Mohs micrographic surgery is accurate 95.1% of the time for melanoma in situ: a prospective study of 167 cases.

Background: Mohs micrographic surgery (MMS) represents a promising option for treatment of melanoma in situ (MIS). However, interpretation of melanocytic lesions by fresh frozen sections may be difficult.

Objective: The objective of this study was to determine if margins called clear by MMS were clear by subsequent paraffin-embedded sections and to compare cure rate with available data for MMS and standard excision.

Materials And Methods: A total of 167 patients with MIS, including 116 patients with MIS in sun-exposed skin of lentigo maligna (LM) type, were treated by MMS with subsequent evaluation of the final margin with paraffin-embedded sections that were cut en face, over a period of 12 years. A total of 143 patients were available for follow-up from 6 months to 12 years (mean, 50 months; median 48 months; 594.5 patient-years), and 109 patients were available for follow-up from 2 to 12 years (mean, 63 months; median, 60 months; 569 patient-years).

Results: The clearance rate by MMS technique using frozen sections was 94.1% for MIS non-LM type, 95.7% for MIS LM type, and 95.1% for both. The cure rate was 97.8% for MIS non-LM type, 99.0% for MIS LM type, and 98.6% for both for mean follow-up of 50 months and 97.4% for MIS non-LM type, 98.6% for MIS LM type, and 98.2% for both for mean follow-up of 63 months.

Conclusion: MMS is a viable option for treatment of MIS that may increase cure rate and reduce the size of the defect especially in cosmetically and functionally sensitive areas.