Factors affecting successful breast conservation for ductal carcinoma in situ

Background: Successful breast-conserving therapy in DCIS is restricted by high rates of residual disease resulting in the need for radiotherapy and/or re-excision. This study identifies patients with DCIS who are most at risk of compromised margins and of residual disease. Methods: All patients undergoing breast-conserving surgery for DCIS over a 6-year period were included. Method of diagnosis, mammographic size, pathological size, DCIS-margin distance and residual disease on re-excision were analysed. Results: One hundred and thirty-five patients underwent initial breast-conserving surgery for DCIS. The compromised margin rate was 72%, and the rate of residual disease on re-operation was 54%. On univariate analysis, underestimation of pathological size by mammography by > 1 cm occurred in 40% of those with compromised margins undergoing a therapeutic operation compared to only 14% of those with clear margins (P = 0.02). However, on multivariate analysis only pathological size (P < 0.0001, OR = 1.0,95% CI 1.037-1.128) and lack of a preoperative diagnosis by core biopsy (P < 0.0001, OR = 5.3,95% CI 1.859-15.08) were predictive of compromised margins. The presence of residual disease on re-excision was associated with increasing pathological size (P < 0.0001, OR = 1.085,95% CI 1.038-1.134) and decreasing DCIS-margin distance (P = 0.03, OR = 6.694,95% CI 1.84-37.855). Twenty-nine percent (n = 13/45) of lesions > 3 cm compared to 84% (n = 27/32) of lesions > 3 cm had residual disease on re-operation (P < 0.0001). Residual disease was present in 62% (n = 34/55), 64% (n = 7/11) and 17% (n = 2/12) of patients with DCIS-margin distances <= 1, 1-2 and 2-5 mm, respectively. Conclusion: Considerable underestimation of DCIS extent by mammography occurs in a high proportion of patients with compromised margins in breast conservation. Patients at particularly high risk of residual disease on re-excision are those with lesions > 3 cm and those with DCIS-margin distances of <= 2mm.