Purpose: To report an interim analysis of a phase II trial of once weekly, hypofractionated breast irradiation (WH-WBI) following breast conserving surgery (BCS).
Methods: Patients had stage 0-II breast cancer treated with breast BCS with negative margins. WH-WBI was 28.5 or 30Gy delivered to the whole breast using tangential beams with no elective coverage of lymph nodes. The primary endpoint was ipsilateral breast tumor recurrence (IBTR). Secondary endpoints were distant disease-free survival (DDFS), recurrence free survival (RFS), overall survival (OS), adverse events and cosmesis.
Results: From 2011 to 2015, 158 patients received WH-WBI. Median follow up was 4.4 years (range 0.2-8.1). Stage distribution was DCIS 22%; invasive pN0 68%; invasive pN1 10%. 80 patients received 30 Gy and 78 received 28.5 Gy with median follow up times of 5.6 and 3.7 years, respectively. There were 5 IBTR events, all in the 30 Gy group. The 5- and 7- year risks of IBRT for all patients were 2.2% (95% CI 0.6-5.8) and 6.0% (95% CI 1.1-17.2), respectively. The 7-year rates of DDFS, RFS, and OS were 96.3%, 91.5% and 89.8%, respectively. Improvement in IBTR-free time was seen in DCIS, lobular histology, low grade tumors, Her2 negative tumors and 28.5 Gy dose (all p < 0.0001).
Conclusions: Disease-specific outcomes after WH-WBI are favorable and parallel those seen with conventional radiation techniques for stage 0-II breast cancer.
© 2021. Society of Surgical Oncology.