Aspirin Appears to Have No Effect on Breast Cancer Risk

N. R. Cook et al., Journal of the American Medical Association, July 6, 2005

Is this for me? You might want to read this article if you're considering taking aspirin to reduce your risk of developing breast cancer.

Background and importance of the study: In recent years, several studies have looked at the possibility that aspirin and other NSAIDs can help protect you from getting breast cancer. NSAIDs, or non-steroidal anti-inflammatory drugs, are medicines that reduce fever as well as the swelling and redness caused by injury, infection, or sores. Some of these drugs also reduce pain. They are called "non-steroidal" because their chemical structure is different from that of steroids. As a result, they don't cause the side effects that steroids do.

Aspirin (chemical name: salicylic acid) works in a number of ways. Its most important action is to reduce the amount of hormones called prostaglandins that your body makes. These hormones have a significant impact on other hormones and the way cells interact with each other and the tissues that surround them.

One large study of 80,000 women, in April 2003, found that women who regularly took aspirin and the NSAID ibuprofen (brand names: Motrin, Advil) for months or years significantly lowered their risk of breast cancer. Another study in May 2004 found that for 3,000 post-menopausal women who had hormone-receptor-positive cancer, taking aspirin regularly over long periods of time significantly reduced breast cancer risk. But in both of these studies, the women were asked about their use of aspirin or NSAIDs years after they had taken it. The studies were not randomized trials, meaning that the women were not assigned by chance to different groups to see if the aspirin or NSAIDs made a difference.

In the randomized study reviewed here, researchers from Harvard University, the University of Miami, and Florida Atlantic University looked at aspirin's effects on a number of different cancers, including breast cancer. The study was funded by the National Heart, Lung, and Blood Institute (part of the National Institutes of Health) and the National Cancer Institute.

Study design: As part of the Women's Health Study, a 12-year study of 39,876 U.S. women from across the country, the women were randomly assigned to receive either a low dose of aspirin (100 mg every other day) or a placebo (fake aspirin pill). Half the women took the aspirin and the other half took the placebo. The women took the pills for almost three years, from April 1993 to January 1996.

All the women in the study:

• were at least 45 years old,
• had never been diagnosed with any type of cancer,
• had never had heart disease or other major chronic illness,
• had no history of bad reactions to aspirin, and
• were not taking aspirin or NSAIDs more than once a week before the study started.

The women were followed for about 10 years. Every 6 months in the first year, and then once a year after that, the women were mailed questionnaires asking about their health, including any diagnoses of cancer.

Results: During the 10 years of follow-up, the women reported 2,865 cases of invasive cancer. Of these, 1,230 (43%) were breast cancer—reported by 608 women who took aspirin and 622 women who took the placebo.

Conclusions: The researchers concluded that taking a low dose of aspirin every other day appeared to have no effect on reducing the risk of developing breast cancer (or any other kind of cancer).

Take-home message: This large, randomized study is one of the longest studies done so far to look at aspirin and the risk of cancer. The results suggest that aspirin has no effect on the risk of getting breast cancer. This contradicts the results of earlier studies that suggested aspirin might help reduce that risk.

Based on what we know at this time, taking aspirin is not an effective strategy to reduce your risk of breast cancer. Plus, regular use of aspirin has risks. Frequent use of aspirin can occasionally cause bleeding, stomach ulcers, liver and kidney damage, and other serious health problems. If you are having any surgery, you should avoid aspirin for a few weeks before the surgery to minimize your risk of problems with bleeding. (Parents should get the approval of their children's doctor before giving children aspirin, because their bodies may process it differently than adults' bodies do.)

You don't need a prescription to buy aspirin, of course. But it's still very important to talk to your doctor before taking it on a regular basis, even when you take a low dose. (For example, many experts advise men to take daily low-dose aspirin—100 milligrams (mg), compared to a typical dose of 325 mg—to reduce their risk of heart disease.)

Stay tuned to breastcancer.org for the latest news on drugs or lifestyle changes that may reduce your risk of breast cancer.