Study of myoepithelial cell markers in histogenesis of pleomorphic adenoma and mucoepidermoid carcinoma of salivary glands

The application of immunohistochemistry methods has resulted in marked improvement of the microscopic diagnosis of neoplasms combined with H&E staining. Although unique cellular antigens have not been found in salivary gland neoplasms, multiple less specific immunomarkers have been used and may be helpful in elucidating the role of myoepithelial differentiation in those neoplasms. The aim of this study was to evaluate immunohistochemical myoepithelial markers (GFAP, actin, vimentin and s100) in mucoepidermoid carcinoma and pleomorphic adenoma of salivary glands, for differential diagnosis of these tumors and specification of their histogenesis. Method & Materials: Formalin-fixed and parafin embedded tissue sections of 25 pleomorphic adenoma and 25 mucoepidermoid carcinoma were immunohistochemically analyzed for the presence of actin, vimentin, GFAP and S100 protein. A standard biotin-streptavidin procedure after antigen retrieval was used. Immunoreactivity of myoepithlial cells and chondromyxoid areas in pleomorphic adenoma and mucus cell, epidermoid cells and intermediate cells in mucoepidermoid carcinoma were evaluated and immunoreactivity was scored on a scale of 0 to +4 (Regezi method) with o as negative, 1+ scattered staining, 2+ indicate 25% to 50% of positive tumoral cells and 4+ indicating more than 50% positive cells. The data were analyzed with chi-square test, and significant level 0.05 (P<0.05). In 25 pleomorphic adenomas all nonluminal cells and chondromyxoid areas were positive (+4) for GFAP and vimentin and (0 → +3) for muscle-specific actin (12:0, 12:+1, 1:+3) and (+1 → +4) for S100 protein (3:+1, 3:+2, 18:+3, 1:+4). But all mucoepidermoid carcinomas regardless of their grade were negative for all mentioned markers (P<0.001) and there were no immunohistochemical difference in major and minor salivary glands neoplasms. Expression of myoepithelial cell-associated markers in pleomorphic adenoma have confirmed role of myoepithelial cells in histogenesis of this tumor and lack or limited expression of these antigens in mucoepidermoid carcinoma indicates the minimal myoepithelial differentiation in this tumor. Therefore, evaluation of myoepithelial cell markers can be helpful in differential diagnosis of salivary gland neoplasms with myoepithelial cell differentiation, and also specification of histogenesis of these tumors.