Epithelial-myoepithelial carcinoma is an uncommon, biphasic low-grade epithelial neoplasm composed of variable proportions of ductal and large, clear-staining, differentiated myoepithelial cells. It comprises approximately 1 per cent of all epithelial salivary gland neoplasms.
Clinical Features.
This is predominantly a tumor of the parotid gland. In the AFIP case files, the mean age of patients is about 60 years and women are more often affected than men. Localized swelling with a history of steady increase in size over a period of time is the common symptom, but occasionally patients experience facial weakness or pain. Nasal obstruction and facial deformity may represent major complaints of patients with maxillary involvement. Some studies have suggested that patients with these tumors are at increased risk for a second primary malignancy-either in the salivary glands or in a separate site (breast and thyroid have been reported).
Histologic Features.
The histologic features of this tumor may vary greatly from solid lobules that are separated by bands of hyalinized fibrous tissue to irregular, papillary cystic arrangements with tumor cells which partially or completely fill cystic spaces but most tumors show a multinodular growth pattern with islands of tumor cells separated by dense bands of fibrous connective tissue. The islands of tumor cells are composed of small ducts lined by cuboidal epithelium that is surrounded by clear cells which interface with a thickened, hyaline like basement membrane. The inner luminal cuboidal cells have finely granular, dense eosinophilic cytoplasm and central or basally located nucleus. The outer, clear myoepithelial cells vary in shape from colum- nar to ovoid and have a vesicular nucleus located towards the basement membrane.
Treatment.
Surgery is considered the primary mode of treatment. Even with complete surgical resection recurrences and distant metastases remain a concern and may occur from a few months to years after initial surgery.