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The Effect of Low-Dose Aspirin on Colorectal Cancer Risk in Women FREE

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The full report is titled “Alternate-Day, Low-Dose Aspirin and Cancer Risk: Long-Term Observational Follow-up of a Randomized Trial.” It is in the 16 July 2013 issue of Annals of Internal Medicine (volume 159, pages 77-85). The authors are N.R. Cook, I.M. Lee, S.M. Zhang, M.V. Moorthy, and J.E. Buring.

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Ann Intern Med. 2013;159(2):I-24. doi:10.7326/0003-4819-159-2-201307160-00001
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What is the problem and what is known about it so far?

Some studies suggest that aspirin may reduce a person's risk for colorectal cancer. Effects of aspirin on colorectal cancer risk may be delayed and only occur after long-term use. Most studies examining long-term use of aspirin provide data about daily rather than low-dose, “alternate-day” use.

Why did the researchers do this particular study?

To learn about the relationship between cancer risk and long-term, alternate-day use of low-dose aspirin.

Who was studied?

The study involved 39,876 women aged 45 years or older who were enrolled in the Women's Health Study. The Women's Health Study was a landmark trial that sought to determine the benefits and risks of low-dose aspirin and vitamin E in preventing cardiovascular disease and cancer in U.S. women. It started in April 1993 and ended in March 2004. Participants had no history of cancer (except nonmelanoma skin cancer), cardiovascular disease, or other major chronic illness.

How was the study done?

Study participants took a low dose (100 mg) of aspirin or placebo every other day from the time they enrolled in the Women's Health Study until the study ended in 2004. During that time, the researchers tracked the incidence of cancer by regularly mailing questionnaires to the participants. The questionnaires sought information on medication adherence, adverse effects, nonstudy aspirin use, cancer diagnosis, and risk factors. After the trial ended, researchers continued to follow 33,682 of the participants through March 2012, although they no longer provided them with aspirin or placebo.

What did the researchers find?

After 18 years, the incidence of colorectal cancer was 20% lower in the aspirin group than in the placebo group. Women who continued taking aspirin on their own after the trial ended in 2004 had the greatest reduction in colorectal cancer risk. There were no differences between groups in incidence of other cancer types or in overall cancer risk or death. Compared with women who took placebo, those who took aspirin had more gastrointestinal bleeding (8.3% vs. 7.3%) and peptic ulcers (7.3% vs. 6.2%).

What were the limitations of the study?

Not all women received extended follow-up. Information on gastrointestinal bleeding was obtained only from self-report during extended follow-up.

What are the implications of the study?

Long-term use of alternate-day, low-dose aspirin may reduce risk for colorectal cancer but increase risk for gastrointestinal bleeding in healthy women.





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