Tumor location, interval between surgery and radiotherapy, and boost technique influence local control after breast-conserving surgery and radiation: retrospective analysis of monoinstitutional long-term results.

PURPOSE: To obtain long-term data on local tumor control after treatment of invasive breast cancer by breast-conserving surgery and adjuvant radiotherapy (RT), in consideration of the interstitial high-dose-rate boost technique. PATIENTS AND METHODS: A total of 263 women with 268 mammary carcinomas (International Union Against Cancer Stage I-IIB) who had undergone breast-conserving surgery and adjuvant RT between 1990 and 1994 were included. The potential risk factors for local recurrence-free survival were investigated.
RESULTS: During a median follow-up period of 94 months, 27 locoregional recurrences, 25 of which were in breast, were diagnosed. The cumulative rate of in-breast recurrence was 4.1% +/- 1.4% at 5 years of follow-up and 9.9% +/- 2.4% at 10 years. The multivariate analysis identified medial tumor location and delayed RT (defined as an interval of >2 months between surgery and the start of RT) as significant risk factors for in-breast recurrence in the overall study population. Medial tumor location vs. lateral/central location (hazard ratio, 2.48; 95% confidence interval, 1.06-5.84) resulted in a cumulative in-breast recurrence rate of 22.5% +/- 8.3% vs. 6.9% +/- 2.3% at 10 years. Delayed RT (hazard ratio, 2.84; 95% confidence interval, 1.13-7.13) resulted in a cumulative in-breast recurrence rate of 18.5% +/- 6.2% vs. 6.8% +/- 2.4% at 10 years. The multivariate analysis also showed that the risk of in-breast recurrence was lower after high-dose-rate boost therapy than after external beam boost therapy in patients with laterally/centrally located tumors (hazard ratio, 3.25; 95% confidence interval, 0.91-11.65).
CONCLUSION: Tumor location, interval between surgery and RT, and boost technique might influence local control of breast cancer treated by breast-conserving surgery and RT.