Ipsilateral breast tumor control following hypofractionated and conventional fractionated whole-breast irradiation for early breast cancer: a long-term follow-up

Long-term follow-up of Japanese women with breast cancer who underwent hypofractionated whole-breast irradiation (HF-WBI) has not been well documented. Therefore, we compared the treatment results of HF-WBI and conventional fractionated (CF)-WBI. Patients with stage 0–II breast cancer receiving partial mastectomy were eligible for this prospective observational study. The HF-WBI consisted of 43.2 Gy in 16 fractions to the whole breast, with an additional tumor-bed boost of 8.1 Gy in three fractions for patients with positive or less than 5 mm surgical margins. A total of 615 patients (400: HF-WBI and 215: CF-WBI) who were treated between 2006 and 2008 were investigated. Propensity score matching was conducted based on age, tumor grade, and margin status, and 372 matched cases were investigated for examining factors relating to intrabreast tumor recurrence (IBTR). With a median follow-up period of 9.4 years, age and margin status were independent factors associated with IBTR occurrence (P = 0.006 and 0.016, respectively). The 10-year ipsilateral breast tumor control (IBTC) rates after HF-WBI and CF-WBI were 96.5% and 95.3%, respectively (P = 0.606). The 10-year IBTC rates according to margin status were 88.0% with positive margins, 94.9% with 5 mm margins, and 98.0% with negative margins (P = 0.014). There was no difference in IBTC between CF-WBI and HF-WBI in our patients. Positive surgical margin was a risk factor independently associated with IBTC rates after CF-WBI and HF-WBI. Further investigation is required to establish adequate treatment strategies for patients with positive surgical margins.