Colorectal Cancer Prevention (PDQ®): Prevention - Health Professional Information [NCI] - Description of the Evidence
Cardiovascular Risks Associated With Celecoxib and Rofecoxib Dose/Drugs continued...
It is expected that further follow-up in the United Kingdom Flexible Sigmoidoscopy Screening Trial will be able to provide more detail about the long-term effect of polypectomy, at least on the left side of the colon.
Other evidence about the benefit of sigmoidoscopy screening (at which time both polyps and early cancer would be removed) suggests that the impact of endoscopic screening, at least on the left side of the colon, is substantial and prolonged. In an RCT, 170,000 persons were randomly assigned to one-time sigmoidoscopy versus usual care. At sigmoidoscopy, polyps were removed and cancer was detected and referred for treatment. Based on sigmoidoscopy findings, persons were considered to have low risk if they had normal exams or only one or two small (<1 cm) tubular adenomas; such persons were not referred either for colonoscopy workup, or for 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 polyps or small ones, or selection of individuals at lower risk—is yet unclear. 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. As a result of the strong data about the impact of endoscopy on the left colon, evidence from multiple studies has raised questions about the ability of endoscopy to reduce CRC mortality in the right colon.[79,80,81] 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.
Other studies suggest that the polyps with the greatest potential to progress to CRC are larger polyps (i.e., >1.0 cm), which include most of those with villous or high-grade histologic features. Retrospective cohort studies also show the harms associated with polypectomy, including bleeding.[82,83]