Population-based assessment of the performance of sigmoidoscopy in the detection of colorectal cancer: implications for future screening recommendations
Current North American guidelines endorse the use of flexible sigmoidoscopy every 10 years as an alternative to fecal testing for the screening of colorectal cancer (CRC). The present study aims to evaluate its performance in a hypothetical population-based scenario, using data from the Surveillance, Epidemiology and End Results (SEER)-18 database. We explored the SEER database with the SEER*stat software. All cases diagnosed as colorectal carcinoma within the age group of 50–74 years during the year 2010 were included. Cases were considered either accessible or non-accessible to detection by screening sigmoidoscopy by virtue of their anatomic location. For example, cases within the rectum, sigmoid or descending colon were considered accessible whereas cases within other colorectal sub-sites were considered non-accessible. Assuming that all eligible United States’ citizens underwent screening sigmoidoscopy and assuming that all CRC cases within accessible sites were correctly identified by sigmoidoscopy, true positive, true negative, and false negative cases were calculated. False positive cases, however, were non-calculable. Sensitivity and negative predictive value (NPV) of screening sigmoidoscopy were derived accordingly. A total of 18,794 patients aged between 50–74 years were diagnosed in 2010. The total United States’ population covered by the SEER-18 registry in the same year and within the same age group was 21,613,411 individuals. A total of 10,786 CRC patients (57.4%) were diagnosed in sigmoidoscopy-accessible sites, 7,532 CRC patients (40.1%) were diagnosed in sigmoidoscopy-non-accessible sites, and an additional 476 patients (2.5%) were identified as unknown sub-sites. This translated into 2,853 CRC-related deaths at 5 years for sigmoidoscopy-accessible tumors versus 2,126 CRC-related deaths for sigmoidoscopy-non-accessible tumors. Based on the study’s assumptions, sensitivity of screening sigmoidoscopy would be 58.8% and NPV would be 99.9%. Flexible sigmoidoscopy has an unacceptably low sensitivity for the detection of right-sided CRC; therefore, its use as a first-line screening modality should be questioned. Additional studies on alternative screening options for right-sided CRC are warranted.