Monomorphic adenomas of the salivary glands. A clinico-pathologic study of 12 cases with immunohistochemical observation.

Twelve cases of monomorphic adenoma of the salivary glands were histologically reclassified and their immunohistochemical reactivity for S-100 and cytokeratin was correlated. All patients underwent a benign clinical course. Individual tumors were well encapsulated and frequently showed a focal cystic change. Histologically, 9 cases were of the epithelial basaloid cell type and 3 cases were of the myoepithelioma variant. About one half of the epithelial type featured a mixture of trabecular and tubular patterns. The immunoreactivity to S-100 and cytokeratin varied. All basaloid cell adenomas were positive for cytokeratin, while S-100 positivity was found mostly in the stroma along with the varied reaction and intensity in the epithelial nests. In myoepitheliomas, cytokeratin was totally negative and S-100 was positive in 2 of 3 cases. The above findings suggest that the degree of participation of myoepithelial cells determines the phenotypic expression of monomorphic adenomas, and supports the hypothesis that the basaloid cell and myoepithelial types may be located on extreme ends of the same tumor spectrum with a wide range of pleomorphic adenoma in-between.