Evidence collection29 May 2025

Liquid biopsy in cancer

Evidence-based veterinary medicineSmall animalsEquineMedicine

Introduction

There is growing interest in the use of liquid biopsy (the analysis of blood or other bodily fluids) for detecting biomarkers that can be used to assist in the early detection of cancer as well as in monitoring treatment efficacy and detecting recurrence.

Liquid biopsies can be developed to look for circulating cancer cells, genetic material or protein biomarkers. To use these tests appropriately it is important to understand what they are measuring.

The purpose of this evidence collection is to bring together published evidence about the potential use of biomarkers in the diagnosis and management of cancer in veterinary patients, and to provide an overview of the types of tests currently available.

The first section provides an overview of the potential uses of liquid biopsy in the diagnosis and management of cancer in veterinary patient, this is followed by more detail about the different types of tests currently available, including those looking at genetic material and protein biomarkers. The final section provides links to papers that provide evidence relating to the cancer blood tests that are currently available on the veterinary market.

Types of liquid biopsy

This section provides references to papers giving an overview of the different types of liquid biopsy that are available.

Brown, J.R. et al. (2025) High-sensitivity multicancer detection of stage 1 cancer in dogs. American Journal of Veterinary Research. https://doi.org/10.2460/ajvr.25.02.0068
Flory, A. and Wilson-Robles, H. (2024) Noninvasive blood-based cancer detection in veterinary medicine. Veterinary Clinics of North America: Small Animal Practice, 54 (3), pp. 541-558. https://doi.org/10.1016/j.cvsm.2023.12.008
Chibuk, J. et al. (2021) Horizons in veterinary precision oncology: fundamentals of cancer genomics and applications of liquid biopsy for the detection, characterization, and management of cancer in dogs. Frontiers in Veterinary Science, 8. https://doi.org/10.3389/fvets.2021.664718
Aupperle-Lellbach, H. et al. (2024) Clinical use of molecular biomarkers in canine and feline oncology: Current and future. Veterinary sciences, 11 (5). https://doi.org/10.3390/vetsci11050199
Kehl, A. et al. (2024) Review of molecular technologies for investigating canine cancer. Animals, 14 (5). https://doi.org/10.3390/ani14050769

Molecular, genetic and genomic biomarkers

Cell free DNA and next generation sequencing

These tests use genetic sequencing to look for changes in the cell free DNA such as mutations, including single nucleotide polymorphism (SNP) copy number variations (CNV), which may be associated with particular types of cancer.

Tagawa, M. et al. (2024) Clinical utility of circulating cell‐free DNA as a liquid biopsy in cats with various tumours.Veterinary and Comparative Oncology, 22 (4), pp. 592-601. https://doi.org/10.1111/vco.13013
Kim, J. et al. (2021) Cell-free DNA as a diagnostic and prognostic biomarker in dogs with tumors. Frontiers in Veterinary Science, 8. https://doi.org/10.3389/fvets.2021.735682
Kruglyak, K.M. et al. (2021) Blood-based liquid biopsy for comprehensive cancer genomic profiling using next-generation sequencing: An emerging paradigm for non-invasive cancer detection and management in dogs.Frontiers in Veterinary Science, 8, no. 704835. https://doi.org/10.3389/fvets.2021.704835
McCleary-Wheeler, A.L. et al. (2024) Next-generation sequencing-based liquid biopsy may be used for detection of residual disease and cancer recurrence monitoring in dogs. American Journal of Veterinary Research, 85 (3). https://doi.org/10.2460/ajvr.23.07.0163
Ruiz-Perez, C.A. et al. (2024) Proof-of-concept evaluation of next-generation sequencing-based liquid biopsy for non-invasive cancer detection in cats. Frontiers in Veterinary Science, 11. https://doi.org/10.3389/fvets.2024.1394686

Circulating nucleosomes

Nucleosomes are fragments of DNA wrapped around a histone protein core which are released into the blood stream, primarily from dying cells. Depending on the analysis carried out tests for circulating nucleosomes can provide different types of information which may be used in cancer diagnosis. In addition to the quantitative analysis of nucleosome levels they may contain tumour specific genetic mutations or histone modifications (acetylation, methylation), that may be altered in cancer.

Westerback, E. et. al. (2025) Evaluation of plasma nucleosome concentrations and the effect of pre-analytical variables in healthy cats. BMC Veterinary Research, 21, no. 355. https://doi.org/10.1186/s12917-025-04785-x
Dolan, C. et al. (2021) Characterizing circulating nucleosomes in the plasma of dogs with lymphoma. BMC Veterinary Research, 17. https://doi.org/10.1186/s12917-021-02991-x
Goggs, R. (2019) Effect of sample type on plasma concentrations of cell‐free DNA and nucleosomes in dogs. Veterinary Record Open, 6 (1). https://doi.org/10.1136/vetreco-2019-000357

Extracellular vesicles/ Exosomes

Extracellular vesicles are small (30-150nm) membrane-bound vesicles actively secreted by living cells (both cancerous and normal) containing a range of proteins (including tumour-specific antigens), lipids, and genetic material including microRNAs.

