Low-Dose Aspirin Fails to Protect Women Against Cancer
Aspirin, NSAIDs, chemoprevention, Women’s Health Study. (Definitions of many terms related to cancer can be found in the Cancer.gov Dictionary.)
Low-dose aspirin (100 mg) taken every other day failed to protect women from developing cancer, according to results from a 10-year, randomized trial called the Women’s Health Study. However, researchers say that more studies are needed to determine whether moderate or high doses of aspirin may yet prove protective.
Journal of the American Medical Association, July 6, 2005 (see the journal abstract).
Aspirin belongs to a group of drugs called nonsteroidal anti-inflammatory drugs (NSAIDs) Many studies have suggested that NSAIDs may do something to protect against cancer, particularly colorectal cancer. However, few of these studies have been clinical trials, which are the kind of study that can most reliably answer the question of whether aspirin and other NSAIDs really do help prevent cancer in people.
A 1996 clinical trial called the Physician’s Health Study found that a 325 mg dose of aspirin (the typical amount found in a single aspirin sold in stores) taken every other day did not prevent colorectal cancer. However, findings published in 2003 from two other clinical trials showed that low-to-moderate doses of aspirin (80 mg and 325 mg) taken every day by persons at high-risk for colorectal cancer reduced their chances of developing potentially cancerous colon polyps (see Aspirin Reduces Risk of Colon Polyps). The protective effect appeared to be particularly strong with the lower dose.
Researchers with the current study wanted to learn more about what role low-dose aspirin might play in the fight against cancer.
Between 1992 and 2004, researchers with the Women’s Health Study (WHS) enrolled over 39,000 women health professionals at least 45 years of age; the mean age at the start of the trial was about 54 years. The goal of the study was to investigate the protective effects of low-dose aspirin (100 mg), vitamin E, and beta-carotene on cardiovascular disease and cancer. (The beta-carotene part of the study was stopped early, in 1996, when other studies showed no protection and even a possible risk of cancer.)
Women were randomly assigned to receive aspirin, vitamin E, both, or placebos (dummy pills). Neither they or their doctors knew which group they were in (meaning the study was double-blinded) and all participants were free of disease at the start of the trial. The aspirin and vitamin E aspects of the study were conducted together but analyzed and reported independently. Only the cancer-related aspirin analysis is described here. A total of 19,934 women took the low-dose aspirin and 19,942 took a placebo every other day. The participants were followed for an average of about 10 years.
The lead author for the aspirin analysis was Nancy R. Cook, Sc.D., from the Brigham and Women’s Hospital and Harvard Medical School, Boston, Mass. The study was supported by the National Cancer Institute (NCI) and the National Heart, Lung, and Blood Institute. Medications were provided by Bayer HealthCare and the Natural Source Vitamin E Association.
Researchers found that the aspirin group received no protection against cancer: 1,438 developed invasive cancer (that is, cancer that spread beyond the layer of tissue in which it first developed) as compared to 1,427 in the placebo group. The slight difference in cancer deaths was also not statistically significant, with 284 dying in the aspirin group and 299 in the placebo group.
When analyzed for certain specific types of cancer, the results showed that there were fewer lung cancer cases (90 versus 115) among the aspirin group. However, this was not a statistically strong enough finding to prove that aspirin helps protect against lung cancer. There were also no statistically significant differences between the aspirin and placebo groups in terms of other types of cancer: for example, breast cancer (608 cases in the aspirin group vs. 622 in the placebo group) and colorectal cancer (133 vs. 136).
These results apply only to a very limited group of people, said Lori Minasian, M.D., of the NCI's Division of Cancer Prevention. “This study says nothing at all about men, nor about younger women, and especially not about women who have had cancer” or who may have a family history of cancer.
“I don’t think we have the final story on aspirin and its effects on cancer,” said Peter Greenwald, M.D., director of NCI’s Division of Cancer Prevention. He and others in the field are not prepared to generalize these results to other groups and dosages. In an editorial accompanying the journal article, Eric J. Jacobs, Ph.D., and Michael J. Thun, M.D., of the American Cancer Society emphasized that these results “do not refute previous evidence that moderate or high doses of aspirin may reduce the risk of certain cancers.”
However, more clinical trials must be done, said Minasian, before aspirin’s role in the prevention of cancer can be fully understood and the risks properly balanced against the benefits. Aspirin can have serious side effects, including gastrointestinal bleeding.
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