Immunohistochemical expression of S-100 protein in reactive and neoplastic myoepithelial cells of variant salivary pleomorphic adenomas.

Immunohistochemically detectable S-100 protein in 76 salivary pleomorphic adenomas was found in two types of myoepithelium derived neoplastic cells; spindle-shaped anastomosing cells and round cells. Spindle-shaped tumor cells displayed a strong presence of S-100 protein-like immunoreactive substance (LIS), and they were usually located in the outer layer of duct-like structures and showed a continued proliferation into the stroma. Round tumor cells abundantly gave a S-100 protein LIS staining, and they were distributed in the outer layer of duct-like structures. Chondroid cells and chondrocytes in hyalinous and myxomatous tissue were also reactive for S-100 protein LIS. In rare cases, stromal connective tissue fibers exhibited an intense S-100 protein LIS staining. Peripheral nerve fibers and myoepithelial cells in the affected salivary glands were also positive for S-100 protein LIS.