• 1. Evaluate the effect on CRC mortality and morbidity by screen detection of CRC and removal of precursor lesions (polypectomy of adenomatous polyps).First evaluation after 5 years. [ Time Frame: Evaluations in 2007,2012,2017 ]
  
• 2. Evaluation of cost/effectiveness of screening for CRC and significant, benign lesions using flex-sig only compared to flex-sig in combination with faecal tests. First evaluation after 5 years. [ Time Frame: Evaluations in 2007, 2012, 2017 ]
  
• 3. To evaluate to which extent (and in which direction) the study may influence overall endoscopic activity in the general population in the screening areas and in areas where controlled screening is not established. [ Time Frame: Evaluation i 2012 ]
  

• 1. Determine the prevalence of known types familial CRC in a general population and try to define other groups with intermediate increased risk. Results "in press" 2005. [ Time Frame: Evaluated in 2005 (published) ]
  
• 2. Clarify possible psychosocial effects of endoscopic screening and how it may influence lifestyle and lifestyle related morbidity and overall mortality. Evaluation in 2005. [ Time Frame: Evaluated in 2005 (published) ]
  

Although flexible sigmoidoscopy (FS) as a screening tool has a much higher test sensitivity than fecal occult blood tests (FOBT) for colorectal cancer and high-risk adenomas, randomised trials with long-term follow-up are missing. The primary aims are as follows:

1. Evaluate the effect on CRC mortality and morbidity by screen detection of CRC and removal of precursor lesions (polypectomy of adenomatous polyps)
2. Evaluation of cost/effectiveness of screening for CRC and significant, benign lesions using flex-sig only compared to flex-sig in combination with faecal tests
3. To evaluate to which extent (and in which direction) the study may influence overall endoscopic activity in the general population in the screening areas and in areas where controlled screening is not established

Secondary aims:

1. Determine the prevalence of known types familial CRC in a general population and try to define other groups with intermediate increased risk
2. Clarify possible psychosocial effects of endoscopic screening and how it may influence lifestyle and lifestyle related morbidity and overall mortality

Population:

21,000 men and women, aged 50-64 years, living in the city of Oslo or the county of Telemark are drawn by randomisation (approx. 1:5) from the population registry and invited to have a flexible sigmoidoscopy examination. The control group constitutes 79,000 individuals. Those invited for flexible sigmoidoscopy are further randomised (1:1) to bring or not to bring 3 successive stool samples for FOBT on attendance for FS.

Method:

This is a once-only screening concept with bowel cleansing being limited to a 240 ml Sorbitol enema given on attendance. The threshold for work-up colonoscopy is low as a positive screening test is defined as any polyp >9mm, any histologically verified adenoma irrespective of size and a positive FOBT. The screening phase is limited to the period January 1999- January 2002 and the first follow-up results will not be reported until all entries have passed the 5-year mark (i.e. in early 2007).