An early colorectal cancer screening programme based on bisulfite-free sequencing of methylated circulating tumor DNA.

3617 Background: Colorectal cancer (CRC) screening tests based on colonoscopy and fecal DNA testing are limited due to their invasive nature and low compliance rates. Herein, we develop a non-invasive early screening test for CRC based on ColoSeer assay, which combines methylated DNA immunoprecipitation and bisulfite-free sequencing to analyze methylation patterns of circulating tumor DNA (ctDNA). Methods: Tumor and ctDNA methylation patterns in 1,336 subjects (430 healthy controls, 202 colorectal precursor lesions (CPLs), 704 CRCs) undergoing colonoscopy were evaluated using the ColoSeer assay. Results: In the discovery phase, we identified a set of 46 differential methylation markers to screen for CPLs or CRCs from healthy controls. The overall detection sensitivity of ColoSeer was 85.6% for CPL and 97.5% for TMN stage (0-II) CRC, with 92.8% specificity. Conclusions: The ColoSeer assay demonstrated a high degree of accuracy for predicting subjects with CPL or early-stage malignant tumors and has potential as a first-tier health screen for early detection of CRC.