Trial Information

Effects of Soy Isoflavones on the Prostate, Breast and Bone

In the United States, consumption of soy products has dramatically increased in the past
several years. Foods made from soy are high in isoflavones and evidence suggests that these
isoflavones, genistein in particular, have many beneficial properties such as alleviating
menopausal side effects and reducing the risk of osteoporosis, breast cancer, and prostate
cancer. However, this data has been derived largely from studies with animal or cell models;
human trials are limited. This study will determine the effects of soy isoflavones on
quality of life and cancer and bone density markers.

While isoflavones have been purported to inhibit the proliferation of cancer cells, the
concentrations required for this anti-cancer effect were determined to be much higher than
the concentrations that can be achieved in plasma after intake of isoflavones. Recent animal
studies have suggested that isoflavones may be concentrated 10-fold in tissue compared to
blood concentrations. If this is true, then the higher concentration would be in the range
found in the cancer cell line research to be protective of cancer. This study will
determine whether tissue concentrations are similar to, higher than, or different than blood
concentrations.

This study will last 5 years and will comprise three populations: men with prostate cancer
on androgen ablation therapy, postmenopausal women on hormone replacement therapy (HRT), and
postmenopausal women not on HRT. Participants will be randomly assigned to receive either
isoflavone or placebo for two to four weeks. Participants' serum and serum extracts will be
incubated with cultured human cell lines (prostate cancer, breast cancer and osteoblasts)
and estrogenic and non-estrogenic mechanisms of action investigated. The human sera data
will be complemented by parallel studies of direct addition of crystalline isoflavones
(genistein, daidzein and equol) to the same cultured human cell lines. Participant's serum
and urine also will be tested for markers of bone resorption and formation. Quality of life
issues will be assessed with questionnaires.