Flow Cytometry and Liquid Biopsy in Veterinary Blood-Based Cancer Diagnostics: A Comparative Pathology Approach

Abstract

Cancer continues to be among the top causes of morbidity and mortality in companion and production animals, warranting the development of efficient, rapid, accurate, and minimally invasive diagnostic approaches. This review compares the diagnostic utility of flow cytometry and liquid biopsy in veterinary oncology and highlights the complementary nature of these two assays in blood-based cancer detection and monitoring. Flow cytometry provides quantitative multiparameter information on cell morphology, immune status, and tumor heterogeneity that cannot be achieved using other methods for the diagnosis of hematologic malignancies and monitoring response to treatment. Liquid biopsy provides a real-time assessment of the tumor burden and genetic alterations by detecting circulating tumor cells (CTCs), circulating tumor DNA (ctDNA), microRNAs, and extracellular vesicles at the molecular level, which does not require tissue biopsy sampling. Collectively, these two approaches serve as a morpho-molecular diagnostic continuum and enable the early detection of cancer and surveillance of diseases in animals, as well as precision oncology therapy based on veterinary species. This review also incorporates a comparative pathological approach, underscoring the translational importance of spontaneous animal cancers as surrogates for human oncology. Although there are issues with regard to assay standardization, species-specific reagents, and a paucity of reference databases, continuous improvements have been reported in the combination of multi-omics integration, AI-assisted data interpretation, and bioinformatics, which will extend the clinical applications of these tools. Finally, it should be emphasized that flow cytometry and liquid biopsy meet thanks to a remarkable case of convergence, which will contribute in a transformative fashion to precision veterinary oncology, reducing diagnostic bias and ethical feasibility, and making translation more relevant between species.