Combination of sigmoidoscopy and a fecal immunochemical test to detect proximal colon neoplasia

The combination of sigmoidoscopy and a sensitive fecal occult blood test was recommended as one strategy for colorectal cancer screening by the US Preventive Services Task Force in 2008. However, there have been no studies to evaluate the sensitivity of a one-time screen that uses both flexible sigmoidoscopy and a fecal immunochemical test (FIT) to detect advanced colorectal neoplasia.

We analyzed data from 21,794 asymptomatic persons who had undergone colonoscopy and a FIT. Analyses were performed with the following assumptions: colonoscopy would be performed for any positive FIT result; colonoscopy would be performed if the FIT result was negative and if advanced neoplasia was detected in the rectosigmoid (or plus descending) colon. The sensitivities and specificities of the combination of sigmoidoscopy and the FIT in detecting advanced neoplasia in the proximal colon were determined.

When colonoscopy was performed for a positive FIT result alone, for a positive sigmoidoscopy finding, and for a positive FIT result or sigmoidoscopy finding, the sensitivities in detection of advanced proximal neoplasia were 22.3%, 16.3%, and 31.7%, respectively. The sensitivities for detection of proximal invasive cancer were 58.3%, 8.3%, and 62.5%, respectively.

The combination of sigmoidoscopy and FIT can detect advanced proximal neoplasia better than either test alone. The incremental yield of advanced neoplasm detection by a screening program that uses both a FIT and sigmoidoscopy is approximately 10%. The FIT adds the most in terms of finding proximal cancers in a screening program that uses both tests. The combination of sigmoidoscopy and FIT is a viable and useful screening option.