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Short pieces of DNA floating in the blood, shed by dying cells all over the body. Most is from normal cells; the small tumour-derived fraction (ctDNA) is what liquid biopsies fish out.
A tube of blood contains nanograms of cell-free DNA, of which tumour DNA may be 0.01-10%. Assays detect it by deep sequencing with error correction (Guardant360, FoundationOne Liquid, MSK-ACCESS), by tumour-informed panels built from the patient's own tumour mutations (Signatera, RaDaR), or by methylation and fragment-size patterns that also reveal the tissue of origin (Galleri, fragmentomics). Uses span genotyping when tissue is scarce, resistance monitoring, MRD after surgery and multi-cancer screening. Pitfalls are CHIP-derived variants, low shedding by some tumours (brain, kidney) and pre-analytic handling, hence dedicated collection tubes.
Showing the technology this term belongs to: Liquid biopsy (ctDNA).
The glossary entry explains the word; the readout page carries the scoring rule, the thresholds approvals use, the companion diagnostics and the tests.
The current honest statement of where early detection stands: no blood test is ready, and the research is about finding the threshold at which to operate.
It reframes the blood test from a yes-or-no residual disease result into a measure of how well chemotherapy is working and how fast a relapse is coming, which is what an escalation trial would need.
It is the right shape of answer for a transition that is epigenetic rather than genetic, and it could in principle spare the biopsy that is currently the only way to make this diagnosis.
It identifies a way that a good test produces a wrong answer, and it names the fix. Any plasma repair-gene result used to decide on a PARP inhibitor should be run with a paired blood control, or an older man may be treated for a marrow clone rather than for his prostate cancer.
It is the proof that plasma genotyping can enrol patients for a targeted colorectal trial, which matters most for a 2 to 3% alteration where archival tissue is often exhausted or out of date.
Methylation-based screening is real but weakest exactly where pancreatic cancer needs it, at stage I, which is why high-risk surveillance rather than population screening carries the field here.
It established plasma profiling as a routine alternative to tissue for the BRCA question in advanced prostate cancer, with a sensible rule attached: if plasma finds nothing actionable, go back to tissue. It also documents at scale both the extra resistance information plasma gives and the clonal haematopoiesis noise that comes with it.
A blood test can find early, treatable cancers in people who feel well, including cancers for which no screening exists. It is not a replacement for mammography or colonoscopy but a possible addition. Larger randomised trials are needed to show benefit outweighs harm.
Shares Minimal / molecular residual disease (MRD), Circulating tumour DNA (ctDNA), MRD / molecular residual disease testing, Non-small-cell lung cancer and the tag precision.
Shares Blood-based tumor mutational burden as a predictor of clinical benefit in non-small-cell lung cancer patients treated with atezolizumab, Pancreatic ductal adenocarcinoma, Colorectal cancer, Non-small-cell lung cancer and the tag precision.
Shares ctDNA tests roadmap: from a curiosity in plasma to blood tests that decide treatment, Minimal / molecular residual disease (MRD), Circulating tumour DNA (ctDNA), MRD / molecular residual disease testing and the tag precision.
Shares Association of clonal haematopoiesis in DNA repair genes with prostate cancer plasma cell-free DNA testing interference, Circulating tumor DNA-guided treatment with pertuzumab plus trastuzumab for HER2-amplified metastatic colorectal cancer: a phase 2 trial (TRIUMPH), Clinical implications of plasma-based genotyping with the delivery of personalized therapy in metastatic non-small cell lung cancer, NILE: clinical utility of comprehensive cell-free DNA analysis to identify genomic biomarkers in patients with newly diagnosed metastatic non-small cell lung cancer and the tag precision.
Shares Circulating tumour DNA (ctDNA), Liquid biopsy (ctDNA) and the tag precision.
Shares Pancreatic ductal adenocarcinoma, Colorectal cancer, Non-small-cell lung cancer and the tag precision.
Shares Prostate cancer, Non-small-cell lung cancer and the tag precision.
Shares Minimal / molecular residual disease (MRD), MRD / molecular residual disease testing and the tag precision.