S-100 protein in salivary gland tumors: an immunohistochemical study of 129 cases.

Immunohistochemical distribution of S-100 protein was evaluated in 129 tumors from major and minor salivary glands. Also, two sensitive immunoperoxidase avidin-biotin methods using either overnight incubation with primary antibody or pretreatment trypsin digestion and half-hour incubation were compared. Tumors with S-100 protein immunoreactivity were demonstrated in numerous benign and malignant histologic categories. Adenoid cystic carcinomas, carcinomas ex pleomorphic adenoma, clear cell carcinomas, and adenocarcinomas NOS showed inconsistent positive staining, whereas all monomorphic and pleomorphic adenomas and polymorphous low grade adenocarcinomas examined stained positively. No staining was observed in mucoepidermoid carcinomas or acinic cell carcinomas. Mesenchymal-like tumor cells with positive immunostaining were seen only in pleomorphic adenomas and trabecular-tubular adenomas. Equivalent results were found with both overnight and same-day digestion techniques. The consistent S-100 protein staining in some histologic tumor categories (pleomorphic and monomorphic adenoma and polymorphous low grade adenocarcinoma) compared to mucoepidermoid carcinoma that is devoid of S-100 protein immunoreactivity has application to some microscopic differential diagnostic situations. Inconsistent staining of adenoid cystic carcinomas and adenocarcinomas did not allow discrimination from other benign and malignant salivary gland tumors with similar histomorphology.