A new glycoprotein set, specifically associated with human breast carcinoma cells, has been identified, purified to homogeneity, and characterized. This glycoprotein set was first identified in the perchloric acid-soluble glycoprotein fraction of human ductal carcinoma of the breast after removal of known glycoproteins by affinity chromatography. Prototype antiserum to this glycoprotein, after absorption with normal tissues, reacted by gel diffusion with a single constituent of breast tumors but not with other benign or malignant tissues. This antiserum was used to isolate two types of soluble mammary tumor-associated glycoprotein (MTGP). Both types of MTGP appeared to have m.w. of about 19,500 and possess common antigenic determinants. In addition, a firmly integrated insoluble form of MTGP was identified. The soluble types of MTGP differed one from the other in respect to: a) isoelectric point, b) sedimentation velocity, c) carbohydrate composition, and d) buoyant density in cesium chloride. MTGP was found in all six metastatic breast tumors and was independent from plasma and tissue glycoproteins. Antisera to purified MTGP of Types I and II both gave reactions of identity one with the other and with both types of aqueous soluble MTGP. Each antiserum reacted only with extracts of breast tumors and not with any other tissue or type of tumor. MTGP was localized by immunohistochemical methods to both the surface and the cytoplasm of breast ductal carcinoma cells but not normal ductal cells. Positive reactions were also observed in immunologic assays with some spontaneous murine mammary carcinomas but not with the mouse mammary tumor virus. MTGP appears to provide a discrete and characterized new marker for breast carcinoma cells and thus a candidate tumor-specific antigen.

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