Nikolaos G. Kostomitsopoulos

Τhe oestrogen receptor is a ligand-activated transcription factor that modulates specific gene expression by binding to short DΝΑ sequences. Τhe study of the role of oestrogen receptor on the expression of the mitogenic action of oestrogens and oncogenesis lead biomedical research in new approaches of the treatment of oestrogen-dependent tumors by using antioestrogens. Μain mechanism of action of antioestrogens is the prevention of oestrogen action by blocking the binding of oestradiol to the oestrogen receptor. Τamoxifen, the most wellknown antioestrogen, is widely used as adjuvant therapy in all stages of human breast cancer. Recently interest is focused on the potential use of pure antioestrogens. Τhe use of antioestrogens in veterinary oncology is also under discussion.