clinical N3 patients (15.7% vs 1.0%) while the non IMNI group had lower pathological staging with more pathological N1 patients (57.1% vs 33.7%). The total radiation dose was also higher in patients which received IMNI (5651 Gy vs 5420 Gy, p<0.001). No ≥ grade 3 radiation -related adverse effects were identified. In our study cohort, 38 patients developed recurrence and 16 breast-cancer specific deaths were counted. There were no significant differences in DFS and OS between patients who received RNI with or without IMNI. Both groups had a higher rate of distal recurrence (10/14 in the IMNI group and 14/24 in the non-IMNI group). Subgroup analysis showed a survival benefit which favored sparing IMNI in patients with pathological N3 (p=0.03) and ER/PR-negative breast cancer (p=0.02).