Colonoscopy reduced distal colorectal cancer risk and excess cancer risk associated with family history.

Purpose: Colonoscopy efficacy at preventing proximal colorectal cancer (CRC) is questioned, and little is known about efficacy in high-risk versus medium-risk populations. We investigated the relationship between colonoscopy screening, family history of colorectal cancer (FHCC), and CRC risk by site.
Methods: Among 92,078 women of the E3N prospective cohort, 692 CRCs have been diagnosed after a median follow-up of 15.4 years. Cox proportional hazard models estimated adjusted hazards ratios according to subsites of cancer and FHCC.
Results: A personal history of colonoscopy (PHC; n = 37,470) was associated with decreased rectal and distal colon cancer risks (hazard ratio (HR) = 0.57; 95% Confidence Interval (CI) = 0.42-0.78 and HR = 0.37; 95% CI = 0.26-0.52, respectively), but not proximal colon cancer risk (HR = 0.87; 95% CI = 0.64-1.18). In women with no prior colonoscopy, those with FHCC had a 80% higher CRC risk than those without FHCC. In women with previous colonoscopy, CRC risk was similar in women with and without FHCC (p for interaction = 0.04).
Conclusions: Results showed colonoscopy ability to prevent distal cancers, but not proximal cancers in women. Colonoscopy screening also reduced the excess risk of women with FHCC to that of women with no FHCC.