Early breast cancer with positive margins: excellent local control with an upfront brachytherapy boost

Standard breast conservation therapy consists of lumpectomy and whole breast radiation with boost. The effectiveness of radiation in cases of positive margins is controversial. Two potential treatment-related factors are time to initiation of radiation and localization of the boost. Here, we examine long-term outcomes of positive margin cases treated with an upfront interstitial brachytherapy boost. This particular treatment arrangement may reduce those treatment-related effects on local control. Historically, a low dose interstitial implant was a common boost technique. One approach administered the boost before external beam. A review of 521 cases treated at our institution was conducted. Patients were selected for this study if they received an upfront brachytherapy boost and had close or positive margins. Forty-four breast cancers were identified. Median follow-up of survivors was 11.3 years (8.1-21.7). Implant was performed at lumpectomy (12) or axillary dissection (32). Margin statuses were: focal carcinoma at ink (37), multifocal carcinoma at ink (1), carcinoma <1 mm from ink (2), and DCIS at ink (4). Median tumor size was 1.2 cm (0.5-3.5 cm). Ten patients had nodal involvement. Total median dose was 60 Gy (58.6-65.3 Gy). Median boost dose was 15 Gy (12-20.3 Gy). Lumpectomy to boost interval was median of 3 weeks (0-10.8). No ipsilateral breast recurrences or second primaries were identified. Four developed contralateral breast cancer. Eleven are deceased, four from breast cancer-all from metastasis. 12-year Kaplan-Meier estimates were: overall survival 78 ± 7 %, cause specific survival 93 ± 4 %, and recurrence-free survival 82 ± 6 %. Univariate analysis identified nodal disease as significant for cause specific survival (log rank p = 0.005). No ipsilateral breast recurrences were found. Early administered radiation and accurate boost localization were identified as suspected treatment-related factors for local recurrence. When these two treatment-related factors are minimized, long-term local control rates do not suffer.