Background Mohs micrographic surgery (MMS) offers an unparalleled cure rate for cutaneous malignancy. Its success hinges on achieving reliably negative histologic margins. When assessing margins, Mohs surgeons generally examine multiple histologic sections per Mohs stage. In some cases, the most-peripheral section or sections are clear, but tumor is identified in deeper sections within the same tissue block. Objective To explore approaches to margin analysis in these scenarios. Methods A web-based survey was administered to members of the American College of Mohs Surgery investigating their standard practice when definitively tumor-free section(s) are examined during a Mohs stage before finding cancer in a deep section. Factors influencing the decision were explored. Results The number of clear sections required to declare margin negativity and terminate MMS (margin threshold) varied widely among respondents; 25% were comfortable with one clear section, whereas 19% would obtain an additional layer with eight clear sections. Margin thresholds depended on tumor type but were independent of surgeon experience. Conclusion Although no consensus emerged, a majority of respondents would not take an additional layer with four clear sections if resecting basal cell carcinoma. Prospective outcomes data are needed to standardize management of this important oncologic issue.
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