Data regarding the role of phytoestrogens in breast cancer prevention is conflicting, but suggest
early exposure in childhood or early adolescence may be protective. In several placebo-controlled
randomized trials among breast cancer survivors, soy has not been found to decrease
menopausal symptoms. There is very little human data on the role of phytoestrogens in preventing
breast cancer recurrence, but the few studies conducted do not support a protective role. There is in vivo animal data suggesting
the phytoestrogen genistein may interfere with the inhibitive effects of tamoxifen on breast cancer cell growth.