Estrogen regulation of H59 antigen in vivo and in vitro.

H59 antibody, a murine monoclonal antibody, recognizes a cell surface peptide of approximately 30,000 MW which is estrogen regulated. The data supporting this conclusion have been generated from in vitro systems and indirectly from human tissue specimens. The antigen is detected only in estrogen regulated breast cancer cells in culture and is not detected in two estrogen independent cell lines, R3 and R27, which were derived from estrogen sensitive MCF-7 that contain the antigen. The antigen is increased in estrogen stimulated cells and decreased in tamoxifen inhibited cells. H59 antigen appears estrogen regulated in human breast colostrum and milk and in endometrium. The antigen is found in 40% of breast cancer and most, if not all, normal breast tissue. In the more than 300 breast cancer specimens studied, H59 antigen was detected in predominately estrogen and/or progesterone receptor containing tumors. This antigen was found only in about 50% of ER positive tumors. When the presence of H59 was compared to other prognostic factors in breast cancer, it appeared to be an independent variable and correlated only with the presence of estrogen and progesterone receptor. The antigen can be detected in normal serum, and studies are underway to determine if it will serve as a circulating marker protein in hormone dependent breast cancer.