Currently removing the affected eye is the only way to diagnose a common form of malignant melanoma of the iris in cats. However, cats also get benign tumors of the iris, so it is important to correctly distinguish between the two tumors. If incorrectly diagnosed, the cancer could spread or the cat could lose an eye unnecessarily. In human cancer patients, the level of cell-free DNA (cfDNA) is significantly higher in the bloodstream than in healthy individuals. This form of DNA can show evidence of tumor specific mutations as well. Elevated cfDNA has been identified in both dogs and humans with breast cancer. Detecting tumor related DNA in a cat’s bloodstream could provide a way to diagnose feline diffuse iris melanoma without risking the removal of the eye unnecessarily.