Fecal immunochemical test in cancer screening–colonoscopy outcome in FIT positives and negatives

Abstract

Objectives: Fecal immunochemical test (FIT) is used in colorectal cancer (CRC) screening, but evaluations of multiple sample strategies in colonoscopy screening cohorts are rare. The aim of this study was to assess accuracy of FIT for advanced neoplasia (AN) with two fecal samples in a colonoscopy screening cohort. Materials and methods: The study comprised 1155 participants of the colonoscopy arm in SCREESCO (Screening of Swedish Colons, NCT02078804), a randomized controlled study on CRC screening of 60-year-olds from the Swedish average-risk population. Participants provided two FIT samples prior to colonoscopy. First sample, mean of two, and any of the two samples above cut off level were assessed. Colonoscopy findings (CRC, advanced adenoma (AA), AN (CRC + AA) and adenoma characteristics) were evaluated in uni- and multivariable analysis in relation to FIT positivity (at ≥10 µg hemoglobin (Hb)/g). Results: Of 1155 invited, 806 (416 women, 390 men) participated. CRC, AA and non-AA were found in one (0.1%), 80 (9.9%) and 145 (18%), respectively. Sensitivity and specificity for AN were 20%/93%, 25%/92% and 26%/89% for first, mean of two and any of the two samples respectively at cut off level 10 µg/g, corresponding to 60 (74%)–65 (80%) participants with missed AN. The difference in sensitivity between screening strategies was non-significant. The specificity for first sample was significantly higher than for any of the two samples at cut off 10 µg/g (p =.02) and 20 µg/g (p =.04). FIT positivity in participants with adenoma was associated with pedunculated shape (p =.007) and high-risk dysplasia (p =.009). Conclusions: In an average-risk colonoscopy screening cohort of 60-year-olds, sensitivity for AN was modest and did not increase when using two samples instead of one. FIT predominantly detected adenomas with pedunculated shape and high-risk dysplasia, and participants with flat or broad based adenomas may thus be missed in screening.