[Effects and mechanism of action of antiestrogens in breast cancer].

Tamoxifen, a non-steroidal antiestrogen, is currently used to treat post-menopausal breast cancer. In estrogen-sensitive breast cancer cell lines, tamoxifen and some of its metabolites display, for the induction of estrogen-regulated proteins, a partial agonist/antagonist activity. They also inhibit totally the proliferation of these cells. Evidence is given, which suggests that the pharmacological properties of these antiestrogens are mediated by the estrogen receptor. These antiestrogens interact with the estrogen receptor but they appear to induce only a partial or altered activation of the receptor. This partial or altered activation and the competition with estrogens for binding to the estrogen receptor could explain the estrogen agonist/antagonist properties of antiestrogens.