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Tamoxifen Side Effect: Higher Stroke Risk

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

Risks and Benefits continued...

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.

Several drugs of another class known as aromatase inhibitors are also now being used for breast cancer prevention. American Cancer Society spokesman Len Lichtenfeld, MD, says it remains to be seen if any of the drugs now under study will emerge as clearly safer and more effective than tamoxifen. Lichtenfeld is deputy chief medical officer for ACS.

"In the scheme of risks and benefits [the stroke risk with tamoxifen] is small when compared, for example, with the risk of breast cancer coming back," he says. "But it still may not be acceptable to some because we are talking about giving this drug to essentially healthy women. This is one factor among many that has to be weighed in making this decision, and I can't stress enough the importance of a patient becoming a partner in that decision by discussing it with her doctor."

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