Five-Year Report of the Institutional Phase II Trial of Once Weekly Hypofractionated Whole Breast Irradiation for Early-Stage Breast Cancer

Abstract

Elderly and underserved patients often have difficulty completing a traditional course of conventional or hypofractionated breast irradiation after breast conserving surgery (BCS). We hypothesized that five-fraction once weekly hypofractionated whole breast irradiation (WH-WBI) would be safe and effective following BCS in this group of patients. We report a planned 5-year analysis of our institutional phase II trial.Patients treated with WH-WBI after BCS were followed prospectively on an institutional IRB-approved protocol. Women included in this study had stage 0-II breast cancer treated with breast BCS with negative margins and met pre-specified criteria for being underserved. WH-WBI was 28.5 or 30 Gy delivered to the whole breast using tangential beams with no elective coverage of lymph nodes. Radiotherapy boost was utilized at the discretion of the treating radiation oncologist ranging from 5.7 Gy in one fraction to 10 Gy in five fractions. 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.158 patients received WH-WBI on protocol from 2011 to 2015. Median follow up was 5.5 years (range, 0.2-10.0). Stage distribution was DCIS 22%; invasive pN0 68%; invasive pN1 10%. 28% of patients had grade 3 tumors, 10% were estrogen receptor negative and 24% required adjuvant chemotherapy. 80 patients received 30 Gy and 78 received 28.5 Gy with median follow up times of 6.2 and 5.2 years, respectively. There were six IBTR events, five in the 30 Gy group. The 5-, 7- and 10-year risks of IBRT for all patients were 2.7% (95% CI 0.89-6.34), 4.7% (95% CI 1.4-11.0) and 7.2% (95% CI 2.4-15.8) respectively. The 5, 7 and 10-year rates of DDFS were 96.4, 96.4 and 86.4%, RFS were 95.8%, 93.6 and 80.7%, and OS were 96.7, 88.6 and 76.7%, respectively. Improvement in IBTR-free time was seen in DCIS, lobular histology, low grade tumors, T1 stage, Her2 negative tumors and 28.5 Gy dose (all P < 0.0001). The cosmetic outcomes have been reported in a separate publication.WH-WBI after BCS had favorable disease-specific outcomes and comparable to those seen with conventional and other hypofractionated radiation techniques for a medically underserved population of women with stage 0-II breast cancer. This combined with prospective data from the FAST and FAST-Forward trials support a five-fraction whole breast irradiation approach after BCS.