For example, soybean plants produce glyceollinI, II, and IIIphytoalexins derived from daidzeininresponse to fungal stress. We previouslyexamined the antiestrogenic activity of soy glyceollin in vitro and in vivo, demonstratingthese compounds, unlike constitutive soy isoflavones such as daidzeinand genistein, exert significant antiestrogenic effects on ER signaling.This was further correlated to reduced estrogen-induced proliferationin breast cancer cells. This evidence concerns the gene ESR1 and breast cancer.