July 25, 2013
Alternate-Day Aspirin Use Lowers Colorectal Cancer Risks
in Women

Boston—A new study found that long-term use of alternate-day, low-dose aspirin reduced the risk for colorectal cancer in women, but that doesn’t necessarily mean health care professionals should recommend the therapy prophylactically.

The research, reported in the Annals of Internal Medicine, found that the drug regimen took a long time to show effect—the differences between the treatment and control groups emerged after a decade—and also increased the risk of gastrointestinal bleeding.

The U.S. Preventive Services Task Force currently recommends that the harms outweigh the benefits of aspirin and nonsteroidal anti-inflammatory drug (NSAID) use for the prevention of colorectal cancer in people of average risk but has commissioned a systematic review to update the recommendation. It says a draft research plan to assess the risks and benefits of the use of aspirin to prevent all types of cancer, in addition to colorectal cancer, will also be available in the near future.

Researchers from Brigham and Women's Hospital, Harvard Medical School, and Harvard School of Public Health, all in Boston, write that they embarked on the study because, while studies suggested that daily aspirin could help prevent several types of cancer, including colorectal, there was little evidence about alternate-day dosing strategy.

For the study, initiated between 1994 and 1996, around 39,000 female health professionals aged 45 years or older were randomly assigned to take either 100 mg of aspirin or placebo every other day. Monthly calendar packs containing aspirin or placebo were sent annually to participants.

After 6 and 12 months of treatment—and then yearly through the trial’s end in March 2004—patients received questionnaires asking about adherence, adverse effects, nonstudy aspirin use, clinical endpoints, and risk factors. At the end of the intervention period, the women were asked to sign up for further annual follow up, with the more than 33,000 who did not opt out continuing through March 2012.

During the study and follow-up periods, 1,391 participants died of cancer with another 5,071 total cancer cases confirmed. Those included 2,070 cases of breast cancer, 451 colorectal cases, and 431 lung cancer cases.

Over the entire follow-up, no association was demonstrated between aspirin and total (hazard ratio [HR], 0.97 [95% CI, 0.92-1.03]; P = 0.31), breast (HR, 0.98 [CI, 0.90-1.07]; P = 0.65), or lung (HR, 1.04 [CI, 0.86-1.26]; P = 0.67) cancer occurrence.

Colorectal cancer, however, was shown to be reduced in the aspirin group (HR, 0.80 [CI, 0.67-0.97]; P = 0.021), primarily for proximal colon cancer (HR, 0.73 [CI, 0.55-0.95]; P = 0.022). The difference took 10 years to emerge, with a post-trial reduction of 42% (HR, 0.58 [CI, 0.42-0.80]; P < 0.001).

No extended effect on cancer deaths or colorectal polyps was shown, and the group receiving alternate-day aspirin therapy reported more gastrointestinal bleeding (HR, 1.14 [CI, 1.06-1.22]; P < 0.001) and peptic ulcers (HR, 1.17 [CI, 1.09-1.27]; P < 0.001).

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