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Brian Bressler¹, Lawrence Paszat¹, Chris Vinden², Cindy Li¹, Jingsong He¹, Linda Rabeneck¹

Institute for Clinical Evaluative Sciences, University of Toronto, Toronto, Ontario¹, University of Western Ontario, London, Ontario²

BACKGROUND: Colonoscopy is the gold standard for the diagnosis of colorectal cancer (CRC). However, colonoscopy does contain an inherent miss rate for CRC. Previous reports that evaluated miss rates are from academic centers or units particularly known for their endoscopic expertise. The CRC miss rate of colonoscopy performed in the course of “usual clinical practice” is unknown.

OBJECTIVE: To conduct a population-based study to estimate the proportion of right-sided CRCs missed during colonoscopy in Ontario.

METHODS: We identified all individuals 18 years or older, with a new diagnosis of right CRC, defined as CRC in the ascending colon or cecum, admitted to hospital for surgical resection from 4/1/97 – 3/31/01. We identified all patients from this group who had a colonoscopy within 3 years prior to their diagnosis and divided them into two. The first group (detected cancers) consisted of individuals who had a colonoscopy within 6 months prior to the diagnosis (in this group we assumed the colonoscopy identified the cancer). The other group (missed cancers) consisted of those who had a colonoscopy 6-36 months prior to the diagnosis (in this group we assumed the colonoscopy missed the cancer). Data were obtained from the Canadian Institute for Health Information Discharge Abstract Database and from the Ontario Health Insurance Plan database.

RESULTS: Between 4/1/97 – 3/31/01 we identified 19,202 patients with a new diagnosis of CRC who were admitted to hospital for surgical resection of whom 4,920 (25.6%) had right CRC. The mean age was 71.5±11.3 yrs, and 54.5% were women. Of the patients diagnosed with right CRC, 2,654 (53.9%) individuals had at least one colonoscopy within 3 years of their admission for surgical resection. The majority (96.0%) had their most recent colonoscopy within 6 months prior to admission (detected cancers). However, 105 patients (4.0%) had their most recent colonoscopy 6-36 months prior to admission to hospital (missed cancers). Of these 105 patients, only 6 had a barium enema in the immediate 6 months after the colonoscopy.

CONCLUSION: Among individuals undergoing resection for right CRC, the miss rate of colonoscopy for detecting the cancer in “usual clinical practice” is 4%.

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