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Tamoxifen Side Effect: Higher Stroke Risk

Experts Say Small Risk Seen From Five-Year Treatment With Breast Cancer Drug
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WebMD Health News

Oct. 11, 2004 -- A new study shows a small but real risk of stroke is one of the side effects of using tamoxifen for breast cancer treatment in women.

After analyzing nine prior studies the researchers find that tamoxifen use was associated with an 82% increase in ischemic [clot-related] stroke risk and a 29% increase in the risk for all strokes.

The study is published in the October issue of the journal Neurology.

The increase in risk translated into seven additional strokes among 1,000 patients taking the drug for five years, study co-author Cheryl D. Bushnell, MD, tells WebMD.

"The absolute risk is small but it still appears to be statistically significant," she says. "These findings should give oncologists pause to at least discuss the risks and benefits with their patients before starting them on this therapy and to be vigilant about screening them for other stroke risk factors."

Risks and Benefits

Tamoxifen has been used for just more than three decades to lower the risk of recurrence in women treated for breast cancer, and it is now also widely prescribed as a preventive treatment for healthy women considered at high risk for getting the disease. Tamoxifen is usually prescribed for five years.

Millions of women have taken tamoxifen during the last 30 years, but the risks and benefits of the drug have long been debated. On the plus side, in addition to reducing the risk of breast cancer, tamoxifen has been shown to reduce the risk of osteoporosis and hip fracture and lower cholesterol and C-reactive protein levels -- potentially improving heart disease.

But there are also harmful side effects. Since the drug can act like an estrogen in certain tissue, it can increase the risk of blood clots and endometrial cancer.

It has been unclear whether tamoxifen use increases a woman's stroke risk. A recently published review of studies showed almost a 50% increase in the risk of all types of stroke, but Bushnell and colleague Larry Goldstein, MD, of Duke University Medical Center guessed the risk of blood clot-related strokes might be higher.

To test this theory, the authors conducted their own review of studies that had information about so-called ischemic, or blood clot-induced, strokes, as well as a few that did not. Their analysis included nine trials with a total of 39,600 participants. Roughly half took tamoxifen and the other half took placebos or other breast cancer-fighting drugs.

Tamoxifen use was associated with an 82% increase in ischemic stroke risk and a 29% increase in the risk for all strokes.

"These findings quantify stroke risk, but there are still a lot of unanswered questions," Bushnell says.

Newer Drugs, Fewer Side Effects?

It is hoped, the researchers wrote, that these questions will be answered by several large ongoing studies comparing tamoxifen with the osteoporosis drug raloxifene, which is also used to prevent breast cancer. Both drugs are in the class known as selective estrogen receptor modulators (SERMs). These drugs block or stimulate the estrogen receptors of different tissues. It is hoped other SERMs might share some of the positive properties that tamoxifen has demonstrated in the prevention of breast cancer but without the adverse side effects.

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