1123 Background: Ductal Carcinoma in Situ (DCIS) is a non-invasive form of breast cancer which is often treated by breast-conserving surgery. The addition of radiotherapy to surgery has been shown to reduce the risk of local recurrence (LR), but use of radiotherapy varies. It is not known to what extent women with DCIS are at risk for recurrent cancer due to the omission of radiation therapy. We studied a large provincial cohort of women with DCIS who were treated with breast-conserving surgery for factors which predict local recurrence and estimate the impact of radiotherapy on local recurrence and long-term rates of breast preservation. Methods: All women diagnosed with DCIS in Ontario from 1994 to 2003 were identified. Treatments and outcomes were identified through administrative databases and validated by chart review. Women treated with breast-conserving surgery, alone or with radiotherapy, were included. Survival analyses were used to study local recurrence (DCIS or invasive) in relation to patient characteristics, tumour characteristics and treatment. Results: The cohort included 3975 women who were treated with breast-conserving therapy; of these, 1949 (49%) received radiation. At 10 years median follow-up, 736 developed LR(19%). LR developed in 259 of 1949 women who received radiotherapy (13%) and in 477 of 2026 women who did not (24%;p<0.001). The differences were significant for both invasive LR (7% vs. 14%; p<0.001) and DCIS recurrence (6% vs.9%; p<0.001). The 10-year cumulative rate of mastectomy was 13% for women who received radiotherapy compared to 17% for those who did not (p<0.01).We estimate that 29% (N=214) of all local recurrences diagnosed in Ontario in women treated for DCIS between 1994 and 2003 would be prevented if all patients received radiotherapy. Conclusions: The omission of radiation therapy after breast-conserving surgery in women with DCIS resulted in a substantial number of local recurrences that might have been avoided and lower rates of breast preservation. Improvements in guidelines that facilitate the selection of women in whom radiotherapy can be avoided are needed.
Long-term outcome after breast-conservation treatment with radiation for mammographically detected ductal carcinoma in situ of the breast
