Significance of colonoscopy in screening for colorectal cancer:
Colonoscopy is the final common pathway of all screening for colorectal cancer (CRC) and is used for biopsy and polyp removal. For a screening-test in the (healthy) general population colonoscopy is invasive and prone to serious complications. Screening-yield and rates of complications are strongly dependent on the individual operator and on quality assurance. As a result, training and continued education of endoscopists as well as monitoring of both detection and complication rates are key to high screening-quality.

Effectiveness of screening for CRC:
No data is currently available on the impact of CRC-screening on all-cause mortality. Four randomized controlled trials on screening for faecal occult blood as a first-line test (gFOBT) showed a relative risk reduction of 15% for disease-specific CRC-mortality. Results from one large randomized controlled trial in the UK on once only flexible sigmoidoscopy as a first-line test showed a relative risk reduction of 31% for diseases-specific CRC-mortality and a reduction in CRC-incidence of 23%. Preliminary findings from a randomized controlled trial in Norway showed no impact of screening. Results from ongoing sigmoidoscopy trials in the USA and Italy are expected later, as well as results after longer follow up from the Norwegian trial. Two randomized controlled studies on screening with colonoscopy as a first-line test will yield results no sooner than ten years from now. There is only limited evidence on test characteristics (sensitivity, specificity, complication rates) in real life screening-settings.

International screening-activities:
In many countries the evaluation of evidence, the planning and at times the coordination of CRC-screening are done by a national institution. A few countries – England, Scotland, Finland and Australia – run organized population-based programs. However, most screening is not population-based but opportunistic. Participation rates are often low. Some countries – Japan, Italy and Germany – have programs that have been under way for many years. In the European Union about 70% of the population has access to some mode of CRC-screening. The most common first-line screening-test is gFOBT, to a degree also iFOBT. In some countries endoscopic-screening – colonoscopy, flexible sigmoidoscopy – is used as an alternative or in combination with FOBT. Also due to health insurers’ remuneration decisions in the US, colonoscopy is the most common first-line screening-test there.

Choice of first-line test:
When considering first-line screening-tests on which to base an organized program, the test’s impact on participation is more important than its individual test-sensitivity. Program-sensitivity largely depends on participation rates. Recent developments in first-line screening include quantitative iFOBTs. CT-colonoscopy, capsule endoscopy and new molecular tests are not yet viable alternatives for use in population-based mass-screening.

Improving screening-effectiveness:
An upper age-limit for CRC-screening is recommended. An integrated screening-program combines screening with screening-relevant considerations in diagnosis, treatment and surveillance. Along with standardized documentation and regular evaluation, this integrated program-design provides the quality necessary to justify screening average risk-populations. Giving thorough attention to the design of the surveillance regime is important, because its thresholds determine the numbers of surveillance-colonoscopies resulting from CRC-screening. Incremental implementation of a national population-based screening-program, with pilot testing and incremental roll-out, should be considered.

Securing comprehensive program-financing
Apart from the narrower screening-services, population-based screening-programs require significant initial investment in creating the infrastructure for the program’s overhead and sustainable financing of ongoing documentation, quality assurance and evaluation. Also, ongoing financing of both program- and provider-independent information dissemination to potential screening-participants and funds for regular program evaluation through an external institution needs to be secured.