Dose also plays a critical role in the biological effects ofgenistein; although doses greater than 10 μM over an extended period of timeinhibit the growth of both ER+ and ER− breast cancer cells, low doses ofgenistein (<1 μM) appear to stimulate the growth of ER+ breast cancer cells [21, 22].Interestingly, CXCL12 has been shown to mediate the proliferativeeffects of estradiol in breast cancer cells [23]. This evidence concerns the gene ESR1 and breast cancer.