Caution with Tamoxifen as a Preventive Measure
Questions about side effects from the use of the drug tamoxifen to prevent breast cancer have been raised by a new study published in the British Journal of Cancer.
Researchers from Ontario in Canada used the results from a major clinical trial of the drug-the Breast Cancer Prevention Trial (P-1) involving 13,000 women-to simulate with a computer model the overall impact of giving tamoxifen to women at high risk of breast cancer.
Their results highlight some of the potentially serious side effects from giving the drug to healthy women over the age of 50, including a possible four-fold greater risk of endometrial cancer (cancer of the womb lining) and twice the risk of deep vein thrombosis.
Researchers in the U.S. had earlier taken the unusual step of stopping a clinical trial on tamoxifen because the preliminary indications of its preventive benefits were surprisingly strong. Their results indicated that the drug could reduce the risk of developing breast cancer in high-risk women by nearly 50 percent.
This new study, however, suggests that their action may have been premature, at least in terms of quantifying tamoxifen's potential side effects. In the U.K., The Cancer Research Campaign and Imperial Cancer Research Fund are funding another trial, called IBIS, which is also evaluating the use of tamoxifen as a preventive measure. This trial is due to finish in 2002 and researchers hope that it will provide a definitive answer on how the drug should be used.
Tamoxifen has been one of the greatest advances in the treatment of breast cancer and is currently given to 70 per cent of all women already diagnosed with the disease. There is no doubt that it is invaluable in the treatment of breast cancer, but the Canadian researchers caution that the jury is still out on whether the drug should be used as a way of preventing the disease in otherwise healthy women.
The Canadian researchers developed a sophisticated computer model that allowed them to project what would happen to women if those considered to be at higher risk of breast cancer were given tamoxifen.
The model worked through a range of scenarios to explore how high a woman's estimated risk of breast cancer had to be before it was worth her while to take tamoxifen as a preventive measure.
The researchers estimated that, given the drug's side effects, it may only be beneficial for women whose predicted risk is 3 times greater than average. They believe that for women whose risk is lower than this, the potential risks of taking tamoxifen could outweigh its benefits.
The researchers concede that their results are based on a simulation model and a range of assumptions and warn that additional prevention trials and longer follow-up are still needed. They say that such studies will determine which women, if any, should be offered preventive tamoxifen to reduce their risk of breast cancer, taking into account its potentially serious side effects.
SOURCES:
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British Journal of Cancer, November 4, 2001
The British Cancer Research Campaign (www.crc.org.uk)