Rate of residual tumor after repeat surgery for positive margins in ductal carcinoma in Situ, and predictive factors.

Aims: To evaluate the rate of residual tumor in re-excision specimen of patients with positive margins in ductal carcinoma in situ (DCIS) following breast-conservative surgery, and to identify predictive factors of residual tumor.

Material And Methods: We conducted a monocentric, retrospective study, from January 2010 to December 2020. All 103 patients who underwent re-excision for positive margins in DCIS following breast-conservative surgery for in situ or invasive breast carcinoma were included. Positive margins were defined as inferior to 2 mm from the DCIS component. Two groups were defined, depending on the presence of residual tumor or not, and were compared on their clinical and histopathological characteristics to identify predictive factors of residual tumor.

Results: Residual tumor was found in re-excision specimen of 46 patients (44.7 %). The risk of residual tumor was increased in patients with more than 2 tumor foci (aOR: 12.4; 95 % CI: 1.2 -124.1; p = 0.032) and in those with extensive margin involvement (aOR: 3.2; 95 % CI: 1.3-8.2; p = 0.013). Finally, surgery performed after 2013 was associated with a lower risk of residual tumor (aOR: 0.23; 95 % CI: 0.09-0.058; p = 0.002).

Conclusion: The rate of residual tumor in re-excision specimen of patients with positive margins in DCIS is high. Both the number of tumor foci and the extension of positive margins were identified as risk factors. Finally, the surgical learning curve for this procedure seems to be significantly correlated with the risk of residual tumor and needs to be considered.