Colonoscopy contains an inherent miss rate for colorectal cancer. Although miss rates from academic centers or units known for their endoscopic expertise have been previously reported, the colorectal cancer miss rate of colonoscopy performed in usual clinical practice is unknown. As such, researchers conducted a population-based study to estimate the proportion of right-sided colon cancers missed during colonoscopy in Ontario.

All persons greater than 20 years old with a new diagnosis of right-sided colon cancer admitted to the hospital for surgical resection in Ontario from April 1, 1997, to March 31, 2001, were identified. Patients who had a colonoscopy within 3 years of their diagnosis were divided into 2 groups: detected cancers (those who had a colonoscopy up to 6 months before the diagnosis) and missed cancers (those who had a colonoscopy between 6 and 36 months before the diagnosis). Data were obtained from the Canadian Institute for Health Information Discharge Abstract Database, the Ontario Health Insurance Plan database, and the Registered Persons Database.

Between April 1, 1997, and March 31, 2001, researchers identified 4920 persons with a new diagnosis of right-sided colon cancer, of whom 2654 (53.9%) had had at least 1 colonoscopy within 3 years of their admission for surgical resection. Most (96.0%) had had their most recent colonoscopy up to 6 months before admission (detected cancers). However, 105 patients (4.0%) had their most recent colonoscopy between 6 and 36 months before admission to the hospital (missed cancers).

Among persons undergoing resection for right-sided colon cancer, the miss rate of colonoscopy for detecting cancer in usual clinical practice was 4.0%.