Medications That Lower Breast Cancer Risk Carry Other Dangers

MONDAY Sept. 14, 2009 -- Medications given to women at high risk for developing breast cancer do reduce their cancer risk, but the drugs carry other health risks, a new analysis suggests.

That was the conclusion of researchers who looked at numerous published studies, including randomized clinical trials and a head-to-head assessment of the medications used for risk reduction. Those include tamoxifen, raloxifene and tibolone. The third drug is not currently on the U.S. market but is available in other countries, and there is some research on its risk-reduction benefits.

"We found that the three drugs actually did reduce the risk for invasive breast cancer by 30 to 68 percent," said review author Dr. Heidi D. Nelson, a research professor at Oregon Health & Science University. The report is published in the Sept. 15 issue of the Annals of Internal Medicine.

While the medications provided similar reductions in breast cancer risk, each carries its own level of side effects. "They did differ on the harm side," Nelson said. "That's important to know."

The use of the drugs to reduce breast cancer risk in healthy, high-risk women is not as common, Nelson noted, as their use to prevent recurrence in women already diagnosed with and treated for breast cancer. For instance, tamoxifen has been used for years to lower the chances of recurrence among breast cancer survivors. Recently, however, other researchers found tamoxifen only lowers the risk of a more common type of breast cancer, called ER-positive, while it raises the risk of developing ER-negative breast cancer, a more aggressive disease, in breast cancer survivors.

A similar story appears to be unfolding when the drugs are used for risk reduction in women who are cancer-free but at high risk of breast cancer. The women may be termed high risk due to genetic mutations such as BRCA1 and BRCA2, a strong family history, both, or other factors. Some choose to take the drugs to reduce risk. "It's important to call this [strategy] risk reduction, not prevention," Nelson said.

When Nelson's team evaluated the results from the studies, they found that tamoxifen and raloxifene boosted blood clots by 60 percent to 90 percent. Raloxifene caused fewer blood clots than tamoxifen.

Tamoxifen was also more likely than a placebo to lead to endometrial cancer and more likely to cause cataracts than was raloxifene.

In women over age 70, tibolone was associated with strokes.

Much of the information about this particular risk-and-benefit picture is already known, said Dr. Scott Maul, a medical oncologist at Oncology Alliance in Milwaukee. "They wanted to bring together all these studies under one publication, and try to quantify the benefit of these three different medications and their risk."

The decision to use the medications to reduce risk is not a simple one, Maul said. He urged women to talk it over with their doctors first. Nelson encourages women to get genetic testing and to use that genetic information -- including any findings about genetic mutations that boost breast cancer risk -- to get a more accurate picture of risk than other models may provide.

"The discussion on whether to use these drugs is a very detailed one with women," Maul said. While the decision is extremely individual, he did offer this advice: "Women should only take these [to reduce first-time breast cancer risk] if they are truly at higher risk for breast cancer." Even then, they may decide not to take them, he said, for good reasons. "If someone has risk factors for heart attack or stroke, these medications may not be a good idea."

More information

To learn more about a tool health professionals use to assess breast cancer risk, visit the U.S. National Cancer Institute.

Posted: September 2009


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