Cells are similar to those in other myoepithelial lesions, with prominent basal lamina production. Image
Nuclear pleomorphism is variable, but here one easily sees features of a malignant epithelial process. Cells vary in their morphology as well, in that they can be spindled, ovoid, plasmacytoid, or show prominent clear cell change.
The tumor is growing outside the parotid adjacent to a nerve, an unequivocal sign of malignancy.
Enlarged cells with mitotic activity is often seen in those tumors which behave more aggressively.
Overall the neoplasm is highly cellular, with no specific features. Immunoreactivity for calponin, p63, smooth muscle actin (often), and keratins is found.
Myoepithelial carcinoma is defined as a salivary gland neoplasm composed exclusively of cells wtih myoepithelial differentiation (as determined by light microscopy, immunohistochemistry, and/or electron microscopy). Tumors show invasive growth and may metastasize as well.
Affects adults, M+F. Usually involves parotid gland but can involve other major glands as well as palate. Presents as an asymptomatic mass or swelling in the area. Usually a de novo tumor, but may be a malignant component arising from a long standing pleomorphic adenoma.
Complete surgical excision with negative margins. Neck dissection is not usually performed unless there is evidence of nodal disease.
The clinical behavior and outcome of myoepithelial carcinomas are variable, with no discernible histologic features that correlate clearly with behavior. Overall, most tumors that display marked histologic aggressiveness (cytologic atypia, high mitotic rate, and necrosis) behaved adversely. Occasional low-grade tumors with minimal mitotic activity have metastasized, and a few have caused death (Michal).
Yu G, Ma D, Sun K, Li T, Zhang Y. Myoepithelial carcinoma of the salivary glands: behavior and management. Chin Med J (Engl). 2003 Feb;116(2):163-5.
Savera, Adnan T. M.D.; Sloman, Andrew M.D.; Huvos, Andrew G. M.D.; Klimstra, David S. M.D. Myoepithelial Carcinoma of the Salivary Glands: A Clinicopathologic Study of 25 Patients. American Journal of Surgical Pathology 24(6) June 2000
Michal M, Skalova A, Simpson RW, Rychterova V, Leivo I. Clear cell malignant myoepithelioma of the salivary glands. Histopathology 1996; 28:309–15.