ESTRO 2025 - Abstract Book

S633

Clinical - Breast

ESTRO 2025

4577

Digital Poster Re-irradiation of breast cancer in-field recurrences: locoregional practice patterns, toxicity, and survival outcomes Conrad Bayley 1 , Allison Rau 1 , Jessica Bertschmann 1 , Sarah Weppler 1 , Hali Morrison 1 , Ericka Wiebe 2 , Natalie Logie 1 1 Oncology, University of Calgary, Calgary, Canada. 2 Oncology, University of Alberta, Edmonton, Canada Purpose/Objective: Breast cancer (BCa) local recurrences are increasingly prevalent. 1–6 Treatment options are limited, especially in the 60-95% of patients with in-field recurrences (IFR). 7–9 Historically, surgery was preferred due to concerns regarding toxicity of field-overlap re-irradiation (re-RT). 10-14 There is limited evidence to support the safety and local control benefit of re-RT in the curative setting, and it is established in the palliative setting. 15 A standardized approach to re RT for IFRs is not established. Material/Methods: We retrospectively identified patients who received adjuvant RT for resected BCa prior to 2021 and subsequently received curative- or palliative-intent re-RT for IFRs between 2010 and 2024 at our centre. A chart review obtained treatment, patient, and tumor characteristics. Descriptive statistics were calculated to characterize practice patterns, toxicity, and survival outcomes. Results: Forty-three patients were identified. Median follow up was 72 months. All received an initial course of definitive 3DCRT post-operatively (70% lumpectomy, 47% sentinel lymph node biopsy (SLNB)). Seven patents received a seroma boost, all were 10 Gy in 4 fractions. Neoadjuvant and adjuvant systemic therapy were given in 21% and 53, respectively. Mean time to recurrence from initial RT was 37 months [0-239]. Local recurrences occurred in 28 patients, while 15 recurred locally and systemically. Molecular subtype was different from presentation in 30% of patients. Four patients had additional IFRs after re-RT; two were within both previous fields. Other treatments for IFR include chemotherapy in 58% of patients and surgery in 44% (89% mastectomy), with 40% to nodes (65% SLNB). All re-RT utilized 3DCRT except one via orthovoltage and one via VMAT. The intent was palliative in 28 patients and definitive in 15, with 40% to the breast/chest wall (CW) alone, 37% to the breast/CW and nodes, and 23% to the node(s) alone. Table 1 summarizes the molecular subtypes, RT courses, recurrences, time between courses, and toxicities. Adjuvant or palliative chemotherapy was given in 60% of patients, and 28% received hormonal therapy. Of the 12 documented toxicities, 10 pre-dated re-RT, one of which worsened post re-RT. Overall survival three years after initial RT was 95% (39/41, two patients lost to follow up). Of the 30 patients who received re-RT at least two years ago, two-year overall survival was 47% (14/30).

Conclusion: Managing BCa IFRs with re-RT appears to be a safe and viable approach with reasonably consistent practice patterns. Toxicity is driven by the initial treatment course, and survival outcomes are acceptable.