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Purpose: The European Organisation for Research and Treatment of Cancer conducted a randomized trial investigating the role of radiotherapy (RT) after local excision (LE) of ductal carcinoma-in-situ (DCIS) of the breast. We analyzed the efficacy of RT with 10 years follow-up on both the overall risk of local recurrence (LR) and related to clinical, histologic, and treatment factors., Patients and Methods: After complete LE, women with DCIS were randomly assigned to no further treatment or RT (50 Gy). One thousand ten women with mostly (71%) mammographically detected DCIS were included. The median follow-up was 10.5 years., Results: The 10-year LR-free rate was 74% in the group treated with LE alone compared with 85% in the women treated by LE plus RT (log-rank P < .0001; hazard ratio [HR] = 0.53). The risk of DCIS and invasive LR was reduced by 48% (P = .0011) and 42% (P = .0065) respectively. Both groups had similar low risks of metastases and death. At multivariate analysis, factors significantly associated with an increased LR risk were young age (< or = 40 years; HR = 1.89), symptomatic detection (HR = 1.55), intermediately or poorly differentiated DCIS (as opposed to well-differentiated DCIS; HR = 1.85 and HR = 1.61 respectively), cribriform or solid growth pattern (as opposed to clinging/micropapillary subtypes; HR = 2.39 and HR = 2.25 respectively), doubtful margins (HR = 1.84), and treatment by LE alone (HR = 1.82). The effect of RT was homogeneous across all assessed risk factors., Conclusion: With long-term follow-up, RT after LE for DCIS continued to reduce the risk of LR, with a 47% reduction at 10 years. All patient subgroups benefited from RT.