Summary

There is no consensus yet over what the interval should be between colonoscopy screens for colorectal cancer. Researchers have now monitored a group of people after a negative colonoscopy. During five years of follow up, there were no cases of cancer. Therefore, there is no need for a repeat colonoscopy within five years of having a negative result.

Introduction

Colonoscopy - the detailed examination of the colon with a miniature camera - is a proven method for picking up early cases of cancer and pre-cancer. The technique can detect not just tumors, but also polyps of various stages which may go on to develop into cancer. Once detected, these lesions can be removed promptly. Since colon cancer is one of the leading causes of cancer death, regular colonoscopy is recommended beyond the age of 50. However, it has not been clear how often colonoscopy ought to be repeated.

What was done

Researchers at Indiana University and the University of North Carolina, Chapel Hill, identified 2346 people with no adenomas at initial colonoscopy. The findings were classified as follows: no polyps, hyperplastic polyp, adenoma less than one centimeter in diameter, adenoma equal to or greater than one centimeter in diameter, other lesions with pre-cancerous properties, or cancer. They then rescreened half of them around five years later. The average age of the group was nearly 57 years and half were men.

What was found

No cancers were found on rescreening. One or more adenomas were found in 16 percent (201 people) of whom 16 had one or more advanced adenomas. The risk of having an advanced adenoma did not differ between those who had no polyps at the initial screen and those who did have polyps. Men were more likely than women to have any kind of adenoma and to have an advanced adenoma.

What this study means

Among people who have a negative result at initial colonoscopy, the risk of going on to develop colorectal cancer in the next five years is extremely low. We cannot say it is zero, even though no cases were found in the current study, because a large study may have found some cases. The risk of advanced adenoma is also extremely low, although higher among men than women. This study suggests a rescreening of five years or more would be appropriate following a normal colonoscopy. Repeating colonoscopy earlier than this is not justified, unless the person is at risk.