S290
Clinical - Breast
ESTRO 2026
Germany. 9 Radiotherapy Med 360 Grad, Radiotherapy Med 360 Grad, Aachen, Germany. 10 Department of Radiation Oncology, University Medical Center Schleswig-Holstein, Kiel, Germany. 11 Department of Radiotherapy, Klinikum Bayreuth GmbH, Bayreuth, Germany. 12 Department of Radiation Oncology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany. 13 Clinic for Radiation Therapy and Radio-Oncology Gera, Waldklinikum Gera, Gera, Germany. 14 Department of Therapeutic Radiology and Oncology, Comprehensive Cancer Center, Graz, Austria. 15 Department of Radiation Oncology, Kantonsspital Graubünden, Grisons, Switzerland. 16 Department of Radiation Oncology, Rostock University Medical Center, Rostock, Germany. 17 Department of Radiotherapy and Radiation Oncology, Faculty of Medicine and University Hospital Carl Gustav Carus, Dresden, Germany. 18 German Cancer Consortium (DKTK), Partner Site Dresden, German Cancer Research Center (DKFZ), Heidelberg, Germany. 19 European Radiosurgery Center Munich, European Radiosurgery Center Munich, Munich, Germany. 20 Department of Radiation Oncology, Charité – Universitätsmedizin Berlin, Berlin, Germany. 21 Department of Radiation Oncology, Faculty of Medicine and University Hospital Bonn, Bonn, Germany. 22 Center for Integrated Oncology CIO Aachen Bonn Cologne Duesseldorf, Department of Internal Medicine, Faculty of Medicine and University Hospital Cologne, Cologne, Germany. 23 Department of Therapeutic Radiology and Oncology, Medical University of Graz, Graz, Austria Purpose/Objective: Metastasis-directed radiotherapy is a key component of multidisciplinary care for oligometastatic breast cancer with bone metastases (BoM). We assessed oncologic outcomes after stereotactic body radiotherapy (SBRT) for BoM in a large, multi-center European cohort. Material/Methods: We retrospectively collected data from 17 European cancer centers on breast cancer patients treated with SBRT for BoM between 2010–2024. We analyzed treatment concepts and dose parameters in relation to overall survival (OS), freedom from local recurrence (FFLR), progression-free survival (PFS), and toxicity. Results: A total of 109 patients with 147 BoM were included; median follow-up was 29.6 months (range 0.0–90.15). SBRT prescriptions had a median dose of 35Gy in a median of 5 fractions. Achieving a mean biologically effective dose (BED10) ≥ 55Gy in the gross tumor volume (GTVmean) was associated with improved PFS (p < 0.001) for both spine and non-spine lesions (both p < 0.01, Figure 1). For GTVmean BED10 ≥ 55Gy, 1-/3- year FFLR was 97.7% (95% CI, 91.0–99.4%) and 93.8%
Results: Median age was 74 years (range 57–91). No grade ≥ 3 toxicities occurred. At one month, 79% of patients developed only mild (grade 1) acute toxicity, mainly erythema (43%) and hyperpigmentation (22%); grade 2 events occurred in 10%. At 12 months, overall and disease-free survival were 100%, with no local or distant recurrences. Late toxicity was mild or moderate in 44% of cases, predominantly breast induration and hyperpigmentation; in 5.2% of cases grade 2 fibrosis was experienced. Cosmetic results were “excellent” or “good” in 94% of cases. QoL scores remained stable throughout follow-up (mean LASA ≈ 7/10), with transient declines in fatigue and emotional well-being at 6 months, followed by recovery at 12 months. No dosimetric parameters correlated significantly with toxicity. Conclusion: Adjuvant ultra-hypofractionated radiotherapy (26 Gy in 5 fractions) proved safe, well tolerated, and associated with excellent cosmetic and QoL outcomes. This regimen offers a clinically effective and resource- efficient alternative for elderly or low-risk breast cancer patients, supporting its adoption in daily clinical practice. Keywords: ultra-hypofractionation, fast-forward Stereotactic body radiotherapy in patients with bone oligometastases from breast cancer – results from a european multicenter cohort study Sebastian Schäfer 1,2 , Isabell Seiler 1,2 , Lena Kästner 3,4 , Marek Slavik 5 , Mauro Loi 6 , Panagiotis Balermpas 7 , Sophia Drabke 8 , Richard Holy 9 , Olaf Wittenstein 10 , Jochen Willner 11 , Andrea Baehr 12 , Priska Bank 13 , Richard Partl 14 , Thomas Mader 15 , Bernd Frerker 16 , Fabian Lohaus 17,18 , Felix Ehret 19,20 , Elena Gkika 21,22 , Matthias Guckenberger 7 , Christos Moustakis 1,2 , Thomas Brunner 23 , Oliver Blanck 10 , Judit Boda- Heggemann 3,4 , Nils Henrik Nicolay 1,2 , Franziska Nägler 1,2 1 Department of Radiotherapy, University Hospital Leipzig, Leipzig, Germany. 2 Comprehensive Cancer Center Central Germany, Partner Site Leipzig, Leipzig, Germany. 3 Department of Radiation Oncology, University Medicine Mannheim, Mannheim, Germany. 4 DKFZ Hector Cancer Institute, University Medical Center Mannheim, Mannheim, Germany. 5 Department of Radiation Oncology, Masaryk Memorial Cancer Institute and Medical Faculty, Brno, Czech Republic. 6 Radiation Oncology Unit, University of Florence, Florence, Italy. 7 Department of Radiation Oncology, University Hospital Zurich, Zurich, Switzerland. 8 Department of Radiation Oncology and Radiation Oncology, University Medical Center Mainz, Mainz, Digital Poster Highlight 2877
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