The increasing knowledge regarding breast cancer carcinogenesis has provided possible opportunities to prevent breast cancer. This paper reviews the issues related to breast cancer chemoprevention including the identification of high-risk groups, biomarkers and potential chemopreventive agents. Trials with tamoxifen have clearly shown that the risk of developing estrogen receptor (ER)-positive breast cancer can be reduced at the later stage of this malignancy. However, there was no beneficial effect on ER-negative cancers. The challenge is to find new agents, which achieve same or better efficacy but with fewer side effects. Raloxifene has similar efficacy to tamoxifen, but leads to more favorable histologic profiles of endometrial tumors and fewer gynecologic symptoms and thrombo-embolic events. Adjuvant trials for contralateral tumors suggest that aromatase inhibitors may be able to prevent up to 70-80% of ER-positive breast cancers. This is currently being investigated in two large prevention trials, the IBIS-II trial using anastrozole and the MAP.3 trial using exemestane. We therefore need to discover novel agents for ER-negative breast cancer.
Keywords: Breast cancer, chemoprevention, prevention trials, tamoxifen, aromatase inhibitors, SERMs
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