ESTRO 2025 - Abstract Book

S451

Clinical - Breast

ESTRO 2025

683

Digital Poster 2nd ipsilateral breast cancer event: new primary, true recurrence or true recurrence like? Nina Pujol 1 , Jocelyn Gal 2 , Mathieu Gautier 1 , Yassine Rizzi 1 , Flora COURTAULT-DESLANDES 1 , Renaud Schiappa 3 , Jean Michel Hannoun-Levi 1 1 Radiation Oncology, Antoine Lacassagne Cancer Centre, University Côte d’Azur, Nice, France. 2 Biostatistics, Antoine Lacassagne Cancer Centre, University Cote d’Azur, nice, France. 3 Biostatistics, Antoine Lacassagne Cancer Centre, University Cote d’Azur, Nice, France Purpose/Objective: In case of second ipsilateral breast cancer event (2 nd iBCE) after breast-conserving treatment (BCT), histo-prognostic factors and topography are the two main features used to define the new breast cancer event as a true recurrence (TR) or a new primary (NP); this difference leads to the view that TR has a poorer oncological outcome than NP, consequently warranting salvage mastectomy. We aimed to address the lack of data accurately to define TR and NP and possible therapeutic consequences. Material/Methods: We used a prospective database of patients who experienced 2 nd iBCE with a 2 nd BCT (lumpectomy+adjuvant brachytherapy). Data regarding histology (type, grade, hormonal receptor and Her2 over-expression status) and topography of the 1 st and 2 nd iBCE were used to build a score ranging from 5 to 15 (Table 1). Patients with low- (<9) and high-scores (≥9) were considered TR and NP respectively. Oncological outcomes of TR and NP were compared by using cumulative incidence rate of 3 rd iBCE (CI-3 rd iBCE), contra-lateral relapse (CI-CLR), regional relapse (CI-RR), distant metastasis disease (CI-DMD), as well as disease-free (DFS), cause specific (CSS) and overall survival (OS).

Results: From 09/2000 to 01/2024, 113 pts with 2 nd BCT met inclusion criteria. Median age was 52.1 [24.2–81.9] and 65.4 [30.5-85] for 1 st and 2 nd iBCE respectively. Median time interval between the two breast surgeries (TI S1S2 ) was 149.3 months [23.5–348.3]. Regarding 2 nd iBCE, median tumor size was 10 mm [1-40], occurred at a distance from the 1 st iBCE in 82.3% of cases and was invasive ductal carcinoma in 83.2%, while positive hormonal receptor and Her2 negative overexpression status were 92.1% and 92% respectively. With a median follow-up of 78.9 months [CI95% 62.4–101.8], for the whole cohort, CI-3 rd iBCE, CI-DMD, DFS and OS were 4% [CI95% 0-8], 8% [CI95% 2-13], 87% [CI95% 81-94] and 90% [CI95% 84-97] respectively. Median TI S1S2 was significantly shorter for TR compared to NP (124.5 months [23.5-344.9] versus 194.5 months [25.3-348.3]; p=0.002). No significant difference was observed in terms of oncological outcome (CI-3 rd iBCE: 3 vs 6%; p=0.9/CI-DMD: 9 vs 5%; p=0.6/OS: 90 vs 91%; p=0.5) while TR DMD-free survival curves shown early and late waves (Figure 1).