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There are two homologous nuclear receptors for the hormone 17β-estradiol (estrogen), commonly called ERα and ERβ. Receptor activation leads to the formation of homo- and hetero-dimers, which in turn interact with accessory proteins to regulate gene transcription.
Tamoxifen is a selective estrogen receptor modulator, evoking tissue-dependent effects. It is an antagonist of ER action in breast tissue and breast cancer cells and is reported to be effective in the treatment of early breast cancer to prevent tumor growth.1,2 Importantly, tamoxifen has been reported to act as an ER agonist in bone and blood vessels, helping to minimize osteoporosis and reduce the risk of cardiovascular disease in post-menopausal women.3 Also, tamoxifen is a partial ER agonist in uterine tissues and is reported to increase the risk of endometrial carcinoma.4
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1
Horwitz, K.B., McGuire, W.L. Nuclear mechanisms of estrogen action. Effects of estradiol and anti-estrogens on estrogen receptors and nuclear receptor processing. The Journal of Biological Chemistry 253(22) 8185-8191 (1978).
2
Clarke, M., Collins, R., Davies, C., et al. Tamoxifen for early breast cancer: An overview of the randomised trials. Lancet 351 1451-1467 (1998).
3
Tonetti, D.A., Jordan, V.C. Targeted anti-estrogens to treat and prevent diseases in women. Molecular Medicine Today (1996).
4
Jordan, V.C., Assikis, V.J. Endometrial carcinoma and tamoxifen: Clearing up a controversy. Clinical Cancer Research 1 467-472 (1995).
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