S312
Clinical - Breast
ESTRO 2026
Autonoma, Madrid, Spain. 11 Radiation Phisics, GenesisCare, Madrid, Spain. 12 Radiation oncology, Iridium Netwerk, Wilrijk-Antwerp, Belgium. 13 Medicine and Health Sciences, Medicine University of Antwerp, Antwerp, Belgium. 14 Radiation oncology, GenesisCare, Algeziras, Spain Purpose/Objective: Ultra-hypofractionated radiotherapy regimens, particularly the FAST-Forward protocol (26 Gy in 5 fractions), have demonstrated efficacy and safety comparable to standard approaches in early-stage breast cancer. In response to the COVID-19 pandemic, we implemented the FAST-Forward regimen with a simultaneous integrated boost (SIB), initially reporting on acute toxicity at 6 months. Recent studies have further confirmed the feasibility of this boost strategy. Material/Methods: Between March and October 2020, 246 early breast cancer patients received ultra-hypofractionated whole- breast irradiation (26 Gy in 5 fractions over one week); 147 high-risk patients (58.9%) received SIB to 29 Gy. The mean age was 61.8 ± 11.3 years. IMRT or VMAT techniques were applied in 96.7% of cases. Chemotherapy (primary or adjuvant) was given to 28.5%, and 84.6% received adjuvant endocrine therapy. Follow-up evaluations were performed on the last day of radiotherapy, at 2 weeks, and at 1, 3, 6, 12, 18, and 24 months, then annually. Toxicity was assessed clinically and via photographic documentation. Results: A total of 227 patients reached a minimum of 5 years follow-up (median 63.2 months). Estimated 5-year overall survival was 95.9%. Local recurrence was 1.6%, lower in the boost group (0.6% vs. 3.4%, p = 0.136). G1 pain occurred in 9.3%; no G2 pain was observed. G1 fibrosis occurred in 8.8%, G2 in 0.44%, with no G3 cases. No significant differences in 5-year fibrosis rates were found between boost and non-boost groups (p = 0.26). Pain at 5 years was significantly higher with boost (12.5% G1, 1.4% G3) compared to non-boost (3.6% G1, 0% G3; p = 0.044). G1 breast edema occurred in 4.8%; no arm edema reported. Conclusion: Ultra-hypofractionated whole-breast irradiation with SIB up to 29 Gy is safe and effective, achieving high survival and low long-term toxicity at 5 years. Further studies with larger cohorts are required. References: Murray Brunt, A. FAST-Forward Trial Management Group (2020). Hypofractionated breast radiotherapy for 1 week versus 3 weeks (FAST-Forward): 5-year efficacy and late normal tissue effects results from a multicentre, non-inferiority, randomised, phase 3 trial. Lancet (London, England), 395(10237), 1613– 1626. https://doi.org/10.1016/S0140-6736(20)30932-
6).Chakraborty, S. HYPORT adjuvant acute toxicity and patient dosimetry quality assurance results - Interim analysis. https://doi.org/10.1016/j.radonc.2022.07.003Dzhugas hvili, M. (2025). Ultrahypofractionation and Simultaneous Integrated Boost in Breast Cancer: Early Side Effects Analysis. https://doi.org/10.1016/j.ijrobp.2025.02.003 Keywords: ULTRAHYPOFRACTIONATION, BREAST, SIB Safety of sacituzumab govitecan and concomitant radiation therapy in triple negative breast cancer: an international retrospective cohort study Luca Visani 1 , Ivica Ratosa 2,3 , Barbro Linderholm 4 , Francesco Pantano 5 , Domen Ribnikar 2,6 , Astrid Nilsson Ek 4 , Sara Ramella 7 , Edy Ippolito 8 , Peter Kus 9 , Chiara Mattioli 1,10 , Luisa Caprara 1,10 , Marianna Valzano 1 , Viola Salvestrini 1 , Carlotta Becherini 1 , Andrea Rampini 1 , Francesca Gensini 10 , Jacopo Nori 11 , Lorenzo Orzalesi 12 , Simonetta Bianchi 13 , Lorenzo Livi 10,1 , Icro Meattini 10,1 1 Radiation Oncology and Breast Unit, Department of Oncology, Azienda Ospedaliero-Universitaria Careggi, Firenze, Italy. 2 Faculty of Medicine, University of Ljubljana, Ljubljana, Slovenia. 3 Division of Digital Poster Highlight 3895 Radiotherapy, Institute of Oncology, Ljubljana, Slovenia. 4 Medical Oncology Unit, Department of Oncology, Sahlgrenska Academy and University Hospital, Gothenburg, Sweden. 5 Medical Oncology Department, Fondazione Policlinico Campus Biomedico, Roma, Italy. 6 Division of Medical Oncology, Institute of Oncology, Ljubljana, Slovenia. 7 Research Unit Radiation Oncology, Università Campus Biomedico, Roma, Italy. 8 Operative Research Unit Radiation Oncology, Fondazione Policlinico Campus Biomedico, Roma, Italy. 9 Department of Oncology, University Medical Centre Maribor, Maribor, Slovenia. 10 Department of Experimental and Clinical Biomedical Sciences "M. Serio", University of Florence, Firenze, Italy. 11 Breast Imaging Unit, Department of Radiology, Azienda Ospedaliero-Universitaria Careggi, Firenze, Italy. 12 Breast Surgery Unit, Azienda Ospedaliero- Universitaria Careggi, Firenze, Italy. 13 Division of Pathological Anatomy, Department of Health Sciences, University of Florence, Firenze, Italy Purpose/Objective: Sacituzumab Govitecan (SG) has demonstrated a significant increased efficacy in terms of progression free survival (PFS) and overall survival (OS) in patients with metastatic triple negative breast cancer (TNBC). In the advanced disease setting, radiation therapy (RT) is commonly used as part of palliative therapy for pain
relief. Moreover, in oligometastatic patients, stereotactic body radiotherapy (SBRT) may
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