Flat polyps may explain colorectal cancer screening discrepancy

Jun 27 2012

By Lynda Williams

Poor ability to detect sessile serrated polyps (SSPs) may explain why endoscopy is more effective at reducing cancer in the distal than the proximal colon, US researchers have discovered.

The team found that in a population of patients aged 50-75 years, receipt of previous endoscopy was associated with a significant reduction in the overall likelihood for detecting colorectal polyps at the index procedure, which occurred between 1998 and 2007 (odds ratio [OR]=0.36).

This was true when considering polyps in the rectum/distal colon (OR=0.38), or proximal colon (OR=0.31), and did not significantly differ between colonoscopy and sigmoidoscopy.

By contrast, there was no significant association between prior endoscopy and the likelihood for detecting SSPs (OR=0.80), possibly because these flat lesions are more difficult to detect than pedunculated or protruding advanced adenomas.

"Our results support the hypothesis that the effect of endoscopy differs between advanced adenomas and SSPs," say Andrea Burnett-Hartman (Fred Hutchinson Cancer Research Center, Seattle, Washington) and co-authors.

"This may have implications for proximal colon cancer prevention and may be due to the failure of endoscopy to detect/remove SSPs, or the hypothesized rapid development of SSPs."

The study examined pathology reports from 213 patients with advanced adenoma (10 mm in diameter with 20% villous component or high-grade dysplasia), 172 patients with SSPs (exaggerated crypt serration, dilatation or branching, or other distortions), and 1704 patients with no findings on their index examination.

Just over half of the patients (54%) had at least one previous sigmoidoscopy before the index procedure, 13% had colonoscopy, and 15% had undergone both types of examination.

Writing in the American Journal of Gastroenterology, the team concludes: "There is now a growing awareness of the importance of SSPs, and future studies should assess whether this increased vigilance for SSPs results in better effectiveness of endoscopy for the prevention of SSPs, and more importantly, proximal colon cancer."

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