Impact of the number of cautionary and/or unsuitable risk factors on outcomes after accelerated partial breast irradiation.

PURPOSE: To examine clinical outcomes of accelerated partial-breast irradiation (APBI) stratified by the number of American Society for Radiation Oncology consensus statement cautionary/unsuitable risk factors (RFs) present.

METHODS AND MATERIALS: A total of 692 patients were treated with APBI at a single institution between April 1993 and January 2012 using interstitial (n=195), balloon (n=292), and 3-dimensional conformal radiation therapy (n=205) techniques. Clinical outcomes were evaluated by risk group and number of RFs.

RESULTS: Median follow-up was 5.2 years (range, 0-18.3 years). Most patients were classified as suitable (n=240, 34%) or cautionary (n=343, 50%) risk, whereas 16% (n=109) were unsuitable. In patients with increasing total RFs (1 RF, 2 RF, 3+ RF), higher rates of grade 3 histology (10% vs 18% vs 32%, P<.001), estrogen receptor negativity (0 vs 12% vs 29%, P<.001), close/positive margins (0 vs 6% vs 17%, P<.001), and use of adjuvant chemotherapy (3% vs 12% vs 33%, P<.001) were noted. When pooling cautionary and unsuitable patients, increased ipsilateral breast tumor recurrence/regional recurrence was most notable for patients with 3 or more combined RFs versus 2 or fewer combined RFs (P<.001).

CONCLUSIONS: Patients with 3 or more cautionary or unsuitable RFs may be at risk for higher local, regional, and distant recurrence after breast-conserving therapy using APBI. Patients with 2 or fewer total RFs have 98% locoregional control at 5 years. Inclusion of total number of RFs in future risk stratification schemes for APBI may be warranted.