Secretory carcinoma of the breast: light microscopical, immunohistochemical and flow cytometric study.

We studied five cases of secretory carcinoma of the breast (SC) by light microscopy, by immunohistochemistry, and by flow cytometry. Four cases were retrieved from the series of 7038 cases of breast carcinoma seen in our department during the 20-yr period of 1973 to 1992; one case was seen recently. Histologically, different growth patterns in SC were observed; the most characteristic feature was prominent intra- and extracellular secretion. Immunohistochemically, all tumors showed strong positive reaction for alpha-lactalbumin and S-100 protein, whereas the reactions to carcinoembryonic antigen and gross cystic disease fluid protein were variable. By flow cytometry, four tumors were examined (three of them were diploid and one near diploid), and they all showed low S-phase fraction. Immunohistochemical findings in SC were compared to a group of 13 cases of nonsecretory carcinoma that all showed an appreciable degree of secretion or morphological similarities to SC. In a single case of cystic hypersecretory carcinoma an unequivocal positive reaction for alpha-lactalbumin was demonstrated; S-100 positive reaction was seen in two cases. It was concluded that in an appropriate morphological setting, positive reaction for alpha-lactalbumin is an essential feature in diagnosing SC. S-100 protein positivity and diploid flow cytometric pattern are also characteristics of SC.