Multi-institutional phase II study of ultra-hypofractionated whole-breast irradiation after breast-conserving surgery for breast cancer in Japan: Kyoto Radiation Oncology Study Group (UPBEAT study)

PURPOSE: The UK-FAST-Forward study showed that ultra-hypofractionated whole-breast irradiation (ultra-HF-WBI) involving five fractions of 26 Gy radiation over 1 week was not inferior to HF-WBI. However, it is not used in Japan due to safety concerns. In April 2022, we commenced a multi-institutional, single-arm, phase II trial. Our aim is to confirm the safety of ultra-HF-WBI after breast-conserving surgery (BCS) for breast cancer in Japanese women. METHOD: We plan to enroll 98 patients from 13 institutions. The primary endpoint is the proportion of late adverse events of grades ≥2 within 3 years. DISCUSSION: We believe that this highly promising clinical study can positively impact the Japanese guidelines for breast cancer treatment. The results will help us decide whether or not ultra-HF-WBI can be used as a more convenient alternative to WBI. REGISTRATION NUMBER AND DATE: This trial was registered in the UMIN Clinical Trials Registry (UMIN000047080) on March 4, 2022.