Salivary gland tumors are characterized by a wide variety of histological types which makes their classification and diagnosis difficult. It should be noted that the diversity in the occurrence and dilemma regarding the pathogenesis of salivary gland tumors is due to lack in distinguishing the cells participating in its oncogenesis, especially the Myoepithelial cells (MECs). MECs are normal constituent of the major and minor salivary glands, they are found between the basal lamina and the acinar or ductal cells. Proper and extensive studies regarding MECs are varied and thus have posed difficulty for a pathologist to understand this cell. Numerous functions of MECs have been described, the most important of them being important for contraction of the glands, also, it has been found to prevent tumor progression. In this study we try to make a thorough description of this cell and its role in some salivary gland tumors. 24 formalin-fixed, paraffin-embedded specimens of salivary gland tumors (7 cases of pleomorphic adenoma, 6 cases of mucoepidermoid carcinoma,
6 cases of Adenoid cystic carcinoma, and 5 cases of clear cell carcinoma) were used in this study.
The specimens were cut at 5μm thick for H&E staining as a routine stain and calponin immunostaining. Calponin is a 34 kDa protein, it is a family of actin filament-associated proteins and it is a sensitive immunohistochemical marker for MECs. The present study revealed positive staining reaction for calponin in pleomorphic adenoma and adenoid cystic carcinoma and negative calponin reaction in mucoepidermoid carcinoma and clear cell carcinoma. These findings demonstrate that myoepithelial cells play a role in the pathogenesis of some salivary gland neoplasms and no or minimal role in others.