The researchers prospectively studied all patients referred for an initial colonoscopy between 1980 and 1990 at NPS clinical centers located throughout the U.S. and were found to have polyps (adenomas and nonadenomas). The National Death Index was used to determine the cause of death. Deaths from colorectal cancer among patients with adenomas that were removed were compared with the expected incidence-based mortality from colorectal cancer in the general population, as estimated from the Surveillance Epidemiology and End Results (SEER) Program, and with the observed death rates from colorectal cancer among patients with nonadenomatous polyps (control group).
Of the 2,602 people who had adenomas removed, 1,246 had died from any cause and 12 had died from colorectal cancer. The researchers calculated the number of expected deaths from colorectal cancer in the general population (25.4 expected deaths) and concluded that there is a 53% reduction in the death rate when polyps are removed during colonoscopy. Although colonoscopy is one of the more unpleasant screening tests available, the National Polyp Study has generated important data to support its utilization.