Normal and neoplastic myoepithelial cells in salivary glands: an immunohistochemical study

To determine the difference between normal and neoplastic myoepithelial cells, we performed immunoperoxidase staining for contractile proteins (actin and myosin) and intermediate filament proteins (vimentin and 55- to 57-kilodalton keratin) on paraffin sections from salivary gland tumors. Normal myoepithelial cells were positive for actin and myosin but negative for vimentin and keratin. Outer tubular cells of organoid double-layered tubular structures seen in pleomorphic and monomorphic adenoma and adenoid cystic carcinoma, and "cyst"-lining cells and outermost cells of adenoid cystic carcinoma were occasionally positive for actin and myosin. These outer tubular cells, "cyst"-lining cells, and outermost cells were considered to be neoplastic myoepithelial cells. However, their stainability was much lower than that of normal myoepithelial cells. On the other hand, these neoplastic myoepithelial cell were always positive for vimentin. "Mesenchymal" cells and hyaline cells of pleomorphic adenoma and indifferent cells of adenoid cystic carcinoma were negative for both actin and myosin but positive for vimentin and occasionally also positive for keratin. The significance of vimentin staining in neoplastic myoepithelial cells and the coexpression of vimentin and keratin in some tumor cells is discussed.