Permanent section margin concordance after Mohs micrographic surgery with immunohistochemistry for invasive melanoma and melanoma in situ: A retrospective dual-center analysis

Background: Mohs micrographic surgery (MMS) for melanoma practices vary among dermatologic surgeons. The implementation of immunohistochemical staining in MMS for melanoma mitigates challenges associated with slide interpretation; however, the reliability of melanoma antigen recognized by T cells 1 (MART-1), the preferred immunostain for melanoma, has yet to be compared with permanent section pathology. Objective: To assess concordance rates of MART-1 frozen sections and permanent section pathologic interpretation of melanoma treated with MMS. Methods: A dual-center retrospective analysis was conducted to collect concordance and demographic data. Chi-square tests were performed for group comparisons of categorical variables. Results: Of the 379 permanent sections sent, 367 were concordant with frozen section pathology for an overall concordance rate of 96.8%. Cases were stratified into indeterminately concordant and indisputably concordant. Twenty-two (6%) of cases were indeterminately concordant, whereas 345 (94.0%) of cases were indisputably concordant. Limitations: The concordance rate is derived from a comparison of adjacent tissue margins, an inevitable consequence of utilizing 2 techniques. Conclusion: To the author's knowledge, this study represents the largest investigation examining concordance rates of MART-1 frozen sections in Mohs for melanoma. High concordance disputes the ongoing need for additional permanent margins when using MART-1 in routine cases.