TORONTO — Canadian Press Published on Tuesday, Jan. 30, 2007 2:07PM EST Last updated on Tuesday, Mar. 31, 2009 9:58PM EDT
Certain risk factors make it more likely that colorectal cancer will be missed during a colonoscopy in some patients, a study by the Institute for Clinical Evaluative Sciences says.
The study of more than 12,000 patients with colorectal cancer found that women, older individuals, those with a right-sided tumour, those who had a colonoscopy done by an internist or family physician or had a colonoscopy done in an office or clinic had a higher risk of having a missed colorectal cancer (CRC).
As well, patients with diverticular disease – in which small sacs or pockets develop in the wall of the colon – also are at increased risk.
The rate of new or missed colorectal cancers after colonoscopy – a procedure in which a flexible tube carrying a tiny camera is fed up through the large bowel – is 2 per cent to 6 per cent in “real world” clinical practice, depending on the site of the cancer, the study found.
“This information is crucial to help increase the accuracy of these procedures and catch and treat the cancer in its early stages,” Dr. Linda Rabeneck, a senior scientist for the institute and principal author of the study, said Tuesday in a release.
Colorectal cancer – the second leading cause of cancer-related deaths in Canada and the United States – accounts for 10 per cent of all cancer deaths. In 2006, an estimated 20,000 Canadians were diagnosed with colorectal cancer, which kills about 8,500 a year.
Using 1997-2002 health records, researchers tracked 12,487 Ontarians who had undergone colonoscopy to detect possible malignancies in the three years before diagnosis for colorectal cancer. The investigators then examined characteristics that might be risk factors for new or missed cancers (defined as individuals whose most recent colonoscopy was six to 36 months before diagnosis).
“Patients should be made aware of the small 2-to-6-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,” Dr. Rabeneck said. “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 is published in the January issue of the journal Gastroenterology.
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