MALIGNANT PLASMACYTOID MYOEPITHELIOMA OF THE PALATE - HISTOLOGICAL OBSERVATIONS COMPARED TO BENIGN PREDOMINANT PLASMACYTOID MYOEPITHELIAL CELLS IN PLEOMORPHIC ADENOMA OF THE PALATE

Predominant benign plasmacytoid myoepithelial cells in pleomorphic ade noma and malignant plasmacytoid myoepithelioma cells were investigated morphologically. The cells of both tumors were plasmacytoid in appear ance and sheet-like. Immunohistochemically, they were positive for ker atin, vimentin, and S-100 protein, and negative for oi-smooth muscle a ctin. In the malignant cells, large nuclei with irregular nuclear memb ranes and distinct nucleoi and occasional intranuclear inclusions and nuclear grooves were seen. Ultrastructural findings showed that the be nign cells were richer in intermediate filaments and had fewer mitocho ndria. The intranuclear inclusions and nuclear grooves of the malignan t cells were caused by invagination of the irregular nuclear membranes . Taken in their entirety, the above light microscopical nuclear findi ngs may be useful as an adjunct for distinguishing malignant from beni gn plasmacytoid neoplastic myoepithelial cells of the salivary gland.