The researchers studied 1,442 Long Island (N.Y.) women with breast cancer and 1,420 disease-free women, and examined aspirin use in the period before those in the first group were diagnosed with the disease. They found 301 women in the breast-cancer group -- or 20.9% of the total -- who used aspirin at least once a week for six months or longer, and 345 women, or 24.3%, in the control group. That 4.6% difference works out to a 20% lower risk of breast cancer for aspirin users vs. non-users.
Aspirin was most effective, however, against tumors that are dependent on estrogen, reducing the risk of such cancers by 26%. About 60% of all breast cancers are estrogen-positive. The protective effect rose with daily aspirin use, but was not as strong for ibuprofen, another NSAID. The researchers found that acetaminophen, yet another aspirin-like drug, offered no protective effect.
TARGET GROUP. The Columbia scientists also went a long way toward explaining why aspirin might protect against breast cancer by basing their study on a decade's worth of lab research into aspirin's effect on animals by Dr. Andrew Dannenberg, professor of medicine at Weill-Cornell Medical College.
Dannenberg discovered that an enzyme in the blood called COX-2 stimulates the production of estrogen. Aspirin targets COX-2, and in mice it reduced the level of both estrogen and breast-cancer tumors. "There have been many, many studies on NSAIDs," says Dannenberg, "but this is the first which stratifies its effect based on a molecular hypothesis." He adds, "Now we know which women would be most helped by taking aspirin."
Doctors determine a woman's risk of breast cancer by analyzing a variety of factors, including family history, estrogen levels, body mass, and lifestyle. The authors of the JAMA study did not recommend that women start popping a daily aspirin, however. Dr. Alfred Neugut, professor of medicine at Columbia and a co-author of the study, notes that aspirin can have significant gastrointestinal side effects. Clinical trials just now under way are testing Celebrex, a COX-2 drug for arthritis with far fewer side effects, as a breast-cancer preventive, but those results won't be available for a few years.
In an editorial accompanying the article, Dr. Raymond DuBois of the Vanderbilt-Ingram Cancer Center in Nashville does say women who already take daily aspirin to prevent heart disease "may gain additional benefits with regard to reduction in their risk for certain cancers, such as hormone receptor-positive breast cancer." He adds, however, that "the optimal aspirin dose or regimen required to achieve a maximal reduction in cancer risk remains unknown." By Catherine Arnst in New York