Role of boost radiotherapy for local control of pure ductal carcinoma in situ after breast-conserving surgery: a multicenter, retrospective study of 622 patients

To evaluate the effect of boost radiotherapy on ipsilateral breast tumor recurrence (IBTR) for ductal carcinoma in situ (DCIS) after breast-conserving surgery and whole breast radiotherapy (WBRT) with or without boost.

Retrospective, multicentre study of 622 patients (624 tumors) diagnosed with pure DCIS from 1993–2011.

Most tumors (377/624; 60.4%) received a boost. At a median follow-up of 8.8 years, IBTR occurred in 64 cases (10.3%). A higher percentage of patients with risk factors for IBTR received a boost (p < 0.05). Boost was not associated with lower rates of IBTR than WBRT alone (HR 0.75, 95% CI 0.42–1.35). On the univariate analyses, IBTR was significantly associated with tumor size (11–20 mm, HR 2.32, 95% CI 1.27–4.24; and > 20 mm, HR 2.10, 95% CI 1.14–3.88), re-excision (HR 1.76, 95% CI 1.04–2.96), and tamoxifen (HR 2.03, 95% CI 1.12–3.70). Boost dose > 16 Gy had a protective effect (HR 0.39, 95% CI 0.187–0.824). Multivariate analyses confirmed the independent associations between IBTR and 11–20 mm (p = 0.02) and > 20 mm (p = 0.009) tumours, and re-excision (p = 0.006). On the margin-stratified multivariate analysis, tamoxifen was a poor prognostic factor in the close/positive margin subgroup (HR 4.28 95% CI 1.23–14.88), while the highest boost dose ( > 16 Gy) had a significant positive effect (HR 0.34, 95% CI 0.13–0.86) in the negative margin subgroup.

Radiotherapy boost did not improve the risk of IBTR. Boost radiotherapy was more common in patients with high-risk disease. Tumor size and re-excision were significant independent prognostic factors.