Outcomes of Node-positive Breast Cancer Patients Treated With Accelerated Partial Breast Irradiation Via Multicatheter Interstitial Brachytherapy: The Pooled Registry of Multicatheter Interstitial Sites (PROMIS) Experience

Objectives To report outcomes for breast-conserving therapy using adjuvant accelerated partial breast irradiation (APBI) with interstitial multicatheter brachytherapy in node-positive compared with node-negative patients. Materials and methods From 1992 to 2013, 1351 patients (1369 breast cancers) were treated with breast-conserving surgery and adjuvant APBI using interstitial multicatheter brachytherapy. A total of 907 patients (835 node negative, 59 N1a, and 13 N1mic) had >1 year of data available and nodal status information and are the subject of this analysis. Median age (range) was 59 years old (22 to 90 y). T stage was 90% T1 and ER/PR/Her2 was positive in 87%, 71%, and 7%. Mean number of axillary nodes removed was 12 (SD, 6). Cox multivariate analysis for local/regional control was performed using age, nodal stage, ER/PR/Her2 receptor status, tumor size, grade, margin, and adjuvant chemotherapy/antiestrogen therapy. Results The mean (SD) follow-up was 7.5 years (4.6). The 5-year actuarial local control (95% confidence interval) in node-negative versus node-positive patients was 96.3% (94.5-97.5) versus 95.8% (87.6-98.6) (P=0.62). The 5-year actuarial regional control in node-negative versus node-positive patients was 98.5% (97.3-99.2) versus 96.7% (87.4-99.2) (P=0.33). The 5-year actuarial freedom from distant metastasis and cause-specific survival were significantly lower in node-positive versus node-negative patients at 92.3% (82.4-96.7) versus 97.8% (96.3-98.7) (P=0.006) and 91.3% (80.2-96.3) versus 98.7% (97.3-99.3) (P=0.0001). Overall survival was not significantly different. On multivariate analysis age 50 years and below, Her2 positive, positive margin status, and not receiving chemotherapy or antiestrogen therapy were associated with a higher risk of local/regional recurrence. Conclusions Patients who have had an axillary lymph node dissection and limited node-positive disease may be candidates for treatment with APBI. Further research is ultimately needed to better define specific criteria for APBI in node-positive patients.