Introduction: Why liquid biopsies matter for today’s researchers

Liquid biopsy, the capture and molecular profiling of disease‐derived material from body fluids, has moved from proof-of-concept to clinical reality in less than a decade. Circulating-tumor DNA (ctDNA) testing is now Medicare-reimbursed in the United States, incorporated into National Comprehensive Cancer Network (NCCN) guidelines and, as announced at ASCO 2025, set to roll out across the NHS for rapid treatment adaptation in lung and breast cancer patients. Yet the science is maturing far beyond fragmentary DNA. Multi-omics, ultrahigh-sensitivity assays are opening the door to earlier cancer detection, real-time therapeutic monitoring, and even liquid biopsies for neurological and cardiovascular disease. For researchers at the interface of molecular biology, bioengineering, and data science, this is a field rich in unanswered questions and translational potential.

ctDNA 2.0: From mutation hunting to clinical decision support

First-generation ctDNA tests focused on hot-spot mutation calling for therapy selection in metastatic disease. Today’s platforms combine error-corrected next-generation sequencing with epigenetic (methylation) and fragmentomic signatures, pushing analytical sensitivity below 0.01% variant allele frequency. Routine blood draws can now reveal tumor heterogeneity, sub-clonal evolution and actionable resistance mutations weeks before radiographic progression¹.

Minimal residual disease (MRD): Catching the last cell

The largest ctDNA MRD study to date, presented at ASCO 2025, analyzed >2,000 stage III colon-cancer patients. A single Guardant Reveal™ sample collected after surgery but before adjuvant chemotherapy stratified three-year recurrence risk from 15% (ctDNA-negative) to 63% (ctDNA-positive), informing escalation or de-escalation of treatment². Similar prospective trials such as VICTORI in colorectal³, TOMBOLA in bladder⁴ and ADAPT-Lung in NSCLC⁵, are testing ctDNA-guided therapy decisions. For researchers, key challenges include suppressing false positives from clonal hematopoiesis, integrating quantitative “tumor-fraction” dynamics with classical risk models, and designing interventional trials powered on molecular rather than imaging endpoints.

Multi-Cancer Early Detection (MCED): Screening with one tube of blood

MCED tests aim to find a tumor signal before symptoms arise and to localize its tissue of origin. The Galleri® assay interrogates >100,000 methylation loci and now screens for 50+ cancers⁶. Guardant’s Shield™ test, recently granted FDA Breakthrough Device designation, reported 98.6 % specificity and a median 75% sensitivity (62-96% across eight tumor types) in its validation dataset⁷. Active population trials (NHS-GRAIL in the UK⁸; NCI Vanguard⁹, and SHIELD-US⁶) will generate the prospective performance data regulators require. Open research questions include:

How do we balance panel breadth with cost and sequencing depth?

Can fragmentomics, cfRNA or proteomics improve detection of notoriously “ctDNA-cold” tumors such as renal cell carcinoma or glioma?

What is the optimal screening interval given biological lead-time and tumor growth kinetics?

Beyond DNA: Exosomes, proteins and cell-free RNA

Exosomes & extracellular vesicles (EVs)

Exosomes (30-150 nm) carry intact DNA, mRNA, miRNA, proteins, and lipids behind a protective lipid bilayer, offering higher stability than naked cfDNA. A 2024 review highlights omics-scale profiling of exosomes for breast, lung, and GI cancers and their capacity to reflect tumor heterogeneity more comprehensively than a single tissue biopsy¹⁰. Isolation methods, from ultracentrifugation to microfluidic immuno-capture, remain a bottleneck ripe for innovation.

Proteomic & multiplex panels

Mass-spectrometry workflows and aptamer-based arrays (eg, SomaScan¹¹) are uncovering pan-cancer protein signatures that may complement nucleic-acid approaches, improving positive predictive value and tissue localisation. Integration of multi-analyte data demands advanced machine-learning pipelines and rigorous cross-cohort validation.

Cell-free RNA (cfRNA)

Unlike DNA, cfRNA captures gene-expression dynamics. In cardiovascular disease, cfRNA signatures detect myocardial injury, atherosclerotic activity, and transplant rejection earlier than troponin or imaging. A 2024 Atherosclerosis review outlines RNA biotypes, isolation pitfalls, and clinical opportunities¹². Transcript-stabilizing chemistries, single-molecule sequencing, and fragment-specific reverse-transcriptase primers are active research areas.

Monitoring the therapeutic response: Real-time molecular pharmacodynamics

Serial ctDNA profiling can reveal molecular progression a median of eight weeks before RECIST imaging in EGFR-mutant lung cancer, enabling earlier switch to Osimertinib and prolonging progression-free survival¹³. Similar kinetics are reported in metastatic prostate, pancreatic, and bladder cancers. Algorithms that integrate baseline tumor fraction, clearance half-life, and emergence of resistance variants are being incorporated into adaptive trials (eg, BR.36 NSCLC). For researchers, opportunities lie in modelling ctDNA decay curves, harmonizing multi-center sequencing pipelines, and linking liquid-biopsy endpoints to overall survival in meta-analyses.

Beyond oncology: Liquid biopsy for brain and heart

Neurodegenerative disease

CNS-derived exosomes cross the blood–brain barrier and can be immuno-captured from plasma using cell-surface markers such as L1CAM(neurons) or GLAST (astrocytes). Protein and RNA cargo correlate with Alzheimer’s pathology, Parkinson’s α-synuclein burden, and multiple sclerosis activity, positioning exosomes as minimally invasive biomarkers and potential drug-delivery vehicles¹⁴.

Cardiovascular disease

Cardiologists are evaluating cfRNA profiles for early detection of myocardial infarction, heart-failure phenotyping and even monitoring response to RNA therapeutics. The 2024 Sharma et al. review frames cfRNA liquid biopsy as “what troponin did for acute MI, multi-omic cfRNA may do for chronic CVD”¹⁵.

Other emerging applications include infectious-disease pathogen sequencing directly from plasma, transplant rejection via donor-derived cfDNA, and cell-free mitochondrial DNA as a stress biomarker in spaceflight.

Conclusion: Liquid biopsy as a multi-omic, multi-disease platform

The trajectory is clear: liquid biopsy is evolving from a late-stage cancer companion test to a universal, system-wide diagnostic modality. ctDNA unlocked the paradigm, but exosomes, cfRNA, and proteomic signatures are expanding its reach into early detection, therapy monitoring, and entirely new disease domains. For doctoral researchers, the field offers a rare convergence of unmet clinical need, technological challenge, and commercial momentum. Whether your expertise lies in nanofluidics, machine learning, synthetic biology, or health-economics modelling, liquid biopsy research in 2025 is a playground where fundamental discovery meets real-world impact.

References

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3.      A Liquid Biopsy-based Assay Could Detect Recurrence Prior to Imaging in Patients With Resectable Colorectal Cancer | News Releases | AACR

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