Tamoxifen May Increase Blood Clot Risk
But Risk of Blood Clots May Raise Chance of Dying
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.
"The best possible scenario is that there would be a
continued reduction of cancers with a cessation of side effects," he says.
"But we just don't know. And there are hints that tamoxifen may increase
the long-term risk of [hard to treat] tumors. We need to look at that more
Oncologist Herman Kattlove, MD, tells WebMD that though
tamoxifen does appear to prevent breast cancers in women without breast cancer,
it is not yet clear whether its use in high-risk women will save lives.
Most women don't die of breast cancer, and the cancers that
tamoxifen prevents are very receptive to treatment, Kattlove tells WebMD.
Kattlove, who now serves as a medical editor for the American
Cancer Society, has used tamoxifen to treat women with breast cancer. He says
most of his patients found the drug's more common side effects, such as hot
flashes and vaginal dryness, difficult to tolerate.
"A lot of my patients were unhappy on this drug," he
says. "This is not some benign therapy. Most women experience side effects
while taking it, and even if those side effects aren't life threatening, they
Several large trials are now under way assessing tamoxifen's
usefulness in preventing breast cancers in women who have not had the disease
but are at high risk for it.