also significantly associated with invasive lr (hr: 1.6; 95% ci: 1.0 to 2.4; p = 0.04). ConclusionsAge at diagnosis is a strong predictor of lr in women with dcis after treatment with bcs and radiotherapy. KEY WORDSDuctal carcinoma in situ, age, recurrence, young patients, radiation BACKGROUNDDuctal carcinoma in situ (dcis) is a noninvasive form of breast cancer that is most often diagnosed during mammographic screening. Although dcis is not life-threatening, up to 20% of women with dcis can develop invasive breast cancer at 10 years, which is associated with an increased risk of breast cancer mortality [1][2][3][4][5][6] . The goals of treating dcis are to maximize breast conservation, optimize cosmesis, and prevent the development of invasive breast cancer. Most women with dcis are treated with breastconserving surgery (bcs), followed by whole-breast irradiation. Radiotherapy after bcs has been proved to reduce the rate of local recurrence (both in situ and invasive) 7-12 . Randomized and nonrandomized clinical trials report that after bcs and radiation, approximately 12%-15% of women will experience a local recurrence within 10 years, and 5%-10% will develop an invasive local recurrence [7][8][9][10][11][12] .It is important to identify factors associated with the development of local recurrence and subsequent invasive breast cancer, because women with such factors may be candidates for more extensive therapy. It has been suggested that younger age at diagnosis is a risk factor for local recurrence after treatment for dcis 7,12-14 . Multivariable analyses from randomized clinical trials suggest that the efficacy of radiation ABSTRACT PurposeThe main goal of treating ductal carcinoma in situ (dcis) is to prevent the development of invasive breast cancer. Most women are treated with breastconserving surgery (bcs) and radiotherapy. Age at diagnosis may be a risk factor for recurrence, leading to concerns that additional treatment may be necessary for younger women. We report a populationbased study of women with dcis treated with bcs and radiotherapy and an evaluation of the effect of age on local recurrence (lr). MethodsAll women diagnosed with dcis in Ontario from 1994 to 2003 were identified. Treatments and outcomes were collected through administrative databases and validated by chart review. Women treated with bcs and radiotherapy were included. Survival analyses were performed to evaluate the effect of age on outcomes. ResultsWe identified 5752 cases of dcis; 1607 women received bcs and radiotherapy. The median follow-up was 10.0 years. The 10-year cumulative lr rate was 27% for women younger than 45 years, 14% for women 45-50 years, and 11% for women more than 50 years of age (p < 0.0001). The 10-year cumulative invasive lr rate was 22% for women younger than 45 years, 10% for women 45-50 years, and 7% for women more than 50 years of age (p < 0.0001). On multivariate analyses, young age (<45 years) was significantly associated with lr and invasive lr [hazard ratio (hr) for lr: 2.6; 95% confidence interval...

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