Comparison of MITF and Melan-A Immunohistochemistry During Mohs Surgery for Lentigo Maligna-Type Melanoma In Situ and Lentigo Maligna Melanoma.

Mohs micrographic surgery (MMS) with frozen section immunohistochemistry is a treatment option for malignant melanoma in situ (MMIS) and lentigo maligna melanoma (LMM). Melan-A is a cytoplasmic melanocyte immunostain useful on frozen sections but may lack specificity. Microphthalmia transcription factor (MITF) is a more specific nuclear melanocyte immunostain less frequently used in MMS.To quantify melanocyte density in chronic sun-damaged skin (CSDS), negative margin, and tumor from patients undergoing MMS for MMIS and LMM using MITF and melan-A.Sixteen patients with MMIS or LMM had frozen sections from CSDS, negative margin, and 12 tumor samples, stained with MITF and melan-A. Melanocyte counts were performed.Chronic sun-damaged skin mean melanocyte count (MMC) for MITF and melan-A was 9.8 and 13.7, respectively, (p <.001). Negative margin MMC for MITF and melan-A was 8.84 and 14.06, respectively, (p <.001). Tumor MMC for MITF and melan-A was 63.5 and 62.4, respectively.Although both MITF and melan-A facilitate the identification of tumor during MMS for MMIS and LMM, the apparent melanocyte density on tumor-free CSDS appears higher with melan-A than MITF. Microphthalmia transcription factor provides a crisp outline of melanocyte nuclei and is a useful alternative stain to melan-A for MMS of melanoma.