Objectives: Understanding the epidemiology of colorectal adenomas is a prerequisite for designing follow-up programs after polypectomy. The aim of the study was to investigate the effect of polypectomy on the long-term prevalence of adenomas.
Methods: In 1983, a total of 799 men and women aged 50-59 yr were drawn from the general population register. Of these, 400 comprised a screening group and 399 a matched control group. The screenees were invited to undergo a once-only flexible sigmoidoscopy. Persons with polyps had a baseline colonoscopy with follow-ups in 1985 and 1989. In 1996, both the screenees and the controls were invited to a colonoscopic examination.
Results: In 1996, a total of 451 (71%) individuals attended. Adenomas were found in 78 (37%) individuals in the screening group and 103 (43%) in the control group, relative risk (95% confidence interval): 0.9 (0.7-1.1), p = 0.3, and high-risk adenomas (severe dysplasia, adenomas > or = 10 mm, villous components) were found in 16 (8%) and 32 (13%), respectively; relative risk (95% confidence interval): 0.6 (0.3-1.0), p = 0.07.
Conclusions: There was no significant difference in adenoma prevalence between the group after the screening program and the controls after the usual care. There was a trend toward more high-risk adenomas in the control group. This suggests a very limited effect of one-time screening sigmoidoscopy with surveillance colonoscopy on the prevalence of adenomas, but a preventive effect on the development of high-risk adenomas consistent with the reported effect on cancer prevention.