Lower endoscopy reduces colorectal cancer incidence in older individuals.

BACKGROUND & AIMS: In older individuals, there are unclear effects of lower endoscopy on incidence of colorectal cancer (CRC) and of colonoscopy on site of CRC. We investigated whether sigmoidoscopy or colonoscopy is associated with a decreased incidence of CRC in older individuals, and whether the effect of colonoscopy differs by anatomic location.

METHODS: We performed a case-control study using linked US Veterans Affairs and Medicare data. Cases were veterans aged 75 years or older diagnosed with CRC in fiscal year 2007. Cases were matched for age and sex to 3 individuals without a CRC diagnosis (controls). We 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 CRC (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 CRC risk in different anatomic locations, the proximal colon was defined as proximal to the splenic flexure.

RESULTS: We identified 623 cases and 1869 controls (mean age, 81 y; 98.7% male, 86.2% Caucasian). Among cases, 243 (39.0%) underwent any lower endoscopy (177 colonoscopies). Among controls, 978 (52.3%) underwent any lower endoscopy (758 colonoscopies). Cases were significantly less likely than controls to have undergone lower endoscopy within the preceding 10 years (adjusted odds ratio [aOR], 0.58; 95% confidence interval [CI], 0.48-0.69). This effect was significant for colonoscopy (aOR, 0.57; 95% CI, 0.47-0.70), but not sigmoidoscopy. Similar results were observed when a 5-year exposure window was applied. Colonoscopy was associated with a reduced risk of distal CRC (aOR, 0.45; 95% CI, 0.32-0.62) and proximal CRC (aOR, 0.65; 95% CI, 0.46-0.92).

CONCLUSIONS: 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 CRC.