PREVENTION OF COLORECTAL-CANCER BY COLONOSCOPIC POLYPECTOMY

Background. The current practice of removing adenomatous polyps of the colon and rectum is based on the belief that this will prevent colore ctal cancer. To address the hypothesis that colonoscopic polypectomy r educes the incidence of colorectal cancer, we analyzed the results of the National Polyp Study with reference to other published results. Me thods. The study cohort consisted of 1418 patients who had a complete colonoscopy during which one or more adenomas of the colon or rectum w ere removed. The patients subsequently underwent periodic colonoscopy during an average follow-up of 5.9 years, and the incidence of colorec tal cancer was ascertained. The incidence rate of colorectal cancer wa s compared with that in three reference groups, including two cohorts in which colonic polyps were not removed and one general-population re gistry, after adjustment for sex, age, and polyp size.Results. Ninety- seven percent of the patients were followed clinically for a total of 8401 person-years, and 80 percent returned for one or more of their sc heduled colonoscopies. Five asymptomatic early-stage colorectal cancer s (malignant polyps) were detected by colonoscopy (three at three year s, one at six years, and one at seven years). No symptomatic cancers w ere detected. The numbers of colorectal cancers expected on the basis of the rates in the three reference groups were 48.3, 43.4, and 20.7, for reductions in the incidence of colorectal cancer of 90, 88, and 76 percent, respectively (P<0.001). Conclusions. Colonoscopic polypectom y resulted in a lower-than-expected incidence of colorectal cancer. Th ese results support the view that colorectal adenomas progress to aden ocarcinomas, as well as the current practice of searching for and remo ving adenomatous polyps to prevent colorectal cancer.