September 2, 2005

Long-term aspirin use reduces risk for colorectal cancer

A new report from the Nurses' Health Study (NHS) finds that regular, long-term aspirin use can significantly reduce the risk of colorectal cancer. However, the benefit appears to require more than a decade of use and is strongest at dose levels associated with a greater risk of side effects. The report from researchers at the MGH, BWH and Dana-Farber Cancer Institute appeared in the Aug. 24 issue of the Journal of the American Medical Association.

"Several studies have found that, among patients with a history of colon polyps or cancer, regular aspirin treatment prevents the recurrence of polyps," says Andrew Chan, MD, MPH, of the MGH Gastrointestinal Unit and the paper's lead author. "However, the ability of aspirin to reduce the long-term incidence of cancer has not been well-demonstrated."

The report analyzes information from almost 83,000 NHS participants, among which 962 cases of colorectal cancer were diagnosed during the 20-year study period. While the rate of cancer was lower in the women who took aspirin regularly, the risk reduction was significant only for those taking aspirin 10 years or longer.

The benefit increased as dosage levels rose, with the greatest reduction seen in those taking more than 14 standard tablets per week. Similar results were seen for participants taking non-steroidal anti-inflammatory drugs (NSAIDS) such as ibuprofen and naproxen. The risk of serious gastrointestinal bleeding, a known side effect of both classes of drug, also rose as dosage levels increased, with bleeding occurring nearly twice as often in those taking the highest doses.

"Before we can make recommendations about whether patients should take these medications to reduce their cancer risk, we're going to need studies that clarify the risks and benefits of such an approach," says Chan. "For now, individuals need to discuss the options with their physicians."

Chan and his colleagues have already initiated studies to further clarify the impact of long-term use of aspirin and NSAIDs.