Background and purpose: Fecal occult blood tests (FOBT) and flexible sigmoidoscopy have previously been recommended for colon cancer screening. More recently, studies have recommended colonoscopy due to the high rates of advanced neoplasm not detected by FOBT and sigmoidoscopy. Previous studies of the effectiveness of colonoscopic screening in Taiwan were limited to families of patients with colorectal cancer. This study compared colonoscopy, sigmoidoscopy and FOBT for colorectal cancer screening in asymptomatic adults.
Methods: Screening colonoscopies and FOBT were performed in asymptomatic adults enrolled in our health-screening program between January 1997 and December 2000. Advanced neoplasm was defined as the presence of a polyp larger than 1 cm, polyps with villous or severe dysplastic features, or cancer. The junction of the splenic flexure and descending colon was defined as the boundary of the proximal and distal colon, and it was presumed that the distal colon would be examined using sigmoidoscopy in all patients. Data on the prevalence of polyps, advanced neoplasm, and cancer among different age groups were obtained. The results of chemical and immunologic FOBT were compared. The anatomic distributions of advanced neoplasm and cancer were analyzed.
Results: A total of 7,411 colonoscopic examinations were included in the analysis. Advanced neoplasms were present in 93 examinations (1.3%), including 16 cancers (0.2%). Chemical FOBT detected 20.2% of advanced neoplasms and 37.5% of cancers. Immunologic FOBT detected 48.3% of advanced neoplasms and 87.5% of cancers. If sigmoidoscopy had been performed in place of colonoscopy, 26.9% of advanced neoplasms and 12.5% of cancers would not have been detected.
Conclusions: Colonoscopy can detect neoplastic lesions undetectable by FOBT and sigmoidoscopy in asymptomatic subjects. These results suggest that colonoscopy should be the method of choice in colon cancer screening.