PARTIAL BREAST RADIOTHERAPY

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.

Study Details

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.

Local Relapse

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.