ESTRO 2025 - Abstract Book

S4430

Late-breaking abstracts

ESTRO 2025

1 Medicine, Keele University, Stoke-on-Trent, United Kingdom. 2 Clinical Trials and Statistics Unit, The Institute of Cancer Research, Sutton, United Kingdom. 3 Sunrise Centre, Royal Cornwall Hospital, Trurs, United Kingdom. 4 Breast Unit, The Royal Marsden NHS Foundation Trust, Sutton, United Kingdom. 5 Department of Oncology, University of Cambridge, Cambridge, United Kingdom. 6 Radiotherapy, Beatson West of Scotland Cancer Centre, Glasgow, United Kingdom. 7 Oncology Centre, Royal Sussex County Hospital, Brighton, United Kingdom. 8 Department of Breast Surgery, Nuffield Hospital, Cheltenham, United Kingdom. 9 Oncology Centre, Worcestershire Royal Hospital, Worcester, United Kingdom. 10 Radiotherapy, Charing Cross Hospital, London, United Kingdom. 11 Radiotherapy, Torbay District General Hospital, Torbay, United Kingdom. 12 Wolfson Institute of Population Health, Queen Mary University of London, London, United Kingdom. 13 Surgical Oncology, University Hospital of South Manchester, Manchester, United Kingdom. 14 Radiotherapy Trials Quality Assurance Group, Mount Vernon Hospital, Northwood, United Kingdom. 15 Guys Cancer Centre, Guys and St Thomas Foundation Trust, London, United Kingdom. 16 Translational Breast Radiobiology, The Institute of Cancer Research, Sutton, United Kingdom. 17 Oncology, Clatterbridge Centre for Oncology, Wirral, United Kingdom. 18 Department of Radiotherapy and Imaging, The Institute of Cancer Research, Sutton, United Kingdom Purpose/Objective The FAST-Forward trial (ISRCTN19906132) aimed to identify a 5 fraction (1 week) schedule of adjuvant breast radiotherapy that was as safe and effective as the standard 3-week schedule (40 Gray in 15 fractions, Fr). Two test schedules were evaluated with 4110 patients randomised between 27Gy/5Fr, 26Gy/5Fr or control (40Gy/15Fr). The primary analysis, reporting 5-year outcomes, demonstrated non-inferiority for both 27Gy and 26Gy in terms of ipsilateral breast recurrence (primary endpoint, 79 events in total). Cumulative incidence of ipsilateral breast recurrence at 5 years was 2·1% (31 events) for 40Gy, 1·7% (27 events) for 27Gy and 1·4% (21 events) for 26Gy. Normal tissue effect data showed similar effects for 26Gy/5Fr and 40Gy/15Fr which suggested that the 26Gy schedule would be optimal. Here, we report 10-year outcomes in the trial. Material/Methods Patients with invasive breast cancer (pT1-3 pN0-1 M0) who had undergone breast surgery were randomised (1:1:1) to 40Gy/15Fr over 3 weeks (control), 27Gy/5Fr over 1 week or 26Gy/5Fr over 1 week of radiotherapy to the whole breast/chest wall. The primary endpoint of 5-year ipsilateral breast recurrence and secondary endpoints were reported at a median of 71.5 months follow up. Follow-up continued to 10 years to provide long-term data on the primary and secondary endpoints, including other breast cancer events, clinician- and patient-reported late normal tissue effects, and survival. Results Data collection for 10-year follow-up in the trial is now complete (median 10.0 years, IQR 9.9 – 10.2) and 116 ipsilateral breast recurrences have been reported. Data is currently being cleaned and analysed. The presentation will report on ipsilateral breast recurrences, locoregional recurrences, new contralateral primaries, breast cancer-free interval and overall survival at 10 years. Clinician-reported breast symptoms and late adverse events as well as patient-reported breast symptoms and quality of life will also be presented. Conclusion The FAST-Forward primary results have been practice-changing. This pre-planned 10-year analysis will provide definitive evidence to characterise the long term safety and efficacy of adjuvant breast radiotherapy delivered with 1-week, 5-fraction schedules.

Keywords: Breast cancer, radiotherapy, hypofractionation

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Proffered Paper DBCG Skagen trial 1: Phase III randomised trial of hypo- vs standard fractionated loco-regional radiotherapy in node-positive breast cancer patients Birgitte Vrou Offersen 1,2 , Jan Alsner 1 , Hanne Melgaard Nielsen 3 , Else Maae 4 , Mette Holck Nielsen 5 , Ingvil Mjaaland 6 , Maja Maraldo 7 , Carine Kirkove 8 , Tamaz Lörincz 9 , Sami Al-Rawi 10 , Egil Støre Blix 11 , Andreas