Coexpression of keratin and desmin in a carcinosarcoma involving the maxillary alveolar ridge

Immunohistochemical determination of the class of intermediate filaments (keratins, vimentin, desmin, neurofilaments, and glial fibrillary acidic protein) expressed by tumors has become an important diagnostic procedure for the histogenetic classification of neoplasms. A case of a poorly differentiated malignant neoplasm of the maxillary alveolar ridge which coexpressed keratin and desmin types of intermediate filaments is reported. These intermediate filaments have been associated with epithelial and muscle cell differentiation, respectively. The morphologic features of the tumor plus the expression of both these intermediate filaments indicate that this neoplasm represents a true carcinosarcoma.