ESTRO 2025 - Abstract Book

S453

Clinical - Breast

ESTRO 2025

2 nd iBCE with high-risk molecular profile by comparing oncological outcomes after 2 nd BCT or salvage mastectomy (SM).

Material/Methods: Oncological outcomes were analyzed using a propensity score-matched cohort analysis study on patients diagnosed with a 2 nd iBCE between 01/1995 and 06/2017. Patient data were collected from 15 hospitals/cancer centres (7 European countries). Patients were offered SM or lumpectomy plus interstitial brachytherapy. Propensity scores were calculated with logistic regression and multiple imputations. Matching (1:1) was achieved using 10 clinical/pathological data related to 2 nd iBCE. The primary endpoint was 5-year overall survival (OS) from the salvage surgery date. Secondary endpoints were 5-year cumulative incidence of 3 rd ipsilateral breast event (3 rd iBCE-CI), regional relapse (RR-CI) and distant metastasis (DM-CI), and disease-free (DFS) and cause-specific (CSS) survivals. Results: Among the 1327 analyzed patients (SM: 945 pts and 2 nd BCT: 382 pts), 244 were matched by propensity score with 70 SM versus 62 2 nd BCT and 55 SM versus 54 2 nd BCT for HER2+ and TN patients respectively. For HER2+ pts, median tumor size was 17 mm [1-50] and 13 mm [1-55] (p=0.221) for SM and 2 nd BCT respectively. For TN pts, median tumor size was 13 mm [2-40] and 12 mm [3-25] (p=0.294) for SM and 2 nd BCT respectively. Median follow-up was 79.9 months (95%CI 44.8–140) and 80.5 months [95%CI 46.4–115.6) for HER2+ and TN respectively (no difference between SM and 2 nd BCT). In the matched analyses, no difference in 5-year OS between SM and 2 nd BCT for HER2+ and TN patients (HER2+: 85% (95%CI 76.0-95) vs. 79% (69–92); p=0.85 [Figure 1A] and TN: 89% (95%CI 80-99) vs. 81% (95%CI 70-94); p=0.4 [Figure 1B], for SM and 2 nd BCT respectively). Similarly, no differences were observed for all secondary endpoints.

Conclusion: According to our knowledge, this is the first matched analysis between SM and 2 nd BCT combining lumpectomy with brachytherapy for 2 nd iBCE with HER2+ and TN molecular subtypes. This study did not show significant difference in terms of oncological outcome between the two salvage options by limited number of patients. 2 nd BCT could be carefully discussed for patients with aggressive molecular subtype 2 nd iBCE who desire to preserve their breast.

Keywords: breast cancer recurrence, molecular subtype