Effects of Screening Colonoscopy: Evidence From Observational and Interventional Studies

Following a landmark report from the National Polyp Study published in 1993, which suggested that colonoscopic polypectomy can prevent most colorectal cancers (CRCs), screening colonoscopy was widely recommended and used in the United States and a few other countries for CRC prevention. Since then, age-adjusted CRC incidence and mortality have declined by approximately one third in the screening age population in the United States, in contrast to an alarming increase in incidence at younger ages. Furthermore, a number of observational studies, including large-scale cohort studies, have consistently confirmed screening colonoscopy to be associated with strongly reduced CRC incidence and mortality. However, results from randomized trials aimed to assess long-term effects on CRC incidence and mortality have become available only very recently, and they seemed to be less conclusive. In this review article, we review the evidence from observational and interventional studies, paying particular attention to the role of specific design features and potential sources of bias. We conclude that, despite apparent differences in reported results, both observational and interventional studies provide compelling evidence for strong preventive effects of screening colonoscopy. On the population level, similarly strong incidence and mortality reduction might be reached by well-organized screening programs achieving higher adherence rates with less invasive screening tests.