Double Duty

By Christine Gorman

Two years ago there wasn't a pill in the world that had been proved to reduce a woman's risk of developing breast cancer. Today there are two: tamoxifen, which doctors have used for more than 25 years to treat breast tumors after they have formed; and raloxifene, a newer drug that was originally designed to prevent osteoporosis but that, according to a study in last week's issue of the Journal of the American Medical Association, may also afford some protection against breast cancer.

Both drugs have been dubbed "designer estrogens" because they block estrogen's ability to promote tumor growth in the breast while at the same time mimicking the hormone's salutary effects on the spine. (About 75% of all breast cancers are estrogen-sensitive.) But they can also trigger serious side effects, including potentially fatal blood clots. So the good news about designer estrogens must always be tempered with some heavy-duty caveats.

Thus far only tamoxifen has been formally approved by the U.S. Food and Drug Administration for reducing the risk of breast cancer. But ever since preliminary data suggested that raloxifene might also help keep breast cancer at bay, the spotlight has been shifting toward the newer drug. Why? Because raloxifene, unlike tamoxifen, doesn't appear to increase a woman's risk of developing uterine cancer.

Last week's J.A.M.A. study seemed to tip the balance even further in raloxifene's favor. Researchers, led by Dr. Steven Cummings of the University of California at San Francisco, reported that taking the drug for 3 1/2 years reduced a woman's risk of developing breast cancer an average of 75%. By contrast, a study of tamoxifen completed last year showed that it reduced the incidence of breast cancer 45% over four years. As an added bonus, raloxifene also lowered the amount of LDL, or "bad cholesterol," in the blood.

It would be a mistake, however, to conclude that raloxifene must be the better drug; the two studies are not directly comparable. The J.A.M.A. study looked at women who had a low risk of developing breast cancer, whereas the tamoxifen experiment was conducted using women who had a high risk of getting the disease. Yet women with a high risk of breast cancer are less likely to develop the kind of estrogen-sensitive tumors that respond to designer estrogens.

Similarly, neither drug is likely to help women who have inherited the BRCA1 or BRCA2 genes, since they are least likely of all to develop estrogen-sensitive tumors. Nor is there any guarantee that raloxifene's effects are long lasting.

Doctors are starting a head-to-head comparison of tamoxifen and raloxifene, with results expected in about five years. In the meantime, it may be that the only women who should consider raloxifene are those at highest risk of osteoporosis--the group for whom it was originally designed. (If that includes you, you should also consult your doctor about another drug, called alendronate, that may do a better job of preventing osteoporosis, although it gives some people severe heartburn.) The trick, as always, is to weigh the risks and benefits of drug treatment against your particular needs and medical history.

For more about designer estrogens, visit our website at time.com/personal You can e-mail Christine at gorman@time.com