Colorectal Cancer Screening (PDQ®): Screening - Health Professional Information [NCI] - Evidence of Benefit
Table 3. Randomized Controlled Screening Trials: Fecal Occult Blood Testing continued...
A RCT of sigmoidoscopy screening in the United Kingdom suggests that the impact of endoscopic screening, at least on the left side of the colon, is substantial and prolonged. In this RCT, 170,000 persons were randomly assigned to one-time sigmoidoscopy versus usual care. At sigmoidoscopy, polyps were removed and patients with cancer were referred for treatment. Based on sigmoidoscopy findings, persons were considered to be low risk if they had normal exams or only one or two small (<1 cm) tubular adenomas; such persons were not referred for either colonoscopy workup or colonoscopic surveillance. In a follow-up of 10 years, the left-sided CRC incidence in the low-risk group (about 95% of attendees were low risk) was 0.02% to 0.04% per year—a very low risk of CRC compared with average risk. The cause of reduced risk—whether due to detection and removal of large or small polyps, or selection of individuals at lower risk—is yet unclear, but may be assessed in further analysis. The natural history of large polyps is not well known, but some evidence suggests that such lesions become clinical CRC at a rate of approximately 1% per year. Evidence from multiple studies has raised questions about the ability of endoscopy to reduce CRC mortality in the right colon.[46,47,48] Thus, it is unclear what the overall impact of endoscopy (e.g., colonoscopy screening) is, and whether there may be a large difference in impact on the left side of the colon compared with the right side.
The SCORE RCT from Italy randomly assigned 34,272 participants aged 55 to 64 years to either one-time FS or control. About 58% of FS group participants actually had an FS. After 10.5 years of follow-up, CRC incidence was reduced in the FS group by 18% (RR, 0.82; 95% CI, 0.69–0.96), with the reduction beginning about 5 years after randomization. CRC mortality in the FS group was also lower than in the control group, but not to a statistically significant degree (RR, 0.78; 95% CI, 0.56–1.08). Overall, these results are consistent with the United Kingdom results.
Sigmoidoscopy screening was also evaluated in the Prostate, Lung, Colorectal, and Ovarian Cancer (PLCO) screening randomized trial. Results were very similar to those of the United Kingdom trial. In PLCO, 77,445 men and women aged 55 to 74 years were randomly assigned to receive 60 cm flexible sigmoidoscopy screening at baseline and again at 3 or 5 years from 1993 to 2001 depending on their date of entry into the trial. The 77,455 men and women randomly allocated to the control arm received usual medical care. An examination was considered positive if a polyp or mass was detected. Participants were then referred to their primary care physicians for diagnostic follow-up. A total of 86.6% of participants underwent at least one sigmoidoscopy screening and 28.5% were positive. Of these, 80.5% had a diagnostic evaluation, of which 95.6% underwent colonoscopy. Thus 21.9% of participants in the intervention arm had a colonoscopy. Colorectal cancer screening in the control arm (contamination) was assessed by a questionnaire in a small sample of participants. The rate was estimated as 46.5%. In addition, the rate of colonoscopy after the screening phase was estimated as 47.7% in the intervention arm and 48.0% in the control arm.