Microphthalmia transcription factor expression in cutaneous benign, malignant melanocytic, and nonmelanocytic tumors

The protein encoded by the microphthalmia (mi) gene is a transcription fact or essential for the development and survival of melanocytes. Using a monoc lonal antibody generated against human Mi transcription factor protein (Mit f) the authors previously demonstrated that Mitf expression is conserved in primary and metastatic malignant melanomas, and appears to be a highly sen sitive and specific melanocytic marker. Mitf expression in various cutaneou s nevi and cutaneous nonmelanocytic tumors has not been documented systemat ically. The authors evaluated Mitf immunostaining in 62 benign nevi, 58 pri mary cutaneous melanomas, and 53 nonmelanocytic tumors. Mitf immunostaining was conserved in all benign nevi, with Spitz nevi and neurotized nevi demo nstrating decreased staining intensity. With the exception of desmoplastic melanomas, all primary cutaneous melanomas were immunopositive regardless o f the cell type. Only one of 14 desmoplastic melanomas was Mitf positive. N one of the nonmelanocytic tumors was immunopositive, including those lesion s that may resemble melanoma histologically (spindle cell carcinomas, atypi cal fibroxanthomas, and leiomyosarcomas). The results demonstrate that Mitf antibody expression is conserved in the majority of benign and malignant m elanocytic lesions, and that it may be helpful in the diagnosis of primary melanocytic skin lesions. Its use in desmoplastic melanomas is limited and is reflective of other melanocyte-associated antigens. Mitf discriminates b etween spindle cell nonmelanocytic tumors and melanomas with a spindle cell morphology, and is useful in a panel with other appropriate antibodies.