[Estrogen dependent plasminogen activator in breast cancer cells; experimental and clinical studies]

Hormonal regulation of plasminogen activator (PA) in rat mammary tumor induced by 7,12-dimethylbenz (a) anthracene (DMBA) was studied both in vivo and in vitro. PA activity in DMBA-tumor was markedly decreased by ovariectomy, and recovered in a dose-dependent fashion upon estradiol administration. This estrogen-stimulated production of the enzyme was prevented by actinomycin D, cycloheximide and tamoxifen. Furthermore DMBA-tumor cells in primary culture displayed similar estrogen-dependency toward the production of the enzyme without any cell proliferation. This indicates that estrogen might regulate de novo synthesis of PA at a transcriptional level via an estrogen receptor system, and that this hormone might support the growth of DMBA-tumor into adjacent tissues by inducing PA in a direct manner via a route distinct from a prolactin pathway. To examine whether PA reflects the functional state of estrogen receptors in human breast cancer, the enzyme activities were determined in extracts prepared from 160 breast cancer specimens and compared on qualitative and quantitative bases with the levels of steroid receptors. The results strongly suggest that PA can be used as an effective functional marker for hormone dependence in human breast cancer.