Even among those people who have had pre-cancerous growths on previous colonoscopies, waiting ten years after two negative such tests could be safe, according to a new study.

The United States Preventive Services Task Force recommends colonoscopy every ten years starting at the age of 50, as a screening test for colon cancer. However, it was unclear whether those with clean colonoscopies after earlier tests that had shown precancerous growths could wait that long between exams.

Dr. Douglas J. Robertson from the Veterans Affairs Medical Center in White River Junction, Vermont, and co-authors looked at 564 patients whose colonoscopies had revealed precancerous growths known as adenomas and who then had a second examination about three years later. If that second exam, or a third one, found cancer, the patients were excluded.

Dr. Robertson's group reports in the Annals of Internal Medicine that high-risk adenoma findings were found in just 5 percent of patients with low-risk findings on the first two colonoscopies. That compared with 18 percent of patients with high-risk adenomas on both previous colonoscopies, and 20 percent of patients with low-risk baseline examination and high-risk adenomas at the second exam, and 12 percent of those with high risk findings at baseline and no adenomas on the second.

Given that relatively few participants...with low-risk findings on their first 2 examinations had high-risk results on their third colonoscopy....a longer follow-up interval may be appropriate for this...much larger group, the researchers said.

Our results, the investigators conclude, may provide clinicians with a rationale to suggest a 10-year surveillance interval in this lowest-risk group.

However, they suggest, A risk profile based on multiple examinations might better delineate high- and low-risk patients than a single examination.

SOURCE: Annals of Internal Medicine, July 21, 2009.