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

Tamoxifen, a non-steroidal antioestrogen, is currently used to treat post-menopausal breast cancer. In oestrogen-sensitive breast cancer cell lines, tamoxifen and some of its metabolites display, for the induction of oestrogen-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 antioestrogens are mediated by the oestrogen receptor. These antioestrogens interact with the oestrogen receptor but they appear to induce only a partial or altered activation of the receptor. This partial or altered activation and the competition with oestrogens for binding to the oestrogen receptor could explain the oestrogen agonist/antagonist properties of antioestrogens.