[Cancer of the breast, mechanism of action of anti-estrogens].

Estrone sulfate (E1-S) is quantitatively the main estrogen in human breast cancer tissue. This sulfate is converted with a great yield into estradiol (E2) in different hormone-dependent mammary cancer cell lines (MCF-7, R-27, T-47D). In opposition, there is small or no conversion in the hormone-independent cell lines (MDA-231 and MDA-436). The anti-estrogen tamoxifen blocks the conversion of E1-S to E2 in the MCF-7 and R-27 lines but not in the T-47D cell line. A new anti-estrogen: ICI 164,384 is also very active to block this conversion. In conclusion, the most probable way of action of the antiestrogen in through the competitive binding to the estrogen receptor; however recent date suggests other possible pathways.