Xiong, Y. et al. (2024) Emerging role of extracellular vesicles in veterinary practice: novel opportunities and potential challenges. Frontiers in Veterinary Science, 11. https://doi.org/10.3389/fvets.2024.1335107
Kehl, A. et al. (2025) Stability of microRNAs in canine serum – A prerequisite for use as biomarkers in tumour diagnostics. Veterinary Sciences, 12 (4). https://doi.org/10.3390/vetsci12040390
Ludwig, L. et al. (2025) Classification and prognostication of B‐cell and T‐cell multicentric lymphoma in dogs using serum MicroRNAs. Veterinary and Comparative Oncology, 23 (2), pp. 310-319. https://doi.org/10.1111/vco.13057

Protein biomarkers

Serum TK1 (Thymidine Kinase 1)

Thymine Kinase1 is an enzyme involved in the recovery of the nucleotide thymidine in the DNA salvage pathway. Levels of serum TK1 are a general measure of cellular proliferation rate in the body and may therefore be raised in conditions other than cancer.

Dogs

von Euler, H.P. et al. (2006) A non-radiometric method for measuring serum thymidine kinase activity in malignant lymphoma in dogs. Research in Veterinary Science, 80 (1), pp. 17–24. https://doi.org/10.1016/j.rvsc.2005.05.001
von Euler, H.P. (1992) Monitoring therapy in canine malignant lymphoma and leukemia with serum thymidine kinase 1 activity – Evaluation of a new, fully automated non-radiometric assay. International Journal of Oncology, https://doi.org/10.3892/ijo_00000175
von Euler, H.P. et al. (2004) Serum thymidine kinase activity in dogs with malignant lymphoma: A potent marker for prognosis and monitoring the disease. Journal of Veterinary Internal Medicine, 18 (5), p. 696-702. https://doi.org/10.1111/j.1939-1676.2004.tb02608.x
Kim, Y. et al. (2024) Serum thymidine kinase 1 protein concentrations and presence of its autoantibody as biomarkers for screening dogs with malignant tumors. Journal of Veterinary Internal Medicine, 38 (1), pp. 300-307. https://doi.org/10.1111/jvim.16946
Kim, Y. et al. (2025) Use of thymidine kinase 1 autoantibody, thymidine kinase antigen, extracellular protein kinase A autoantibody, and C‐reactive protein for early detection of malignant tumors in dogs.Journal of Veterinary Internal Medicine, 39 (1). https://doi.org/10.1111/jvim.17266
Boyé, P. et al. (2019) Evaluation of serum thymidine kinase 1 activity as a biomarker for treatment effectiveness and prediction of relapse in dogs with non‐Hodgkin lymphoma. Journal of Veterinary Internal Medicine, 33 (4), pp. 1728–1739. https://doi.org/10.1111/jvim.15513
Nakamura, N. et al. (1997) Plasma thymidine kinase activity in dogs with lymphoma and leukemia. Journal of Veterinary Medical Science, 59 (10), pp. 957–960. https://doi.org/10.1292/jvms.59.957
Sharif, H. et al. (2023) A monoclonal antibody-based sandwich ELISA for measuring canine Thymidine kinase 1 protein and its role as biomarker in canine lymphoma. Frontiers in Veterinary Science, 10. https://doi.org/10.3389/fvets.2023.1243853
Saellström, S. et al. (2022) Serum TK1 protein and C-reactive protein correlate to treatment response and predict survival in dogs with hematologic malignancies. Research in Veterinary Science, 145, pp. 213-221. https://doi.org/10.1016/j.rvsc.2022.02.019
Thamm, D. H. et al. (2011) Elevated serum thymidine kinase activity in canine splenic hemangiosarcoma. Veterinary and Comparative Oncology, 10 (4), pp. 292–302. https://doi.org/10.1111/j.1476-5829.2011.00298.x

Cats

Taylor, Samantha S. et al. (2012) Serum thymidine kinase activity in clinically healthy and diseased cats: A potential biomarker for lymphoma. Journal of Feline Medicine and Surgery, 15 (2), pp. 142–47. https://doi.org/10.1177/1098612×12463928

Horses

Larsdotter, S. et al. (2015) Serum thymidine kinase activity in clinically healthy and diseased horses: A potential marker for lymphoma. The Veterinary Journal, 205 (2), pp. 313–316. https://doi.org/10.1016/j.tvjl.2015.01.019.

