Cell-free DNA methylation and its potential as a biomarker in liquid biopsy: A systematic review.

DNA methylation is a critical epigenetic modification that regulates gene expression. Changes in cell-free DNA (cfDNA) methylation typically precede the clinical manifestations of diseases. Trace amounts in body fluid samples, fragmented feature, and high background noise are the challenges to be addressed before implementation of cfDNA methylation assay in clinical application. With advances in genomic analysis and methylation detection technologies, analysis of cfDNA methylation has emerged as a promising biomarker for early diagnosis, prognostic prediction, and tracing tissue origin. The tissue-specific methylation patterns of cfDNA further facilitate the determination of its tissue of origin, making cfDNA methylation invaluable in liquid biopsies. This review highlights the advanced technologies to analyze methylated cfDNA, summarizes the recent progress of cfDNA methylation assays in clinical applications, and underscores the value of the integration of cfDNA methylation with multi-omics analysis in future research.