Plasmacytoid myoepithelioma of minor salivary glands: report of case with emphasis in the immunohistochemical findings

Abstract

Myoepithelioma is a rare benign tumor of the salivary glands and is usually seen in the parotid gland and the minor salivary glands. It was once considered to be a type of pleomorphic adenoma (PA), but myoepitheliomas are today believed to be relatively aggressive tumors. Myoepitheliomas are most common in young adults between the ages of 30 and 50 and there are very few cases reported in individuals less than 18 years of age. We report a case of myoepithelioma located in the hard palate in a 15-year-old Brazilian male. The tumor was composed of plasmacytoid myoepithelial cells. An analysis of the immunohistochemical profile of the tumor cells showed positivity for vimentin, S-100 protein, and glial fibrillary acidic protein (GFAP), but not for smooth muscle actin (α-SMA) and cytokeratin 14 (CK14). We report this case because of the rarity of this tumor, especially in adolescents. We also discuss the histological parameters of the differential diagnosis of this tumor as well as its immunohistochemical profile.

Myoepithelioma of hard palate: A case report

“…Besides, ductal/luminal differentiation is not normally expected in ME and when present, it constitutes <5% of the tumor parenchyma; which is considered to be the best diagnostic factor by many authors to distinguish it from PA. [5,9,10,12,13] The present case showed similar findings.…”

“…Majority of the cases are reported in parotid gland and the minor salivary glands especially the soft palate. [3,5] The tumour is also recently reported in skin, soft tissue and bone. [6,7] The tumour is now considered as a separate pathological entity with biological behaviour distinct from PA and not a variant of PA.…”

“…In salivary gland, most ME affect the parotid and minor salivary glands of the palate. [5] Majority of the cases are benign and constitute only 1/10 th of salivary gland tumors. [6,8] Most of the authors consider ME as a one of the entity in the continuous histologic spectrum of salivary gland adenoma, one end being represented by canalicular adenoma where there is only luminal cell/epithelial cell proliferation with no myoepithelial component, followed by the basal cell adenoma with very few myoepithelial cells, continuing with PA where there is significant proportion of myoepithelial cells, then the myoepithelial cell rich PA and other extreme end represented by pure ME.…”

“…Ki-67 labelling index of more than 10% in ME is highly suggestive of malignant biological behaviour. [5,8,9,10,12] The other clinical criteria for malignant ME are that the lesion will be painful, frequently exhibiting sudden and rapid growth. Histologically, the multinodular appearance of the lesion, presence of infiltrative growth, necrosis, increased and abnormal mitotic figures indicates malignancy.…”

“…[1] The tumor was first described and classified by Sheldon in 1943 as a different entity which was till then considered as a variant of pleomorphic adenoma (PA). [4,5] Burke et al in 1995 were the first to report primary ME of soft tissue from retroperitoneal region.…”