Two-year outcomes from the HyPORT-BC study: hypofractionated radiotherapy for Japanese breast cancer patients after surgery

Background International guidelines now prefer hypofractionated radiotherapy for breast cancer, yet prospective data for Japanese patients remain limited. In our prospective observational study of hypofractionated radiotherapy for Japanese breast cancer patients (HyPORT-BC), acute adverse events were found to be within an acceptable range. Herein, we report the 2-year follow-up data. Methods Between January and December 2023, 123 Japanese patients were enrolled: 81 received moderately hypofractionated radiotherapy (42.5 Gy/16 fractions) including the supraclavicular lymph node region (Cohort M), and 42 received ultra-hypofractionated radiotherapy (26 Gy/5 fractions) for the conserved breast (Cohort U). For endpoints, overall survival (OS), relapse-free survival (RFS), ipsilateral breast relapse-free survival (IBRS), locoregional relapse-free survival (LRFS), late adverse events (CTCAE v5.0), and cosmetic deterioration were evaluated. Results At a median follow-up of 28.8 months for Cohort M and 25.2 months for Cohort U, the 2-year OS, RFS, IBRS, and LRFS were 96.2%, 91.3%, 100%, and 95.0% for Cohort M, and 97.0%, 94.5%, 97.0%, and 97.0% for Cohort U, respectively. Grade ≥ 2 late AEs occurred in 9.1% of patients at 24 months in Cohort M; no Grade ≥ 2 late AEs were observed in Cohort U. Regarding cosmetic outcomes, the proportion of patients who showed any worsening from baseline was 12.5% in Cohort M and 20.0% in Cohort U. Conclusion Both moderately hypofractionated and ultra-hypofractionated radiotherapy demonstrated favorable 2-year efficacy and safety with acceptable cosmetic preservation in Japanese patients.