Eccrine ductal and acrosyringeal differentiation of the breast epithelium--a lesion associated with some metaplastic breast carcinomas.

Two cases of metaplastic breast carcinoma associated with eccrine ductal metaplasia in the surrounding breast tissue are reported. The metaplastic epithelium deviated from the normal in its immunophenotype not expressing glandular cytokeratins (Cam 5.2) and estrogen receptors, being maspin-positive, and resembling morphologically different segments of dermal eccrine duct and acrosyringium. In addition, in one of the cases, basalioma-like intraductal cell proliferation was observed, also showing focal acrosyringeal differentiation. The invasive carcinomas, one of them representing "syringomatous squamous tumor of the breast" while the other diagnosed as high-grade metaplastic carcinoma, also showed focal eccrine and acrosyringeal differentiation and intensive diffuse maspin expression. These previously unrecognized metaplastic changes of the breast epithelium may represent precursor lesions of certain types of metaplastic breast carcinomas.