Soy reduces the risk of postmenopausal breast cancer

In this study the urinary excretion of genistein was measured.

Urinary phytoestrogen excretion and postmenopausal breast cancer risk: the multiethnic cohort study

"Our results provide some support to the hypothesis that a diet rich in isoflavones from soy products reduces the risk of postmenopausal breast cancer, particularly in populations with comparatively high excretion of phytoestrogens."

Cancer Prev Res (Phila Pa). 2009 Oct;2(10):887-94. Epub 2009 Sep 29.