Immunohistochemical Expression of Actin and S100 in Pleomorphic Adenoma and Mucoepidermoid Carcinoma

Tumors of the salivary glands constitute an important area in the field of oral and maxillofacial pathology. These tumors have a special status in human neoplasia and probably the most complex histopathologic features of the body organs and being heterogeneous. Pleomorphic adenoma (PA) is the most common benign; and mucoepidermoid carcinoma(MEC) is the most common malignant salivary gland tumors. Many investigations have showed that myoepithelial cells play a major role in the histogenesis of PA and may be important in many MECs. The aims of the study are to determine the presence and distribution of myoepithelial cell related immunomarkers Actin and S100 in PA and MEC and to explore the histogenesis of these tumors in relation to the above mentioned markers. Materials and methods: Seventeen formalin fixed paraffin embedded tissue blocks of PA, and other fifteen tissue blocks of MEC were included in the study. Diagnostic confirmation was performed through examination of hematoxylin and eosin sections. Both tumors were immunohistochemically analyzed for the presence of actin and S100 protein. Results: There was a positive immunoreactivity for the expression of actin in PA (100%) with different score values, while for MEC, actin was negatively expressed in all of the cases (except in one case). There was a highly statistical significant difference in the actin immunoexpression between the two tumors (p=0.000). There was a positive immunoreactivity for S100 protein expression in all of the cases of PA and MEC (100%) with different score values; however, there was no statistically significant difference in the S100 immunoexpression between them (p=0.545). Conclusion: The myoepithelial cells are associated with the histogenesis of salivary PA, and the negative expression of actin in squamous, intermediate and mucous cells of MEC can be explained by the non-involvement of the myoepithelial cells in the histogenesis of this tumor.