Regulation of breast tumor growth by high dose estrogen is independent of the presence of estrogen receptors.

17 beta-estradiol stimulated the clonogenic growth of four established human breast tumor cell lines independent of the estrogen receptor status of the cells. Likewise, tamoxifen citrate, a nonsteroidal antiestrogen, inhibited the in vitro growth of both estrogen receptor-negative and estrogen receptor-positive cell lines to a similar degree. These findings indicate that, at pharmacologic doses, the growth stimulatory and inhibitory effects of estrogen and antiestrogens are not necessarily mediated by hormone-specific receptors.