More Evidence Suggests Aspirin May Prevent Colorectal Cancer
Adapted from the NCI Cancer Bulletin.
While previous results have shown that aspirin and celecoxib (a selective COX-2 inhibitor) reduce the risk of colorectal adenomas and precancerous polyps in people at high risk, a new meta-analysis showed that both colorectal cancer and deaths from the disease may be reduced by long-term daily use of aspirin. The results were published online October 21, 2010, in The Lancet.
Peter Rothwell, M.D., Ph.D., of the University of Oxford and his colleagues calculated 20-year risk estimates by pooling data from more than 14,000 patients enrolled in five randomized trials conducted in the United Kingdom, Sweden, and the Netherlands. The trials were designed to study the effect of aspirin on the risk of heart attack and stroke, but cancer data were collected as well. The researchers found that patients who took at least 75 mg of aspirin daily for about 5 years had a 24 percent lower risk of colorectal cancer and a 35 percent lower risk of dying from the disease.
For those trials where data were available for sites within the colon, the preventive benefit of aspirin appeared to be confined primarily to the proximal colon, with a reduction in incidence of about 55 percent. Cancer incidence in the distal colon was not reduced. This distinction is important because colorectal cancer screening with sigmoidoscopy, the screening approach more commonly used in Europe, does not detect cancer in the proximal colon. (Although colonoscopy, the approach more commonly used in the United States, surveys the entire colon, its benefits may be limited mainly to the more distal part of the colon.)
The authors acknowledged a number of limitations to the study. They noted, for example, that they “did not model the effect of the reduction in deaths due to colorectal cancer on the overall balance of risk and benefit of long-term use of aspirin,” which can cause nausea, heartburn, and irritation and bleeding in the intestines, bowel, and stomach. In addition, they noted, the five trials included in the study “predated endoscopic screening for adenomas, which also reduces colorectal cancer incidence and mortality, and might therefore reduce the absolute benefit of aspirin.”
“These findings represent some of the longest follow-up data following 5 years of treatment,” said Ernest Hawk, M.D., of the University of Texas M. D. Anderson Cancer Center. “They also answer a long-standing question: what dose is required for a protective benefit? This study suggests that 75 mg is adequate.”