Selective estrogen receptor modulators are agents that bind to estrogen receptors but act either as agonists or antagonists in different tissues. For example, some selective estrogen receptor modulators act as agonists on the bone and uterus estrogen receptors, and antagonists on the breast estrogen receptors.
Growth of some forms of breast cancers is dependent on estrogen. Selective estrogen receptor modulators that act as antagonists on breast tissue are used in the treatment of breast cancer.
Estrogen is important in maintaining bone structure in women, so selective estrogen receptor modulators can also be useful in preventing post-menopausal osteoporosis.