A total of 520 women aged >40 years with stage 1 or stage 2 breast cancer (with a maximum pathological tumour size of 25 mm and final surgical margins ≥5 mm) were included in the randomised phase 3 APBI IMRT trial [1]. Between 2005 and 2013, the patients were randomly assigned in a 1:1 ratio to receive either accelerated partial breast irradiation or whole breast irradiation. The patients in the accelerated partial breast irradiation arm (n=260) received a total of 30 Gray (Gy) of radiation to the tumour bed in 5 daily fractions; patients in the whole breast irradiation arm (n=260) received a total of 50 Gy in 25 daily fractions to the whole breast, plus a boost of 10 Gy to the tumour bed in 5 daily fractions. Primary endpoint of the study was ipsilateral breast tumour recurrence (IBTR); secondary endpoints were overall survival (OS), breast cancer specific survival, contralateral breast cancer, early and late toxicity, and physician-related cosmesis. Both treatment arms were comparable in terms of age, tumour size, tumour type, and adjuvant endocrine treatment, and both achieved a median 10-year follow-up. The majority of the patients had hormone receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative breast cancer.
After 10 years, 3.3% of patients in the accelerated partial breast irradiation group had a recurrence of breast cancer versus 2.6% of patients in the whole breast irradiation group, which was comparable to the 5-year results. At that time point, the patients receiving accelerated partial breast irradiation had a 2.4% recurrence rate versus 1.2% of patients in the whole breast irradiation group (no statistically significant differences). The OS at the 10-year mark was 92.7% for women who received accelerated partial breast irradiation and 93.3% for women who received whole breast irradiation. The breast cancer-specific survival was 97.6% for women having received accelerated partial breast irradiation and 97.5% for women who received whole breast irradiation. The distant metastasis-free survival rate was 96.9% both for the women who received accelerated partial breast irradiation and for those who received whole breast irradiation.
A comparison of the rates of acute adverse events (AEs) demonstrated that any grade skin toxicity occurred in 21.1% of patients treated with accelerated partial breast irradiation versus 66.5% of patients who were treated with whole breast irradiation. The majority of these AEs was grade 0-1 (98.0% vs 62.3%), however, 37.7% of whole breast irradiation patients had grade ≥2 skin toxicity, compared to 2.0% of accelerated partial breast irradiation patients. Late AEs of any grade occurred in 4.5% of patients treated with accelerated partial breast versus 30.0% of patients treated with whole breast irradiation. It was concluded that 10-year cumulative IBTR incidence in early breast cancer treated with external accelerated partial breast irradiation using intensity-modulated radiotherapy (IMRT) in 5 once-daily fractions (30 Gy in 5 times) is low and not significantly different from patients who are treated with conventionally fractionated (CF)-whole breast irradiation. Thus, accelerated partial breast irradiation may be considered a standard alternative to whole breast irradiation in low risk early breast cancer patients.
1. Meattini I, et al. GS4-06. SABCS 2019.
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Table of Contents: SABCS 2019
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