[Mixed tumor or myoepithelioma of the skin? Histologic and immunohistochemical features].

: Mixed tumor, first reported in the parotid gland, is formed from the proliferation of epithelial and myoepithelial cells in a mesenchymatous stroma. We report the case of a woman hospitalized for a subcutaneous nodule of the thigh, characterized by a fast increased in size in 8 months. Microscopic analysis showed a proliferation of grouped and isolated spindle cells, without atypia or mitotic features. Few tubular features were noted. Stroma was hyalinized or myxoid. Neoplastic cells displayed immunohistochemical positivity with smooth muscle actin, keratin and S-100 protein. This neoplasm appeared mesenchymatous. The diagnosis was mixed tumor with a predominant myoepithelial component. This case underlines the difficulties encountered in defining this neoplasm. Some authors consider that myoepithelioma is a monophasic variant of mixed tumor; others consider that myoepithelioma is different from mixed tumor because its is more aggressive prognosis. The evolution of our case suggests that a myoepithelial differentiation should be a ma of poor prognosis.