Tamoxifen shows potential in preventing breast cancer
29 January 2003
Findings from a recently published review of trials of the drug tamoxifen in preventing breast cancer clearly show that tamoxifen can reduce the risk of oestrogen receptor-positive (ER-positive) breast cancer in women.
More than 10,000 women are affected by breast cancer in Australia each year and the majority of these women have ER-positive tumours, which means that the cancer is stimulated to grow in the presence of the female hormone oestrogen.
The review, published in The Lancet (2003; 361: 296-300), examined the results of 4 clinical trials lasting 5 or more years that compared a daily dose of tamoxifen with placebo (a dummy medication) in the prevention of breast cancer. The review also examined one clinical trial that compared raloxifene, a related drug, to placebo for breast cancer prevention.
These 5 trials were conducted between 1986 and 2001 and included more than 35,000 women.
(Both tamoxifen and raloxifene are drugs that have anti-oestrogen effects. Raloxifene is known as a selective oestrogen receptor modulator (SERM), as it blocks the effects of oestrogen in some tissues including breast cells, but in other tissues such as bone it has an oestrogen-like effect. Tamoxifen is primarily an anti-oestrogen, although it too has some oestrogen-like properties in some tissues. In Australia, tamoxifen can be used for the treatment of breast cancer, but not for its prevention; raloxifene can be used for the prevention and treatment of osteoporosis in women after the menopause.)
By combining the results of the 5 trials the reviewers were able to provide not only an overview of the effectiveness of tamoxifen and raloxifene in preventing breast cancer, but also a picture of their side effects.
Tamoxifen reduced the risk of developing ER-positive breast cancer by 38 per cent in women at high risk for developing this disease.
There was, however, no effect on reducing the rate of oestrogen receptor-negative breast cancer.
In terms of side effects, the review found an increased rate of cancer of the uterus in women taking tamoxifen, and an increased rate of blood clotting disorders in those taking either tamoxifen or raloxifene.
Therefore, before tamoxifen can be considered for prevention of ER-positive breast cancer, the reviewers urged further research to find ways to reduce its side effects, and to further investigate other drugs such as raloxifene and the aromatase inhibitors (for example, anastrazole), which show promise in preventing breast cancer, but with reduced side effects. Anastrazole is currently used in Australia to treat advanced breast cancer in women after the menopause.
Last Reviewed: 09 May 2003
