A combined analysis of three randomized controlled trials that compared taking aspirin to a placebo after adenomas were removed found that people who took a daily low dose or baby aspirin had almost a 20 percent lower chance of another adenoma during their next colonoscopy.  High-dose or regular adult strength aspirin reduced risk of polyp recurrence by about 15 percent.

Any aspirin reduced the risk of advanced adenomas by more than 35 percent.

Advanced adenomas include polyps over 10 millimeters or polyps that are especially risky for developing into cancer including those with significant villous features,high-grade dysplasia, or early invasive cancer.

In the three studies, over 2300 people with polyps on their initial colonoscopy were randomly assigned to aspirin or a placebo in the three studies, and 2,175 had a second colonoscopy to look for new polyps.

F. Gao and colleagues concluded,

This meta-analysis suggests that aspirin prevents recurrent colorectal adenomas among patients with a history of colorectal adenomas.

SOURCE:  Gao et al., Colorectal Disease, Volume 11, Number 9, November, 2009.

Even if a second colonoscopy, done three years after the first, showed no adenomas at all, 8 in 100 study participants with high-risk polyps on their first exam had developed a high-risk polyp by six years when they had a third colonoscopy.

In the Aspirin/Folate Colorectal Polyp Prevention Study, 564 participants had three colonoscopies:  one at the beginning of the study, one three years later, and a third three years after that.  All of the people in the study had at least one polyp at the beginning of the study, but not all had polyps considered to be high-risk.

High risk patients had an adenoma 1 centimeter or larger, three or more adenomas, or a polyp with advanced pre-cancerous changes.

• Patients whose first colonoscopy had high risk polyps but had no adenomas at all on a second study, had a 7.7 percent chance that their third exam would reveal a high-risk polyp.
• Those with initial high-risk adenomas and a low-risk second exam had a 1 in 10 chance of a high-risk third exam.
• Those who were low-risk on both a first and second colonoscopy had a less than 5 percent chance of having a high-risk polyp found during the third exam.
• Patients were were high risk at their second exam had a 1 in 5 (20 percent) chance that an advanced polyp would be found during their third test.  For these patients, it made no difference whether they were high or low risk with their first colonoscopy.

Douglas J. Robertson, MD, MPH, and colleagues concluded,

Information from 2 previous examinations may help identify low-risk populations that benefit little from intense surveillance. Surveillance guidelines might be tailored in selected patients to use information from 2 previous examinations, not just the most recent one.

SOURCE: Robertson et al., Annals of Internal Medicine, Volume 151, Issue 2, July 21, 2009.

Analyzing published studies of blood levels of vitamin D, researchers found a 30 percent decrease in the risk of adenomas among people with the most circulating vitamin D compared to those with the least.  The highest vitamin D intake decreased adenomatous polyp risk by 11 percent.

In addition, there appeared to be an even stronger relationship between both blood levels and vitamin D intake for advanced adenomas, with the highest risk of cancer.  Higher blood levels decreased risk of advanced adenomas by 46 percent, greater intake of vitamin D by 23 percent.

Melissa Wei and her colleagues concluded,

Both circulating 25(OH)D and vitamin D intake were inversely associated with colorectal adenoma incidence and recurrent adenomas. These results further support a role of vitamin D in prevention of colorectal adenoma incidence and recurrence.

SOURCE: Wei et al., Cancer Epidemiology, Biomarkers, and Prevention, Volume 17, Number 11, November 2008.