ESR2 and breast cancer: In vitro studies suggest that they also have the promise as anti-tumor agents [3]-a number of flavonoids can induce apoptosis in cancer (including breast cancer) cell lines, arreste proliferation at the G2/M cell cycle checkpoint [36,37], and bound strongly with Estrogen Receptor β, (ER-β), which opposes the proliferative effects of ERα activation [38].