Genistein is one of several known isoflavones. Isoflavones, such as genistein and daidzein, are found in a number of plants, with soybeans and soy products like tofu and textured vegetable protein being the primary food source. Soy isoflavones are a group of compounds found in and isolated from the soybean. Besides functioning as antioxidants, many isoflavones have been shown to interact with animal and human estrogen receptors, causing effects in the body similar to those caused by the hormone estrogen. Soy isoflavones also produce non-hormonal effects.
Studies show that gastrointestinal cancer occurs less frequently among North Americans who do not learn to eat meat. North Americans who go to other continents without learning to eat vegetables show more digestive tract cancer than neighbours.
Timing of phytoestrogen use is important.
Genistein makes some cells more sensitive to radio-therapy.
Though research is still ongoing, some recent studies have indicated that soy's phytoestrogens could be contributive factors in some forms of breast cancer, penile birth defects, and infantile leukemia.
Some studies have raised the concern that genistein might increase the risk of leukemia, because it inhibits the enzyme topoisomerase which results in double strand DNA breaks, which are, in turn, mutagenic. Some cancer patients whose chemotherapy drugs inhibited topoisomerase later developed leukemia.
NCI researchers have completed animal studies on genistein with no adverse effects being seen. [see discussion page]
Regardless, soy's phytoestrogens, or isoflavones, have been definitely shown to depress thyroid function and to cause infertility in every animal species studied so far.
Genistein's chief method of activity is as a tyrosine kinase inhibitor. Tyrosine kinases are less widespread than their ser/thr counterparts but implicated in almost all cell growth and proliferation signal cascades. Genistein has been used to selectively target pre B-cells via conjugation with an antibody. This highly successful study in mice has promising benefits for future chemotherapy