Dr. John Baron was lead author of the article, and co-author of another report in the NEJM that also found that aspirin protected against adenomas of the colon and rectum. He noted that the findings of the two studies show that low doses of aspirin do protect against the pre-cancerous polyps, and so there is good reason to believe aspirin probably reduces rates of colorectal cancer itself. This will be particularly valuable for people who are at increased risk for cancer because they have had colon adenomas (polyps) or because they have previously been treated for colorectal cancer.

The randomized, double-blind study, conducted between 1994 and 2001, looked at over 1100 patients with previously diagnosed colorectal adenomas. Some patients received aspirin – either 81 mg or 325 mg – while others received a placebo. Interestingly, the group receiving the smaller dose of aspirin – 81-mg, or the equivalent of one baby aspirin – showed a lower incidence of recurring polyps than did those treated with the larger dose of aspirin – 325 mg or the equivalent of a standard adult aspirin.

Overall, those treated with a daily dose of baby aspirin found their risk of polyps reduced 19 percent and their risk of advanced lesions reduced by more than 40 percent.

The companion study, conducted among patients with a history of cancer of the colon or rectum, tested a regular aspirin tablet (325 mg) against placebo. It showed even larger reductions in the occurrence of adenoma – about a 35% reduction.

Although aspirin is generally a safe drug, Baron noted that it can have adverse effects for some individuals. Before people embark on a daily aspirin regimen, they should check with their doctor, he said. And, he stressed that just taking aspirin is not enough to assure freedom from colon cancer.

"Aspirin is not a magic bullet. Although the incidence was reduced, all the polyps didn't go away in our study. Regular screenings, perhaps including colonoscopies, are still important."