Proponents of a chemopreventive approach to breast cancer strive to develop and distribute a safe drug that will prevent breast cancer. It is widely presumed that preventing breast cancer will prevent death from breast cancer and the benefit of chemoprevention could be measured in terms of lives saved. The rationale for using antiestrogen agents as primary prevention is based on several observations that when tamoxifen was used to treat breast cancer, a reduction in the risk of contralateral breast cancer was seen. Protection against first primary and contralateral breast cancers has also been noted for raloxifene and for the aromatase inhibitors exemestane and anastrozole. Randomized clinical trials of these drugs were conducted1-6 (Table), based on the premise that by blocking estrogen signaling (through receptor blockade or inhibition of aromatase) cancers that are dependent on estrogen might be prevented in the first place, or that small latent cancers could be stopped in their tracks. The trials consistently show that up to one-half of estrogen receptor (ER)-positive first primary breast cancers can be prevented. The authors were optimistic that if a drug could be shown to prevent breast cancer and had acceptable adverse effects, women would be enthusiastic about taking it for 5 years.
Narod SA. Tamoxifen Chemoprevention—End of the Road? JAMA Oncol. 2015;1(8):1033–1034. doi:10.1001/jamaoncol.2015.2247
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