In the past, most cancer research has focused on identifying and modifying the lifestyle factors that were known to increase or decrease one’s cancer risk (eg, quitting smoking to reduce the risk of lung cancer). Recently, researchers have also been focusing on the role of chemoprevention, the use of chemicals (ie, drugs) to prevent or inhibit the development of cancer.

One area in which chemoprevention has shown some success is in the treatment of breast cancer . For years, researchers have understood that estrogen plays an important role in the development of breast cancer. Further research led to the discovery of hormone receptors on breast cancer cells. Now, when a woman is diagnosed with breast cancer, one of the first things her doctor does is determine whether her cancer cells are hormone receptor-negative or hormone receptor-positive. This is important because if a woman has hormone receptor-positive cancer cells, she is much more likely to respond to tamoxifen and similar drugs, which block the stimulating effects of estrogen on these receptors.

In light of the recent findings regarding the role of prostaglandins in the development of breast cancer, and the role of aspirin (and other NSAIDs such as ibuprofen) in inhibiting the production of the enzyme needed to produce prostaglandins, researchers began to wonder whether aspirin had significant protective effects, and if so, whether this protection varied according to hormone receptor status.

To answer this question, researchers conducted a study to determine whether there is an association between the frequency and duration of aspirin (and other NSAIDS) use and the risk of breast cancer, and whether this association is stronger for women with hormone receptor-positive breast cancer. The results of their study were published in the May 26, 2004 issue of The Journal of the American Medical Association. The researchers found regular use of aspirin was associated with a reduction in risk for breast cancer.

About the Study

The researchers conducted a population-based, case-control study including 2862 women between the ages of 20 and 98. Of these, 1442 were diagnosed with breast cancer and 1420 were not. During in-person interviews, the researchers collected information on aspirin, NSAID, or acetaminophen (eg, Tylenol) use, as well as a complete medical history.

The Findings

The researchers found that 301 (20.9%) of the women with breast cancer and 345 (24.3%) of the women without breast cancer reported using aspirin or NSAIDS at least once per week for a period of six months or more. This amounted to a 20% reduction in age-adjusted risk of breast cancer among these women.

The most dramatic reduction occurred among women who took seven or more tablets of aspirin a week. They experienced a risk reduction of 28%. Women who took ibuprofen on a regular basis saw a weaker response than aspirin, but it was not statistically significant. Women who used acetaminophen (which does not inhibit prostaglandin production) saw no reduction in their risk of breast cancer.

The researchers went on to show that this reduction in risk essentially only applied to breast cancers containing hormone receptors. Aspirin did not appear to protect against breast cancers containing no such receptors at all.

How Does This Affect You?

In the end, the researchers found an inverse association between aspirin use and the risk of developing breast cancer. While there was a slight reduction in risk with the regular use of ibuprofen, there was no such reduction with acetaminophen. The protective affect of aspirin seemed to be reserved for breast cancers containing hormone receptors, suggesting that aspirin works, at least in part, by interfering with the production of estrogen. The researchers concluded that these results add to the growing evidence that regular use of aspirin may be helpful in reducing a woman’s risk for breast cancer.

One drawback to the study, however, is the fact that it is a case controlled design, not a clinical, randomized controlled trial (RCT). In case control studies, patients who already have a certain condition are compared with people who do not. This type of study is less reliable than RCTs because, among other things, it is harder to establish a cause and effect relationship between the exposure (in this case aspirin) and the disease (breast cancer). For example, lung cancer rates are higher for people who do not have a college education. However, that does not mean that you can reduce your risk for developing lung cancer simply by going to college (a conclusion you might draw unless you know that college graduates are less likely to smoke).

An editorial published in the same issue of the Journal , states that possibly the most important finding from this study is the observation that hormone receptor-positive tumors appear to be responsive to aspirin therapy. Clearly, clinical trials are needed before women can be advised to take aspirin simply to reduce their risk of breast cancer. Although aspirin is inexpensive, it is not without its risks (eg, peptic ulcers). In the meantime, however, women taking daily aspirin therapy to protect against heart disease and stroke may soon find that they’ve been receiving an additional benefit.