Extensive Intraductal Component (EIC) as the Most Predictive Factor for Residual Disease Post-Breast-Conserving Surgery With Close DCIS Margins: A Single Institutional Experience.

Purpose: We set out to assess whether the extensive intraductal component (EIC) status in invasive breast cancers serves as an independent predictor of residual disease (RD) in re-excisions performed at our institution. This laboratory-based study provides insights into the thresholds for additional surgical intervention in cases with close ductal carcinoma in situ (DCIS) margins following initial breast-conserving surgery (BCS). We also examined the unique characteristics specific to EIC-positive cases. Methods: BCS cases with invasive breast cancer and DCIS with close margins that had re-excisions following initial surgery (Dec 2019-Dec 2024) were selected and classified into EIC positive or EIC negative. Data collected on the initial excision included the EIC status and other clinicopathological information such as margin status, DCIS extent, cancer type and focality, TNM stage, biomarker status, and OncotypeDX Recurrence Score (RS). The RD status was collected on re-excision specimens. Results: Ninety-one cases were included (57 EIC positive and 34 EIC negative), with most being invasive ductal carcinoma. The rate of RD on re-excision was 70.2% and 32.4% in EIC-positive and EIC-negative cases, respectively ( Conclusion: Findings show that EIC status is the most significant predictor of RD following BCSs with close DCIS margins. This emphasizes the importance of identifying EIC-positive cases in pathology reports and prioritizing them for additional re-excision when DCIS margins are close.