Taking daily aspirin for as little as three years was shown to reduce the development of colorectal polyps by 19 percent to 35 percent in people at high risk for colorectal cancer in two randomized, controlled clinical trials published in today's New England Journal of Medicine. These data confirm numerous, earlier observational studies that suggested that people who regularly take aspirin have lower rates of colorectal adenomas. Adenomas are abnormal growths (polyps) that are a critical midpoint in the development of most colorectal cancers.

"These trials are very encouraging because they prove that we can disrupt the development of colorectal cancer by preventing the polyps that can become cancer," said Ernest Hawk, M.D., M.P.H, chief of the Gastrointestinal and Other Cancers Research Group in the National Cancer Institute's Division of Cancer Prevention. "If we can prevent adenomas from forming, we believe we ultimately can reduce colorectal cancers and colorectal cancer deaths."

Epidemiologic studies have shown that people who regularly take aspirin and aspirin-like drugs to treat conditions such as arthritis have lower rates of colorectal polyps, colorectal cancer, and colorectal cancer deaths. Based on these promising epidemiologic data, as well as animal models and laboratory data, NCI supported both of today's trials, in which people were randomly assigned to aspirin or a placebo and followed for a number of years. NCI continues to support clinical trials of other prevention agents that may work in similar ways; current studies are looking at agents alone and in combination to prevent or reverse the growth of precursors of colorectal cancer in people at increased risk due to adenomas, early stage colon cancer, or certain inherited syndromes.

The data published today suggest that daily aspirin may be an appropriate supplement to regular surveillance procedures in individuals at an increased risk of colorectal cancer similar to the level of risk in the people in these trials. Trial participants were adult men and women with either a previous colorectal adenoma or previous early-stage cancer successfully treated with surgery.

Long-term aspirin therapy is not appropriate for everyone: most people do not have the same elevated risk for developing colorectal cancer as the people in these trials, and aspirin, like many drugs, can have side effects. All people age 50 and older should continue to get colorectal cancer screening exams regularly.

The trials published today were carried out by a research network headed by John A. Baron, M.D., of the Norris Cotton Cancer Center, Lebanon, N.H., and by the Cancer and Leukemia Group B, with Robert Sandler, M.D., M.P.H., of the University of North Carolina, Chapel Hill.