Cell-Free DNA Methylation-Based Liquid Biopsy Assay to Identify Lymph Node Metastasis in T1 Gastric Cancer.

BACKGROUND: Most T1 gastric cancer (GC) harbor lymph node metastasis (LNM) at a rate of < 20%; however, owing to the difficulty in accurately diagnosing LNM preoperatively, many patients with T1 GC undergo unnecessary invasive radical gastrectomy with lymphadenectomy. In the present study, we established an epigenetic liquid biopsy assay for the preoperative diagnosis of LNM in T1 GC. METHODS: A comprehensive biomarker discovery was performed by analyzing genome-wide DNA methylation profiling. We obtained 277 clinical specimens, including 177 surgical tissues and 100 pre-operative plasmas. DNA methylation biomarkers were trained and validated using quantitative methylation-specific polymerase chain reaction (qMSP) assays. RESULTS: We identified six novel differentially methylated regions, including at least two differentially methylated CpG probes (|Delta-beta| > 0.12 and p < 0.05) within 100 bp, through genome-wide biomarker discovery. A DNA methylation panel was generated using qMSP assays in clinical tissue specimens, with an area under the curve (AUC) of 0.80. This panel was validated in an independent clinical cohort, and a combined model, which integrated the DNA methylation model with preoperative computed tomography -based findings, was established through multivariate logistic regression analyses (AUC: 0.84). Finally, we translated this model into a liquid biopsy, and this cell-free DNA (cfDNA) methylation model exhibited robust performance for LNM identification in T1 GC (AUC: 0.86) and allowed 44% of patients to avoid unnecessary invasive operations, without missing any LNM-positive patients. CONCLUSIONS: We have successfully developed a cfDNA methylation signature-based liquid biopsy diagnostic assay that allows for robust and less-invasive LNM detection in patients with T1 GC.