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Partial breast irradiation could be as effective as whole breast irradiation

Conference
SABCS 2019
Trial
Phase 3, APBI IMRT

Results of a 10-year follow-up study of breast cancer patients who had been treated with accelerated partial breast irradiation after surgery demonstrated that the rates of recurrence were similar to those of patients who were treated with whole breast irradiation. Based on these findings, accelerated partial breast irradiation should be considered a reasonable alternative for whole breast irradiation in early breast cancer patients.

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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