TGF-β-stimulated clone-22 (TSC-22) was reported to be a differentiation-inducing factor which negatively regulates the growth of salivary gland cancer cells. In the present study, we examined the expression of TSC-22 in salivary gland tumors by immunohistochemistry. In pleomorphic adenoma (PA), most of the sparse myoepithelial-like tumor cells, which are considered as the differentiated cells because they produce extracellular matrix, expressed TSC-22. However, only a limited number of cases of the solid myoepithelial-like tumor cells in PA, which are considered as the growing cells, expressed TSC-22. In adenoid cystic carcinoma (ACC), inner ductal cells in the tubular structure, strongly expressed TSC-22, though the outer myoepithelial-like tumor cells did not express TSC-22. In the cribriform structure, myoepithelial-like tumor cells did not express TSC-22. However, a small ductal structure in the micro-cyst wall strongly expressed TSC-22. Sparse type myoepithelial-like tumor cells in ACC also expressed TSC-22. In mucoepidermoid carcinoma, epidermoid tumor cells and mucous-producing tumor cells in mucoepidermoid carcinoma frequently expressed TSC-22. Thus, the expression of TSC-22 was frequently observed in the cells with differentiated-phenotypes, although rarely in the cells with growing potentials. These results suggest that TSC-22 may play an important role in maintaining the differentiated phenotype in salivary gland tumors.

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