"Genistein is an antioxidant that may inhibit the formation of new blood vessel, thereby inhibiting tumor growth (1)."
It is an isoflavone.
"Genistein is one of several known isoflavones. Isoflavones, such as genistein and daidzein, are found in a number of plants includinglupin, fava beans, soybeans, kudzu, and psoralea being the primary food source, also in the medicinal plant, Flemingia vestitaand coffee. Besides functioning as antioxidant and anthelmintic, many isoflavones have been shown to interact with animal andhuman estrogen receptors, causing effects in the body similar to those caused by the hormone estrogen. Isoflavones also produce non-hormonal effects (4)."