Association between early stage colon neoplasms and false-negative results from the fecal immunochemical test.

BACKGROUND & AIMS: The fecal immunochemical test (FIT) can identify patients with advanced colorectal neoplasms, but it also has a high rate of false-negative results. It would be helpful to characterize colorectal neoplasms that are not detected by FIT to aid in development of new tests. We characterized colorectal neoplasms from patients who had negative results from the FIT.
METHODS: We analyzed data from 18,296 subjects who were screened for colorectal cancer by colonoscopy and the FIT at the Health Management Center of National Taiwan University Hospital from September 2005 through September 2010. We identified 4045 subjects with colorectal neoplasms (3385 with nonadvanced adenomas, 632 with advanced adenomas, and 28 with cancer). We analyzed the sensitivity of the FIT in identifying these patients, along with information on lesion size, location, and morphology.
RESULTS: The FIT identified patients with nonadvanced adenomas, advanced adenomas, and cancer with sensitivity values of 10.6% (95% confidence interval [CI], 10.2%-12.3%), 28.0% (95% CI, 24.6%-31.7%), and 78.6% (95% CI, 58.5%-91.0%), respectively. The FIT detected proximal advanced adenomas and nonpolypoid lesions with lower levels of sensitivity than distal advanced adenomas; it had a high false-negative rate in detection of adenomas <15 mm (adjusted odds ratio, 2.85; 95% CI, 1.79-4.54) and nonpolypoid adenomas (adjusted odds ratio, 2.15; 95% CI, 1.22-3.80), after adjusting for demographic characteristics, colonoscopy findings, and potential confounders. The FIT produced a higher percentage of false-negative results in detection of carcinoma in situ and T1 cancer than in T2-T4 cancers (66.7% sensitivity vs 100%; P = .049).
CONCLUSIONS: The FIT produces a high rate of false-negative results for patients with small or nonpolypoid adenomas. Early-stage cancers are associated with a high rate of false-negative results from the FIT.