Fine-needle aspiration of epithelial-myoepithelial carcinoma of the parotid gland with prominent adenoid cystic carcinoma-like cribriform features avoiding a diagnostic pitfall

Abstract

Objectives: Epithelial-myoepithelial carcinoma (EMC) is a rare salivary gland malignancy associated with an overall good prognosis. Fine-needle aspiration (FNA) typically shows a dual population of myoepithelial and ductal cells. Rarely, acellular matrix globules are present, raising a differential diagnosis of adenoid cystic carcinoma (AdCC), a more aggressive salivary gland malignancy associated with a poor long-term prognosis. We report an FNA case of EMC containing a predominant pattern of AdCC-like spherical globules. Methods: We compare features of an unusual case of EMC with those of cribriform AdCC to arrive at morphologic clues to the correct diagnosis. Results: Distinguishing features of EMC on FNA include (1) a prominent population of myoepithelial cells vs the predominance of basaloid cells in AdCC and (2) cohesive matrix globules with a peripheral rim of pale-staining basement membrane material compared with the dyscohesive matrix globules of AdCC. Immunochemical markers (S100, CD117, and MyB) are also useful. Conclusions: Although EMC and AdCC can both contain spherical matrix globules, close evaluation of the cytomorphology of the globules and their relationship to surrounding cells provides a clue to distinguish the two neoplasms.