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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a targeted colorectal trial, which matters most for a 2 to 3% alteration where archival tissue is often exhausted or out of date.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 Combined circulating tumor DNA and protein biomarker-based liquid biopsy for the earlier detection of pancreatic cancers, Detection and localization of surgically resectable cancers with a multi-analyte blood test, DETECT-A: a blood test plus PET-CT to screen 10,006 women with no symptoms, DETECT-A: a blood test plus PET-CT found treatable cancers in 10,000 women with no symptoms.
Shares cfDNA fragmentomics, Analysis of plasma cell-free DNA by ultradeep sequencing in patients with stages I to III colorectal cancer, Circulating tumor DNA in stage III colorectal cancer, beyond minimal residual disease detection, toward assessment of adjuvant therapy efficacy and clinical behavior of recurrences, Assessment of resistance mechanisms and clinical implications in patients with EGFR T790M-positive lung cancer and acquired resistance to osimertinib.
Shares CCGA: the Circulating Cell-free Genome Atlas behind the Galleri methylation test, Clinical validation of a targeted methylation-based multi-cancer early detection test using an independent validation set, Tumour-informed versus tumour-naive ctDNA assays, Multi-cancer early detection (MCED).
Shares 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, Concordance of circulating tumour DNA and matched metastatic tissue biopsy in prostate cancer, Circulating tumour DNA fraction (and what a negative plasma result means).
Shares Combined circulating tumor DNA and protein biomarker-based liquid biopsy for the earlier detection of pancreatic cancers, Detection and localization of surgically resectable cancers with a multi-analyte blood test, DETECT-A: a blood test plus PET-CT to screen 10,006 women with no symptoms, The molecular evolution of acquired resistance to targeted EGFR blockade in colorectal cancers.
Shares The molecular evolution of acquired resistance to targeted EGFR blockade in colorectal cancers, Circulating tumor DNA-guided treatment with pertuzumab plus trastuzumab for HER2-amplified metastatic colorectal cancer: a phase 2 trial (TRIUMPH), NILE: clinical utility of comprehensive cell-free DNA analysis to identify genomic biomarkers in patients with newly diagnosed metastatic non-small cell lung cancer, Assessment of resistance mechanisms and clinical implications in patients with EGFR T790M-positive lung cancer and acquired resistance to osimertinib.
Shares Tumour-informed versus tumour-naive ctDNA assays, ctDNA MRD positivity (molecular residual disease after curative treatment), ctDNA tests roadmap: from a curiosity in plasma to blood tests that decide treatment, Minimal / molecular residual disease (MRD).
Shares Tumour-informed versus tumour-naive ctDNA assays, ctDNA MRD positivity (molecular residual disease after curative treatment), ctDNA tests roadmap: from a curiosity in plasma to blood tests that decide treatment, Minimal / molecular residual disease (MRD).