Immunohistochemical expression of metallothionein in pleomorphic adenoma of minor salivary glands: A role in the control of apoptosis?

Pleomorphic adenoma is the most common benign neoplasm of both the major and minor salivary glands. The histological features are diverse and are characterized by the involvement of epithelial–myoepithelial structures. Metallothionein is a cysteine-rich protein present in myoepithelial cells of several benign and malignant neoplasms. The function of metallothionein is associated with DNA protection, oxidative stress and apoptosis. The purpose of this study was to evaluate the expression of metallothionein in pleomorphic adenoma of the minor salivary glands. Additionally, we investigated the association of the clinicopathological features of the lesions with metallothionein, specifically its association with Bcl-2, in an attempt to evaluate the role of metallothionein in the control of apoptosis. Thirty-five cases of pleomorphic adenoma were selected and immunohistochemistry was performed for metallothionein and Bcl-2 proteins. The proteins were quantified by the Quickscore method. The samples showed epidemiological characteristics similar to those described in the literature. We did not find an association between the clinicopathological characteristics of pleomorphic adenomas and the proteins studied, but an association between metallothionein and Bcl-2 was demonstrated. The results suggest that metallothionein may have a role in the control of apoptosis in pleomorphic adenoma.