S1125 Differences in Fit Results Between Screening and Referred Colorectal Cancer Patients are Explained by Differences in Tissue Tumor Stage

Background Fecal immunochemical tests (FITs) are state of the art in colorectal cancer(CRC) screening. Sensitivity of a single FIT for advanced neoplasia is around 50%. Theoretically, as blood loss from colon tumors can be intermittent, sensitivity of FITs could improve by double sampling. This study aims to compare the sensitivity of single FIT sampling and double FIT sampling at different cut-off values, for the detection of advanced neoplasia. Methods All subjects (≥18 years) scheduled for elective colonoscopy in three participating centers in the Amsterdam area were asked to perform FITs (OC sensor®) on two consecutive days. FIT results were compared with colonoscopy and histology as gold standard. Test performance of single FIT was compared to the sensitivity of double FIT sampling. Double FIT sampling was considered positive if one of both FITs was higher than the cut-off value. Test performances were evaluated at cut-off values ranging from 50-150ng/ml (incremental steps of 25ng/ml). Results Of 1105 subjects who performed two FITs and underwent total colonoscopy, 140 (9,4%) had advanced neoplasia (AN), of which 34 were CRC and 106 were advanced adenomas (AA). Of the CRC cases, 70% were Dukes stage A or B (stage unknown in 2). Positivity rates for single FIT ranged from 11-17%, and for double FIT from 14-23%. At the same cut-off value for positivity, sensitivity of double FIT sampling was higher than sensitivity of single FIT sampling. For any particular specificity (e.g. 90%), the sensitivity of double FIT was slightly higher than that of single FIT at a lower cut-off value (see table), but these differences were not statistically significant. Conclusions Two fold sampling of FIT does increase sensitivity for advanced neoplasia. However, at a given specificity, sensitivity of double sampling is comparable to single sampling at a lower cutoff value. Sensitivity and specificity of single and double FIT testing for the detection of advanced neoplasia