S2971
Late-Breaking
ESTRO 2026
tumours). Material/Methods: The primary endpoint was overall survival (OS). Secondary endpoints were disease-free survival (DFS), distant metastases-free survival (DMFS), breast cancer mortality (BCM), breast cancer recurrence (BR), and late side-effects. Analysis included Kaplan-Meier, cumulative incidence curves, and unadjusted Cox and Fine-Gray models. All tests were conducted at the 5% significance level. Results: Between 1996 and 2004, a total of 4004 patients were randomised. Of those, 1778 patients (44.4%) were pN0 with centrally or medially located tumours, with median age 55 years and 66.3% receiving adjuvant systemic treatment. At a median follow-up of 22.2 years, 553 (31.1%) pN0 patients died, of whom 209 (37.8%) due to breast cancer. At 20 years, OS rate was 69.0% versus 68.4% (HR=0.98; 95%CI: 0.83-1.15; P=0.766); DFS was 53.9% versus 53.6% (HR=0.93; 0.81- 1.07; P=0.318); DMFS was 67.2% versus 67.4% (HR=0.93; 0.78-1.10; P=0.397); and BR rate was 20.2% versus 23.1% (HR=0.83; 0.68-1.03; p=0.084), with versus without IM-MS-RT, respectively. While breast cancer mortality was significantly lower with 10.0% versus 14.2% (HR=0.70; 0.53-0.92; P=0.010), cumulative mortality not due to breast cancer (including cause unknown) was significantly higher with 20.9% versus 17.4% (HR=1.24; 1.00-1.53; p=0.048) in the arm with versus without IM-MS RT, respectively. No major differences were seen for the cumulative incidence of late side effects, any second cancer (24.4% versus 24.9%) and second breast cancer (12.0% versus 11.6%).
Conclusion: - The both favourable and disadvantageous effects of IM-MS RT for pN0 patients with a centrally/medially located tumour are identical to the overall population of 4004 patients which included also 56% of pN+ patients. This calls for revisiting the role of nodal irradiation for axillary-node-negative patients. - The cumulative incidence of breast cancer mortality at 20 years was statistically significantly lower after IM-MS- RT, while the analysis of deaths not due to breast cancer (including cause unknown) showed a late separation of curves after about 15 years, resulting in no long-term benefit of IM-MS RT on overall survival. - Our results strongly emphasise the importance of very long-term follow up after treatment for prognostically favourable cancers such as early-stage breast cancer, including further research in prevention and treatment of possibly associated long-term effects. Keywords: pN0 breast cancer, Nodal RT, Randomised trial Combination of L19-IL2 immunocytokine & SABR for stage IV NSCLC with limited metastatic burden: the randomized, multicentre, phase II ImmunoSABR trial Philippe Lambin 1 , Amir Abdollahi 2 , Frank Aboubakar 3 , Charlotte Billiet 4 , Johan Bussink 4 , Anne-Marie Dingemans 5 , Christophe Dooms 6 , Piet Dirix 7 , Dirk De Ruysscher 8 , Ludwig Dubois 1 , Berta Ganizada 1 , Xavier Geets 9 , Crispin Hiley 10 , Sine Reker Hadrup 11 , Monique de Jong 12 , Mohammad Kadivar 11 , Sander van Kuijk 13 , Maarten Lambrecht 14 , Relinde Lieverse 15 , Yolande Lievens 16 , Dario Neri 17 , David Pasquier 18 , Veerle 2 Surmont 19 , Yousif Widaatalla 1 , Lizza EL Hendriks 20 1 Precision Medicine, Research Institute for Oncology and Reproduction, Maastricht University Medical Center, Maastricht, Netherlands. 2 Radiation Oncology, Heidelberg University Hospita, Heidelberg, Germany. 3 Pneumology, Cliniques universitaires Saint-Luc, Proffered Paper 5597
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