Extracellular chromatin fragments as biomarkers for cancer screening

Extracellular chromatin fragments, including cell-free DNA (cfDNA) and histones, have emerged as promising non-invasive biomarkers for cancer screening and monitoring. While aberrant DNA methylation patterns in cfDNA are already established hallmarks of cancer and are increasingly used in liquid biopsy assays, circulating histones and nucleosomes reflect complementary aspects of tumor-associated epigenetic dysregulation and chromatin remodeling. This review integrates current knowledge on intracellular and extracellular histones in cancer, highlighting their release via necrosis, apoptosis, or neutrophil extracellular traps (NETs), and their dual roles as damage-associated molecular patterns and modulators of the tumor microenvironment. We discuss the intricate mechanistic links between DNA methylation and histone modifications, histone variants, and post-translational modifications, including the bidirectional crosstalk mediated by enzymes such as DNMTs, UHRF1, and PAD4. Special emphasis is placed on NETosis and its epigenetic regulation, which further connects histone citrullination with DNA methylation machinery and tumor progression. We evaluate the clinical potential of combining cfDNA methylation profiling with circulating histone levels, histone variants, and nucleosome-associated post-translational modifications. Evidence from multiple cancer types demonstrates that multimodal epigenetic approaches, incorporating fragmentomics, histone marks, and methylation signatures, significantly improve diagnostic accuracy, tissue-of-origin identification, and early detection compared to single-modality or conventional protein biomarkers in several cancer types. Fragmentomics, reflecting nucleosome positioning and chromatin accessibility, adds a functional layer to methylation-based assays. Collectively, extracellular chromatin components offer a rich, biologically interconnected source of information. Their integrated analysis holds substantial promise for advancing precision oncology through improved screening, prognosis, treatment monitoring, and development of safer epigenetic therapies.