In older individuals, there are unclear effects of lower endoscopy on incidence of colorectal cancer, and of colonoscopy on site of colorectal cancer.
Dr Charles Kahi and colleagues from the Indiana, USA investigated whether sigmoidoscopy or colonoscopy is associated with a decreased incidence of colorectal cancer in older individuals, and whether the effect of colonoscopy differs by anatomic location.
The researchers performed a case-control study using linked US Veterans Affairs and Medicare data.
Cases were veterans aged 75 years or older diagnosed with colorectal cancer in fiscal year 2007.
Cases were matched for age and sex to 3 individuals without a colorectal cancer diagnosis.
|39% underwent any lower endoscopy|
The research team determined the number of cases and controls who received colonoscopies or sigmoidoscopies from fiscal year 1997 to a date 6 months before the diagnosis of colorectal cancer (for cases) or to a corresponding index date (for controls).
The probability of exposure was modeled using generalized linear mixed equations, adjusted for potential confounders.
For the analysis of colorectal cancer risk in different anatomic locations, the proximal colon was defined as proximal to the splenic flexure.
The researchers identified 623 cases and 1869 controls.
The research team found that among cases, 39% underwent any lower endoscopy.
Among controls, 52% underwent any lower endoscopy.
The researchers observed that cases were significantly less likely than controls to have undergone lower endoscopy within the preceding 10 years.
This effect was significant for colonoscopy, but not sigmoidoscopy.
The team observed similar results when a 5-year exposure window was applied.
Colonoscopy was associated with a reduced risk of distal colorectal cancer.
Dr Kahi's team comments, "In a study of the US Veterans Affairs and Medicare databases, lower endoscopy in the preceding 10 years was associated with a significant reduction in CRC incidence among older veterans."
"Colonoscopy was associated with significant reductions in distal and proximal colorectal cancer."