Mohs micrographic surgery for melanoma: a case series, a comparative study of immunostains, an informative case report, and a unique mapping technique.

BACKGROUND: Mohs micrographic surgery (MMS) has been established as an alternative to standard surgical excision for local cutaneous malignant melanoma (MM) and melanoma in situ (MIS). The use of melanocyte-specific immunohistochemical stains may improve the diagnostic accuracy of MMS frozen sections.
OBJECTIVE: We used MMS with immunostains to determine the maximum and minimum margins required to clear 52 melanomas, mostly MIS of the head and neck. We sought to identify the most sensitive melanocyte immunostain for use in MMS frozen sections and to improve the clinicopathologic correlation of perilesional pigmented lesions.
METHODS: We studied 52 consecutive cases of invasive melanoma (n = 10) and MIS (n = 42), tabulating the maximum and minimum margins required for complete tumor resection in any one direction during MMS. In 10 of these cases we studied the relative sensitivity of the immunostains MART-1, S-100, and HMB-45 in Mohs frozen sections. We describe a case highlighting the importance of the increased sensitivity of MART-1. In 12 patients we used a unique mapping technique to help determine the clinical relevance of a total of 35 perilesional pigmented foci.
RESULTS: The maximum margin averaged 10.1 mm (range 3-26 mm) for MM and 9.4 mm (range 3-18 mm) for MIS. The minimum margin averaged 7.0 mm (range 3-13 mm) for MM and 5.5 mm (range 3-11 mm) for MIS. For individual tumors, the difference between the minimum and maximum margin averaged 3.7 mm (range 0-13 mm). This difference was >or=5 mm in 38% (20/52) and >or=10 mm in 10% (5/52), highlighting that subclinical tumor extension is often broad and asymmetric. While five of six MM less than 1.0 mm in depth would have been cleared with a routine 1 cm excision, a standard 5 mm margin would have cleared less than one-quarter of the cases of MIS (10/42). In Mohs frozen sections, MART-1 proved superior in sensitivity to both HMB-45 and S-100. Our mapping technique provided clinically relevant histologic correlation for perilesional pigmented lesions, improving the Mohs surgeon's ability to evaluate equivocal foci in frozen sections.
CONCLUSION: MM, especially MIS on the head and neck, often exhibits an asymmetric growth pattern, making it quite suitable for treatment with MMS. The use of MART-1 immunostain may improve the diagnostic accuracy of Mohs surgeons. We believe that HMB-45 should not be used to rule out the diagnosis of MIS in equivocal sections because of its inferior sensitivity. We introduce a new mapping technique as an adjunctive measure to aid in the clinicopathologic evaluation of perilesional skin.