ESTRO 2025 - Abstract Book

S548

Clinical - Breast

ESTRO 2025

two patients developed a single local recurrence, the other two were also diagnosed with distant metastases. One patient developed a contralateral breast cancer, while another patient was diagnosed with a second breast tumor of a different histological subtype. Conclusion: Long-term follow-up data confirm that IOERT boost during BCS is a safe treatment option with only mild long-term toxicity. Long-term recurrence rates are promising, comparable to previously published data and emphasize, that IOERT as boost is an effective treatment.

Keywords: Intraoperative ,radiation, breast tumor

2886

Digital Poster Patterns of care and follow-up of patients with an ipsilateral breast tumor event: a multicenter retrospective cohort study in the Netherlands Lisca Wurfbain 1 , Desiree HJG Van Den Bongard 1 , Robert-Jan Schipper 2 1 Radiation Oncology, Amsterdam UMC, Amsterdam, Netherlands. 2 Surgery, Catharina Ziekenhuis, Eindhoven, Netherlands Purpose/Objective: This study aims to investigate the patterns of care in patients treated for an ipsilateral breast tumor event (IBTE) with curative intent and to provide insights in the oncologic short term follow up. Material/Methods: A retrospective cohort study was conducted using data from 549 [Dv1] IBTE patients treated between 2016 and 2017 at 34 hospitals in the Netherlands. Data on tumor characteristics, locoregional, and systemic treatments were collected from electronic case report files. Survival outcomes at 3 and 5 years post-treatment were evaluated using Kaplan-Meier analysis. Results: Of the 486 patients treated with curative intent, 74.5% were diagnosed with IBTE over five years after the primary tumor diagnosis. Tumor receptor discordance between primary and IBTE tumors was observed in 21.1% of cases. A total of 72 (14.8%) received neoadjuvant systemic therapy for IBTE. Salvage mastectomy was performed in 89.5%, while 10.5% underwent repeat breast-conserving surgery (BCS). Out of the 51 patients treated with repeat BCS, 31 (60.8%) received postoperative whole-breast irradiation (WBI). Among those treated with salvage mastectomy, 411 (94.5%) received radiotherapy for the primary tumor and 54 (13.1%) received repeat radiotherapy for IBTE, alone (24.1%) or in combination with hyperthermia (75.9%). Overall, adjuvant systemic therapy was administered to 56.6% of patients with IBTE. Recurrence occurred in 17.4% of patients, with 39.8% presenting local recurrence and 49.4% distant metastasis. The 3- and 5-year survival rates were 89.0% and 72.5%, respectively. Conclusion: Salvage mastectomy was still the predominant treatment for IBTE, although second BCS with re-irradiation is emerging for low-risk patients. Receptor discordance between primary and IBTE tumors emphasizes the need for individualized treatment. This study highlights the heterogeneity of IBTE management and underscores the necessity for more standardized guidelines.

Keywords: Ipsilateral breast tumor event, patterns of care