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Aspirin and breast cancer - it may reduce the occurrence to a modest extent, or it may not
(November 2004)

There are now multiple studies suggesting that regular aspirin use can reduce the occurrence of breast cancer by 20 to 30 percent. But, not all studies are in agreement. In a study reported in the Journal of the American Medical Association, May 26, 2004, investigators compared 1,442 breast cancer cases with 1,420 controls in regard to aspirin use. Those taking seven or more aspirin tablets a week (strength of the aspirin tablet not specified) had a 28 percent reduced risk of breast cancer that was statistically significant. Less frequent use did not reduce risk and longer duration of use (less than five years versus more than five years) did not produce additional benefit. The reduced risk was found for postmenopausal, but not for premenopausal women, and was found only in women with the more common estrogen-positive type of breast cancer. The investigators also analyzed Motrin (ibuprofen) use and breast cancer risk. Motrin, like aspirin, is a non-steroidal anti-inflammatory drug, but the results with Motrin were not clear and were not statistically significant.

The investigators suggest that aspirin is acting by interfering with estrogen production.

Commentary: A better study than this one, conducted on 80,741 postmenopausal women as part of the Women’s Health Initiative found generally similar results, but unlike this study, Motrin was actually more effective. Roughly two-thirds of the studies are supportive of the conclusion that aspirin and other non-steroidal anti-inflammatories (such as Motrin, Feldene, Indocin, Naprosyn) reduce breast cancer risk in postmenopausal women by about 20 percent. It is not clear how many tablets a week are needed to achieve the benefit nor is there adequate evidence on the needed duration of use. There is no evidence that low strength aspirin tablets are effective.

BUT - and it is a big BUT,

there appears to be only one true intervention study in which women were randomized to aspirin or no aspirin. This is the famed Nurses’ Health Study which followed 89,528 nurses for 12 years, during which time 2,414 cases of breast cancer occurred. There was no evidence that use of two to more than 14 regular aspirin tablets a week for any duration (less than five years to more than 20 years) had any beneficial effect on breast cancer - no reduction in occurrence at all, no matter how they analyzed the data. This is a very important negative study because it has the best design.



Only randomized prospective studies like the Nurses’ Health Study will provide a definitive answer. The epidemiologic literature is littered with studies that looked impressive when cases were compared with controls, but were not confirmed with the gold standard type of study, a randomized controlled clinical trial. At present, aspirin should not be recommended for prevention of breast cancer. It is well to remember that aspirin, which has many benefits, can infrequently cause intestinal bleeding and, rarely, bleeding into the head; and the bigger the daily or weekly dosage, the greater the risk. There are no free rides.

Terry, M.B., et al. Association of frequency and duration of aspirin use and hormone receptor status with breast cancer risk. Journal of the American Medical Association. Vol 291 (May 26) Pgs 2433-2440. 2004.

Harris, R.E., et al. Breast cancer and nonsteroidal anti-inflammatory drugs: Results from the Women’s Health Initiative. Cancer Research. Vol 63 (Sept 15) Pgs 6096-6101. 2003.

Egan, K.M., et al. Prospective study of regular aspirin use and the risk of breast cancer. Journal of the National Cancer Institute. Vol 88 (July 17) Pgs 988-993. 1996.