Liquid Biopsy and Circulating Tumor DNA: Where Veterinary Oncology Diagnostics Are Headed
Cutting Edge Diagnostics · Canine, Feline · Oncology
Liquid biopsy — the detection of tumor-derived material circulating in peripheral blood — has moved from a research concept to a commercially available diagnostic tool in veterinary oncology over the past several years. It is not yet a replacement for tissue histopathology, and it may never be. But the trajectory of where this technology is going is worth understanding now, because the way oncology cases are worked up, monitored, and followed is likely to look meaningfully different within the next three to five years.
What liquid biopsy detects and how
The primary analyte in veterinary liquid biopsy testing is circulating tumor DNA (ctDNA) — fragments of DNA shed from tumor cells into the bloodstream through apoptosis, necrosis, and active secretion. In a patient with an active malignancy, a proportion of the cell-free DNA circulating in plasma is tumor-derived and carries the somatic mutations, copy number alterations, and methylation signatures of the primary tumor. The challenge is detecting that signal against the background of cell-free DNA from normal tissues, which constitutes the overwhelming majority of circulating DNA in most patients.
Modern liquid biopsy platforms address this through several approaches. Mutation-based detection identifies specific oncogenic variants — point mutations, insertions, deletions — known to be associated with canine or feline malignancies. Copy number alteration analysis detects chromosomal gains and losses across the genome that are characteristic of malignant versus benign tissue. Methylation profiling, the most recently developed approach, identifies epigenetic signatures on circulating DNA fragments that distinguish tumor-derived from normal DNA and can in principle identify tissue of origin — pointing toward where in the body the tumor is located before any imaging is performed.
Blood collection for ctDNA testing uses standard peripheral venipuncture into EDTA tubes, with plasma separated and shipped to the reference laboratory. The procedure is minimally invasive, can be repeated serially without anesthesia or sedation, and adds no procedural risk to the patient. This is a meaningful practical advantage over tissue biopsy in patients where repeated sampling is desirable for monitoring purposes.
What is commercially available now
The canine liquid biopsy market has developed faster than the feline market, driven by larger patient populations, more established oncology infrastructure, and greater commercial investment in canine cancer diagnostics. The most widely referenced platform in dogs is OncoK9 (PetDx), which uses a genome-wide copy number alteration approach to detect malignancy and, in multi-cancer positive cases, provides a signal that correlates with the likely tissue of origin. Published validation data for OncoK9 report an overall sensitivity of approximately 54% across cancer types with high specificity — meaning the test misses a meaningful proportion of confirmed cancers but rarely returns a positive result in a healthy dog. Sensitivity varies substantially by tumor type and stage, with hematologic malignancies and high-burden solid tumors detected more reliably than early-stage or low-shedding tumors.
IDEXX launched a canine lymphoma-specific liquid biopsy test in early 2025, targeting a narrower diagnostic question with correspondingly higher sensitivity for that indication. Additional platforms are in development or limited commercial release from other vendors. The field is active and the commercial landscape is shifting quickly enough that specific product details warrant verification against current laboratory offerings at the time of ordering.
In cats, commercial liquid biopsy options are more limited. Feline oncology has historically received less commercial diagnostic investment than canine, and the ctDNA reference databases and validation datasets needed to develop robust feline-specific platforms are still being assembled. This does not mean liquid biopsy is without utility in cats — it means the sensitivity and specificity data needed to interpret results confidently are less mature. Clinicians using liquid biopsy in feline patients should apply results with appropriate caution and a clear understanding of the current evidence base.
Current clinical utility: where the test adds value today
Liquid biopsy in its current form is most useful in specific clinical scenarios rather than as a universal screening or diagnostic tool. Understanding where it adds genuine value — and where it does not — avoids both over-reliance and underutilization.
The clearest current utility is in patients where tissue biopsy is technically difficult, high-risk, or likely to yield non-diagnostic material. A dog with a pulmonary mass, hepatic lesions, or a deep mediastinal mass that would require CT-guided biopsy under anesthesia is a patient where a blood draw that returns a positive ctDNA result meaningfully advances the diagnostic picture, even if it cannot replace tissue characterization entirely. A positive liquid biopsy result in that context elevates malignancy on the differential list, supports the decision to pursue more invasive sampling, and in some cases may be sufficient to initiate oncologic consultation.
Serial monitoring is a second area of genuine near-term utility. If a patient has undergone treatment for a confirmed malignancy, serial ctDNA measurements over time provide a minimally invasive window into treatment response and recurrence. Rising ctDNA burden in a patient in clinical remission may predate radiographically detectable recurrence by weeks to months — a lead time that could allow earlier therapeutic intervention. This application does not depend on the test being perfect at initial detection; it depends on consistency and sensitivity to change over time, which is a somewhat different performance criterion.
