Mastectomy or Margin Re-excision? A Nomogram for Close/Positive Margins After Lumpectomy for DCIS

Anatomic extent of ductal carcinoma in situ (DCIS) may be uncertain in spite of clinical, pathologic, and imaging data. Consequently close/positive margins are common with lumpectomy for DCIS and often lead to a challenge in deciding whether to perform a re-excision or mastectomy.From a single health system, we identified cases of lumpectomy for DCIS with close/positive margins who underwent re-excision for the purpose of constructing a nomogram. In total, 289 patients were available for analysis. The patients were randomly divided into two sets allocating 70% to the modeling and 30% to the validation set. A multivariable logistic regression model was used to estimate the probability of overall positive margin status using multiple clinicopathologic predictors. Nomogram validation included internal tenfold cross-validation, internal bootstrap validation, and external validation for which a concordance index was calculated to assess the external validity.Significant predictors of persistent positive margins from regression modeling included necrosis at diagnosis (non-comedo or comedo); DCIS not associated with calcifications on core biopsy; high-grade DCIS; progesterone receptor positivity; and number of positive margins at initial surgery. When subjected to internal validation, the nomogram achieved an uncorrected concordance index of 0.7332, a tenfold cross-validation concordance index of 0.6795, and a bootstrap-corrected concordance index of 0.6881. External validation yielded an estimated concordance index of 0.7095.Using clinical and pathologic variables from initial diagnosis and surgery for DCIS, this nomogram predicts persistent positive margins with margin re-excision, and may be a valuable tool in surgical decision-making.