Dr Harminder Singh and colleagues from Winnipeg determined the duration and risk of developing colorectal cancer after a negative colonoscopy.
The investigative team conducted a population-based retrospective analysis of colonoscopy evaluations that did not result in a diagnosis of colorectal neoplasia.
Patients who had been evaluated between 1989 and 2003 were identified using Manitoba Health's physician billing claims database.
The investigators identified 35,975 patients using this database.
|The standardized incidence ratio was 0.28 at 10 years|
|Journal of the American Medical Association|
The team then calculated standardized incidence ratios to compare colorectal cancer incidence in their cohort with the incidence in the provincial population.
Stratified analysis was performed to determine the duration of the reduced risk.
Patients with a history of colorectal cancer prior to the index colonoscopy, and inflammatory bowel disease within 5 years before, were excluded.
In addition, patients with resective colorectal surgery, and lower gastrointestinal endoscopy within the 5 years before the index colonoscopy were excluded.
Cohort members were followed up from the time of colonoscopy until diagnosis of colorectal cancer, death, out-migration from Manitoba, or end of the study period.
The investigators found that a negative colonoscopy was associated with standardized incidence ratios of 0.7 at 6 months.
The standardized incidence ratios were 0.66, 0.59, 0.55, and 0.28 at 1, 2, 5, and 10 years.
The team noted that the proportion of colorectal cancer located in the right side of the colon was higher in the colonoscopy cohort than the rate in the Manitoba population.
Dr Singh's team concluded, “The risk of developing colorectal cancer remains decreased for more than 10 years following the performance of a negative colonoscopy.”
“There is a need to improve the early detection rate of right-sided colorectal neoplasia in usual clinical practice.”