Screening in high-risk breeds — Golden Retrievers, Boxers, Bernese Mountain Dogs, and others with documented elevated cancer prevalence — is an application frequently discussed but currently limited by sensitivity. A test that misses roughly half of all cancers in symptomatic patients will miss a higher proportion in asymptomatic patients with lower tumor burden and lower shedding rates. Screening utility will improve as platform sensitivity improves, but it is not the primary value proposition of current-generation tests.
The relationship with tissue histopathology
Liquid biopsy and tissue histopathology answer different questions and are not interchangeable. Histopathology establishes tissue architecture, cell morphology, grade, margin status, lymphovascular invasion, and the specific diagnostic category of the tumor — information that drives surgical planning, treatment selection, and prognosis in ways that a blood-based molecular signal cannot. A ctDNA result that is positive for malignancy does not specify tumor type with sufficient resolution to replace histopathology in most cases, and a negative ctDNA result in a patient with a palpable mass does not exclude malignancy.
The more productive framing is complementary rather than competitive. Liquid biopsy can support the decision to pursue biopsy, guide monitoring after diagnosis and treatment, and in select cases provide early evidence of recurrence before lesions are imaging-detectable. Histopathology establishes the diagnosis, characterizes the tumor, and provides the pathologic information needed for informed oncologic decision-making. Both have a role; they occupy different parts of the clinical workflow.
Where this is going: the next three to five years
The trajectory of liquid biopsy in veterinary oncology over the next several years is shaped by three converging developments: improving platform sensitivity, expanding tissue-of-origin resolution, and integration into longitudinal monitoring protocols.
Platform sensitivity is the most fundamental constraint on current utility, and it is actively being addressed. Next-generation sequencing chemistries, error-correction algorithms, and larger training datasets are all pushing detection limits lower. As sensitivity improves — particularly for early-stage and low-shedding tumor types — the range of clinical scenarios where liquid biopsy adds meaningful information will expand. The goal of detecting cancer at a stage where intervention is curative rather than palliative is the most transformative potential application, and it is not yet achievable with current platforms in most tumor types.
Tissue-of-origin resolution is improving rapidly through methylation profiling. Unlike mutation-based or copy number approaches, methylation signatures carry information about the cell type from which a DNA fragment originated — because methylation patterns are established during cellular differentiation and are largely preserved in tumor cells derived from that lineage. Multi-cancer early detection tests in human medicine have demonstrated that methylation-based liquid biopsy can identify not just that cancer is present but where in the body it is located, with accuracy that improves as the signal-to-noise ratio in the assay improves. Translating this to veterinary species requires large, well-annotated training datasets spanning canine and feline tumor types — datasets that are being assembled now through academic veterinary oncology consortia and commercial partnerships.
Longitudinal monitoring integration is perhaps the nearest-term development with broad clinical impact. Standardized ctDNA monitoring protocols — defined sampling intervals, established thresholds for clinical action, and integration with imaging and clinical assessment — would transform liquid biopsy from an episodic diagnostic tool into a continuous window on disease status. For patients in remission after treatment for lymphoma, osteosarcoma, hemangiosarcoma, or other high-recurrence-rate malignancies, a validated monitoring protocol using serial ctDNA measurement would represent a meaningful advance in post-treatment surveillance. The technical capability is closer than the clinical validation, and the clinical validation work is underway.
The feline gap is worth acknowledging explicitly. The development curve for feline liquid biopsy lags canine by several years, and cats with cancer remain underserved by molecular diagnostics relative to their canine counterparts. Whether commercial investment follows the science into the feline market at pace depends partly on clinical demand — which is itself a function of how well the veterinary community understands and requests these tools. That conversation is worth starting now.
What to tell clients today
Liquid biopsy is a legitimate and available diagnostic tool with real clinical utility in specific scenarios. It is not a replacement for biopsy and histopathology, it misses a meaningful proportion of cancers at current sensitivity levels, and a negative result does not rule out malignancy. A positive result in a patient with a suspicious mass or clinical signs consistent with cancer is meaningful and warrants follow-up. Serial monitoring after treatment is a well-supported application that adds information not available from imaging alone.
The honest framing for a client whose dog or cat is being worked up for possible cancer: liquid biopsy is one tool among several, it adds information without replacing the others, and its value will increase substantially over the next few years as the technology matures. That is a reasonable and accurate summary of where the field stands.
Eric Snook, DVM, PhD, DACVP — Vetopathy. Histopathology remains the foundation of oncologic diagnosis. Questions about integrating liquid biopsy findings with tissue pathology reports? Reach out directly.