By digesting plasminogen, PSA releases antiangiogenic fragments (similar to angiostatin) and promotes the conversion of the more potent estradiol to the less potent estrone, thus mitigating the procarcinogenic effects of estrogen [28].Using an ultrasensitive time-resolved immunofluorometric assay for PSA, we found that 30% of female breast tumor cytosols from a cohort of more than 1,200 breast cancer patients contained PSA immunoreactivity higher than 0.03 ng/mg of total protein [6, 16]. Here, KLK3 is linked to breast cancer.