Study Supports Role of Aspirin in Reducing Risk of Colorectal Cancer

A new study has found that regular intake of aspirin does appear to be associated with a reduced risk of the type of colon polyps that can develop into cancer. However, since risk reduction was strongest with aspirin doses higher than those used to prevent cardiovascular disease, the researchers say further study is needed to determine for whom the benefits of such treatment would outweigh any potential risks.

The report – from researchers at Massachusetts General Hospital (MGH), Brigham and Women's Hospital and affiliated institutions – appears in the journal Annals of Internal Medicine.

"We would love to have a simple, daily tablet that could reduce the risk of colorectal cancer for everyone, but right now we don't have that," says Andrew Chan, MD, of the MGH Gastrointestinal Unit, the paper's lead author. "However, confirming that aspirin, especially at higher doses, may reduce cancer risk is very exciting and opens many avenues of research for better understanding the mechanism of this disease."

Earlier studies at a number of centers suggested that aspirin could reduce the risk of colorectal polyps but had not established the most effective dose. The current investigation is part of the Nurses Health Study, which has followed more than 120,000 female registered nurses since the mid–1970s, asking them to complete a questionnaire on risk factors for cancer and cardiovascular disease every two years. In 1980, assessments of diet, aspirin use, and colon examination were added to the NHS questionnaire.

The report in Annals examines data from about 27,000 Nurses Health Study participants, ages 34 to 77 with no history of cancer, who reported having endoscopic colon examinations between 1980 and 1998. Among that study group, almost 1,400 participants were diagnosed with adenoma – a type of colorectal polyp that may develop into cancer – during the 18–year period.

Participants who reported taking aspirin regularly had a 25 percent lower risk of adenoma than did women who took no aspirin, with the lowest risk seen among those who took more than two standard aspirin tablets per day. Current guidelines for heart disease prevention suggest that low doses – one baby aspirin tablet per day – are as effective as higher doses. The authors caution that high doses of aspirin have been shown to pose a greater risk of side effects such as bleeding.

"Before these findings can be translated into clinical recommendation, we need better ways of identifying exactly who should take aspirin to reduce colorectal cancer risk," says Chan, a research fellow at Harvard Medical School. "Other potential risk factors or genetic markers could be associated with levels of benefit that might outweigh the risks posed by higher doses of aspirin. Until those questions are answered, people should follow current screening recommendations, which are proven to save lives."

SOURCES:
Annals of Internal Medicine, February 2004
Massachusetts General Hospital (http://www.mgh.harvard.edu)

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