Tamoxifen

The growth of some breast tumor cells is activated by estrogen. The drug, tamoxifen binds to estrogen receptors without activating estrogen-responsive genes. Tamoxifen treatment of patients with such tumors after surgery or chemotherapy often antagonizes estrogen binding in residual tumor cells and retards their growth.

See also: Estrogens, Hormone Receptors, Steroid Hormones, Steroid and Thyroid Hormones - Intracellular Receptors