Monoclonal antibody 7B10, raised against the human
breast cancer cell line T47D, identifies an
antigen found in human
breast carcinomas and in normal breast. Western blot and immunoprecipitation studies detected a Mr 76,000
antigen in cytosol, cell membrane, and cell culture supernatants of T47D cells. 7B10 binding to T47D
cell extracts was affected by proteolytic digestion with
protease type VI,
trypsin, and
subtilisin while it was not altered by
neuraminidase digestion. Adsorption of
breast cancer cell line extracts with
concanavalin A reduced 7B10 immunoreactivity more than 70%. These results suggest that the
antigen is a
glycoprotein and that the
epitope does not contain
sialic acid. 7B10 was reactive with neither human milk fat globule membrane, nor skimmed milk, nor the milk-derived HBL 100 cell line. Conversely binding was detected in more than 50% of normal breast epithelial cells in culture. 7B10 immunostaining was positive on frozen sections of normal breast and nonmalignant mastopathies in 30 to 90% cells. In frozen sections of other normal tissues, 7B10 immunoreactivity was detected only in colon, apocrine glands of skin, parotid ducts, and luteal phase endometrium, confirming previous data on
paraffin sections. Strong, homogeneous immunostaining was observed on frozen sections of intraductal and invasive lobular
breast carcinomas (100% of cases), while more heterogeneous staining was found on invasive
ductal carcinomas. Colon and rectal
carcinomas, one
carcinoma of the esophagus, and some cells in serous ovarian
carcinomas also showed 7B10 reactivity. Immunoblotting of the 7B10-immunoreactive fraction isolated by
Sepharose CL-6B chromatography of a
breast carcinoma tissue sample extract identified the Mr 76,000
antigen, which was also detected in several
breast cancer specimens, in
colon adenocarcinomas, and in serous ovarian
carcinoma fresh
tumor extracts. The Mr 76,000
glycoprotein described here represents a
breast cancer-associated
antigen previously undescribed, mainly expressed in normal breast and
breast tumors.