Abstract
Cell-free DNA (cfDNA) is changing the face of liquid biopsy as a minimally invasive tool for disease detection and monitoring, with its main applications in oncology and prenatal testing, and rising roles in transplant patient monitoring. However, the processes of cfDNA biogenesis, fragmentation, and clearance are complex and require further investigation. Evidence suggests that cfDNA production relates to mechanisms of cell death and DNA repair, both of which further influence fragment size and its applicability as a biomarker. An emerging domain, cfDNA fragmentomics is being explored for advancing the field of diagnostics using non-mutational signatures such as fragment size ratios and methylation patterns. Thus, this review examines structural diversity in cfDNA with various fragment sizes. In examining these cfDNA subsets, we discuss their distinct biological origins and potential clinical utility. Development of sequencing methodologies has broadened the application of cfDNA in diagnosing cancers and organ-specific pathologies, as well as directing personalized therapies. This has been achieved by identifying and uncovering different subsets of cfDNA in biofluids using different methodologies and biofluids. Different cfDNA subsets provide important insights regarding genomic and epigenetic features, enhancing the understanding of gene regulation, tissue-specific functions, and disease progression. Advancement of these key areas further asserts increasing clinical relevance for the use of cfDNA as a biomarker. Continued exploration of cfDNA subsets is expected to drive further innovation in liquid biopsy and its integration into routine clinical practice.