TUESDAY, Feb. 10 (HealthDay News) -- Prolonged use of low-dose aspirin or other nonsteroidal anti-inflammatory drugs (NSAIDs) appears to reduce the risk of precancerous lesions that can lead to colorectal cancer.

That's the conclusion of a new study of people at high risk for the disease.

"It's increasingly clear, and arguably proven, that NSAID drugs do interfere with the development of cancer in the large bowel," said study co-author Dr. John A Baron, a professor of both medicine and community and family medicine at Dartmouth Medical School.

"And this study," he added, "is a building block in our understanding of all that because it shows two things: One, if you take the NSAID drug for a while and then stop, you won't get a big rebound in terms of adenoma tumor risk. And two, if you don't stop taking an NSAID, but instead continue its use over time, the protective benefit will continue."

Baron and his colleagues presented their findings in the Feb. 18 issue of the Journal of the National Cancer Institute.

For the study, the researchers focused on people who had embarked on the long-term use of aspirin as part of the Aspirin/Folate Polyp Prevention Study. The more than 1,100 participants were considered at high risk for developing colorectal cancer because of a history of polyp development. After enrolling between 1994 and 1998, all were tracked for three years while regularly taking either 81 milligrams or 325 milligrams of aspirin, or a placebo.

The result: The low-dose aspirin reduced the risk of developing colorectal polyps.

Baron and his colleagues then continued to track 850 of the patients for an average of four years, until each underwent a follow-up colonoscopy. During this time, aspirin use was monitored and classified as either "sporadic" (less than two days a week), "moderate" (two to four days a week), or "frequent" (more than four days a week).

Patients who'd initially been assigned to low-dose aspirin in the first trial and continued to take the drug on a "frequent" basis had a 13 percent lower risk for developing precancerous lesions (known as colorectal adenomas), compared with those who had initially taken a placebo and then went on to use NSAIDs "sporadically." The risk difference between the two groups was approximately 27 percent versus 40 percent, the study found.