Clear Cell Neoplasms and Secondary Tumors: Epithelial-Myoepithelial Carcinoma

Salivary gland tumors with clear cell features include a broad range of entities (Fig. 12.1) several of which have already been discussed in other contexts within this book. Epithelial-myoepithelial carcinoma will be the focus of this chapter; it is a rare primary salivary gland tumor that is characterized cytologically by a biphasic pattern of numerous large clear myoepithelial cells admixed with ductal cells. The differential diagnosis of clear cell neoplasms also includes other salivary gland tumors that are comprised predominantly of clear cells such as clear cell carcinoma, sebaceous lymphadenoma, and lipoma, as well as salivary gland tumors that have clear cell variants such as myoepithelioma, myoepithelial carcinoma, oncocytoma, mucoepidermoid carcinoma, and acinic cell carcinoma. Finally, certain metastatic tumors such as renal cell carcinoma and sebaceous carcinoma can also appear clear in FNA samples.

Epithelial-myoepithelial carcinoma is an unusual tumor that represents approximately 1% of all salivary gland neoplasms. Most epithelial-myoepithelial carcinomas are low grade, although a small subset is intermediate to high grade. Between 60% and 80% of epithelial-myoepithelial carcinomas occur in the parotid gland, where they are locally aggressive, but they can also be seen in the palate and other minor salivary gland sites of the oral cavity and upper respiratory tract. In minor salivary gland sites, epithelial-myoepithelial carcinoma can present as an ulcerative nodular lesion. It was first described as a distinct entity by Donath in 1972. Epithelial-myoepithelial carcinoma is a tumor of adults, and it occurs in middle-age to elderly individuals. The average age at presentation is 62 years, and in most studies there is an approximately 2:1 female-to-male ratio. In the parotid gland, epithelial-myoepithelial carcinoma typically presents as a welldefined, painless, slowly enlarging mass that in some cases has been present for many years. Despite its relatively bland cytologic appearance, most cases are reported as “malignant” or “suspicious for malignancy” by FNA.