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Colorectal cancer: Are we missing something?


New research from Ontario’s Institute for Clinical Evaluative Sciences (ICES) raises the alarm bell on the effectiveness of colonoscopy.

“This ICES study is very significant, because it shows that the risk of cancer in the upper (or right) colon is higher than the lower colon following a negative colonoscopy,” says lead ICES investigator, Dr. Linda Rabeneck. "We used to think that a colorectal cancer was a colorectal cancer but evidence is accumulating that there is something different about cancers in the upper (or right) colon.”

The research was published in the October issue of Clinical Gastroenterology and Hepatology. In the study, 110,402 persons age 50–80 years old who had a negative colonoscopy in Ontario between 1992–97 were identified. These 110,402 persons were then followed for 14 years and the number of subsequent colorectal cancers was counted and compared the number occurring in the general population to help answer the question: How good is a negative colonoscopy?

The results:

  • During the 14 year follow-up period, colorectal cancer was diagnosed in 1,461 persons who had a negative colonoscopy
  • The risk of colorectal cancer in the lower colon was reduced during each year of the 14 year follow-up period
  • The risk of colorectal cancer in the upper (right) colon was reduced in only half of the follow-up years, mainly in the later follow-up years

The interpretation:

  • Colonoscopy may not be equally effective in the detection and removal of abnormalities in the lower and upper (right) colon
  • Future research is needed to determine whether this is an issue of colonoscopy quality or whether this is an issue of differences in tumour biology

“Colonoscopy is not a perfect test," says Rabeneck who is also chief of the Odette Cancer Centre at Sunnybrook Health Sciences Centre and regional vice-president, Cancer Care Ontario. “But it’s the only procedure that visualizes the entire colon and allows for the biopsy and removal of abnormalities such as polyps or cancers. However, this study raises fundamental questions about the effectiveness of colonoscopy – Is it an issue of colonoscopy quality? Or is it the biology of the disease where lesions in the upper (right) colon are more difficult to detect or progress more rapidly? These findings have profound implications because they raise questions on how we are going after the disease," says Rabeneck.

In Canada, colorectal cancer is second only to lung cancer as the leading cause of cancer death. In 2007, an estimated 20,800 Canadians were diagnosed with the cancer and almost 9,000 died from the disease. Colorectal cancer screening rates in Canada remain low.

Author Affiliations: ICES (Drs. Rabeneck, Paszat, Saskin); Department of Medicine, University of Toronto (Dr. Rabeneck, Mr. Lakoff); Health Policy, Management and Evaluation, University of Toronto (Drs. Rabeneck, Paszat)



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