A growing body of literature has supported a protective effect of aspirin and other nonsteroidal anti-inflammatory drugs (NSAIDs) on the development of cancer, according to background information in the first article. Observational epidemiological investigations suggest a strong inverse association, with risk reductions as high as 20 percent to 50 percent for various cancer sites. In contrast with the observational evidence on cancer incidence, data from randomized trials, which provide more definitive results due to their ability to minimize bias and confounding, have been far more limited. The Physicians' Health Study (PHS) found no effect on colorectal cancer of 325 mg aspirin administered every other day over a 5-year randomized period or in post trial follow-up. In addition, no randomized trial has yet assessed the impact of aspirin on the development of breast cancer.
The Women's Health Study (WHS) was a randomized, double-blind, placebo-controlled trial, conducted between September 1992 and March 2004, evaluating the balance of benefits and risks of 100 mg of aspirin every other day, and 600 IU of vitamin E every other day on the primary prevention of cardiovascular disease and cancer in a cohort of 39,876 healthy female health care professionals over an average duration of 10.1 years.
In the first article, Nancy R. Cook, Sc.D., of Brigham and Women's Hospital and Harvard Medical School, Boston, and colleagues evaluated the findings for the aspirin component of the WHS with regard to cancer risk. In this part of the study, 19,934 women received a dose of 100 mg of aspirin every other day and 19,942 women received placebo.
The researchers found that aspirin had no observed effect on total cancer, breast cancer, colorectal cancer, or cancer of any other site, with the exception of lung cancer for which there was a trend toward reduction in risk (22 percent reduced risk). There was also no reduction in cancer death either overall or by site, except for lung cancer death (30 percent reduced risk). No evidence of differential effects of aspirin by follow-up time or interaction with vitamin E was found.
"The findings from the WHS suggest that aspirin at a dose of 100 mg every other day is not effective in reducing risk of cancer in healthy women, although a beneficial effect on lung cancer cannot be ruled out. This large study of almost 40,000 women had a duration of 10 years of treatment and follow-up, which was the longest of any trial completed to date, and should be sufficient to detect long-term effects. To determine whether higher doses of aspirin taken daily would be effective in cancer prevention requires direct randomized trial data. Such data would need to be considered in the context of risk of gastrointestinal adverse effects before recommending higher-dose aspirin for cancer chemoprevention among low-risk individuals," the authors conclude.
(JAMA. 2005;294:47-55. Available pre-embargo to the media at www.jamamedia.org)
Editor's Note: For funding/support and financial disclosure information, please see the JAMA article.
Editorial: Low-Dose Aspirin and Vitamin E - Challenges and Opportunities in Cancer Prevention
In an accompanying editorial, Eric J. Jacobs, Ph.D., and Michael J. Thun, M.D., of the American Cancer Society, Atlanta, comment on the findings by Cook et al.
"Should the null results with respect to cancer from this large, well-conducted, long-term randomized trial, or from other chemoprevention trials, be considered discouraging news for cancer chemoprevention in general? There have been some successes in cancer chemoprevention, such as the use of tamoxifen to prevent breast cancer in high-risk women. However, currently, no agent has been shown to do for cancer what statins do for cardiovascular disease, namely substantially and relatively safely reduce disease occurrence in individuals not at especially high risk."
"Pharmacological primary prevention of diseases as heterogeneous as cancer is inherently difficult. Randomized trials of cancer chemoprevention will undoubtedly produce many null results. Nevertheless, continued systematic research on cancer chemoprevention, including long-term randomized trials of carefully chosen agents, is essential given the large potential benefits. At the same time, it is unrealistic to expect the discovery of an agent that will produce substantial reductions in overall cancer rates in the immediate future," authors write.
(JAMA. 2005;294:105-106. Available pre-embargo to the media at www.jamamedia.org)
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