Clinical validation of a novel circulating tumor DNA methylation assay for predicting recurrence of colorectal cancer in patients with curative-intent surgery by monitoring minimal residual disease.

3620 Background: Circulating tumor DNA (ctDNA)-based liquid biopsy has emerged as a promising tool for early detection and monitoring of cancer. In this study, we developed COLO eDX, a digital-PCR based colorectal cancer (CRC) diagnostic assay using a single CRC-specific methylation biomarker. This study aimed to evaluate the prognostic value as the universal assay for recurrence monitoring in CRC patients with curative-intent surgery. Methods: A total of 116 CRC patients who underwent surgery at Seoul National University Boramae Medical Center were enrolled in the study from Mar 2017 to January 2020. For each patient, postoperative plasma specimens were collected at 7 days and at each regular clinical follow-up visit up to 2 years. The enrolled patients were followed up with radiological and clinical measures for maximally 5 years after surgery. The primary outcome was recurrence-free survival (RFS) according to ctDNA status. Results: The majority of samples collected at 7 days after surgery were ctDNA positive by COLO eDX (65/83, 78.3%) and the ctDNA status was not significantly associated with RFS, suggesting that cancer signatures can still be detected in most cancer patients at least 1 week after surgery. However, ctDNA positivity at 1 month or later was associated significantly worse RFS. In plasma taken between 1- and 9-months after surgery, ctDNA positive group had a significantly higher recurrence rate than ctDNA negative group (hazard ratio [HR], 11.4, 95% confidence interval [CI], 3.8-34.4; P<0.0001). Incorporating serial longitudinal samples, ctDNA status was significantly associated with recurrence (HR, 13.4, 95% CI, 4.3-40.6; P<0.0001). Notably, ctDNA analysis by COLO eDX was a more powerful predictor for predicting recurrence than carcinoembryonic antigen (CEA) assessment (HR, 4.0, 95% CI, 1.4-11.8; P=0.0107 and HR, 1.5, 95% CI, 0.3-8.2; P=0.5949). Conclusions: Postoperative ctDNA monitoring using a CRC-specific epigenetic biomarker-based digital PCR assay is a promising strategy for recurrence prediction and personalized clinical management of CRC through early detection of minimal residual disease (MRD).