The Risk of Colorectal Cancer Incidence and Mortality after Screening and Adenoma Removal

Abstract

Colorectal cancer is a major health burden worldwide. Screening for colorectal cancers and surveillance programmes after adenoma removal have been implemented in many countries to decrease the risk of colorectal cancer incidence and mortality. This thesis aims to investigate the effect of colorectal cancer screening and adenoma removal on colorectal cancer incidence and mortality, as well as the risk of colorectal cancer death from an interval cancer occurring between two screening episodes. The thesis includes a systematic review and meta-analysis of existing randomised controlled trials on colorectal cancer screening, a subanalysis of a randomised controlled trial on colorectal cancer screening (the NORCCAP study), as well as a cohort study of 40,000 Norwegian individuals 40 years or older who have had an adenoma removed. Colorectal cancer screening with guaiac faecal occult blood test and sigmoidoscopy had a long-lasting effect on colorectal cancer mortality of at least 15 years. Individuals who experienced an interval cancer after a negative screening exam had similar prognosis to clinically detected cancers. Both sigmoidoscopy screening and adenoma removal had less effect in women than in men, thus sex-specific guidelines should be considered.