Detection of Age-Related Somatic Alterations in Canine Blood Using Next-Generation Sequencing-Based Liquid Biopsy: An Analysis of over 4800 Dogs

Simple Summary In humans there is a biological phenomenon known as CHIP (clonal hematopoiesis of indeterminate potential) in which somatic (acquired) mutations cause blood cells of a certain type to grow disproportionately by making many copies (or "clones") of themselves. Although most people who are found to have CHIP do not have cancer, they are known to be at higher risk of developing cancer. CHIP has been studied extensively in humans, where it occurs more frequently with increasing age and is thought to be present in 10-20% of people over the of age 70; however, CHIP has not been well-studied in other species. This study provides the first population-level evidence for the potential existence of CHIP-like findings in dogs. Further research is needed to determine the clinical significance of these findings in canine patients. Age-related somatic genomic alterations in hematopoietic cell lines have been well characterized in humans; however, this phenomenon has not been well studied in other species. Next-generation sequencing-based liquid biopsy testing for cancer detection was recently developed for dogs and has been used to study the genomic profiles of blood samples from thousands of canine patients since 2021. In this study, 4870 client-owned dogs with and without a diagnosis or suspicion of cancer underwent liquid biopsy testing by this method. Copy number variants detected exclusively in genomic DNA derived from white blood cells (WBC gDNA-specific CNVs) were observed in 126 dogs (2.6%; 95% CI: 2.2-3.1); these copy number variants were absent from matched plasma cell-free DNA, and from tumor tissue in dogs with concurrent cancer. These findings were more common in older dogs and were persistent in WBC gDNA in over 70% of patients, with little to no change in the amplitude of the signal across longitudinal samples. Many of these alterations were observed at recurrent locations in the genome across subjects; the most common finding was a partial loss on CFA25, typically accompanied by a partial gain on the same chromosome. These early findings suggest that age-related somatic alterations may be present at an appreciable frequency in the general canine population. Further research is needed to determine the clinical significance of these findings.