Maintenance of polarity and a dual cell population in adenoid cystic carcinoma of the breast: an immunohistochemical study.

AIMS: Adenoid cystic carcinoma (ACC) of the breast, although quite uncommon, is histologically distinct and has an excellent prognosis. Our purpose was to characterize molecular markers of cellular differentiation and polarity to define better the role that these combined features might play in the excellent prognosis of ACC in this site. METHODS AND
RESULTS: We performed immunohistochemical stains for expression of vimentin (VM), cytokeratin (CK), smooth muscle actin (SMA), laminin (LAM), E-cadherin (E-cad), beta-catenin (beta-cat) and fodrin in 14 examples of ACC. Two types of intercellular lumens and defining lining cells were detected: true epithelial lumens were lined by CK positive cells that maintained the normal glandular luminal cells with an intact polarity and basolateral membrane compartment indicators: fodrin, E-cad and beta-cat. The second type of intercellular space was a pseudolumen, surrounded by myoepithelial cells that were strongly positive for VM and SMA, and lined by LAM. Double staining for VM and CK, VM and SMA, and CK and SMA detected occasional cytoplasmic co-expression of these markers in the myoepithelial cell compartment, but VM and SMA did not stain epithelial lumenal cells.
CONCLUSIONS: ACC of the breast is characterized by the presence of two types of intercellular lumens, one conserving basolateral markers of normal polarity (epithelial) with the other containing basement membrane material (abutted by myoepithelial cells). Dominance of VM staining may be a hallmark of ACC, along with maintained epithelial and myoeithelial compartments. This status of advanced, normal differentiation despite local invasion may be responsible for lack of distant metastasis.