Myoepitheliomas and myoepithelial adenomas of salivary gland origin. Immunohistochemical evaluation of filament proteins, S-100 alpha and beta, glial fibrillary acidic proteins, neuron-specific enolase, and lactoferrin.

Immunohistochemical identification of keratin proteins (TK, KL1 and PKK1), vimentin, myosin, S-100 protein (using polyclonal antiserum) and S-100 alpha and beta subunits, glial fibrillary acidic protein (GFAP), neuron-specific enolase (NSE), lactoferrin, and lysozyme was made in myoepitheliomas, myoepithelial adenomas, and clear cell adenomas of salivary gland origin. Myoepithelioma cells were divided into two types: plasmacytoid cells, which showed great heterogeneity in terms of keratins and S-100 alpha and beta proteins and a lack of GFAP, NSE, lactoferrin, and lysozyme in most the cells, and fibrous and dendritic tumor cells, which displayed variable staining for keratin and S-100 alpha and beta proteins. Myoepithelial adenomas were composed of small-, intermediate-, and large-sized spindle cells that showed irregular positive reactions for keratins and S-100 alpha and beta. Immunohistochemical deposition of S-100 protein was restricted strongly to the dendritic cells present in hyalinous and myxomatous areas. Clear cell adenomas revealed uniformly slight staining of keratins and S-100 proteins, and negative staining or rarely positivity for GFAP, NSE, lactoferrin, and lysozyme. When the immunohistochemical deposition of these proteins was compared between normal glands and myoepithelial tumors, heterogeneity of expression of keratins, S-100 proteins, GFAP, and NSE was notable in the tumors. Progenitor cells of several kinds of myoepithelioma were suggested to be intercalated reserve cells, which are thought to be the same cell that gives rise to pleomorphic adenoma of salivary glands.