Clinical and pathologic features of malignant myoepithelioma of salivary glands

Abstract

To analyze the clinical features, morphology and biologic behavior of primary malignant myoepithelioma (MME) of salivary glands. The H&E sections of 16 MME cases were reviewed. Immunohistochemical study using EnVision method for cytokeratin (CK), epithelial membrane antigen (EMA), vimentin, S-100 protein, desmin, muscle-specific actin (MSA), smooth muscle actin (SMA), Myo, proliferation cell nuclear antigen (PCNA), leukocyte common antigen (LCA) and glial fibrillary acidic protein (GFAP) was carried out. Of the 16 patients studied, 6 were males and 10 were females. Their ages ranged from 12 to 65 years (with an average age of 44 years). The tumor occurred predominantly in the parotid gland and minor salivary gland of the palate. Common clinical features included sudden and rapid tumor growth, superficial ulceration, bony destruction and nerve infiltration. Seven of the 16 patients developed local recurrences, while 2 patients had metastasis in the lymph nodes of submandibular or other cervical regions. Most tumors infiltrated adjacent normal salivary gland, adipose, muscular and bony tissues. The extent of local invasion however varied. Histologically, MME showed a wide range of morphologic appearance, with various combinations of clear, spindle, epithelioid or plasmacytoid cells. The tumor cells were atypical and demonstrated high mitotic activity. In this study, 9 cases were composed predominantly of clear tumor cells. Immunohistochemically the tumor cells were positive for CK, EMA, MSA, desmin and S-100 protein. In general, MME is a rare and low-grade malignant salivary gland tumor. It carries a low potential for lymph node or distant metastasis but relatively high tendency for local recurrences, resulting in destruction of adjacent soft and bony tissues. The biologic behavior also varies, depending on the site of involvement. Morphologic diagnosis of MME can be difficult in view of the wide spectrum of histologic changes. A definitive diagnosis however is possible with the application of immunohistochemistry.