Oncocytic Tumors in the Salivary Gland: Cytopathological, Pathological, and Molecular Features

Primary oncocytic salivary gland tumors and oncocytic subtypes of traditionally non-oncocytic salivary gland neoplasms are occasionally encountered in fine needle aspiration (FNA) specimens, biopsies, and resections. Oncocytes are cells, either non-neoplastic or neoplastic, containing increased numbers of mitochondria resulting in cells with abundant eosinophilic cytoplasm and a low N/C ratio. A broad range of salivary gland tumors can be oncocytic including oncocytoma, Warthin tumor, mucoepidermoid carcinoma, salivary duct carcinoma, and others. Especially those tumors where the oncocytic pattern represents a subtype of neoplasm, the oncocytic pattern can create a diagnostic challenge due to marked similarities in the oncocytic pattern of cells. While their microscopic cytologic and histologic features may be similar, these tumors differ instrinscially at the molecular level. Ancillary studies such as immunologic and (e.g. androgen receptor for salivary duct carcinoma) molecular analysis, e.g. FISH for detecting the MAML2 or PLAG1/HMGA2 gene alterations in mucoepidermoid carcinoma and pleomorphic adenoma, respectively, can be used to classify these oncocytic tumors in difficult cases.