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 Collections under
which this article appears: Cancer:
breast |
Debashis Singh London
Prophylactic use of tamoxifen over five years reduces the incidence of breast cancer by 38% in healthy women with a high risk of developing the disease, a study published in the Lancet says (2003;361:296-300).
The authors, from Cancer Research UK, conducted an extensive review of 14 trials involving over 40 000 women. Four of the trials tested the role of tamoxifen as a preventive treatment in 28 000 women, and another trial, involving 7700 women, tested the role of raloxifene instead. Both drugs were compared with a placebo. In nine trials 15 000 women who had had a tumour removed from one breast were treated with tamoxifen to prevent the cancer returning.
The study found that in healthy women with a high chance of developing the disease tamoxifen reduced the incidence of oestrogen positive breast cancer by 38% (95% confidence interval 28% to 46%; P<0.0001). In women with tumours negative for oestrogen receptor the incidence was not reduced (hazard ratio 1.22 (0.89 to 1.67)).
Women who had had a tumour removed from one breast were shown to have an even greater reduction in incidence, and were 46% (31% to 57%) less likely to develop cancer in the opposite breast if they took tamoxifen. Use of raloxifene showed a 64% (44% to 78%) reduction of the incidence of breast cancer.
The main side effects of tamoxifen, namely increased risk of a venous thromboembolic event or developing the rarer endometrial cancer were also explored. Women in all the trials had an increased risk of developing a clotting disorder, with more than a twofold increased risk for both drugs (relative risk 1.9 (1.4 to 2.6) in the prevention trials; P<0.0001).
The study also found that, although women taking tamoxifen had a twofold increased risk of developing endometrial cancer (consensus relative risk 2.4 (1.5 to 4.0), P=0.0005), women taking raloxifene showed no increased risk of the disease.
Summarising the effect on breast cancer mortality, the study says that for 1000 high risk women, "deaths from breast cancer within 10 years of diagnosis would be reduced by 18% from 17.25 to 14.10." Over this time, there would be less than one death from thromboembolic events and endometrial cancer, the authors told the BMJ.
The lead author, Professor Jack Cuzick, of the Wolfson Institute of Preventive Medicine, London, said: "It is crucial that we follow all the trials to their conclusions and find ways to reduce the side effects of tamoxifen before we can recommend that high risk women take the drug to prevent breast cancer." He suggests either giving a lower dose of tamoxifen or adding low dose aspirin could be possible solutions as well as considering newer agents.
He added: "The early data on raloxifene looks very promising. The trial shows that the drug can reduce the risk of breast cancer by 64% and cause fewer side effects than tamoxifen. We will be awaiting the results of its direct comparison with tamoxifen in the American STAR [study of tamoxifen and raloxifene] trial with great interest."
To clarify the findings, Professor Cuzick gave the BMJ estimates of how many high risk women would develop breast cancer, venous thromboembolic events, and endometrial cancer if they took tamoxifen for five years. He provided comparative figures for a group of 1000 high risk women not taking the drug.
In a group of 1000 high risk women taking tamoxifen for five years, 19 would develop breast cancer, 12 would have a venous thromboembolic event, and six would get endometrial cancer.
In a similar group of women not taking the drug, 30 would develop breast cancer, six would have a venous thromboembolic event, and three would get endometrial cancer.
Over a 10 year period, there would be three fewer breast cancer deaths among
1000 high risk women taking tamoxifen, and there would be less than one death
from thromboembolic events and endometrial cancer in this group, compared with a
similar group not taking the drug.
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