Mohs micrographic excision of melanoma using immunostains.

Background: Mohs excision of melanoma remains controversial, in part because of concerns regarding evaluation of frozen section margins. Several immunohistochemical stains are available for melanoma that can be used on frozen sections.
Objective: To review our experience with Mohs micrographic excision of melanoma using immunostains.
Methods: Sixty-eight patients were treated, including 46 with melanoma in situ and 22 with invasive melanoma, 62 of which were on the head or neck. HMB-45, MEL-5, Melan-A (A-103), and S-100 stains were employed.
Results: Sixty-seven of 68 tumors were excised to clear margins, requiring an average of 2.0 layers. Immunostains greatly enhanced detection of melanoma on frozen sections. The average margin required for clearance of in situ melanoma was 8.3 mm and of invasive melanoma was 11.1 mm. Only 23 of 46 (50%) in situ melanomas were clear with < or =6 mm margins; 15 mm margins were required to clear 96% of the tumors. Eleven of 22 (50%) invasive melanomas were clear with < or =6 mm margins; 26 mm margins were required to clear 95% of the tumors. Melan-A (A-103) was the most consistently crisp and easily interpreted immunostain.
Conclusions: Mohs excision of melanoma using immunostains can be useful, especially for tumors on the head and neck. For routine excision, margins wider than those currently recommended may be required to ensure tumor clearance. We recommend that (1) biopsies be stained preoperatively for Melan-A and/or HMB-45, (2) a debulking layer be obtained for permanent sections prior to Mohs layers, and positive and negative control specimens from the tumor and distant skin should be employed for comparison of staining patterns. Large-scale prospective studies of in situ and invasive melanoma on the head and neck are necessary.