tamoxifen - Side effects, 4-hydroxytamoxifen, Pharmacogenetics

A drug used in the treatment of breast cancer, first developed by the British pharmaceutical company ICI. In the 1980s it was shown to be helpful in the treatment of about half of all breast cancer cases. It works by blocking the action of the female sex hormone oestrogen on cancers whose growth is linked to oestrogen levels. Some new studies have shown that tamoxifen given prophylactically may also prevent, or at least delay, the development of breast cancer in some women.

Tamoxifen is an oral selective estrogen receptor modulator which is used in breast cancer treatment, and is currently the world's largest selling breast cancer treatment.

Tamoxifen competes with oestrogen in the body for oestrogen receptors in breast tissue so that transcription of oestrogen-responsive genes is inhibited.

Tamoxifen was invented by ICI Pharmaceuticals (now AstraZeneca) and is sold under the brand names Nolvadex, Istubal, and Valodex.

A rare condition occasionally treated with tamoxifen is retroperitoneal fibrosis.

Tamoxifen is sometimes used to treat gynecomastia in men. Tamoxifen is also used by bodybuilders in a steroid cycle to try and prevent or reduce drug-induced gynecomastia caused by steroids that are used in the same cycle.

Tamoxifen is also used to treat infertility in women with anovulatory disorders.

On April 17, 2006, it was announced that raloxifene is equally effective in reducing the incidence of breast cancer, but caused fewer side effects.

Side effects

Tamoxifen is a selective estrogen receptor modulator. Therefore endometrial changes, including cancer, are among tamoxifen's side effects.

4-hydroxytamoxifen

4-hydroxytamoxifen is a form of the drug tamoxifen that is made by the body after taking tamoxifen.

Pharmacogenetics

Patients with variant forms of the gene CYP2D6 (also called simply 2D6) may not receive full benefit from tamoxifen. On Oct 18, 2006 the Subcommittee for Clinical Pharmacology recommended relabeling tamoxifen to include information about this gene in the package insert.