Tubular adenoma of the breast: an immunohistochemical study of ten cases.

Ten cases of so-called "tubular" adenoma and six cases of fibroadenoma of the breast have been investigated with an immunohistochemical technique with the aim of providing both more details on their immunophenotype and of ascertaining the possible relationships between tubular adenoma and fibroadenoma. Smooth Muscle Actin, Cytokeratin 14, GFAP, S-100 Protein and Vimentin immunoreactivity have clearly demonstrated that cells with myoepithelial immunophenotype are one of the major cell components in breast adenomas. Epithelial Membrane Antigen (EMA), Human Milk Fat Globule II (HMFG II), Estrogen and Progesterone receptors have been detected in adluminal epithelial cells exclusively. Furthermore, Smooth Muscle Actin and Vimentin highlighted an abundant myofibroblastic component, intermingled with tubular structures in both tumor types. A low percentage (10-22%) of adluminal cells and of myofibroblasts showed Ki-67 immunoreactivity in tubular adenomas and in fibroadenomas, whereas only rare myoepithelial cells demonstrated Ki-67 positivity in both tumor types. These data seem to indicate that several cell components of both epithelial and mesenchymal origin (epithelial cells, myoepithelial cells, myofibroblasts) are involved in the genesis of tubular adenomas. The morphological and immunohistochemical features of tubular adenomas closely resemble, in some areas of the tumors, those of fibroadenoma. Therefore, they may represent histogenetically related neoplasms with exuberant ductular component in tubular adenomas and predominant stromal component in fibroadenoma.