World Gastroenterology Organisation

Global Guardian of Digestive Health. Serving the World.


Where We Miss Cancers During Colonoscopy

Review by Prof. Mark Topazian (USA)

Study Summary 

Post-colonoscopy colorectal cancer (PCCRC) refers to colorectal cancers diagnosed 6 to 48 months after a negative colonoscopy. PCCRC rates of 3% to 5% of all CRC have been previously reported. In this study, investigators used a national Danish registry to identify cases of PCCRC, and categorized them as either A) possible missed lesion, prior examination adequate, B) possible missed lesion, prior examination inadequate, C) detected lesion, not resected, or D) likely incomplete resection of previously identified lesion. Colonoscopy was considered adequate if the bowel preparation was recorded as excellent, good or fair, and the cecum was reached.

Of the 762 PCCRCs, 31% were located in the cecum or ascending colon, 9% were in a flexure, and 23% were located in the rectum. 81% were category A (possible missed lesion, prior exam reported as adequate); categories B, C and D comprised 5%, 3% and 11%, respectively.


This study confirms previous reports that the right colon and rectum are the commonest sites for PCCRC. The great majority of PCCRCs occurred after a colonoscopy deemed adequate by the endoscopist. Several factors likely contributed to this finding, including quality of bowel preparation, withdrawal time (not evaluated in this study), completeness of polypectomy and colonoscopy technique. The study suggests that even “fair” bowel preparation may not be good enough to adequately exclude CRC. Expert recommendations aimed at decreasing the rate of PCCRC include either performing a retroflexed examination of the right colon or examining the right colon twice, and examining the rectum using both antegrade and retroflexed views.


Troelsen FS, et al. Root-cause analysis of 762 post-colonoscopy colorectal cancer pateints. Clin Gastroetnerol Hepatol 2023:21, 3160-3169.

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