We have previously shown that treatment of T-47D breast cancer cells with 17β-Estradiol (E2) causes cell proliferation, upregulates tumor suppressor protein p53, and induces hyperphosphorylation of pRb.6,7 The focus of the present study was to investigate the estrogen-like effects of BPA on T-47D and MCF-7 breast cancer cells and determine if these ER-mediated effects of BPA are inhibited in the presence of antiestrogens, such as ICI 164,384, Raloxifene (RAL), and TAM. This evidence concerns the gene ESR1 and breast cancer.