Epithelial-myoepithelial carcinoma of floor of mouth: A case report of double clear cell variant with immunohistochemical correlation

Abstract

Epithelial-myoepithelial carcinoma (EMC) is a rare biphasic low-grade malignancy accounting for only 0.5% of all salivary gland tumors. Commonly, EMC affects parotid gland (70%) and rarely affecting other salivary glands. Clearing of both, epithelial and myoepithelial cell types, is rare and gives an impression of a monocellular neoplasm. Case report: A 42-year-old male reported to Oral and Maxillofacial Surgery Department in Faculty of Oral and Dental Medicine, Misr International University with a painless growth in the floor of mouth since 5 years. The soft tissue window of computerized tomography (CT) revealed a well-circumscribed swelling in the sublingual space. The provisional diagnosis was pleomorphic adenoma. Results: The histopathological examination showed solid sheets of rounded to polyhedral clear cells forming lobes and lobules separated by connective tissue mucoid septa. A thin fibrous capsule, invaded with some tumor cells was also present. The presented pattern of clear cells together with the encapsulation of the tumor provides an impression of clear cell variant of monocellular neoplasm. Conclusion: The presented case relates to an epithelial-myoepithelial carcinoma originating from the sublingual salivary gland, which is a rare site for this lesion. Based on immunohistochemical staining, differentiation between the double clear cell types was confirmed using S-100 protein and SMA for the myoepithelial nature of the outer cells while the epithelial nature of the inner cells was confirmed by CK-19 and EMA. Thus, the diagnosis of double clear cell variant of EMC was given.