VVA-B4 lectin was used to investigate the differences in Tn antigen expression in tissues of different types of human breast cancer (benign lesions, carcinoma in situ, invasive carcinoma) and in normal tissues neighboring lobular carcinoma. Locations in which Tn antigen was expressed were identified using the avidin-biotin-peroxidase labeling system. Tissues collected during cosmetic procedures and classified as normal were completely negative, except for one case. Benign proliferative changes including fibroadenoma, apocrine and cylindrical metaplasia showed a very weak positive reaction, although strongly positive cells were also observed. The reaction in non-invasive cases of atypical hyperplasia was diversified depending on site. Intralobular hyperplasia was characterized by a particularly high percentage of labeled cells. A majority (up to 80%) of ductal and lobular carcinoma in situ showed very strong or moderate staining. In invasive cancers, there were conspicuous differences between stage of cancer development and tendency towards a decrease in intensely labeled cell count in the most advanced stages. In normal tissues in the direct neighborhood of carcinoma in situ, the cytoplasm of 40% of cells was strongly labeled. However, the findings for normal tissues in the close vicinity of invasive cancer were the most surprising, since there was either no or only very weak positive reaction. It can be concluded that glycosylation modifications during carcinogenesis, as demonstrated by the presence of Tn epitope, develop very early, before any destructive changes in proliferation/apoptosis or cell differentiation become discernible.

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