Breast glands and salivary glands can manifest as tumors with similar morphological features. Salivary gland-like tumors of the breast are of two types: tumors with myoepithelial differentiation and those devoid of that. The breast tumors showing pure myoepithelial or epimyoepithelial differentiation are rare.
Adenomyoepithelioma (AME) of the breast is a biphasic tumor, identical to the epithelial-myoepithelial cell carcinoma of the salivary gland. Histologically, AME is composed of two cell types; myoepithelial and epithelial. The epithelial component is composed of columnar cells showing features of apocrine cells. The outer layer is composed of clear cells with the immunohistological profile of myoepithelial cells.
Our case was a 45-year-old woman presenting with a painless mass located peripherally on her right breast. Grossly, on the cut surface of the excision material a solid, well-circumscribed, white-gray, firm mass was seen. Microscopically, the tumoral lesion was composed of epithelial and myoepithelial components and had lobulated and focally infiltrating margins. Both epithelial and myoepithelial components showed marked pleomorphism, mitotic activity, atypia, and focal necrosis. Immunohistochemically SMA, CD10, p63 and CK5/6 were positive in the myoepithelial component and CK7 was positive in the epithelial component, Ki-67 proliferation index was 20% in the tumor. But estrogen and progesterone receptors were negative.
We find our case worthy to report because of the tumor showed high Ki-67 index, and extremely rarity of malignant AME in the breast tissue that it has only rarely been documented in the literature.