Colorectal cancer (CRC) continues to be a prevalent problem in the United States, with 2012 statistics reporting more than 143,000 new cases and more than 53,000 CRC-related deaths. Despite increased insurance coverage for screening colonoscopy, we still have an unacceptably high incidence of CRC, as well as particularly disturbing data on interval CRC after someone has had a colonoscopy.
So, what is the problem? There are 2 key areas where we can make meaningful progress in the prevention of CRC-related mortality: the detection of serrated polyps, and the diagnosis of Lynch syndrome.
Differences in Proximal Serrated Polyp Detection Among Endoscopists Are Associated With Variability in Withdrawal Time
de Wijkerslooth TR, Stoop EM, Bossuyt PM, et al
Gastrointest Endosc. 2013;77:617-623
Serrated Polyps: What We See Is What We Get
It is estimated that the serrated cancers account for 10%-20% of CRC overall, but of greater importance, more than 30% of interval cancers (particularly in the right colon) are serrated cancers. This suggests that these serrated lesions are being missed, contributing to the incidence of CRC.
Between 20% and 30% of CRCs arise through a molecular pathway characterized by hypermethylation of genes, known as CpG island methylator phenotype (CIMP). The principal precursor of hypermethylated cancers is the sessile serrated adenoma. These polyps, although prevalent, are difficult to detect at endoscopy. These lesions may be the same color as the surrounding colonic mucosa, have indiscrete edges, are nearly always flat or sessile, and may have a layer of adherent mucus that obscures the vascular pattern.
According to the recently updated US Multisociety Task Force guidelines, a sessile serrated polyp 10 mm or larger and a sessile serrated polyp with dysplasia should be managed in the same way as a high-risk adenoma, whereas polyps lacking these features should be managed as a low-risk adenoma.
Variation in the rate of proximal serrated polyp detection has been evident among endoscopists. A recent prospective study from the Netherlands compared detection of proximal serrated polyps among experienced endoscopists, and identified patient- and procedure-related factors associated with the detection of these polyps. The investigators found an overall detection rate of 6%-22% for proximal serrated polyps and 24%-40% for adenomas. Associations were observed between detection of proximal serrated polyps and detection of colorectal neoplasia in the entire colon. Better detection of proximal serrated polyps was associated with higher adenoma detection.
When other factors, such as patient age, sex, quality of bowel preparation, and colonoscopy withdrawal time, were examined, only net withdrawal time (corrected by subtracting the time taken for polypectomy) was significantly associated with detection of proximal serrated polyps. Longer withdrawal times were significantly associated with better detection of both adenomas and serrated polyps. Studies from other centers of excellence in colonoscopy have also reported a wide range (1%-18%) of serrated polyp detection, although this rate was also highly correlated with the adenoma detection rate.
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