title: Screening strategies for colorectal cancer: a systematic review of the evidence.
abstract: BACKGROUND
  Colorectal cancer is the third most common cancer in Canada. It is well recognized that there are improved survival rates if the disease is treated in its early stages, and indeed this may be a preventable disease. This paper systematically reviews the effectiveness of specific screening techniques for colorectal cancer in asymptomatic individuals at normal or above average risk.
  
  
  METHODS
  MEDLINE was searched for articles published between January 1966 and January 2001 by using the MESH terms 'screening' and 'colorectal neoplasia'. The reference sections of review articles published before January 2001 were checked, and content experts were surveyed. The evidence was evaluated using the standardized methodology of the Canadian Task Force on Preventive Health Care.
  
  
  CONCLUSIONS
  For individuals at normal risk, there is evidence to support the use of annual or biennial fecal occult blood testing and flexible sigmoidoscopy for asymptomatic individuals over age 50 years. The evidence regarding whether only one or both of fecal occult blood testing and sigmoidoscopy should be performed is unclear, as is the evidence regarding the use of colonoscopy as an initial screen. For individuals at above average risk, the evidence supports either genetic testing or flexible sigmoidoscopy of individuals at risk in familial adenomatous polyposis kindreds, and screening with colonoscopy of patients in kindreds with hereditary nonpolyposis colon cancer. The evidence regarding colonoscopy for individuals who have a family history of colorectal polyps or cancer but do not fit the criteria for hereditary nonpolyposis colon cancer is unclear. Development of better risk stratification for screening is a high research priority, and further research, including randomized, controlled trials, into the effectiveness and feasibility of other screening modalities is necessary.
authors.affiliation: University of Toronto, Samuel Lunenfeld Research Institute, Mount Sinai Hospital, Toronto, Canada. rmcleod@mtsinai.on.ca
authors.forename: R S
authors.initials: RS
authors.lastname: McLeod
mesh_terms: D003113:Colonoscopy; D015179:Colorectal Neoplasms / Q000175:diagnosis* / Q000453:epidemiology / Q000517:prevention & control; D019317:Evidence-Based Medicine; D006801:Humans; D008403:Mass Screening / Q000379:methods*; D009780:Occult Blood; D016017:Odds Ratio; D012307:Risk Factors; D012812:Sigmoidoscopy