Related Pages Colon and Rectal Cancer Home Page 1 NCI's gateway for information about colon and rectal cancer.

Key Words: adenoma, aspirin, colon, precancerous polyps. (Definitions of many terms related to cancer can be found in the Cancer.gov Dictionary ².)

A daily baby aspirin reduced by 19 percent the risk that precancerous polyps (adenomas) in the colon would recur in patients who'd had a previous adenoma surgically removed, researchers reported April 7, 2002, at the American Association for Cancer Research annual meeting in San Francisco. Adenomas are early signs of abnormal colon growth that can progress to colorectal cancer. [Editor's note: The results of this study were subsequently published. See NCI-Funded Clinical Trials Show Aspirin Reduces Recurrence of Polyps ³.]

In patients with advanced adenomas or colorectal cancer, the same daily low-dose aspirin -- 80 milligrams -- reduced the risk of advanced adenoma recurrence by 40 percent.

A daily aspirin dose of 325 milligrams had a lesser preventive effect, according to the researchers, reducing the overall risk of adenoma recurrence by 4 percent and the risk of recurrence of advanced adenomas and colorectal cancers by 19 percent.

"We conclude that aspirin may have a modest chemopreventive effect in the large bowel, apparently more marked for lower-dose aspirin," said John A. Baron, M.D., professor of medicine at Dartmouth Medical School in Lebanon, N.H., who led the research group that conducted the study.

This is the first clinical trial to show that aspirin has a preventive effect on the process of colorectal cancer development, said Ernest Hawk, M.D., chief of the gastrointestinal and other cancers research group at the National Cancer Institute in Bethesda, Maryland.

"These results suggest that Americans who are already taking a daily low-dose aspirin to reduce their risk of a heart attack or stroke may be getting an additional benefit -- a reduced risk of colorectal cancer -- without being aware of it," Hawk said.

Daily low-dose aspirin may be an appropriate supplement to regular screening procedures for colorectal cancer in individuals who are at moderate risk for the disease because they have had a prior adenoma, Hawk said. However, he added, it is premature to recommend aspirin to reduce the risk of colorectal cancer in all Americans over age 50. People in this age group are at mildly elevated risk for the disease because of their age alone.

The current study involved 1,121 patients who were randomly assigned to take 80 milligrams of aspirin (one baby aspirin), 325 milligrams of aspirin (one standard aspirin), or a placebo (dummy pill) daily. Patients were screened for recurrent adenomas with a follow-up colonoscopy (examination of the colon) a minimum of one year after entering the study. The average time to this follow-up was 34 months. Patients were eligible for the study if they had had at least one adenoma removed within the preceding three months, had no known cardiovascular disease or other conditions usually treated with aspirin, and had no hereditary cancer syndromes.

The new study confirms a large, consistent body of evidence from observational studies and animal models that aspirin and other non-steroidal anti-inflammatory drugs (NSAIDs) can reduce the incidence of colorectal adenomas and colorectal cancer deaths. The finding that aspirin reduced recurrence of advanced adenomas strongly suggests, Hawk said, that the drug may be significantly slowing progression of these precancerous tumors.

However, the finding that a low dose of aspirin had a greater preventive effect than a standard dose is unexpected, Hawk added. The study results will have to be analyzed carefully for a possible explanation.

Colorectal cancer is the second leading cause of death from cancer in the United States. An estimated 56,600 Americans will die from the disease this year. Roughly a third of those deaths could be avoided by regular screening tests to detect and remove adenomas before they turn into cancer. Several types of tests can be used, alone or in combination, to screen for colorectal cancer. Regular screening is recommended for all Americans aged 50 and older, and earlier if family members have a history of colorectal adenomas or cancer.

Glossary Terms

A noncancerous tumor.

The use of drugs, vitamins, or other agents to try to reduce the risk of, or delay the development or recurrence of, cancer.

The longest part of the large intestine, which is a tube-like organ connected to the small intestine at one end and the anus at the other. The colon removes water and some nutrients and electrolytes from partially digested food. The remaining material, solid waste called stool, moves through the colon to the rectum and leaves the body through the anus.

A type of study in which individuals are observed or certain outcomes are measured. No attempt is made to affect the outcome (for example, no treatment is given).

Growths that protrude from a mucous membrane. Precancerous polyps may (or are likely to) become cancer.

A study in which the participants are assigned by chance to separate groups that compare different treatments; neither the researchers nor the participants can choose which group. Using chance to assign people to groups means that the groups will be similar and that the treatments they receive can be compared objectively. At the time of the trial, it is not known which treatment is best. It is the patient's choice to be in a randomized trial.