May 10, 2007 -- Five years of daily, full-dose aspirin cuts colon cancer risk by as much as 74%, a U.K. study suggests.
The finding contradicts earlier U.S. studies that saw no effect of aspirin on a person's risk of getting colon cancer.
University of Oxford researchers Enrico Flossman, MRCP; Peter M. Rothwell, MD, PhD; and colleagues studied the effects of aspirin by combining data from two large clinical trials. Neither trial was specifically designed to study colon cancer.
However, pooled data from the studies suggests that people who took a full-dose aspirin tablet every day for at least five years had as much as a 74% lower risk of colon cancer 10 to 14 years later. In the U.S., a full-dose aspirin tablet contains 325 milligrams of the drug.
"Randomized trials show that regular use of at least 300-milligram aspirin daily for about five years seems to be effective in the primary prevention of colorectal cancer, with a latency of about 10 years," Flossman and colleagues conclude.
Aspirin can help prevent heart attack in high-risk individuals, but it can have life-threatening side effects. Nobody should take aspirin regularly without a doctor's advice. Usually, doctors recommend low-dose or baby aspirin for disease prevention.
That may be why U.S. studies found no link between aspirin use and colon cancer. One major study looked at doses of 162.5 milligrams; the other looked at doses of 50 milligrams.
"Lower or less frequent doses of aspirin (than 300 milligrams per day) might be less effective, but long-term follow-up of randomized trials of low-dose aspirin is needed," Flossman and colleagues suggest.
The Flossman study appears in the May 12 issue of The Lancet. An editorial by Andrew T. Chan, MD, MPH, assistant professor of medicine at Harvard Medical School in Boston, accompanies the report.
"These findings are not sufficient to warrant a recommendation for the general population to use aspirin for cancer prevention," Chan warns. "More work is needed to characterize those for whom the potential benefits of aspirin outweigh the hazards."