Evidence of Benefit
Combination of FOBT and Flexible Sigmoidoscopy
A combination of FOBT and sigmoidoscopy might increase the detection of lesions in the left colon (compared with sigmoidoscopy alone) while also increasing the detection of lesions in the right colon. Sigmoidoscopy detects lesions in the left colon directly but detects lesions in the right colon only indirectly when a positive sigmoidoscopy (that may variously be defined as a finding of advanced adenoma, any adenoma, or any polyp) is used to trigger a colonoscopic examination of the whole colon.
In 2,885 veterans (97% male; mean age 63 years), the prevalence of advanced adenoma at colonoscopy was 10.6%. It was estimated that combined screening with one-time FOBT and sigmoidoscopy would detect 75.8% (95% CI, 71.0%-80.6%) of advanced neoplasms. Examination of the rectum and sigmoid colon during colonoscopy was defined as a surrogate for sigmoidoscopy. This represented a small but statistically insignificant increase in the rate of detection of advanced neoplasia when compared with FS alone (70.3%; 95% CI, 65.2%-75.4%). The latter result could be achieved assuming that all patients with an adenoma in the distal colon undergo complete colonoscopy. Advanced neoplasia was defined as a lesion measuring at least 10 mm in diameter, containing 25% or more villous histology, high-grade dysplasia, or invasive cancer. One-time use of FOBT differs from the annual or biennial application reported in those studies summarized in Table 1.
A study of 21,794 asymptomatic persons (72% were men) who had both colonoscopy and fecal immunochemical testing (FIT) for occult blood compared the detection of right-sided cancers as triggered by different test results. FIT alone resulted in a sensitivity of 58.3% and a specificity of 94.5% for proximal cancer diagnosis. FIT plus the finding of advanced neoplasia in the rectosigmoid colon yielded a sensitivity of 62.5% and a specificity of 93%. Thus, in this trial, the addition of sigmoidoscopy to FIT did not substantially improve the detection of right-sided colon cancers, compared with FIT alone.
The NORCCAP once-only screening study randomly assigned 20,780 men and women, aged 50 to 64 years, to FS only or a combination of FS and FOBT with FlexSure OBT. A positive FS was defined as a finding of any neoplasia or any polyp at least 10 mm. A positive FS or FOBT qualified for colonoscopy. Attendance in this study was 65%. Forty-one cases of CRC were detected (0.3% of screened individuals). Adenomas were found in 2,208 participants (17%), and 545 (4.2%) had high-risk adenomas. There was no difference in diagnosis yield between the FS only and the FS and FOBT groups regarding CRC or high-risk adenoma. There were no serious complications after FS, but there were six perforations after therapeutic colonoscopy (1:336).