Immunohistochemical profile and differential diagnosis of microglandular adenosis.

: Twelve examples of microglandular adenosis (MA) were evaluated immunohistochemically using a panel of antibodies directed against actin, S-100 protein, collagen type IV, the c-erb-B2 gene product, and the progesterone receptor, as well as antibodies BER-EP4 and B72.3. The results were compared with the reactions observed in 15 cases of tubular carcinoma and 11 examples of sclerosing adenosis. Three examples of secretory adenosis were also evaluated, but only for S-100 protein and actin. The results confirmed the absence of a myoepithelial cell layer and the presence of basal laminar investiture in MA. Tubular carcinoma lacked a myoepithelial cell layer and basal laminar investiture. Sclerosing adenosis, in contrast, had both a myoepithelial cell layer and displayed basement membrane around the tubules. Secretory adenosis also had a myoepithelial cell layer; the presence of basement membrane could be confirmed easily using periodic acid-Schiff reaction in the three cases of secretory adenosis. An interesting and unexpected finding was the presence of an intensely positive reaction in the epithelial lining cells of the tubules in microglandular adenosis for S-100 protein. A far less intense positivity for S-100 protein was observed sporadically in many normal myoepithelial and some epithelial cells in the adjacent breast lobules. The intensely positive reaction suggests that the proliferating cells in MA correspond to an S-100-positive epithelial cell type that is often present in a small number and in a sporadic manner in the normal breast. The epithelial cells in tubular carcinoma, sclerosing and secretory adenosis were negative for S-100 protein.(ABSTRACT TRUNCATED AT 250 WORDS)