Abstract PO5-19-10: First oncological outcomes of HypoG-01: a UNICANCER phase III trial comparing loco-regional hypo vs normo fractionated radiation therapy in early breast cancer patients

Abstract Objective Normofractionated (NF) radiation therapy (RT) is still standard for loco-regional early breast cancer (EBC) in many countries. HypoG-01, a UNICANCER, non-inferiority, open-label, multicenter, randomized phase III trial (NCT03127995), conducted in parallel with the DBCG Skagen trial 1 (NCT02384733), evaluated hypofractionated (HF) RT with 40 Gy/15 fr (2.67 Gy/fr) versus NF RT 50 Gy/25 fr (2.0 Gy/fr). This is the first report of oncological outcomes, secondary endpoints of the trial. Methods Patients (pts) ≥18 years old were operated for T1-3, N0-3, M0 breast cancer. All pts received nodal and thoracic wall or breast RT. Tumor-bed boost (sequential or simultaneous) and nodal levels treated were decided according to local guidelines. Target volumes were delineated according to the ESTRO consensus. RT technique was left at the investigator’s discretion. Stratification factors included treating center, type of surgery, number of positive nodes and body mass index. The primary endpoint, reported previously, was time to occurrence of arm lymphedema. Oncological outcomes included locoregional relapse free survival (LRFS), invasive disease-free survival (IDFS), distant disease-free survival (DDFS), breast cancer specific survival (BCSS) and overall survival (OS) as defined per DATECAN guidelines. All time to cancer related endpoints were defined as starting from the date of randomization until the event. The primary statistic test was stratified one-sided logrank test: 5% significance level in per-protocol population (PPP) with a pre-specified non-inferiority margin of 1.545. Stratified Cox model was used for calculating hazard ratios of oncological outcomes. Results In total, 1265 pts were randomized to HF versus NF RT from Sep 2016 to Mar 2020 with 1221 in the PPP (HF group 614 pts (50.3%); NF group 607 (49.7%)), 5 consent withdrawn and 39 major deviations. Median age was 58 years (range 23-91), surgery included mastectomy (501 pts; 45%) and axillary clearance (921 pts; 82.8%). Sequential (67.8%) or simultaneous integrated (32.2%) tumor-bed boost was used in 596 pts (48.8%). With a median follow-up for OS in PP analysis of 3.8 years (95% CI 3.3 to 3.9), HF was non-inferior to NF RT in terms of lymphedema (HR=1.07; 90% CI 0.86-1.34, non-inferiority p=0.003). Table 1 reports the hazard ratio and 3-year survival rates for the oncological endpoints LRFS, IDFS, DDFS, BCCS and OS. There was no sign of disadvantage for any of these endpoints comparing HF to NF. Additional analyses will be presented at the meeting. Conclusion Moderately HF loco-regional RT is non-inferior to NF RT in terms of lymphedema risk in EBC and does not show a disadvantage in terms of LRFS, IDFS, DDFS, BCCS and OS with a median follow-up of 3.8 years. Together with the Skagen 1 trial, this study provides level 1A evidence supporting the use of 40 Gy/15 fr for loco-regional radiation therapy in EBC with respect to arm lymphedema risk; Table 1: Oncological outcomes according to treatment arm in the per protocol analysis HF: Moderately hypofractionated radiation therapy; NF: Normofractionated radiation therapy; n:number of patients; N: number of events Citation Format: Sofia Rivera, Eleni Karamouza, Youlia Kirova, Séverine Racadot, Mohamed Benchalal, Jean-Baptiste Clavier, Claire Charra-Brunaud, Marie-Eve Chand-Fouche, Delphine Argo-Leignel, Karine Peignaux, Ahmed Benyoucef, David Pasquier, Philippe Guilbert, Julien Blanchecotte, Agnès Tallet, Adeline Petit, Guillemette Bernadou, Xavier Zasadny, Claire Lemanski, Jacques Fourquet, Emmanuelle Malaurie, Honorine Kouto, Carole Massabeau, Alexandre Henni, Pauline Regnault, Aurélie Belliere, Yazid Belkacemi, Magali Le Blanc-Onfroy, Julien Geffrelot, Jean-Briac Prevost, Marie Bergeaud, Assia Lamrani-Ghaouti, Amandine Ruffier, Naima Bonnet, Stephanie Wong, Christine Rossier, Thomas Brion, Pierre Maroun, Claire Petit, Guillaume Auzac, Stefan Michiels. First oncological outcomes of HypoG-01: a UNICANCER phase III trial comparing loco-regional hypo vs normo fractionated radiation therapy in early breast cancer patients [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO5-19-10.