Is a higher boost dose of radiation necessary after breast-conserving therapy for patients with breast cancer with final close or positive margins?

To determine rates of loco-regional recurrence (LRR), distant failure and overall survival for patients with breast cancer treated with breast-conserving therapy (BCT) with a close or positive surgical margin (C/PM) treated with standard dose boost radiation compared with a higher boost of radiation. We retrospectively studied 1476 patients with T1–T3 invasive breast cancer treated with BCT between 1992 and 2009. Median age was 57 years. Patients were divided into three groups: Group I included 1197 patients (81 %) with negative margins who received a standard boost (median 60 Gy) total dose to the lumpectomy cavity; Group II included 116 patients (8 %) with C/PM who received a standard boost (median 60 Gy); and Group III included 163 patients (11 %) with C/PM who received a higher boost (median 68 Gy). Biological subtypes (e.g., ER, PR, HER2/neu) were available for 858 patients (58 %) and were also assessed for any relationship to LRR rate. The Kaplan–Meier, Cox-regression, and log-rank tests were used to estimate rates of LRR and the significance of risk factors. Median follow-up was 8.6 years. The overall 5- and 10-year cumulative incidences of LRR were 2.1 % (95 % CI 0.8–2.1 %) and 4.5 % (95 % CI 3.4–6.0 %), respectively. The 5- and 10-year cumulative incidences of LRR for Group I (negative margins + standard boost) were 1.9 and 4.4 %; for Group II (C/PM + standard boost) were 3.9 and 7.0 %; and for Group III (C/PM + higher boost) were 2.9 and 3.8 %, respectively. No statistically significant differences in LRR rates were found among the three groups (p = 0.4). Similar results were obtained for distant failure (p = 0.3) and overall survival (p = 0.4). On multivariate analysis, tumor grade (p = 0.03), systemic-therapy (p = 0.005), node positivity (p = 0.05), young age (p = 0.001), and biological subtype (p = 0.04) were statistically significantly associated with higher LRR. Higher boost dose and margin positivity were not significant. Our data suggest that the 10-year risk of local recurrence for patients with close or positive margins receiving a standard boost was 7 % compared to 3.8 % for those receiving a higher boost; however, this difference was not significant. A higher boost dose did not significantly improve local control, nor did margins impact LRR risk in our cohort of patients.