Breast Cancer Prevention by Antiestrogens

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Abstract
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 ∼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.