Mammary cancer antigen recognized by monoclonal antibody B72.3 in apocrine metaplasia of the human breast.

Monoclonal antibody B72.3 recognizing a pan-associated carcinoma antigen expressed also in metastatic human breast cancer cells has been tested using the avidin-biotin peroxidase method applied to paraffin-embedded sections in 50 samples of mammary tissue showing apocrine metaplasia and in 58 cases of other mild or severe focal epithelial proliferative changes of the breast, including mostly in situ lobular or ductal carcinomas collateral to clinical cancer removed after radical mastectomy. The antigen detected by this antibody was present in the apocrine cells of 48 cases (96%). In the majority of these cases the reactivity was localized on the luminal border of the apocrine cells and in the luminal secretion. But ten cases showed positive staining also in the cell cytoplasm either focal or diffuse. The normal structures and mild focal hyperplastic changes collateral to clinical cancer were, in the majority of the cases (43 of 55), negative, and, when positive, displayed positivity only at the luminal border. By contrast, the independent foci of in situ carcinoma (17 of 31 examined), the intraduct papillomas (seven cases of 14), and the intraductal component of breast carcinoma (seven cases of 17) were positive, displaying a cytoplasmic focal or diffuse staining. In conclusion, mammary apocrine metaplasia, a metaplastic change of the normal epithelium that has been associated with increased breast cancer risk, shares antigens in common with breast cancer cells and/or with cells showing severe atypia. The possible clinical significance of the site of antigenic expression (cytoplasm or luminal border) needs further investigation.