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Certain factors predict whether colorectal cancer may be missed, study finds


A new study from the Institute for Clinical Evaluative Sciences (ICES) shows that there are certain risk factors that make it more likely colorectal cancer (CRC) will be missed during colonoscopy in patients.

“CRC is the second leading cause of cancer-related deaths in Canada and the United States, and accounts for ten per cent of all cancer deaths. This information is crucial to help increase the accuracy of these procedures and catch and treat the cancer in its early stages,” said Dr. Linda Rabeneck, ICES senior scientist and senior author of the study.

To conduct their study, investigators tracked 12,487 CRC patients in Ontario between April 1, 1997 and March 31, 2002, who had a colonoscopy to detect their CRC in the three years before their diagnosis. The investigators then examined characteristics that might be risk factors for new or missed CRC (defined as individuals whose most recent colonoscopy was six to 36 months before diagnosis).

The rate of new or missed CRC after colonoscopy in usual “real world” clinical practice was 2%-6%, depending on the site of the cancer. The results also showed that women, older individuals, those who have a right-sided CRC, those who had a colonoscopy done by an internist or family physician, or had a colonoscopy done in an office or clinic, were independently associated with a higher risk of new or missed CRC. In addition, individuals with the condition called diverticular disease (where small sacs or pockets develop in the wall of the colon) also have an increased risk.

“Patients should be made aware of the small two to six per cent risk that a cancer may be missed or may not be detected, because some cancers are rapidly progressing and may not be present,” said Dr. Rabeneck.

“Physicians doing colonoscopies in men and women who are older or who have a history of diverticular disease need to be especially careful so as not to miss a cancer.

“Finally, the influence of type of physician and the setting in which the colonoscopy is done on the accuracy of this procedure for diagnosing CRC must be further studied because these are important, potentially modifiable risk factors.”

The study, “Rates of new or missed colorectal cancers after colonoscopy and their risk factors: a population-based analysis”, is in the January 2007 issue of the journal Gastroenterology.

Author affiliations: ICES (Drs. Paszat, Vinden, Rabeneck, Mr. Chen and Ms. Rothwell); Departments of Medicine (Drs. Bressler and Rabeneck), and Health Policy, Management and Evaluation (Drs. Paszat and Rabeneck), University of Toronto; Department of Surgery, University of Western Ontario (Dr. Vinden).

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


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