The UK IMPORT LOW phase III trial has shown noninferiority in local relapse for partial-breast and reduced-dose vs standard whole-breast radiotherapy after breast-conserving surgery in early breast cancer. These study results were reported by Coles et al in The Lancet.
In the noninferiority trial, 2,016 women aged ≥ 50 years who had undergone breast-conserving surgery for unifocal invasive ductal adenocarcinoma of grade 1 to 3 and who had a tumor size of ≤ 3 cm (pT1–2), 0 to 3 positive axillary nodes (pN0–1), and minimum microscopic margins of noncancerous tissue of ≥ 2 mm from 30 sites were randomized 1:1:1 between May 2007 and October 2010 to receive 40 Gy of whole-breast radiotherapy (control, n = 674), 36 Gy of whole-breast radiotherapy and 40 Gy to the partial breast (reduced-dose group, n = 673), or 40 Gy to the partial breast only (partial-breast group, n = 669) in 15 daily treatment fractions. Field-in-field intensity-modulated radiotherapy was delivered using standard tangential beams, reduced in length for the partial-breast group. The primary endpoint was ipsilateral local relapse at 5 years in the intent-to-treat population, with noninferiority shown in experimental groups if the upper limit of the two-sided 95% confidence interval for the local relapse hazard ratio [HR] was < 2.03.
Median follow-up was 72.2 months. Estimated cumulative 5-year local relapse rates were 1.1% in the control group, 0.2% in the reduced-dose group (difference = –0.73% vs control), and 0.5% in the partial-breast group (difference = –0.38% vs control). Noninferiority (HR > 2.03) vs the control group was established for both the reduced-dose (P = .003) and partial-breast groups (P = .016).
Late Normal Tissue Effects
Photographic, patient, and clinical assessments showed similar adverse effects after reduced-dose and partial-breast radiotherapy; significantly reduced adverse effects vs the whole-breast group were observed for change in breast appearance (35% vs 48%, P = .007) in the partial-breast group and breast harder or firmer in the reduced-dose group (21% vs 35%, P = .002) and in the partial-breast group (15% vs 35%, P < .0001).
The investigators concluded: “We showed non-inferiority of partial-breast and reduced-dose radiotherapy compared with the standard whole-breast radiotherapy in terms of local relapse in a cohort of patients with early breast cancer, and equivalent or fewer late normal-tissue adverse effects were seen. This simple radiotherapy technique is implementable in radiotherapy centres worldwide.”
The study was funded by Cancer Research UK.
Charlotte E. Coles, PhD, of the University of Cambridge, is the corresponding author of The Lancet article.
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