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.