Tamoxifen is an orally active
selective estrogen receptor modulator (SERM) which is used in the treatment of
breast cancer and is currently the world's largest selling drug for that purpose. Tamoxifen was discovered by
ICI Pharmaceuticals (now
AstraZeneca) and is sold under the trade names Nolvadex,® Istubal,® and Valodex.® However, the drug, even before its patent expiration, was and still is widely referred to by its generic name "tamoxifen."
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A form of the drug tamoxifen that is made by the body after taking tamoxifen. It can also be made in the laboratory, and may help decrease breast density. A topical form of 4-hydroxytamoxifen is being studied in breast cancer screening.