Value of immunohistochemistry in the diagnosis of salivary gland tumors.

Salivary gland tumors are rare entities that may hide diagnostic difficulties. Immunohistochemistry is a useful tool in daily diagnostic work to evaluate diagnostic and prognostic features. Mucoepidermoid carcinoma (MEC) is characterized by a zoning pattern, with cytokeratin (CK) 7 present in the central part and CK14 and mitochondria in the peripheral part of the neoplastic nests. High proliferative activity and c-ERB-B2 expression may indicate poor prognosis. Salivary duct carcinoma (SDC) should be differentiated from metastatic breast carcinoma demonstrating an in situ component. Staining the basal membrane with collagen IV and laminin, and the basal cells with CK14 might be useful for this purpose. SDC frequently shows androgen receptor positivity, and a case of tumor regression with antiandrogen therapy has been reported. Acinic cell carcinoma is positive with low-molecular weight CK, and with lysozyme and amylase. Adenoid cystic carcinoma may show areas of dedifferentiation, evidenced by a high proliferative rate with Ki-67 and by the loss of myoepithelial markers. Epithelial–myoepithelial carcinoma shows markers of epithelial and myoepithelial differentiation. Among the latter, smooth muscle actin and calponin are the most frequently expressed.