The Impact of Early Incomplete Sections on Mohs Micrographic Surgery Margin Assessment

Variations exist regarding evaluation of complete circumferential and deep margin assessment between Mohs surgeon's practices including section spacing, physical placement of the first section on the slide, and acceptable tumor-free margins. The impact of early incomplete sections (EIS) on margin interpretation has not been systematically studied. Here, we evaluate how inclusion of EIS affects tumor status interpretation during Mohs Micrographic Surgery. We retrospectively analyzed 500 basal cell carcinoma (BCC) Mohs pieces with EIS and prospective evaluation of 250 serially step-sectioned BCC pieces. In the retrospective cohort, inclusion of EIS reduced interpreted positivity from 47.2% to 41.2% reclassifying 12.7% of initially positive pieces as negative. Prospectively, EIS reduced positivity from 35.6 to 27.2%. Incorporation of EIS may reduce false-positive margin interpretations in Mohs Micrographic Surgery and potentially decrease unnecessary additional stages, depending on surgeon margin thresholds and cutting depth. The clinical application is nuanced and should take into account patient and tumor factors as determined by the Mohs surgeon.