Understanding risk factors for locoregional recurrence (LRR) after accelerated partial breast irradiation (APBI) can help to guide patient selection for treatment with APBI. Published findings to date have not been consistent. More data are needed as these risk factors continue to be defined.

A total of 277 women with early-stage invasive breast cancer underwent lumpectomy and were treated adjuvantly at our institution with APBI using high-dose rate brachytherapy. APBI was delivered using multicatheter interstitial brachytherapy (91 %) or single-entry catheter brachytherapy (9 %) to a dose of 32-34 Gy in 8-10 twice daily fractions. Failure patterns and risk factors for recurrence were analyzed.

With a median follow-up of 61 months, the 5-year locoregional control rate was 94.4 %. Negative estrogen receptor (ER) status was strongly associated with LRR on multivariate analysis (p < 0.005). Lobular histology, the presence of an extensive intraductal component, and lymphovascular invasion also were significant but to a lesser degree than ER-negative status. Patients with multiple risk factors were at highest risk for LRR. Age was not significantly associated with increased risk for LRR.

The presence of specific pathological features, particularly ER negative status, was associated with increased risk of LRR in this cohort of women treated with APBI. Further investigation is warranted to determine whether patients with adverse pathological risk factors are at higher risk of LRR after APBI than after conventional whole breast irradiation (WBI), as these same features also may place women at risk for LRR after WBI.