Who should consider taking the drug tamoxifen to prevent breast cancer?

More than 10 million women in the United States (15.5 percent of all American women) have a high enough risk of developing breast cancer that they may want to consider taking tamoxifen, according to a new National Cancer Institute (NCI) study. Of these 10 million women, about 2 million would likely benefit from the drug without troublesome side effects. The other 8 million might have side effects that outweigh the possible benefits of the drug.

In 1998, the U.S. Food and Drug Administration approved tamoxifen as the first drug to prevent breast cancer.

Rare, but serious, side effects of tamoxifen include endometrial cancer (cancer of the lining of the uterus), stroke, deep vein thrombosis (blockage in the veins), and pulmonary embolism (blockage in the arteries around the lungs). The study weighed the risks of tamoxifen against the benefits. It found that:

• Women age 40 to 59 are more likely than older women to benefit from tamoxifen because they are less likely to experience the drug's side effects.

• White women are more likely than black women to benefit from tamoxifen because they have a higher overall breast cancer risk and are less likely to experience the drug's side effects.

• If all white women who are likely to benefit from tamoxifen took the drug for the next five years, almost 28,500 breast cancers could be prevented or delayed.

Women should talk with their doctor about whether to take tamoxifen. The decision should depend on the woman's age, breast cancer risk factors, family history, medical situation, lifestyle, personal values, and preferences.

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