Numerous studies have looked at whether aspirin and other non-steroidal anti-inflammatory drugs (NSAIDs) reduce breast cancer risk, but the findings have been inconsistent. Some research has shown that the drugs have a protective effect, while other studies have found no association. A few studies have even linked NSAIDs with an increased cancer risk.

"On the whole, these studies have not provided convincing evidence that using either aspirin or other NSAIDs can reduce breast cancer risk," according to Eric Jacobs, PhD, American Cancer Society, strategic director, pharmacoepidemiology. "Further research is needed before any conclusions can be made."

This particular study was based on data from the National Institutes of Health—AARP Diet and Health Study, a questionnaire-based analysis of diet, health habits, and cancer incidence of AARP members during 1996-1997. The researchers, led by the National Cancer Institute's Gretchen Gierach, MPH, PhD, looked at data on breast cancer incidence and NSAID use among 127,383 mostly white, post-menopausal women aged 51 to 72 who were enrolled in the study.

The team found no significant association between NSAID use and breast cancer risk, but when they looked more closely at associations between specific types of NSAIDs and breast cancer tumor characteristics, they found a 16% reduction in ER-positive breast cancer risk with daily aspirin use. No association was found between NSAID use (aspirin or otherwise) and ER-negative breast cancer. (ER-negative breast cancer accounts for approximately 25% of the cases seen in the US.)

NSAIDs inhibit the enzyme cyclooxygenase, which could play a role in disrupting breast cancer growth by suppressing estrogen synthesis. Aspirin is unique among NSAIDs: it irreversibly inhibits cyclooxygenase, which could explain its possibly preventive role. However, scientists are still investigating these processes. In the meantime, experts warn against raiding your medicine cabinet in the hopes of warding off cancer.

"The American Cancer Society does not recommend using aspirin for cancer prevention because aspirin can cause serious gastrointestinal bleeding. Whether or not a person should use aspirin for disease prevention is a question that should be discussed with their doctor who can take their medical history into account," says Jacobs. "This decision should be based on balancing the proven benefits of aspirin in preventing heart disease against the proven risks of serious gastrointestinal bleeding."

Although there is no sure-fire way to prevent breast cancer, there are things women can do to reduce their risk. Avoiding alcohol, exercising regularly, and maintaining a healthy body weight can all help lower risk.

For women at high risk for breast cancer, medicines such as tamoxifen or raloxifene might be options. For more information, see Medicines to Reduce Breast Cancer Risk.

One of the best ways to protect your health is to get a regular mammogram, which can find breast cancer at its earliest stages, when it is easier to treat. The American Cancer Society recommends every woman aged 40 and over schedule a yearly screening mammogram. For more information, see "Can Breast Cancer Be Found Early?," Mammograms and Other Breast Imaging Procedures, and Mammograms Matter.