Expressions of the carcinoembryonic Tn antigen studied with VVA-B4 and GSI-A4 lectins with the monoclonal antibody 83D4 and of N-acetyllactosamine residues with ECA and LSL lectins, were examined in 54 malignant or benign human breast tumors. Positive membrane labelling with lectins and 83D4 MAb occured in benign cases indicating that modification of glycoconjugates may precede the cytologic anomalies. In fibroadenoma, fibrocystic dystrophy, ductal hyperplasia and grade I invasive ductal carcinomas, the binding sites for all lectins and 83D4 MAb were essentially on the cell membrane with labelling of both apical and basolateral compartments. In grade II and III, the labelling involved the cytoplasm, and cell heterogeneity appeared. The disappearance of reactivity observed for a large proportion of cells at grade III may be due either to the loss of glycosyl-transferase, or to the lack of synthesis of the protein back-bone. Invasive lobular carcinomas showed labelling both on apical membrane and the outermost part of the cytoplasm with a distinct cell polarity. Lectin receptors are present at the surface of metastatic cells, possibly related to their involvement in adhesion.

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