Decreased Risk of Colorectal Cancer after Colonoscopy in Patients 76-85 Years Old in the United States

The benefits of colonoscopy in reducing colorectal cancer (CRC) risk for patients over 75 years are controversial. We aimed to determine whether colonoscopy use is associated with a decreased risk of CRC in patients 76-85 years old in the United States (US).

All patients in the Medicare 5% random sample of the Surveillance, Epidemiology and End Results-Medicare linked database 76-85 years old at outpatient colonoscopy between January 1, 1998 and December 31, 2002 were identified. Using the Kaplan-Meier method, we estimated the cumulative incidence of CRC in the above-mentioned colonoscopy group and compared with the control group of patients without colonoscopy. All patients were followed until diagnosis of CRC or carcinoma in situ, death or December 31, 2005. The multivariate Cox proportional hazards model was used in statistical analysis. CRC was separated by location into distal vs. proximal CRC in subgroup analysis.

Of 5,701 patients in the colonoscopy group, 37 (0.65%) patients were diagnosed with CRC, compared to 379 (1.55%) out of 24,437 patients in the control group (p < 0.001). The cumulative incidences of distal and proximal CRC were lower in the colonoscopy group compared to those in the control group (5-year distal CRC: 0.26 vs. 0.77%; 5-year proximal CRC: 0.43 vs. 0.79%, both p < 0.05). In multivariate Cox regression, colonoscopy was associated with decreased risk of all CRC (hazard ratio ((HR) 0.42, 95% CI 0.28-0.65), distal CRC (HR 0.36, 95% CI 0.18-0.70), and proximal CRC (HR 0.53, 95% CI 0.30-0.92)).

Among patients 76-85 years old in the United States, colonoscopy use was associated with decreased risks of both distal and proximal CRC, with a smaller risk reduction in distal colon. Due to inherent limitations associated with our retrospective design, future prospective studies are needed to validate these findings.