Recommendations for population-based colorectal cancer screening - National Committee on Colorectal Cancer Screening
The National Committee on Colorectal Cancer Screening was supported by Health Canada. Health Canada does not necessarily endorse the information nor recommendations presented below.
In 1998, following discussion with experts and stakeholders in Canada, Health Canada established a National Committee on Colorectal Cancer Screening comprised of members from provinces and key organizations from across the country. The Committee's mandate was to explore the scope and issues surrounding population-based colorectal cancer (CRC) screening, and to develop a set of final recommendations. During its 2 years, the Committee examined evidence from randomized controlled trials (RCTs) and statistical modeling. The Committee also reviewed recommendations/reports from other countries which had undertaken similar evaluations, and information from expert opinion. Throughout the process, the Committee members were encouraged to identify issues or gaps in data/knowledge for which they required more information to formulate the final set of recommendations. (A companion document, Technical Report for the National Committee on CRC Screening, presents the technical information that was considered over the 2 years). The National Committee came to a consensus and developed its recommendations for population-based CRC screening in Canada.
Based on evidence from available randomized controlled trialsFootnote 1-4, the National Committee agreed that there was strong evidence to support that fecal occult blood screening could reduce CRC mortality by 15% to 33% in a targeted population of 50 to 74 year olds. Since an estimated 6,400 CRC deaths were expected to occur in Canada in 2001, and since the majority of these would be among Canadians aged 50 or older, the National Committee believed there could be a substantial potential for population benefit with CRC screening. However the National Committee also recognized that CRC screening carries some risks and opportunity costs.
Among the various tests which have been used for screening, only the Fecal Occult Blood Test (FOBT), to date, has been shown to be effective and evaluated in randomized trials as the initial screening test. By itself, and used alone, it carries negligible risk; nonetheless, follow-up with colonoscopy (as has been the practice in most RCT's), presents low but measurable risks of serious complications. The issue of follow-up with another test is important because FOBTs are associated with false positive results.Footnote 5 The Population Health Model (POHEM) developed by Statistics Canada estimated that 75 deaths and 611 perforations could result from diagnostic colonoscopy with a biennial screening program that starts in Canada in 2000 and ends in 2009. This is in contrast to an estimated reduction in CRC mortality of 16.7% (or 7,740 deaths) with biennial screening over the same 10 year period. At the individual level, the lifetime probability of death from CRC would fall from 0.29% to 0.19% for an individual who participates in all screening events, of a biennial program, from the age of 50 to 74; the lifetime risk of colonoscopy-induced death would be 0.005% for that same individual.
Clearly, these estimates are difficult to verify/quantify at the population-level, as most studies reporting colonoscopy complications are carried out in patient groups that include symptomatic individuals. The risks among a healthy screening population are so low that they are difficult to estimate from the RCT's presented to date. Nevertheless, the National Committee concluded that while the benefits clearly outweigh the risks, any individual contemplating screening with the FOBT should be made aware of both the risks and benefits prior to the initial screen, and should give an informed consent to be screened.
For a screening test to have a population-based impact, there must be adequate uptake (i.e. participation) in the target population. Thus, the National Committee evaluated the potential acceptability of the test and concluded that there was little or no information available on the likely participation rate that could be expected with a biennial screening program. In the RCTs to dateFootnote 1-4, adherence to the initial screening test (the FOBT) ranged from 53% to 67% in non-volunteer populations, with 38% to 46% of those invited completing all of the recommended screening and diagnostic tests. However, participation rates in RCTs, where the test efficacy is questionable by definition, may be different than when the test is proven to have a mortality benefit.
Finally, the National Committee recognized that any recommendations about population-based CRC screening will have resource implications. Resources may differ among provinces so provincial strategies may need to take this into account. Prime resource impacts include the costs of the initial medical consultation prior to taking the FOBT, and the availability of resources for colonoscopy or other follow-up diagnostic tests, such as double contrast barium enema or flexible sigmoidscopy for some geographic areas. Based on participation and re-screen rates of 67% and 93% respectively among Canadians aged 50 to 74, the POHEM estimated the cost-effectiveness of a biennial FOBT screening program to be $11,907 per life year gained. The literature has reported that screening average risk individuals for CRC is as cost-effective as screening for other cancers.Footnote 6 The cost per life year gained has been quoted at $20,000 (US), which falls well within the range of commonly accepted, cost-effective screening programs.Footnote 7
The National Committee strongly urges the need for regular, periodic review of new technologies for CRC screening. Furthermore, the National Committee also stresses the importance of on-going research into CRC and evaluation of CRC prevention interventions.
As a result of the aforementioned, the National Committee therefore recommends that:
- Colorectal cancer screening should be made available to Canadians. In order to ensure quality screening which maximizes benefits and minimizes potential risks, ideally screening should be within an organized and structured environment, with the following elements in place:
- clear, concise and understandable information for patients and physicians on the risks and benefits of screening and on the administration of the test.
- informed consent following personal consultation with family practitioner or equivalent
- standardized protocols and procedures with a single entry test and options for follow-up
- systematic tracking and evaluation of all screening invitations (if used), testing frequency, results (including false positive and false negative rates), follow-up, and outcomes
- Resources for screening be built up as appropriate. Recognizing disparity in human and financial resources, provinces may choose to phase in organized screening as resources permit.
- The National Committee further recommends that, based on current evidence:
- Screening be offered to a target population of adults aged 50 to 74 years of age, using unrehydrated Hemoccult II or equivalent as the entry test.
- Individuals be screened at least every two years, recognizing that annual screening would have slight improvement in mortality reduction over biennial, but require increased resources.
- Positive tests be followed up by colonoscopy, with options of barium enema and flexible sigmoidoscopy where appropriate (e.g. patient preference/availability of services)
- The National Committee believes that the benefits of screening outweigh the risks and that high quality population-based screening programs can reduce CRC mortality. Recognizing, however, that there are associated risks including death, the following elements need to be in place to protect the rights of Canadians and to maximize the benefits of screening:
- informed consent at the outset, including awareness of the risks and benefits of the entire screening cascade and not limited to the initial test;
- public awareness campaigns and promotional material including information on primary prevention and awareness of symptoms to inform the public of the availability of screening. These should supplement and not replace consultation with primary care practitioners;
- a high priority on quality assurance and monitoring, including criteria for endoscopy, to minimize potential risks;
- active education of patients and physicians while resources are being built, but that active organized recruitment be delayed pending evaluation of initial screening, i.e. compliance, complication rates, etc., in the Canadian context;
- ongoing evaluation procedures to ensure that organized screening be continued only if appropriate participation rate and level of safety can be maintained in the Canadian context. Targets for participation are important for population-based programs and evaluation; and
- research and evaluation of new tests for CRC screening be an on-going process.
These recommendations represent the consensus opinion of the group, with the exception of one participant. This participant did not feel that population-based screening should be promulgated if there was a possibility to do serious harm. The remainder of the participants acknowledged this risk, but felt that it was outweighed by the possibility of benefit. Consequently, the majority opinion was that this information should be provided to individuals for their own informed decision making.
The recommendations represent the overall consensus of the individual Committee members, andx not necessarily the endorsement by the respective organizations. (See Appendix A of the Technical Report for membership list.)
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