Cellular adenomyoepithelioma of the breast.

This report is the second documented case of an adenomyoepithelioma arising in the breast. The neoplasm was well circumscribed and possessed cytologic features suggestive of a low-grade cancer; however, its biologic behavior remains undefined. The epithelial and myoepithelial elements are characterized ultrastructurally, and both are active participants in the neoplastic process. There are some histologic similarities of this lesion to the salivary gland epithelial-myoepithelial carcinoma; however, the growth pattern of cellular interductal proliferation of myoepithelium is unique.