Performance of a blood-based screening test for the early detection of colorectal cancer.

232 Background: While the clinical benefit of highly sensitive screening tools for colorectal cancer (CRC) has been established, adherence rates remain low. The convenience and familiarity of blood-based testing may reduce disease burden through greater access and compliance to regular and recommended asymptomatic screening. We report on preliminary findings from a minimally invasive blood-based early cancer detection (ECD) screening test for CRC. Methods: Plasma samples from healthy individuals and CRC patients sourced from biobanks were included. A targeted panel composed of differentially methylated genomic regions was developed. Using an independent cohort of plasma samples, a machine-learning model was trained to classify patient samples into cancer-free and CRC based on observed differential methylation patterns in circulating cell-free DNA (cfDNA). The assay performance was calculated based on concordance with clinical diagnosis (CRC, cancer-free). Results: The test set included 440 individuals: 127 with a confirmed CRC diagnosis (47% stage I/II, mean age 65±12 years, male 46%) and 313 without cancer (mean age 56±10 years, male 41%). Overall sensitivity was 95% (95% CI: 88-100%), and specificity was 91% (95% CI: 84-98%). Among patients with stage I disease, sensitivity was 92% overall, and 88% in screen-detected individuals. Sensitivity was 100% (n=14/14) in microsatellite-high tumors and 95% (n=107/113) in microsatellite-stable tumors. Multivariate analysis demonstrated associations between methylation signal and tumor size, cancer stage, and sex. Compared with a tumor-informed, variant-based circulating tumor DNA (ctDNA) test (Signatera), we observed a PPA (positive percent agreement) of 100%. Moreover, the differentially methylated allele fraction (DMAF) across target regions strongly correlated with variant allele frequencies (VAFs) from the tumor-informed test (Spearman’s correlation coefficient, 0.85). Conclusions: Using epigenetic markers specific for CRC, we developed a sensitive and specific blood-based test to detect cfDNA from early-stage and asymptomatic disease. The methylation signal strongly correlated with ctDNA VAFs from a clinically validated tumor-informed test and increased with cancer stage and disease burden. This test could serve as a means to increase patient adherence rates for CRC screening, thereby improving patient outcomes.