Most of those defined as being at high risk for colorectal cancer have one of two hereditary syndromes or inflammatory bowel disease. FAP is caused by a mutation in the APC gene on chromosome 5. People with this condition develop hundreds of colorectal polyps and will almost certainly develop colorectal cancer unless the colon is removed. However, other variants of this classic pedigree clearly exist. Both ulcerative colitis and Crohn's disease that affects the colorectum greatly increase risk for colorectal cancer beginning 8 years after the onset of colorectal symptoms.
Management is by careful endoscopic surveillance for colonic dysplasia and prophylactic colectomy.
Those guidelines called for annual FOBT beginning at age 50. A randomized, controlled trial is now under way to measure the benefits of sigmoidoscopic screening, but results will not be known for several years. The Task Force called for universal screening for everyone after age 50 years, offered a set of reasonable options for screening methods, and specified recommendations for different levels of risk. One of the Task Force options is limited to annual FOBT testing for those at average risk for colorectal cancer. The ACS therefore recommends sigmoidoscopic examinations every 5 years as a reasonable way to intensively monitor the left side of the colorectum for neoplasia while using annual FOBT to monitor the entire colon for bleeding.