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Colonoscopy misses detecting some colon cancers


A new study from the Institute for Clinical Evaluative Sciences (ICES) shows that colonoscopy, the preferred method to screen for colorectal cancer, can miss detecting a concerning number of cases of colorectal cancer (CRC).

ICES researchers identified all adults with a new diagnosis of right-sided CRC admitted to hospital for surgical resection of the cancer in Ontario between 1997 and 2001. Patients who had a colonoscopy within three years of their diagnosis were divided into two groups: detected cancers (those who had a colonoscopy up to six months before the diagnosis), and missed cancers (those who had a colonoscopy between six months and 3 years before the diagnosis).

Among the nearly 5,000 patients with a new diagnosis of right-sided CRC, 54% had at least one colonoscopy within three years of their hospital admission for surgical resection. The majority of these patients (96%) had their most recent colonoscopy up to six months before hospital admission (detected cancers). However, 4% of patients had their most recent colonoscopy between six and 36 months before admission to hospital (missed cancers).

“Although this may seem like a small number of missed cancers, it represents over 100 people over the course of the study period in Ontario alone who, if their cancer was detected earlier, could have had better odds for successful treatment and outcomes,” said senior author and ICES senior scientist Dr. Linda Rabeneck.

“Moreover, because there has been such a marked increase in the use of colonoscopy to screen for colorectal cancer, it’s vital that we are documenting the procedure’s accuracy in clinical practice and identifying ways to improve it.

“As well, as an increasing proportion of new cases of CRC are right-sided, the sensitivity of colonoscopy for detecting right-sided CRC is increasingly important.”

Dr. Rabeneck points to several reasons for colonoscopic miss rates, such as an inability to reach the lesion, inadequate bowel preparation, small cancerous lesions, and physician error in identifying the proper area of the colon that needs to be inspected. “In addition, it is possible that some of these missed cancers had extremely fast growth rates and were not detectable at the time of the colonoscopy,” she added.

The study, “Colonoscopic miss rates for right-sided colon cancer: a population-based analysis”, is in the August 2004 issue of the journal Gastroenterology.

Author affiliations: ICES (Drs. Paszat, Vinden and Rabeneck, Ms. Li and Mr. He); Departments of Medicine (Drs. Bressler and Rabeneck) and Radiation Oncology (Dr. Paszat), University of Toronto; Department of Surgery (Dr. Vinden), University of Western Ontario.

ICES is an independent, non-profit organization that uses population-based health information to produce knowledge on a broad range of healthcare issues. Our unbiased evidence provides measures of health system performance, a clearer understanding of the shifting healthcare needs of Ontarians, and a stimulus for discussion of practical solutions to optimize scarce resources. ICES knowledge is highly regarded in Canada and abroad, and is widely used by government, hospitals, planners and practitioners to make decisions about care delivery and to develop policy.


  • Julie Argles
  • Media Relations Officer, ICES
  • (416) 480-4780 or cell (416) 432-8143


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