The Impact of Hypofractionated Whole Breast Radiotherapy on Local Relapse in Patients With Grade 3 Early Breast Cancer: A Population-Based Cohort Study

Purpose To determine whether patients with Grade 3 early breast cancer have an inferior rate of local disease control at 10 years with hypofractionated radiotherapy compared with more conventionally fractionated schedules. Methods and Materials Local relapse rates were compared between patients receiving hypofractionated radiotherapy or conventionally fractionated radiotherapy to the whole breast in a population-based cohort of women with early-stage (T1-T2, N0, M0) Grade 3 breast cancers diagnosed between 1990 and 2000 and referred to the British Columbia Cancer Agency. Cumulative rates of local relapse were estimated using a competing risk method, and factors significant on univariate analysis were included with fractionation group in a multivariate model. The primary end point was local control at 10 years. Results A total of 1,335 patients with Grade 3 tumors were treated with adjuvant radiotherapy, 252 with conventional fractionation, and 1,083 with a hypofractionated schedule. The 10-year cumulative incidence of local relapse was 6.9% in the hypofractionated group and 6.2% in the conventionally fractionated group ( p = 0.99). Conclusions There is no evidence that hypofractionation is inferior to conventional fractionation for breast conserving therapy in patients with Grade 3 breast cancer in this large population-based series after 10 years of follow-up.