ESR1 and breast cancer: T-47D breast cancer cells express the tumor suppressor protein p53 constitutively.5,23 We have previously shown that E2 treatment in medium containing charcoal-treated serum causes an increase in p53.23 The purpose of this experiment was to study the effects of BPA on the T-47D and MCF-7 breast cancer cell lines and compare the actions of BPA to those of estrogen and other well-known compounds that interact with the ER.