Radiological Underestimation of Tumor Size as a Relevant Risk Factor for Positive Margin Rate in Breast-Conserving Therapy of Pure Ductal Carcinoma In Situ (DCIS)

SIMPLE SUMMARY: Negative margins are the most important prognostic factor in breast-conserving therapy (BCT) of ductal carcinoma in situ (DCIS). The impact of radiological underestimation ≥10 mm (defined as mammographic minus histological tumor size in millimeters) has not been further examined. The purpose was to verify the radiological underestimation of DCIS size as a risk factor for positive margins. A pooled analysis of two trials was performed. Inclusion criteria were patients receiving BCT in DCIS. The results show a clinically relevant radiological underestimation in 37% of patients. Radiological underestimation is an independent risk factor for positive margins in BCT of DCIS with microcalcifications. Furthermore, the influencing factors of radiological underestimation were analysed. In multivariate logistic regression, only a mammographic tumor size ≤20 mm was an independent risk factor associated with radiological underestimation. When planning and executing BCT, it has to be considered that a relevant radiological underestimation is significantly higher in mammographic DCIS sizes ≤20 mm. ABSTRACT: Background: Radiological underestimation of the actual tumor size is a relevant problem in reaching negative margins in ductal carcinoma in situ (DCIS) associated with microcalcifications in breast-conserving therapy (BCT). The aim of this study is to evaluate whether the radiological underestimation of tumor size has an influence on the histopathological margin status. Methods: Patients who underwent BCT with preoperatively diagnosed pure DCIS were included (pooled analysis of two trials). Multiple factors were analysed regarding radiological underestimation ≥10 mm. Radiological underestimation was defined as mammographic minus histological tumor size in mm. Results: Positive margins occurred in 75 of 189 patients. Radiological underestimation ≥10 mm was an independent influencing factor (OR 5.80; 95%CI 2.55–13.17; p < 0.001). A radiological underestimation was seen in 70 patients. The following parameters were statistically significant associated with underestimation: pleomorphic microcalcifications (OR 3.77; 95%CI 1.27–11.18), clustered distribution patterns (OR 4.26; 95%CI 2.25–8.07), and mammographic tumor sizes ≤20 mm (OR 7.47; 95%CI 3.49–15.99). Only a mammographic tumor size ≤20 mm was an independent risk factor (OR 6.49; 95%CI 2.30–18.26; p < 0.001). Grading, estrogen receptor status, and comedo necrosis did not influence the size estimation. Conclusion: Radiological underestimation is an independent risk factor for positive margins in BCT of DCIS associated with microcalcifications predominantly occurring in mammographic small tumors.