Understanding current guidelines for colorectal cancer screening: A case-based approach

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Adenomas: How many? How big? What features?

If adenomas are discovered, three key questions affect how soon the patient should undergo colonoscopy again (Table 2):

Winawer SJ, Zauber AG, Ho MN, et al. Prevention of colorectal cancer by colonoscopic polypectomy. The National Polyp Study Workgroup. N Engl J Med 1993; 329:1977–1981. Copyright © 1993 Massachusetts Medical Society. All rights reserved.

Figure 1. Observed cumulative incidence of colorectal cancer in the National Polyp Study6 compared with the expected incidence based on three reference groups.7–9

How many? Van Stolk et al34 analyzed colonoscopy results from 479 participants in the Polyp Prevention Study and found at 3 years’ follow-up that the strongest predictor of adenoma recurrence was the number of adenomas detected. On multivariate analysis, the finding of three or more adenomas during the baseline colonoscopy was an independent risk factor for having two or more adenomas on the subsequent colonoscopy. Only 3.3% of patients with one or two adenomas at baseline subsequently developed any clinically worrisome adenoma, compared with 6% of those with three or more adenomas.

Other studies also found that the number of adenomas predicts the subsequent development of more adenomas, and in particular advanced colorectal neoplasia.35–38

How big? Noshirwani et al35 retrospectively analyzed data from their adenoma registry and found that polyps 1 cm or larger were significantly associated with the finding of advanced adenomas 3 years later.

What features? Tubulovillous or villous features in an adenoma have been shown to increase the risk of future advanced adenomas and cancer.39,40 Similarly, high-grade dysplasia is associated with the subsequent development of advanced adenomas. In the Veterans Affairs Cooperative Study,41 10.9% of patients who had a polyp of any size with high-grade dysplasia developed an advanced neoplasm within 5 years, compared with only 0.6% of those with small polyps that did not harbor high-grade dysplasia.

Recognizing advanced adenomas is important when interpreting a patient’s colonoscopy results because multiple studies have shown them to predict recurrent advanced neoplasms or colorectal cancer.35,39–42

What does this mean for our patients?

If a patient (like our patient in case 2) who is otherwise at average risk is found to have an adenoma or adenomas without advanced features, the postpolypectomy surveillance interval should be dictated by the number of adenomas found. Current guidelines recommend that patients like this one—with one or two small tubular adenomas without features of advanced colorectal neoplasia—have a low risk of recurrent advanced adenomas and should undergo colonoscopy again in 5 to 10 years (Table 2).33

In contrast, in case 3, the polyp (which was completely removed) had two characteristics of advanced neoplasia: size larger than 1 cm and a villous component. This patient should come back in 3 years.

In colonoscopy, quality matters

An important caveat is that current post-polypectomy surveillance recommendations are based on the assumption that the bowel has been prepared adequately and that the entire colon is examined thoroughly up to the level of the cecum. Therefore, when deciding on the proper surveillance interval, one must take into account certain factors regarding the patient’s colonoscopy. Patients who have had an inadequate bowel preparation, incomplete examination, or large lesions removed piecemeal should be recalled at a shorter interval.

A final observation: another possible reason that patients are being sent back for repeat colonoscopy sooner than recommended is the concern for missed polyps. Nonpolypoid adenomas, which include flat and depressed lesions, can be easily missed using conventional endoscopy.43 A systematic review of six studies involving 465 patients who underwent tandem colonoscopy found a pooled miss rate of 26% for adenomas 1 to 5 mm.44 One way endoscopists can improve adenoma detection is to perform a slow endoscopic withdrawal over at least 6 minutes.45

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