Efficacy Analysis of High-risk Breast Cancer Patients Treated with Accelerated Partial Breast Irradiation from a Single Institution

111 Background: We present the results of an analysis of high-risk breast cancer patients as defined by the NSABP B-39/RTOG 0413 phase III trial, all treated with accelerated partial breast irradiation (APBI) from a single institution. Methods: Between July 1993 and August 2010, 130 patients with any combination of at least one of the high-risk features of estrogen receptor (ER) negativity, age < 50, and/or axillary nodal positivity were treated with 1 of 3 forms of APBI. Sixty-seven patients were treated with interstitial needle-catheter brachytherapy, 44 balloon-based brachytherapy and 19 with 3D conformal external beam radiation therapy. Aside from the high-risk features, general eligibility criteria included infiltrating ductal carcinoma, with inclusion of invasive lobular and DCIS since 2003, margins > 2 mm, and surgically staged axilla. One-hundred eighteen patients had one high-risk factor, 11 had two, and 1 had all three factors. The median tumor size was 12.0 mm with margins > 2 mm in 80% of patients. Greater than 75% had T1 tumors and 50% were ER negative. Thirty-one percent of patients were node positive. Based upon the ASTRO Consensus Guidelines for use of APBI (2009) none of these patients were suitable, 38% cautionary and 62% were unsuitable. Results: Median age was 56.5 yrs (range 40-90). With a median follow-up of 5.3 yrs (0.02-16.9) the 5-yr actuarial local recurrence rate (LR) was 4.2%; regional recurrence (RR) was 2.1%. Median time to LR and RR were 1.2 and 2.8 yrs, respectively. On univariate analysis, the only factor significant for LR was a close/positive margin (p=0.031), as ER/PR, age, nodal status, tumor size, histology, grade, hormonal or chemotherapy were all NS. The 5-yr actuarial cause specific, disease-free, and overall survivals as well as distant metastasis were 94%, 91%, 90%, and 6.4%, respectively. Conclusions: This cohort of NSABP B-39/RTOG 0413 identified high-risk patients who have undergone APBI has yielded local-regional control rates and survival outcomes comparable to standard risk patients undergoing partial breast irradiation. Continued follow-up will be needed to assess the long-term efficacy of such high-risk breast cancer patients treated with APBI.