Enhancing Colorectal Cancer Screening with Droplet Digital PCR (ddPCR) Analysis of Fusobacterium nucleatum in Fecal Immunochemical Test (FIT) Samples.

Fecal immunochemical test (FIT) followed by colonoscopy in positive cases is commonly used for population-based colorectal cancer (CRC) screening. However, specificity of FIT for CRC is not ideal, and has poor performance for advanced adenoma detection. Fecal Fusobacterium nucleatum (Fn) detection has been proposed as a potential non-invasive biomarker for CRC and advanced adenoma detection. We aimed to evaluate the diagnostic performance of Fn detection using droplet digital PCR (ddPCR) in FIT samples from individuals enrolled in a CRC screening program with colorectal adenoma or cancer. We evaluated Fn presence in DNA isolated from FIT leftover material of 300 participants in a CRC Screening Program using ddPCR. The Fn DNA amount was classified as Fn-low/negative and Fn-high, and the association with patients clinicopathological features and accuracy measurements was calculated. Fn high levels were more prevalent in FIT-positive (47.2%n=34 of72) than FIT-negative samples (28.9%, n=66 of 228) (p<0.04). Among FIT-positive samples, high Fn levels were significantly more frequent in cancer patients (CA, n=8) when compared to normal (NT, n=16) (p=0.02), non-advanced adenomas (NAA, n=36) (p=0.01), and advanced adenomas (AA, n=12) (p=0.01). Performance analysis of Fn in FIT-positive samples for colorectal cancer detection yielded an AUC of 0.8203 (CI: 0.6464-0.9942), with high sensitivity (100%) and specificity of 50%%. Concluding, we showed the feasibility of detecting Fn in FIT leftovers using the ultrasensitive ddPCR technique. Furthermore, we highlighted the potential use of Fn levels in fecal samples to ameliorate CRC detection.