Myoepithelioma of minor salivary gland origin. Light and electron microscopical study.

A gingival tumor that invaded the anterior maxilla was removed from a 14-year-old boy and studied by light and electron microscopy. The tumor was composed exclusively of myoepithelial cells and appeared to be malignant. By light microscopy, the tumor appeared to be a poorly differentiated epithelial neoplasm of undetermined origin; however, electron microscopical examination showed myoepithelial differentiation, indicative of a salivary gland origin. To our knowledge, the present case represents the only confirmed myoepithelioma that shows features indicative of malignant potential. Myoepitheliomas may be related to mixed tumors of salivary glands.