Colorectal cancer remains the second leading cause of cancer-death in the United States. It is also one of the most preventable form of cancer if detected early, so concerted efforts have been made to increase colonoscopy screening rates. The routine screening interval after a negative colonoscopy is 10 years, but does this suffice for all populations? Researchers at the University of Manitoba (Canada) performed a large-scale population-based study to evaluate risk factors for development of colorectal cancer after a negative colonoscopy.

The study evaluated Manitoba adults aged 40 years or older who had undergone a negative colonoscopy between 1989 and 2006. Exclusion criteria included prior lower gastrointestinal endoscopies, less than 5 years of coverage prior to index colonoscopy, follow-up of less than 6 months, colorectal cancer, resective colorectal surgery, and inflammatory bowel disease. There remaining cohort included 45,985 individuals (18,606 men; 27,379 women).

Compared to the general population, men had a 41% reduced incidence of colorectal cancer after a negative colonoscopy. Women had a 29% reduced incidence of colorectal cancer during the initial 3 years following a negative colonoscopy. Their colorectal cancer risk among both genders were equivalent during subsequent follow-up. In a regression model limited to age and gender identified older age as a risk factor for colorectal cancer after a negative colonoscopy. Adjusting for age and gender, performance of the colonoscopy by a non-gastroenterologist was also an independent predictor of early colorectal cancer (within 3 years after the index colonoscopy).

The authors conclude that age, female gender, and performance of the colonoscopy by non-gastroenterologists are associated with higher rates of early colorectal cancers after a negative colonoscopy. Proximal lesions are more common in women and are presumably more easily missed on colonoscopy. As for the risk differences among colonoscopy operators, these may stem from differences in training and volume of colonoscopies performed. The authors state that “Additional measures are needed to enhance the detection of proximal cancers and to reduce the differences in outcomes due to the differences among endoscopists.” They, however, do not elaborate on these “additional measures”.

• Source
• Singh H, Nugent Z, Mahmud SM, Demers AA, Bernstein CN. Predictors of colorectal cancer after negative colonoscopy: a population-based study. Am J Gastroenterol 2010;105(3):663-73.