THE QUESTION: For more than a hundred years, people have turned to aspirin for pain relief. In the past two decades, it has become a tool in the fight against heart disease. Now researchers think it could prevent some cancers. Might colorectal cancer be one of them?

THE QUESTION: For more than a hundred years, people have turned to aspirin for pain relief. In the past two decades, it has become a tool in the fight against heart disease. Now researchers think it could prevent some cancers. Might colorectal cancer be one of them?

THIS STUDY: It analyzed data on 7,588 men who had participated in two studies in which they were randomly assigned to take aspirin (300 to 1,200 milligrams) or no aspirin daily for one to seven years. After 20 years, colorectal cancer had been diagnosed in 215 men. Overall, those who had taken aspirin for five years were 37 percent less likely to have cancer than men who had not taken aspirin. The effect was not apparent for 10 years, the minimum time it generally takes for intestinal polyps to become cancerous. It was greatest after 10 to 14 years, when men who had taken aspirin for at least five years had a 63 percent lower risk for cancer than the no-aspirin group.

WHO MAY BE AFFECTED? Men. Although colorectal cancer can occur at any age, 90 percent of people with the disease are 50 or older. Those with a family history of the cancer or who have inflammatory bowel disease also face an increased risk.

CAVEATS: Whether the findings apply to women was not determined. Side effects such as anemia, gastrointestinal bleeding and constipation were more common among those taking aspirin. Lower doses, which generally have fewer side effects, were not tested.

FIND THIS STUDY: It's in the May 12 issue of the Lancet.

LEARN MORE ABOUT colorectal cancer at www.nihseniorhealth.gov and www.cancer.org.

The research described in Quick Study comes from credible, peer-reviewed journals. Nonetheless, conclusive evidence about a treatment's effectiveness is rarely found in a single study. Anyone considering changing or beginning treatment of any kind should consult with a physician.