It was another ten years before tamoxifen was approved in December 1977, not as a contraceptive but as a hormonal treatment to treat and prevent breast cancer. The discovery in 1987 that the SERMs tamoxifen and raloxifene, then thought to be antiestrogens because of antagonist effects in breast tissue, showed estrogenic effects in preventing bone loss in ovariectomized rats had a great effect on our understanding of the function of estrogen receptors and nuclear receptors in general. The term SERM was introduced to describe these compounds that have a combination of estrogen agonist, partial agonist, or antagonist activities depending on the tissue. Toremifene has been shown to be compatible with tamoxifen, and in 1996 it was approved for use in the treatment of breast cancer in postmenopausal women.