Why Do People Still Develop Colorectal Cancer After Colonoscopy?

Some people who receive screening colonoscopies are still at risk for colorectal cancer (CRC) because neoplastic polyps found are not completely removed, according to the January issue of Gastroenterology. While the quality of colonoscopy examinations has focused on polyp detection, better methods are needed to evaluate polyp removal.

The goal of screening colonoscopies is to detect and remove precancerous lesions (adenomatous polyps). This strategy has been reported to reduce the incidence of CRC by 77% and CRC-related deaths by up to 37%, compared with individuals who do not receive colonoscopy examinations. But why do many patients who had polyps removed during colonoscopy still develop cancer?

Incomplete resection of lesions during colonoscopy has been estimated to account for 10%–27% of cancers that develop later in patients.

Heiko Pohl et al. investigated the proportion of incompletely resected neoplasms and factors that could contribute to this problem. After polyps (5–20 mm) were removed from 269 patients undergoing colonoscopy examination, biopsy samples were collected from the sides of the removal site and analyzed for residual adenomatous tissue.

Of 346 neoplastic polyps removed, Pohl et al. found that 10.1% of the removals were incomplete. The rate of incomplete resection increased with polyp size, and was about 2-fold higher for large (10–20 mm) than small (5–9 mm) neoplastic polyps. Furthermore, incomplete removal was almost 4-fold higher for sessile serrated adenomas or polyps than conventional adenomas.

Interestingly, Pohl observed a wide range in the rate of incomplete resection among experienced endoscopists—for the 5 endoscopists who performed at least 20 polyp resections, the rates of incomplete resection ranged from 6.5% to 22.7% (see below figure).

Rates of incompletely resected neoplastic polyps for endoscopists with at least 20 polyp resections and risks of incomplete resection for individual endoscopists compared with the endoscopists with the lowest incomplete resection rate (Endoscopist A). Relative risks (RRs) are adjusted for size and diagnosis of sessile serrated adenoma/polyp.

Rates of incompletely resected neoplastic polyps for endoscopists with at least 20 polyp resections and risks of incomplete resection for individual endoscopists compared with the endoscopists with the lowest incomplete resection rate (Endoscopist A). Relative risks (RRs) are adjusted for size and diagnosis of sessile serrated adenoma/polyp.

In an editorial that accompanies the article, Charles Kahi and Douglas Rex state that this rate of incomplete polypectomy is alarming, considering that the endoscopists participating in the project were aware of the study aims, and probably scrutinized polyp resection margins carefully. So the 10% rate of incomplete resection likely underestimates the true magnitude of the problem in clinical practice.

Pohl et al. state that incomplete polyp resection might contribute to the development of interval CRC following a complete colonoscopy. They explain that variations in endoscopists’ technique and time spent to examine the polypectomy site likely affect the efficacy of the procedure. Polyp resection is not a standardized technique—different endoscopists may use different methods to remove tumors.

They call for efforts to improve resection of neoplastic polyps—especially for large and sessile serrated polyps and adenomas. Pohl et al. propose focusing efforts on preparation for resection, the resection technique, and assessments of complete polyp removal. Polyp margins might be further evaluated using narrow-band imaging, chromoendoscopy, or endomicroscopy techniques.

Read the article online.
Pohl H, Srivastava A, Bensen SP, et al. Incomplete polyp resection during colonoscopy—results of the complete adenoma resection (CARE) study. Gastroenterology 2013;144:74−80.e1.

Read the accompanying editorial.
Kahi CJ, Rex DK. Why we should CARE about polypectomy technique. Gastroenterology 2013;144:16−18.

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About Kristine Novak, PhD, Science Editor

Dr. Kristine Novak is the science editor for Gastroenterology and Clinical Gastroenterology and Hepatology, both published by the American Gastroenterological Association. She has worked as an editor at biomedical research journals and as a science writer for more than 12 years, covering advances in gastroenterology, hepatology, cancer, immunology, biotechnology, molecular genetics, and clinical trials. She has a PhD in cell biology and an interest in all areas of medical research.
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One Response to Why Do People Still Develop Colorectal Cancer After Colonoscopy?

  1. Philip Wight says:

    Would the use of post-polypectomy argon reduce the likely hood of CRC developing from these poorly removed neoplastic polyps?

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