Leiomyosarcoma of the mandible: diagnosis as aided by immunohistochemical demonstration of desmin and laminin.

A mandibular spindle-cell sarcoma originally diagnosed as malignant fibrous histiocytoma displayed a whorl-like histological structure and cellular pleomorphism. By electron microscopy the tumor cells showed prominent basal laminae around the tumor cells and bundles of myofilaments with attachment plaques. In support of the ultrastructural observations, immunofluorescence (IF) microscopy with antibodies to laminin, the major component of basal lamina, gave a bright pericellular staining of the tumor cells. IF microscopy using antibodies against intermediate filament (IMF) proteins revealed the presence of desmin, the muscle-type of IMF protein, in most tumor cells. On the other hand, staining for myoglobin was negative. The data are consistent with the diagnosis of leiomyosarcoma rather than malignant fibrous histiocytoma, and suggest that expression of desmin and laminin can be useful markers of smooth-muscle derivation of sarcomatous tumors.