Myxoid melanoma: immunohistochemical studies and a review of the literature.

Malignant myxoid melanoma (MMM) is a rarely reported variant of malignant melanoma, which can often be confused with other mucin-containing neoplasms. A retrospective study of 3 cases of MMM and a review of the English-language literature was performed. MMM affects an older population and is frequently misdiagnosed. The major pathologic features are atypical spindle cells embedded in a myxoid stroma. Immunohistochemistry analysis of the tumor shows uniform staining of the spindle cells with S-100. In our 3 cases, there were noticeably more mast cells that could be detected with Giemsa stain and with antibody against transforming growth factor. The prognosis appears to be equivalent to other primary melanomas. Diagnosing MMM requires a high index of suspicion. We hypothesize that mast cells and secretion of transforming growth factor beta stimulates fibroblast secretion of mucin, which contributes to the tumor's invasive potential.