Tamoxifen curbs breast cancer risk, study confirms
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Data from additional years of follow-up of a large study of tamoxifen for the prevention of breast cancer confirm that the drug reduces the risk of the disease in high-risk women.
Tamoxifen “remains the only proven chemopreventive treatment for breast cancer risk reduction,” Dr. Bernard Fisher, from the University of Pittsburgh, and colleagues note in their report in the Journal of the National Cancer Institute this week.
In the study, which began in 1992, a total of 13,388 women aged 35 years or older who were at high risk for breast cancer due to family history and other factors were randomly assigned in a blinded fashion to receive either a placebo or tamoxifen for 5 years.
In 1998, when the study was “unblinded,” researchers observed that women taking tamoxifen had a 49 percent lower risk of developing breast cancer.
Tamoxifen was also found to reduce the risk of osteoporotic fractures but to increase the risks of endometrial cancer and thromboembolism (blood clots).
At the time the study was unblinded, the women who were taking placebo were given the option of starting tamoxifen.
The latest data from the trial reported this week shows that the benefits and most undesirable effects of tamoxifen remain. That is, after 7 years of follow-up, using tamoxifen rather than placebo reduced the cumulative rate of invasive cancer by 43 percent, from 42.5 cases per 1,000 women in the placebo group to 24.8 cases per 1,000 women in the tamoxifen group.
The rate of noninvasive breast cancer was reduced by 37 percent, from 15.8 cases per 1,000 women in the placebo group to 10.2 cases per 1,000 women in the tamoxifen group. These changes were similar in magnitude to that seen in the initial report.
Tamoxifen use was also associated with a 32 percent reduction in the risk of fractures, the findings indicate.
In general, tamoxifen raised the risk of adverse events, such as blood clots and cataracts, to a similar extent as in the initial report. The exceptions were a lower risk of developing blood clots in the lungs and a higher risk of endometrial cancer, but the differences fell short of statistical significance. The risk of lung blood clots was about 11 percent lower and the risk of endometrial cancer was about 29 percent higher than first reported, but, again, these differences were not significant.
According to Fisher and colleagues, a series of breast cancer prevention trials now in progress are evaluating other agents that “could be more effective than tamoxifen in curbing the risk of breast cancer and reducing the frequency of undesirable side effects noted with the drug.”
However, “until one of these trials demonstrates a greater net benefit from an alternative therapy, tamoxifen remains the only proven chemopreventive treatment for breast cancer risk reduction.”
SOURCE: Journal of the National Cancer Institute, November 15, 2005.
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