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Breast Cancer Drug Tamoxifen May Affect Brain Function.

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WebMD Health News

Oct. 11, 1999 (Seattle) -- The drug tamoxifen, which has been shown to help women survive breast cancer, may cause a small decline in mental function, researchers reported Monday at the 124th annual meeting of the American Neurological Association. But the researchers say the finding is not conclusive and is not a reason for women with breast cancer to avoid the drug.

Annlia Paganini-Hill, PhD, a professor of preventive medicine at the University of Southern California (USC) in Los Angeles, who helped conduct the study, tells WebMD that the results mean researchers need to take a closer look at tamoxifen. "Clearly the benefits of this drug outweigh its risks for women with breast cancer," she says. "But there is a lot of controversy about using tamoxifen to prevent breast cancer, and any effect on the brain should be considered," she says.

Nicholas Vick, MD, a professor of neurology at Northwestern University Medical School in Chicago, says the USC study is "interesting and potentially very important because of the large number of women taking tamoxifen." But he says it's surprising that there haven't been anecdotal reports of cognitive problems among the huge number of women who have taken tamoxifen.

The USC study was sponsored by Wyeth Ayerst. The company makes a drug that is expected to compete with tamoxifen for the treatment of breast cancer.

The researchers at USC analyzed the results of brain function tests on nearly 1,300 women older than 55 who were participating in a breast cancer study in Los Angeles County. The women completed a mailed questionnaire that included several standard tests to detect thinking problems. The tests included tasks such as drawing a clock face and a cube, and describing what was taking place in a simple drawing.

For each task, women who were taking tamoxifen were slightly more likely to make mistakes than women who had taken the drug in the past, but stopped. However, the women taking tamoxifen did no worse than women who had never taken the drug, a finding for which the researchers have no explanation.

The women in the study also were asked whether they had consulted a physician about memory problems. Women currently taking tamoxifen were at least twice as likely as past users, or women who never used the drug, to report a doctor visit for this reason.

"The results aren't conclusive," says Paganini-Hill. "But the fact that we saw a difference at all with such a crude test is remarkable," she says.

Paganini-Hill says it's reasonable to suspect that tamoxifen could have an effect on thinking. That's because scientists know the drug lowers levels of the hormone estrogen, and previous studies have suggested that women with low estrogen levels are more susceptible to declines in mental function as they age.

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