Ductal Carcinoma in Situ—The Influence of the Radiotherapy Boost on Local Control

Abstract

Local recurrence (LR) of ductal carcinoma in situ (DCIS) is reduced by whole-breast irradiation after breast-conserving surgery (BCS). However, the benefit of adding a radiotherapy boost to the surgical cavity for DCIS is unclear. We sought to determine the impact of the boost on LR in patients with DCIS treated at the McGill University Health Centre. A total of 220 consecutive cases of DCIS treated with BCS and radiotherapy between January 2000 and December 2006 were reviewed. Of the patients, 36% received a radiotherapy boost to the surgical cavity. Median follow-up was 46 months for the boost and no-boost groups. Kaplan-Meier survival analyses and Cox regression analyses were performed. Compared with the no-boost group, patients in the boost group more frequently had positive and <0.1-cm margins (48% vs. 8%) (p < 0.0001) and more frequently were in higher-risk categories as defined by the Van Nuys Prognostic (VNP) index (p = 0.006). Despite being at higher risk for LR, none (0/79) of the patients who received a boost experienced LR, whereas 8 of 141 patients who did not receive a boost experienced an in-breast LR (log-rank p = 0.03). Univariate analysis of prognostic factors (age, tumor size, margin status, histological grade, necrosis, and VNP risk category) revealed only the presence of necrosis to significantly correlate with LR (log-rank p = 0.003). The whole-breast irradiation dose and fractionation schedule did not affect LR rate. Our results suggest that the use of a radiotherapy boost improves local control in DCIS and may outweigh the poor prognostic effect of necrosis.