Post-polypectomy and post-cancer resection surveillance are the most common indications for performing colonoscopy.¹ A summary of the new guidelines on colonoscopy surveillance for patients with these indications appears in this issue of American Family Physician.² Developed jointly by the U.S. Multi-Society Task Force on Colorectal Cancer and the American Cancer Society, and endorsed by the major U.S. gastrointestinal organizations, these new guidelines were made to clarify inconsistencies in previous guidelines and to provide a stronger consensus on when to refer patients for repeat colonoscopy. Studies have shown that a large number of patients have been referred for repeat colonoscopy sooner than appropriate, which raises the concern that more resources are potentially being drained from screening colonoscopies.^3,4 These guidelines are intended to help correct the disparity between patients who have too many colonoscopies and those who have too few or none at all.

What do the new guidelines recommend for post-polypectomy surveillance? Essentially, they place patients into one of three groups: no-risk, low-risk, or high-risk for developing colorectal neoplasia, based on the results of their initial screening colonoscopy. Patients in the no-risk group may have small rectal hyperplastic polyps and should have a repeat colonoscopy in 10 years. Patients in the low-risk group have one or two small adenomas that are smaller than 1 cm and have no or only low-grade dysplasia; they should have a repeat colonoscopy in five to 10 years. Patients in the high-risk group have three or more adenomas or polyps 1 cm or larger, or high-grade dysplasia, and should have a repeat colonoscopy in three years.

Several other complex issues are also addressed in the guidelines, such as patients with hereditary nonpolyposis colorectal cancer, patients with more than 10 adenomas, those who have had a piecemeal polypectomy, and the quality of the colonoscopy.

What do the new guidelines recommend for surveillance after colorectal cancer resection? The initial endoscopic evaluation should be complete and thorough. If an obstructing lesion prevents a high-quality clearing colonoscopy, one should be performed three to six months after resection. Subsequent colonoscopies should occur one, three, and five years from the resection, unless findings warrant an earlier examination. In patients with rectal cancer, local endoscopic examinations every three to six months for two to three years after the resection are important to evaluate for metachro-nous disease (i.e., neoplasia that develops after the initial lesion).

It is important to keep in mind that colonoscopy is not perfect. In rare circumstances, patients undergoing surveillance may develop high-risk lesions or cancer much sooner than would be expected after colonoscopy.^5,6 Current evidence suggests that this may be the result of incomplete polyp removal, missed lesions, and rapidly evolving cancers. The gastroenterolo-gist must assess the quality of the baseline colonoscopy (i.e., quality of the preparation, completeness of polyp removal, and withdrawal time) and make recommendations to the patient and primary care physician. Physicians should use these new guidelines to determine when to repeat colonoscopy. No studies have shown a benefit to repeat colonoscopy sooner than guideline recommendations. The fact remains that the first screening colonoscopy is the most effective in reducing the incidence of colorectal cancer in patients with adenomatous polyps.⁷

These guidelines likely will continue to evolve for two reasons. First, new follow-up data on patients who have adenomas and cancer continue to be presented. Studies that were released after these guidelines continue to support the current risk-stratification classification⁸; however, as our understanding of tumor biology improves, guidelines will certainly change. Second, as more data are presented on newer screening and surveillance methods, especially computed tomography colonography, guidelines will need to address when and how to appropriately follow these patients, based on findings.