Benign and malignant breast diseases were histochemically investigated with regard to their secretory function. Thereby, the labelled lectin from peanut (peanut agglutinin = PNA) which possesses a high affinity for d-galactosyl-(l-3)-N-acetyl-d-galactosamine, showed a binding pattern partly indicating disturbed secretory cell mechanisms. Further studies with a labelled antibody directed against a milk fat globule membrane glycoprotein, which was isolated by PNA affinity chromatography from human milk, confirmed the PNA receptor as a marker of a milk protein in breast carcinomas. Additionally, two other monoclonal antibodies which were raised against other components of the milk fat globule membrane were used for a more detailed characterization of the functional situation of mammary carcinomas. These immuno- and lectin-histochemical investigations revealed that tumors with a high secretory activity responded in about 80% to endocrine treatment, whereas breast carcinomas that exhibited no secretory function failed to respond to endocrine therapy. Thereby, the hormone dependence of tumor tissue showed an inverse correlation with the proliferative activity, as determined by the mitosis index.
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