Comparison of integrin alpha chain expression in benign and malignant salivary gland tumors

This study investigates the distribution of the alpha chain of the integrin family of extracellular matrix receptors in a series of adenomas and carcinomas of salivary gland origin to determine if the malignant phenotype is associated with modification of the expression of these receptors.

Cryostat sections of 36 tumor specimens were stained by a standard streptavidin-biotin-peroxidase technique using primary monoclonal antibodies against alpha 1-6 and alpha v integrin chains. The immunohistochemical reaction was scored using a three-point scale and the results were analyzed using Fisher's exact test.

In salivary adenomas, alpha 2, alpha 3, alpha 4, alpha 6, and alpha v chains were widely expressed in most of the cases studied. The alpha 1 subunit was prominently expressed by the epithelial cells of Warthin's tumor, whereas a minority of pleomorphic adenomas showed immunoreactivity for this antigen. We observed alpha 5 subunit expression only in the mesenchymal-like component of pleomorphic adenomas. In salivary carcinomas, integrin alpha chain expression was heterogeneous, varying greatly between different histotypes and within the same histotype. The distribution of the antigens was similar to that of adenomas, except for the alpha 6 chain, which localized not only at the interface between cell and matrix, but also at sites of cell-cell contact. When the immunohistochemical levels of integrin alpha chain expression were compared in adenomas and carcinomas, expression significantly decreased for the alpha 6 and alpha v chains (p = 0.0007; p = 0.002, respectively).

Loss of alpha 6 and alpha v integrin subunits occurring in salivary gland carcinomas could modify the adhesive properties of malignant cells, contributing to the invasive potential of these tumors.