Fibrinogen-fibrin degradation products

Ke, C.H. et al. (2023) Increased plasma DR‐70 (fibrinogen‐fibrin degradation products) concentrations as a diagnostic biomarker in dogs with neoplasms. Journal of Veterinary Internal Medicine, 37 (6), pp. 2391-2401. https://doi.org/10.1111/jvim.16898

MicroRNA

Kehl, A. et al. (2025) Utility of urinary miRNA biomarkers for canine urothelial carcinoma diagnostics. Veterinary Sciences, 12 (7), no. 621. https://doi.org/10.3390/vetsci12070621

Currently available blood tests for cancer

OncoK9 – Antech

This test uses Next Generation Sequencing (NGS) and is claimed to be able to detect changes associated with 30 types of canine cancer, including lymphoma, hemangiosarcoma, soft tissue sarcoma, mast cell tumor, osteosarcoma, mammary gland carcinoma, anal sac adenocarcinoma, and malignant melanoma.

OncoK9^® — The Liquid Biopsy Test for Dogs™ [Antech_TM] [online]. Available from: https://antechdiagnostics.co.uk/oncok9/ [Accessed 29 May 2025]

Flory, A. et al. (2022) Clinical validation of a next-generation sequencing-based multi-cancer early detection “liquid biopsy” blood test in over 1,000 dogs using an independent testing set: The CANcer Detection in Dogs (CANDiD) study. PLOS ONE, 17 (4), e0266623. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0266623
Flory, A. et al. (2023) Cancer detection in clinical practice and using blood‐based liquid biopsy: A retrospective audit of over 350 dogs. Journal of Veterinary Internal Medicine, 37 (1), pp. 258-267. https://doi.org/10.1111/jvim.16616
O’Kell, A.L. et al. (2023) Clinical experience with next-generation sequencing–based liquid biopsy testing for cancer detection in dogs: a review of 1,500 consecutive clinical cases. Journal of the American Veterinary Medical Association, 261 (6), pp. 827-836. https://doi.org/10.2460/javma.22.11.0526
Flory, A. et al. (2024) Clinical validation of a blood-based liquid biopsy test integrating cell-free DNA quantification and next-generation sequencing for cancer screening in dogs. Journal of the American Veterinary Medical Association, 262 (5), pp. 665-673. https://doi.org/10.2460/javma.23.10.0564

NuQ Vet Cancer test

This test measures and analyses nucleosomes and is being promoted as a screening test for dogs with an increased risk of developing cancer, due to age, breed or genetic predisposition.

NationWide Laboratories now offers Nu.Q® Vet Cancer Screening Test in the UK [NationWide Laboratories] [online]. Available from: https://nwlabs.co.uk/wp-content/uploads/2023/11/Nu.Q-leaflet-NWL-no-ranges.pdf [Accessed 29 May 2025]

Wilson-Robles, H.M. et al. (2022) Evaluation of plasma nucleosome concentrations in dogs with a variety of common cancers and in healthy dogs. BMC Veterinary Research, 18, no. 329. https://doi.org/10.1186/s12917-022-03429-8
Wilson-Robles, H. et al. (2020) Evaluation of nucleosome concentrations in healthy dogs and dogs with cancer. PLoS One, 15 (8), e0236228. https://doi.org/10.1371/journal.pone.0236228
Wilson-Robles, H. et al. (2021) Characterizing circulating nucleosomes in the plasma of dogs with hemangiosarcoma. BMC Veterinary Research, 17, 231. https://doi.org/10.1186/s12917-021-02934-6
Wilson-Robles, H. et al. (2023) Monitoring plasma nucleosome concentrations to measure disease response and progression in dogs with hematopoietic malignancies. PLoS One, 18 (5), e0281796. https://doi.org/10.1371/journal.pone.0281796
Dolan, C. et al. (2021) Characterizing circulating nucleosomes in the plasma of dogs with lymphoma. BMC Veterinary Research, 17, no. 276. https://doi.org/10.1186/s12917-021-02991-x

VDI Laboratories, cancer diagnostic panel

VDI offer a cancer diagnostic panel based on Serum TK1 (Thymidine Kinase 1) and C-Reactive protein, for diagnosing and monitoring a range of cancers in dogs and cats

Cancer diagnostics: A cancer blood test should be more than yes no maybe [VDI Laboratory] [online]. Available from: https://vdilab.com/cancer-diagnostics/ [Accessed 29 May 2025]

Selting, K. A., et al. (2013) Serum thymidine kinase 1 and C‐reactive protein as biomarkers for screening clinically healthy dogs for occult disease. Veterinary and Comparative Oncology, 13 (4), pp. 373–384. https://doi.org/10.1111/vco.12052
Selting, K.A., et al. (2016) Thymidine kinase Type 1 and C‐reactive protein concentrations in dogs with spontaneously occurring cancer. Journal of Veterinary Internal Medicine, 30 (4), pp. 1159–1166. https://doi.org/10.1111/jvim.13954.

About evidence collections

Evidence collections bring together collections of published papers on topics of interest and importance to the veterinary professions. Papers are chosen for relevance and accessibility, with the full text of articles either being available through the RCVS Knowledge library, on open access or from other publications to which a significant number of veterinary professionals are likely to have access. This means that there may be relevant evidence that is not included.

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