Around 16,000 people die from colorectal cancer in the UK every year, with annual health-care costs for treatment of the disease estimated at £300 million.
Survival rates exceed 90% if the disease is detected at an early stage; population screening is feasible as most invasive tumors develop slowly from non-cancerous polyps.
In the UK, flexible sigmoidoscopy is judged a more suitable tool for population screening than colonoscopy (advocated in the USA), because it is safer, cheaper, quicker, and more convenient. In addition, uptake rates are much higher.
Two thirds of adenomas and cancers are located in the rectum and sigmoid colon, which is within reach of the flexible sigmoidoscope, and the procedure takes only 5 minutes.
Wendy Atkin and colleagues from Cancer Research UK led the trial.
Men and women aged 55-64 years from 14 UK centers were randomly assigned screening or control (ratio 1:2). The control group was not contacted.
Small polyps were removed during screening, and individuals were referred for colonoscopy if high-risk polyps were found.
Around 170,000 individuals were randomized. Attendance among those assigned screening was 71%.
Some 2131 (5%) patients were classified as high-risk and referred for colonoscopy; 38,525 (95%) with no polyps or only low-risk polyps detected were discharged.
There was 1 perforation in 40,000 flexible sigmoidoscopy examinations, compared with 4 perforations among 2377 patients given colonoscopy.
| Perforation was 100-times more likely with colonoscopy than sigmoidoscopy.
An average of 48 people were screened, and 2 or 3 colonoscopy referrals generated, per center each week.
In an accompanying Commentary, David Ransohoff from the University of North Carolina, USA, comments, "The UK investigators raise provocative questions about the approach of tailoring not only work-up and surveillance, but also screening itself.
"For example, by suggesting once-in-a-lifetime screening sigmoidoscopy, or by suggesting that some subgroups have such a low risk of proximal colorectal cancer, that sigmoidoscopy alone may be a quite adequate test."
"Implementation of a tailored approach, by adjusting intensity of screening or surveillance to a person's risk, requires consideration of three points.
"These are the individual's absolute risk of colorectal cancer, the degree to which each screening or surveillance strategy reduces that risk, and quantitative definition of the goals of screening (i.e. what level of absolute risk is high enough to justify the effort of reduction)," he adds.
"By contrast, a one-size-fits-all approach to screening and surveillance may be easier to implement, but less efficient.
"In some cases - for example, when people with very low risk of subsequent colorectal cancer undergo potentially hazardous surveillance procedures such as colonoscopy - such an approach may even be harmful.
"A tailored approach, based on a quantitative definition of the goals of screening and surveillance, deserves increased consideration."
"Further reports from the UK trial and its USA counterpart will help guide the design and implementation of screening programs to reduce deaths from colorectal cancer, " he concludes.