THE VALUE OF BREAST LUMPECTOMY MARGIN ASSESSMENT AS A PREDICTOR OF RESIDUAL TUMOR BURDEN

Purpose: Margin assessment is commonly used as a guide to the relative aggressiveness of therapy for breast conserving treatment (BCT), thou gh its value as a predictor of the presence, type, or extent of residu al tumor has not been conclusively studied. Controversy continues to e xist as to what constitutes a margin that is ''positive,'' ''close,'' or ''negative.'' We attempt to address these issues through an analysi s of re-excision specimens. Patients and Methods: As part of an instit utional prospective practice approach for BCT, 265 cases with ATCC Sta ge I/II carcinoma with an initial excision margin that was less than o r equal to 2 mm or indeterminate were subjected to re-excision. The pr obability of residual tumor (+RE) was evaluated with respect to tumor size, histopathologic subtype, relative closeness of the measured marg in, the extent of margin positivity graded as focal, minimal, moderate , or extensive, and the extent of specimen processing as reflected in the number of cut sections per specimen volume (S:V ratio). The amount of residual tumor was graded as microscopic, small, medium, or large. The histopathologic subtype of tumor in the re-excision specimen was classified as having an invasive component (ICa) or pure DCIS (DCIS). Results: The primary excision margin was positive, >0 less than or equ al to 1 mm, 1.1-2 mm, and indeterminate in 60%, 18%, 5%, and 17%, resp ectively. The predominant histopathologies in the initial excision spe cimens were invasive ductal (IDC) (50%) and tumors with an extensive i ntraductal component (EIC) (43%). The histopathology of the initial ex cision specimen was highly predictive of the histopathology of tumor f ound on re-excision, as residual DCIS was found in 60% of +RE specimen s with initial histopathology of EIC compared to 26% for IDC (p = 0.00 1). Neither the extent of margin positivity nor the extent of tumor in the re-excision were significantly related to the initial histopathol ogic subtype; however, a +RE was seen in 59% of EIC, 43% of IDC, and 3 2% of invasive lobular ILC cases (p = 0.01). The extent of margin posi tivity was significantly related to the size of the tumor such that tu mor size less than or equal to 20 mm was associated with a greater pro bability of focal or minimal margin involvement. Positive margins grad ed as focal, minimal, moderate/extensive were associated with a +RE in 26%, 58%, and 84%, respectively (p = 0.001). Further, the extent of p ositivity was significantly correlated with the extent of residual tum or such that focal/minimal positivity was more commonly associated wit h micro/small +RE, whereas moderate/extensive positivity was associate d with medium/large +RE. When the closest margin of the initial excisi on specimen was positive, >0 less than or equal to 1 mm, or 1.1-2 mm, a +RE was found in 56%, 41%, and 17%, respectively (p = 0.01) but did not correlate with the amount of residual tumor. The extent of specime n processing as reflected in the S:V ratio did not correlate with the probability of defining a measured margin as positive nor the probabil ity of a +RE. In a univariate model, the extent of tumor in the re-exc ision and the histologic type of tumor in the re-excision were signifi cantly associated with margin status and initial histopathology, respe ctively. The probability of finding a +RE, based on a multivariate mod el, was associated with the closeness and extent of margin involvement and initial histopathology of an EIC. Conclusion: The relative closen ess of tumor to the specimen edge and the extent of margin positivity are predictive for residual tumor, though with an error consistent wit h its limitations as a sampling procedure. The histopathology of tumor in the initial excision is predictive of the type of residual tumor a nd the extent of margin positivity was correlated with the amount of r esidual tumor. (C) 1997 Elsevier Science Inc.