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.

Figure 1

Clinical and imaging features. (a) Intraoral swelling in the right side of the hard palate. (b) Computed tomography showing large hypodense tumor provoking slight erosion of maxillary cortical bone.

Figure 2

Histopathology findings. Histological sections stained in HE. (a) Well-circumscribed proliferation of sheets, islands, and strings of myoepithelial cells (40×); (b) Strong hyalinization of the connective tissue and foci of hemorrhage seen amidst the tumoral cells (Hematoxyin/Eosin, 40×) (c) Detail of the round-shaped myoepithelial cells showing eccentric nucleus (100×); (d) Tumoral plasmacytoid cells arranged in a pseudo-cribriform pattern within myxomatous background (100×).

Figure 3

Immunohistochemical findings. Immunohistochemical study of tumor plasmacytoid cells revealed (a) strong positivity for S-100 protein, (b) moderate immunoreactivity for vimentin, and (c) focal immunoreactivity for GFAP, (d) Tumor cells failed in immunostaining for α-SMA, although the muscular walls of the blood vessels (positive control) were positive (Streptavidin-Biotin Complex, 100×).