Tumor-derived cell-free DNA fragment (ctDNA (circulating tumor DNA))

Tumor-derived cell-free DNA fragments, also known as circulating tumor DNA (ctDNA), are short fragments of DNA released into the bloodstream from dying tumor cells, typically through apoptosis or necrosis[3][5][7]. These fragments carry tumor-specific genetic and epigenetic alterations, making them powerful non-invasive biomarkers for cancer detection, monitoring of treatment response, minimal residual disease, and recurrence[4][5][6]. ctDNA is a subset of total cell-free DNA (cfDNA), which also contains fragments from normal and other diseased tissues[1][2][7]. While ctDNA enables liquid biopsy approaches in oncology, its diagnostic accuracy can be limited by low abundance, technical assay sensitivity, and biological confounders such as cfDNA released from non-tumor sources including hematopoietic (blood) cells and clonal hematopoiesis[3][5]. ctDNA does not directly serve as a therapeutic target but provides critical information for patient stratification, early cancer detection, and cancer progression monitoring[5][6][7]. **Additional context on structure and classification:** Tumor-derived cfDNA fragments have no coding or regulatory function themselves but reflect the molecular characteristics, genome integrity, and chromatin organization of cancer cells[6][7]. They are typically 150–200 base pairs in length, often corresponding to nucleosome protection patterns[2][3]. This molecular entity is distinct from receptors, enzymes, or other classical drug targets; ctDNA is a biomarker, not a cellular target for therapeutic intervention. **Note on scientific conventions and correctness:** The phrase "tumor-derived cell-free DNA fragments" does not refer to a specific molecular target such as a gene, receptor, or protein, but rather to a type of nucleic acid biomarker. It is not a therapeutic target in the manner of typical drug development targets but is used exclusively for diagnostic and monitoring purposes in oncology[3][6][7].

Other names

circulating tumor DNActDNAtumor-specific cfDNAcancer-derived cell-free DNA