Myoepithelioma is composed exclusively of myoepithelial cells. Myoepithelial are ectodermally derived contractile cells that can be routinely identified in many normal tissues having secretory function such as major and minor salivary glands,
lacrimal
gland and sweat gland. Tumors composed exclusively of myoepithelial cells, so-called myoepitheliomas, are rare-less than 1% of all salivary gland tumors. Grossly, these tumors are well demarcated. The external surface is smooth and may be
bosselated.
The cut surface is white and homogenous. Microscopically, these tumors are surrounded by a thin fibrous capsule. They are composed of benign-appearing spindle-shaped and/or polygonal cells. Mitoses are rare. Frequently these tumors contain
myxomatous
stroma which is susceptible to alcial blue stain.
Clinically, myoepitheliomas present as slow-glowing, painless masses and can not be distinguished from pleomorphic adenomas. Treatment is the same as for pleomorphic adenoma, and the surgical excision should include a margin of normal tissue.
Although
the majority of myoepi theliomas have behaved in a beingn manner, cellular pleomorphism and mitotic activity have been associated with local aggressiveness.
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