Population-based fecal occult blood screening for colon cancer: will the benefits outweigh the harm?

C ancer Care Ontario, the cancer control agency for Ontario, has recommended that population-based fe-cal occult blood screening for colon cancer be instituted in the province. Under this recommendation and at a cost of $20–$30 million per year, all adults in Ontario over 50 years would have the opportunity of submitting stools for oc-cult blood screening and, should the test result be positive, would undergo barium enema or full colonoscopy within 3 weeks. An integral part of the program would be educational interventions for physicians and the public. 1 The rationale for such a screening program is that 3 long-term randomized trials, from Minnesota, 2,3 Great Britain 4 and Denmark, 5 have all shown a decrease in colon cancer mortality with fecal occult blood screening. The initial Minnesota report indicated that, among people who submitted 3 stool samples annually over a mean of 8 years, colon cancer mortality was reduced by 33% at 13 years. Overall mortality was not reduced. The 33% is a relative reduction rate and gives no inkling of the actual numbers of people who benefit. A more clinically meaningful way of reporting these data is in terms of the number needed to be screened to prevent a specific number of deaths from colon cancer. 6 In the Minnesota trial 1000 people had to be screened over a 13-year period to prevent 3 deaths from colon cancer. 2 A second arm of that trial involved screening every second year: after 13 years mortality did not decrease, 2 but after 18 years a decrease in colon cancer mortality (not overall mortality) was noted; it took 3200 stool samples to save 1 life. 3 In the British study, screening every second year resulted in a relative reduction rate of 15% in colon cancer mortality after 8 years (screening 1000 people over 8 years prevented 1 death), 4 and in the Danish study screening every second year resulted in a relative reduction rate of 18% in colon cancer mortality after 10 years (screening 1000 people over 10 years prevented 2 deaths). 5 Fecal occult blood screening has been clearly shown to prevent death from colon cancer, but the number of lives saved is small. According to a systematic review by Towler and associates, 7 1000 people would have to be screened for about 10 years to prevent 1 death from colon cancer. All screening programs cause harm, and this may …