tamoxifen

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Tamoxifen is an oestrogen receptor antagonist which is used in the treatment of breast cancer

a partial oestrogen agonist (has antagonistic actions in breast cancers, but has agonist actions on endometrium, lipids, and bone)
as effective at 20 mg/day as at higher doses
effective in all age groups, and in premenopausal and postmenopausal women
beneficial effects greater when given for five years rather than two - however no evidence shows that tamoxifen is of additional benefit if taken for more than five years, and it may be detrimental
- tamoxifen taken for 5 years following surgical treatment is a standard part of the treatment regime for postmenopausal women with hormone-receptor-positive breast cancer. If used in this context then tamoxifen (4)
  - increases the proportion of women who survive for at least 10 years from about 50% to 60% among those with lymph-node involvement
  - increases the proportion of women who survive for at least 10 years without lymph-node involvement from about 73% to 79%
  - almost halves the risk of development of cancer in the contralateral breast
may less effective against human epidermal growth factor receptor 2 (HER2) positive tumours
more effective when given after chemotherapy (when this is also indicated) rather than concurrently

the International Breast Cancer Intervention Study (5), which investigated the use of tamoxifen in the unlicensed indication of breast cancer prevention, revealed that women treated with tamoxifen had an approximately 2.3x increased risk of venous thromboembolism (VTE) than those treated with placebo. Approximately 40% of the VTE cases occurred within 3 months of surgery or following immobility. This led to the Chairman of the study, in March 2002, recommending that women should no longer be treated with tamoxifen for the PREVENTION of breast cancer (i.e. prevention of occurrence rather than management of diagnosed disease)

Tamoxifen is also used in the treatment of anovulatory infertility.

The summary of product characteristics should be consulted before prescribing this drug.

Reference:

BMJ. 2006 Jan 28;332(7535):223-4.
BMJ 2006;332:34-37
BMJ 2006;332:101-103
Drug and Therapeutics Bulletin (2003), 41 (8), 57-59.
Current Problems in Pharmacovigilance (2002), 28, 10.
BMJ editorial. BMJ 1996; 312: 389-90.

Last reviewed 03/2021

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