- A phase 3 trial of women with early breast cancer (eBCa) finds that accelerated partial breast irradiation (APBI), a shorter course of radiotherapy delivered only to the tumor-bearing quadrant, is nonequivalent to whole-breast irradiation (WBI) in controlling ipsilateral breast tumor recurrence (IBTR).
- The difference, while statistically significant, was less than 1% in the 10-year cumulative incidence of IBTR.
Why this matters
- The authors assert that APBI "might be an acceptable alternative for some women," even though it was nonequivalent.
- Phase 3 equivalence trial in 154 centers in the United States, Canada, Ireland, and Israel in which women were randomly assigned to WBI (n=2036) or APBI (n=2089).
- WBI: 25 daily fractions, 50 Gy, 5 weeks.
- APBI: 34 Gy brachytherapy or 38.5 Gy external beam radiation therapy, 10 fractions, 5 treatment days in 8-day period.
- Funding: NIH.
- At a median follow-up of 10.2 years, after breast-conserving surgery, the APBI group had:
- 22% higher incidence of IBTR;
- 4% vs 3% in the WBI group;
- HR, 1.22 (90% CI, 0.94-1.58).
- The 10-year cumulative incidence of IBTR was 4.6% in the APBI group vs 3.9% in the WBI group.
- The study was not designed for subgroup analyses.