CLEAR-CELL MALIGNANT MYOEPITHELIOMA OF THE SALIVARY-GLANDS

Previous reports of monomorphic clear cell carcinoma of the salivary g lands have shown inconsistent results with immunohistochemistry, espec ially for S-100 protein, and this has led to uncertainty about the nat ure of these tumours. We believe that much can be explained by conside ring this group as comprising not one but two separate neoplasms, one epithelial and the other myoepithelial. The former has been described as hyalinizing clear cell carcinoma-it generally occurs in the minor s alivary glands, and strongly expresses cytokeratins but not S-100 prot ein or alpha smooth muscle actin. In contrast, this study presents fiv e primary malignant tumours of the major salivary glands also composed largely of a single population of clear cells, but displaying histolo gical and immunohistochemical features of myoepithelial differentiatio n, such as the formation of collagenous spherules and expression of S- 100 protein and actin. A small number of similar tumours have been rep orted previously. We, therefore, believe that these neoplasms represen t a clear cell variant of malignant myoepithelioma (myoepithelial carc inoma).