The immunohistochemical reactivity of a new anti-epithelial monoclonal antibody (MAb b-12) against breast carcinoma and other normal and neoplastic human tissues.

A mouse monoclonal antibody, MAb b-12, has been described previously (Stähli et al. 1985) which reacts with a Mr 350 kD glycoprotein with mucin-like characteristics (Stähli et al. 1987) expressed in cytoplasm and on the surface of human breast carcinoma cell lines (MCF-7 and ZR-75-1). In the present report the immunohistochemical reactivity of this MAb with normal and malignant human tissues is analyzed. Pre-experiments showed that the epitope b-12 is resistant to formalin treatment allowing the use of tissue processed by standard paraffin embedding methods. 167 normal and 408 neoplastic tissues were tested by indirect immunofluorescence or the avidin-biotin complex method. MAb b-12 stained the apical cytoplasm of secretory epithelia and their secretions including the acinar and ductular epithelia of the breast. It reacted with all breast carcinomas independent of their histological type or stage, frequently with all but in some cases with a fraction of the tumour cells. Some other carcinomas, primarily those of adenomatous differentiation, were also reactive. In these, however, the fraction of positive tumour cells was usually lower. The b-12 epitope is thus a marker for normal and neoplastic epithelia with secretory functions, particularly for breast carcinomas of all histological types and stages, and perhaps a differentiation marker for abortive adenomatous differentiation in solid carcinomas of the gastro-intestinal, uro-genital or respiratory tract.