Expression of breast epithelial differentiation antigens in human primary breast cancer.

Monoclonal antibody LICR-LON-M18 is a marker of normal human breast epithelial cell differentiation. The epitope recognized by LICR-LON-M18 is a prominent component of luminal plasma membranes of nonneoplastic resting and lactating human breast epithelial cells but is rarely expressed by human breast carcinomas. With the use of competitive binding-inhibition studies, the immunodominant portion of the LICR-LON-M18 epitope was shown to be the following oligosaccharide sequence [with galactose (Gal) and N-acetylglucosamine (GlcNAc)]: Gal beta 1----4GlcNAc beta 1----. This structure was distinct from Gal beta 1----3GalNac, which was bound by peanut agglutinin (PNA) and was not recognized by LICR-LON-M18 [corrected]. With the use of biochemical techniques, the present data not only confirmed sialylation and consequent "masking" of the LICR-LON-M18 epitope and PNA determinants in human breast carcinomas but also identified the particular groups of glycoproteins involved in this process. These studies provided additional support for the thesis that sialylation of human breast carcinoma glycoproteins represented an enhancement of specific differentiation events normally regulated in the morphogenesis of nonneoplastic human breast epithelium and that specific glycoproteins became masked during the genesis of primary human breast cancer.