The value of breast lumpectomy margin assessment as a predictor of residual tumor burden in ductal carcinoma in situ of the breast

BACKGROUND. Margin width is considered the most important risk factor for local recurrence in ductal carcinoma in situ (DCIS) of the breast. The purpose of this report is to assess the predictive utility of lumpectomy specimen margin assessment for the presence and extent of residual DCIS. METHODS. Specimens from 253 DCIS cases with lumpectomy and reexcision were studied to determine to the probability of residual DCIS on reexcision. The probability of residual tumor was evaluated with respect to tumor size, margin status, nuclear grade, presence of necrosis, patient age, and the extent of specimen processing (number of sections/volume tissue). Lesions were grouped by size: less than or equal to 2 mm, greater than 2-15 mm., greater than 15-40 mm, or greater than 40 mm. Margin width was recorded as the distance of DCIS to the closest specimen edge or, for positive margins, scored as: extensive (margin involvement in :8 sections or >4 low-power fields [LPFs]), moderate (5-7 sections or 2-4 LPFs), minimal (2-4 sections or 1 LPF), or focal (1 section, single focus). The amount of residual tumor was graded by maximum dimension on a semiquantitative basis. RESULTS. Initial excision margin significantly predicted for the presence of residual tumor on reexcision. Residual tumor was found on reexcision in 85% of extensively positive, 68% of moderately positive, 46% of minimally positive, 30% of focally positive, 41% of greater than 0-1 mm, 31% of greater than 1-2 mm, and 0% of greater than 2 mm margins (P < 0.0001). On univariate analysis, margin width and lesion size of initial excision specimens significantly predicted for the presence of residual DCIS on reexcision. Age, grade, necrosis, and extent of specimen processing were not significant prognostic factors. On multivariate analysis, both initial margin width (P < 0.0001) and lesion size (P = 0.02) significantly predicted for residual DCIS. As for amount of residual tumor, margin width and initial lesion dimension both significantly predicted for medium to large residuum, whereas age 45 years or younger was of borderline significance on univariate analysis. On multivariate analysis, margin width and lesion size on initial excision both remained significant predictors of larger volume residual tumor. CONCLUSIONS. The margin status of a DCIS lumpectomy specimen is the most important predictive factor for both the presence and amount of residual disease.