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Breast Cancer Health Center

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Tamoxifen May Increase Blood Clot Risk

But Risk of Blood Clots May Raise Chance of Dying
WebMD Health News

Sept. 12, 2002 -- Early results from a large European study show that the cancer drug tamoxifen also prevents first-time breast cancers in high-risk women, but at what cost?

"We have clearly demonstrated that tamoxifen can prevent breast cancers, and that is a big step forward," lead researcher Jack Cuzick, PhD, tells WebMD. "But we still have more work to do to learn how to do that safely with a minimum number of side effects."

In Cuzick's study, some 7,000 women without breast cancer but at high risk for the disease took either tamoxifen or a placebo for five years. The frequency of breast cancer fell by one third among women taking tamoxifen, compared with those taking a placebo. But there was also an increase in potentially dangerous blood clots in the tamoxifen group.

Tamoxifen is routinely used to help prevent breast cancer from coming back. But Cuzick says there are too many unanswered questions about tamoxifen's safety to recommend it for routine use in women who do not already have breast cancer.

Cuzick's preliminary study, reported in the Sept. 14 issue of The Lancet, offers a conflicting profile of tamoxifen's safety.

In the past, tamoxifen has been linked to an increase in uterine cancer. But this was not the case in the present study. The numbers of women who developed uterine cancer in both groups were not significantly different. And when uterine cancer did strike, it was always in the early stages and cured by hysterectomy.

But more women on tamoxifen suffered blood clots-- 43 women vs. 17 women taking a placebo. The blood clots tended to occur following surgery, leading Cuzick to recommend that women on tamoxifen be taken off the drug and put on blood-thinning agents prior to major surgery.

The increase in blood clots may account for the fact that women taking tamoxifen had a higher risk of dying from any cause -- not just from breast cancer -- than women taking placebo.

Cuzick says it may be several years before the long-term risks and benefits of tamoxifen are clarified for women taking it to prevent first-time breast cancers. That is because these women are only now beginning to complete the recommended five-year treatment protocol.

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