[Myoepithelial neoplasms of skin and soft tissues]

Myoepithelial neoplasms of skin and soft tissues comprise cutaneous mixed tumor (chondroid syringoma), mixed tumor of subcutaneous and deep soft tissues, myoepithelioma and rare malignant myoepithelioma (myoepithelial carcinoma). Myoepithelial tumors of skin and soft tissues are characterized by an extreme clinicopathological heterogeneity as in other anatomic locations. The neoplasms arise in childhood as well as in adults and are composed of epithelioid, histiocytoid, spindled, plasmocytoid and/or clear tumour cells in varying combinations, and are set in a myxoid or hyalinised intercellular matrix. Immunohistochemically, neoplastic cells stain positively for epithelial markers (pancytokeratin and/or epithelial membrane antigen), and often for S 100 protein. More rarely muscle actin, glial fibrillary acid protein, calponin, and p63 are expressed, whereas desmin is usually negative. The presence of at least moderate cytological atypia is associated with a significant risk for aggressive behavior and propensity for metastasis.