Preventing colorectal cancer and cancer mortality with colonoscopy: what we know and what we don’t know

Abstract

The goal of most colonoscopies is the prevention of incident colorectal cancer and especially death from colorectal cancer. The effectiveness of colonoscopy is now justly under attack following the publication of studies showing that colonoscopy reduces the risk of distal colorectal cancer and advanced neoplasms but has no [1] [2] or limited [3] effect on the incidence of proximal neoplasms. The reasons for no or limited proximal colon protection by colonoscopy are uncertain, but there are two broad categories of possible explanations. One category is altered biology in the proximal colon. Interval cancers in the proximal colon are more likely to be microsatellite unstable (MSI) and to bear the CpG Island Methylator Phenotype (CIMP) [4]. MSI is known to push tumors through the adenoma–carcinoma sequence rapidly, and CIMP tumors are believed to be the end product of serrated polyps, a group of lesions that are endoscopically subtle and about which little is known compared with adenomas.