Abstract: Mucinous (secretory) myoepithelioma is a very uncommon variant of myoepithelioma characterized by the
presence of intracellular mucin. We herein report the findings of a 51-year-old woman who presented with a
mass in the right parotid region, which had been slowly growing over the previous year. Magnetic resonance
imaging revealed a rounded mass with lobulated margins in the tail of the right parotid gland that showed
heterogeneous uptake in the anterior margin of the mass. A clinical diagnosis of pleomorphic adenoma was
made. Superficial parotidectomy revealed a 3.6 cm encapsulated, round-shaped, light brown, gelatinous, solid
tumor. The neoplasm showed a reticular pattern forming pseudoglandular structures that were filled with
abundant extracellular mucin secretion. Additionally, lakes of mucin of different sizes appeared to be scattered
throughout the neoplasm. The epithelioid tumor cells were medium-sized with eosinophilic cytoplasm, centrally
located, small, uniform nuclei, and inconspicuous nucleoli. Mitoses were not observed. Signet-ring or uni-
vacuolated cells, ductal, and glandular components were absent. The extracellular mucin was positive for
mucicarmine and Alcian blue staining. Immunohistochemical staining revealed that the tumor cells were
diffusely and strongly positive for S100 protein, cytokeratin AE1/AE3, SOX10, and DOG-1. Occasional compact
solid clusters of epithelioid cells showed intense positivity for CK7 and high-molecular-weight CK. The diagnosis
was pure extracellular mucin-producing (colloid) myoepithelioma. To our knowledge, this type of neoplasm has
not been previously published. Knowledge of this new variant will avoid diagnostic difficulties.
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