Risk/Benefit of Tamoxifen in Breast Cancer Prevention Still Unclear
By Steven Reinberg
NEW YORK Sep 12, 2002 (Reuters Health) - Although as primary prevention tamoxifen reduces the risk of breast cancer, its use is associated with an increased risk of thromboembolic events and all-cause mortality, according to the results of a randomized trial.
"This study clearly shows that tamoxifen can reduce the incidence of breast cancer, clarifying conflicting reports from previous studies," Dr. Jack Cuzick from the International Breast Cancer Intervention Study (IBIS) Trials Center, London, told Reuters Health. "However, the reduction in incidence of breast cancer is not as great as suggested by other studies. It is closer to one-third, not the 50% reported elsewhere," he said.
In the September 24th issue of The Lancet, Dr. Cuzick and colleagues report the findings of the IBIS-I trial. In the trial, 7,139 women, 35 to 70 years of age, who were at increased risk for breast cancer were randomly assigned to tamoxifen 20 mg/day for 5 years or to placebo. The primary outcome was the frequency of breast cancer.
Intention-to-treat analysis showed that during a median follow-up of 50 months, 69 of the 3,578 women in the tamoxifen group developed breast cancer compared with 101 of the 3,566 women in the placebo group (32% risk reduction), the researchers report. This reduction in risk was not changed by age, degree of risk, or hormone replacement therapy.
The risk of endometrial cancer was increased 2.2 times among women receiving tamoxifen compared with those taking placebo, but the increase was not statistically significant (p = 0.02). However, there was a statistically significant 2.5-fold increase in thromboembolic events among women receiving tamoxifen compared with placebo (43 versus 17, p = 0.001), particularly after surgery.
In addition, there were significantly more excess deaths from all causes among women in the tamoxifen group compared with the placebo group (25 versus 11), Dr. Cuzick's team reports.
"The benefit of tamoxifen has to be balanced against the side effects, of which thromboembolic events have emerged as the most important," Dr. Cuzick said. "At this stage, tamoxifen cannot be routinely recommended for prevention of breast cancer in high-risk women, and further follow-up of current trials is needed to identify which women are most likely to benefit from tamoxifen therapy," he added.
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