Myoepithelial tumours of the salivary glands

Abstract Myoepithelial cells are a normal constituent of the salivary acini and smaller ducts, and are found between the epithelial cells and the basement membrane. They can be recognized with various immunohistochemical markers, although none is specific or reliable in every case. Neoplastic myoepithelial cells in both benign and malignant tumours can take several forms, including epithelioid, spindle, plasmacytoid and clear, and this variability largely accounts for difficulties in histopathological diagnosis. Benign salivary adenomas form a spectrum with widely differing proportions of luminal, basal and myoepithelial cells and stroma. Whilst clinically similar, benign myoepithelioma differs from basal cell adenoma and pleomorphic adenoma only by being composed almost exclusively of myoepithelial cells, but the very different morphology justifies separation of the entity. Myoepithelial carcinoma is a rare but probably underrecognized malignancy typically with a multinodular architecture. It too can display a wide variety of cytological appearances, and often a most useful diagnostic clue is the presence of plentiful hyaline and/or myxoid stromal material. Its behaviour is variable, and histology is a relatively poor predictor of clinical outcome. Myoepithelial cells are also found in greater or lesser numbers in a few other carcinomas, and are an integral part especially in epithelial–myoepithelial carcinoma.