The researchers’ objective was to compare the incidence of and mortality from CRC among individuals screened by colonoscopy and non-screened individuals. The study involved 1,912 screened patients and 20,774 non-screened control participants. It was a closed cohort study in a population-based setting in a precisely defined area with a low level of population migration (a mainly rural area of Switzerland) from June 1, 2000 to June 1, 2001. Colonoscopies were performed by 11 board-certified gastroenterologists, including three local gastroenterologists who were supported by 10 gastroenterology trainees from the University Hospitals of Basel and Zurich; each of the trainees had performed at least 200 procedures. Study participants were aged 50 to 80 years old.
CRC cases in this closed cohort study were prospectively collected during the screening period of one year and the follow-up period of six years (June 1, 2001 to May 31, 2007). The main outcome measurements included follow-up data that were corrected for negligible migration balance in the area, and included tumor characteristics and risk or protective factors, age and sex, participation in general health screening examinations, history of CRC in a first-degree relative, smoking status, body mass index, frequency of sports activity, eating habits, and patients’ professions. Colorectal cancer and cancer-related death was recorded for all participants. Statistical comparisons were made between the screened and non-screened patient groups.
Polyps were found in 565 of the 1,912 screened individuals (29.6 percent), including 374 persons (19.6 percent) with adenomas (precancerous polyps) by histology. All polyps found during colonoscopy were removed during the procedure, except for very small lesions in the rectum, or later by surgery (surgical polyp removal occurred in seven cases—0.36 percent). Overall, 1,279 polyps were removed. Colorectal cancer incidence was significantly reduced by colonoscopy screening. Overall, 225 colorectal cancers were detected.