The report of the Canadian Coordinating Office for Health Technology Assessment1 (CCOHTA) cited in Richard Schabas's commentary on colorectal cancer screening2 was not a full assessment but a feasibility study based on a limited literature search. CCOHTA undertakes such feasibility studies to determine whether to proceed with a full assessment. In this case, CCOHTA did not proceed, and the feasibility study was published electronically as a quick guide to current assessment information.
We would urge caution before the initiation of a national population-based screening program for people at average risk of colorectal cancer, such as the biennial program (beginning at age 50 years and ending at age 74 years) recommended by the National Committee on Colorectal Cancer Screening (NCCCS).3 Participants should be fully informed of the risks and benefits, as outlined below.
· Screening for colorectal cancer is likely to have only a modest clinical benefit, as Schabas notes.2 The NCCCS study3 estimated that for people at average risk, 1300 fecal occult blood tests and 127 colonoscopies are needed to prevent 1 colorectal cancer death, that the risk of dying from colorectal cancer is 1 in 64 for people 50 to 74 years of age (1 in 345 for those 50 to 59 years of age) if they do not participate in a screening program, that the chance of improved survival is 1 in 204 if they participate fully in screening from 50 to 74 years of age and undertake any indicated follow-up procedures (1 in 1000 for those 50 to 59 years of age) and that only 1.75 life years are gained for each case detected.
· People at average risk who are unlikely to benefit from screening are asked to accept significant risks.4 The rates of complications from follow-up colonoscopy described in the NCCCS study3 (0.17% for perforations, 0.03% for hemorrhage and 0.02% for death) could very well be underestimated for various reasons,5 including screening by operators who are less experienced than those in the studies on which these rates are based. More recent data from 6 prospective studies5 suggest that the rate of perforation and hemorrhage combined could be double (0.4%) the rate given in the NCCCS report.3 In addition, risk of infection and psychological harm and the time that participants must devote to the screening process are not generally accounted for in these evaluations.
· Although all of the published economic evaluations that CCOHTA reviewed showed that screening was cost-effective, the NCCCS3 analysis showed that cost-effectiveness and reduction in deaths from colorectal cancer depend strongly on the assumed participation rate for the first screen (67% in the base case) and the frequency of screening. However, the participation rate that can be achieved in Canada is largely unknown.
To our knowledge, no country has implemented a population-based screening program at the national level, although several countries have undertaken pilot studies or large-scale programs. If Canada embarks on an expensive ($112 million per year, according to the NCCCS study3) community-based screening program for patients at average risk, then health care professionals and the general public should understand that this would be an experiment. Whether the benefits will outweigh the harms is unknown.
Bruce Brady Health Economist Canadian Coordinating Office for Health Technology Assessment Ottawa, Ont.