Characterization of epimyoepithelial islands in benign lymphoepithelial lesions of major salivary gland: an immunohistochemical and ultrastructural study.

Knowledge of the processes leading to the development of epimyoepithelial islands bears on histogenetic and morphogentic processes in salivary gland tumors. Immunohistochemical and ultrastructural investigations of the cellular composition of epimyoepithelial islands were carried out on three examples of benign lymphoepithelial lesions with varying histologic features. The monoclonal anti-keratin antibody 312C8-1, which specifically decorates myoepithelial cells of the normal salivary gland, also stains the myoepithelial cells surrounding residual acini and intercalated ducts in benign lymphoepithelial lesions and the cell population of epimyoepithelial islands, with the exception of persisting luminal epithelial cells. Ultrastructurally, the myoepithelial cells of involuting acini and ducts and the modified myoepithelial cells of epimyoepithelial islands, identified in both locations by the monoclonal antibody 312C8-1, show an increasing complement of tonofilament bundles. In addition, persisting lumens (often distended with lymphocytes) and definite luminal epithelial cells can be seen in electron micrographs of some epimyoepithelial islands. The designation for this characteristic epithelial feature of benign lymphoepithelial lesions is therefore appropriate.