To reduce the risk of disease recurrence after breast-conserving surgery, women with early stage breast cancer typically receive whole-breast irradiation (WBI) daily for 3–5 weeks. Accelerated partial irradiation (APBI), delivered only to the tumour-bearing region over 5 treatment days, has been proposed as a more convenient option. Now, data from two randomized controlled trials reveal similar recurrence rates for both modalities.

In the NSABP B-39/RTOG 0413 and RAPID trials, women with ductal carcinoma in situ or stage I/II invasive ductal carcinoma were randomly assigned to receive either WBI (n = 2,109 patients and 1,065 patients, respectively) or APBI (n = 2,107 patients and 1,070 patients). The median follow-up durations were 10.2 years and 8.6 years, respectively.

In NSABP B-39/RTOG 0413, the 10-year cumulative rates of ipsilateral breast-tumour recurrence (IBTR) were 4.6% and 3.9% with APBI and WBI, respectively. With a hazard ratio (HR) of 1.22 (90% CI 0.94–1.58), the study did not meet the pre-specified limits for equivalence (HR range 0.667–1.5), favouring WBI. In RAPID, the 5-year cumulative rates of IBTR were 2.3% and 1.7% with APBI and WBI, and the 8-year cumulative rates were 3.0% and 2.8%, respectively. The HR was 1.27 (90% CI 0.84–1.91) and did not exceed the pre-specified upper margin for non-inferiority (2.02). In both studies, no statistically significant differences in overall survival were observed between treatment groups.

In NSABP B-39/RTOG 0413, 10% of patients reported grade 3 toxicities with APBI versus 7% with WBI, and <1% of patients reported grade 4–5 toxicities in both arms. In RAPID, the incidence of grade 3 acute toxicity was similar with both treatments (1.8% and 1.7%) but grade 3 late radiation toxicities were more common with APBI than with WBI (4.5% versus 1.0%; P < 0.0001). “The difference in late toxicity is important because it resulted in 16% more patients reporting adverse cosmesis with APBI than with WBI,” explains Tim Whelan, an investigator involved in the RAPID trial.

The difference in late toxicity is important ...

Modifications in the delivery of APBI are underway: the RAPID investigators are evaluating the toxicity of daily APBI, whereas the NSABP B-39/RTOG 0413 investigators aim to reduce the number of treatments below five. “As with all treatment approaches, APBI has limitations that patients should review with their doctor,” concludes Frank Vicini, an investigator involved in NSABP B-39/RTOG 0413.