Breast cancer prevention by antiestrogens

A new era has been entered with the first demonstration that an antiestrogen can prevent breast cancer, In a landmark study tamoxifen was shown to reduce the incidence of breast cancer by similar to 50%, The reduction was observed in pre- and postmenopausal women at increased risk of breast cancer, Invasive cancers were reduced, the reduction being in the estrogen receptor-positive cancers. No preventive effect was observed for estrogen receptor-negative tumors, In situ cancers were also significantly reduced. A collateral benefit was a significant reduction in fractures due to osteoporosis. Adverse effects included a very small increase in the incidence of endometrial cancer, cataracts, and stroke. The benefits appear to outweigh the risks for those at high risk. Preliminary studies of a new selective estrogen receptor modulator (SERM 2), raloxifene, developed for the prevention of osteoporosis, have shown that the breast cancer rate was reduced by more than 50% without any concomitant increase in endometrial cancer. The search for a SERM 3, and beyond, may lead to the development of drugs that have the beneficial effects of estrogen while preventing breast cancer and osteoporosis.