Introduction
Cell free DNA (cfDNA) is a fragment of extracellular DNA that is released by the death of blood lineage cells and tumor cells. In human medicine, it is considered as a biomarker for various diseases, but there is little information in the veterinary field, and its usefulness in cats is unknown. This study aimed to clarify the usefulness of cfDNA as a tumor biomarker by quantifying cfDNA levels in various diseases in cats.
Methods
Plasma samples were collected from 40 cats with various tumors and 22 cats with various diseases except tumors, and 10 healthy controls. cfDNA was isolated from 500 µl plasma and its concentration was quantified by real-time PCR resulting in short (99bp) and long (213bp) fragments of long interspersed nuclear element-1 (LINE-1) gene, then DNA integrity index (DII) was calculated (LINE213/99). The diagnostic values of cfDNA for the prediction of metastasis were assessed by using receiver operation characteristic (ROC) curves. A followup study was conducted on four cats with lymphoma, and the plasma cfDNA level was quantified throughout disease progression.
Results
cfDNA concentrations were significantly lower in cats with various tumors than in those with various diseases except tumors and healthy controls. However, the DII was not change among three groups. In tumor group, significantly higher cfDNA levels were observed in cats with metastasis. The area under the ROC curve of cfDNA level for predicting metastasis was 0.806 with a sensitivity of 72.2% and a specificity of 85.2%. There was a measurable correlation between cfDNA level and clinical status, and fluctuations in cfDNA were observed weeks to months before disease progression during follow-up in lymphoma cases.
Conclusion
These results indicate that measurement of cfDNA levels using LINE-1 gene may be a predictive biomarker for feline malignancies. Additionally, cfDNA analysis may be a potentially useful tool for monitoring the progression of feline lymphoma. Further research is required to establish the true clinical value of cfDNA as a biomarker in cats.
