MYOEPITHELIAL TUMORS OF SALIVARY-GLANDS - A CLINICOPATHOLOGICAL, IMMUNOHISTOCHEMICAL, ULTRASTRUCTURAL, AND FLOW-CYTOMETRIC STUDY

Myoepitheliomas of the salivary glands remain a controversial entity. To contribute to the knowledge of this entity, 16 myoepithelial tumors of the salivary glands were studied: 12 benign myoepitheliomas (BME) and 4 malignant myoepitheliomas (MME). The clinical and the histologic findings of each case were studied. Immunohistochemistry and flow-cyt ometry analysis were performed from the paraffin-embedded material in 15 cases. An electron-microscopy study was performed in 8 cases. The m yoepithelial tumors affected patients of both sexes equally. The mean age of the patients with BME was 54 years, and the mean age of patient s with MME was 62 years. Eight cases of BME originated in the parotid gland and 4 cases originated in the minor salivary glands. Ail the MME developed from a benign preexistent tumor: two developed from a pleom orphic adenoma in the parotid gland, and the other two MME developed i n the minor salivary gland from a BME. The myoepithelial tumors were c omposed of epithelioid, plasmacytoid, spindle, or clear cell types, an d they showed a solid or a myxoid pattern of growth. Immunohistochemic al studies revealed marked and diffuse positivity to cytokeratins, vim entin, and S-100 protein in all cases. Glial fibrillary acidic protein was positive in 8 cases (53%), and muscle-specific actin and smooth-m uscle actin were positive in only 3 cases (20%); they were all cases o f BME. Desmin was negative in all tumors. Ultrastructural studies show ed the presence of basal membrane, tight junctions, intermediate filam ents, and microvilli as well as actin-like filaments lacking focal den sities in all cases. But actin-like filaments with focal densities wer e not identified. Flow cytometry determined that all BME were diploid with a mean proliferative index of 7.73%. Two of the MME were diploid and the other two MME were aneuploid. The mean proliferative index of MME was 11.93%. In conclusion, BME and MME originated in major and min or salivary glands can display different histologic patterns and cellu lar features. Some immunohistochemical and ultrastructural characteris tics have been found in all these neoplasms, which supports the idea t hat myoepitheliomas are composed by neoplastic modified myoepithelial cells, not fully differentiated. These techniques can be useful for th e diagnosis of these tumors. Copyright (C) 1996 by W.B. Saunders Compa ny.