Dietary genistein, which produced circulating concentrations consistent with human exposures, did not act as an aromatase inhibitor; rather, dietary intake of genistein negated the inhibitory effect of an aromatase inhibitor letrozole (a 3rd generation aromatase inhibitor), by stimulating the growth of aromatase-expressing estrogen-dependent breast tumors [106]. The gene discussed is CYP19A1; the disease is breast neoplasm.