Data from randomized controlled trials on the effects of screening colonoscopies on colorectal cancer incidence and mortality are not available.
Observational studies have suggested that colonoscopies strongly reduce the risk of colorectal cancer, but there is little specific evidence on the effects of screening colonoscopies.
Dr Hermann Brenner and colleagues from Germany performed a population-based case-control study of 3148 patients with a first diagnosis of colorectal cancer (cases), and 3274 subjects without colorectal cancer (controls) from the Rhine-Neckar region of Germany from 2003 to 2010.
Detailed information on previous colonoscopy and potential confounding factors was collected by standardized personal interviews.
|Colonoscopy was associated with a reduced risk of cancer in the right colon|
Self-reported information on colonoscopies and their indications was validated by medical records.
The research team used multiple logistic regression to assess the association between colonoscopy conducted for specific indications within the past 10 years and risk of colorectal cancer.
A history of colonoscopy was associated with a reduced subsequent risk of colorectal cancer, independently of the indication for the examination.
However, the team found somewhat stronger associations for examinations with screening indications than for examinations with diagnostic indications, such as positive fecal occult blood test result, surveillance after a preceding colonoscopy, rectal bleeding, abdominal symptoms, or other.
The researchers found that colonoscopy was also associated with a reduced risk of cancer in the right colon, regardless of the indication, although to a smaller extent than for other areas of the colon.
Dr Brenner's team concludes, "In a population-based case-control study, the risk of colorectal cancer was strongly reduced up to 10 years after colonoscopy for any indication."
"Risk was particularly low after screening colonoscopy, even for cancer in the right colon."