As reported in the Journal of Clinical Oncology by Offersen et al, the phase III Danish Breast Cancer Group Partial Breast Irradiation Trial showed that partial-breast irradiation was noninferior to whole-breast irradiation in terms of the risk for breast induration in women aged ≥ 60 years undergoing breast-conserving surgery for node-negative early breast cancer. No increased risk of locoregional recurrence was observed with partial-breast irradiation.
Study Details
In the open-label multicenter trial, 865 evaluable patients were randomly assigned between 2009 and 2016 to receive external-beam partial-breast irradiation (n = 431) or whole-breast irradiation (n = 434) with a dose of 40 Gy in 15 fractions. The primary endpoint was the incidence of grade 2 or 3 breast induration at 3 years.
Key Findings
Median follow-up was 5 years for induration and 7.6 years for locoregional recurrence. The 3-year incidence of grade 2 or 3 induration was 9.7% (95% confidence interval [CI] = 7.0%–12.9%) in the whole-breast irradiation group vs 5.1% (95% CI = 3.2%–7.6%) in the partial-breast irradiation group (risk difference = –4.6%, 95% CI = –8.2% to –0.9%, P = .014). Since the upper 90% confidence interval for the difference in incidence was below 0% (–1.5%), the statistical criterion (< 10%) for noninferiority of partial-breast irradiation was satisfied.
The hazard ratio for grade 2 or 3 induration for partial-breast irradiation vs whole-breast irradiation was 0.50 (95% CI = 0.29–0.86). At 5 years, overall induration risk was 12% in the whole-breast irradiation group vs 8% in the partial-breast irradiation group (odds ratio [OR] = 0.59, 95% CI = 0.43–0.82).
At 5 years, patients with large vs small breasts had an increased risk of induration (12% vs 7%; OR = 1.71, 95% CI = 1.23–2.38, P = .0014). At 3 years, risks with whole-breast irradiation vs partial-breast irradiation were 13% vs 6% among large-breasted patients and 6% vs 5% among small-breasted patients.
Partial-breast irradiation was not associated with an increased risk of dyspigmentation, telangiectasia, edema, or pain. Excellent or good cosmetic outcome was reported by 85% of the whole-breast irradiation group and 89% of the partial-breast irradiation group. Letrozole use and current smoking were not associated with the risk of radiation-associated morbidity.
No significant difference in locoregional recurrence risk was observed; 5-year risks were 0.7% (95% CI = 0.2%–1.9%) in the whole-breast irradiation group vs 1.2% (95% CI = 0.4%–2.6%) in the partial-breast irradiation group (P = .47). Estimated 9-year risks were 1.7% vs 3.1% (P = .30). No differences between the whole-breast irradiation and partial-breast irradiation groups were observed for contralateral breast cancer (7 vs 13 patients overall; 4 vs 6 during the first 5 years); distant failure (5 vs 3 patients); or nonbreast second cancers (observed in 8.4% of patients overall).
The investigators concluded, “External-beam [partial-breast irradiation] for patients with low-risk breast cancer was noninferior to [whole-breast irradiation] in terms of breast induration. Large breast size was a risk factor for radiation-associated induration. Few recurrences were detected and unrelated to [partial-breast irradiation].”
Birgitte V. Offersen, MD, PhD, of Aarhus University Hospital, is the corresponding author for the Journal of Clinical Oncology article.
Disclosure: The study was supported by the Danish Cancer Society, Centre for Interventional Research in Radiation Oncology, and others. For full disclosures of the study authors, visit ascopubs.org.
