The use of ROC analysis to distinguish between non-neoplastic diseased dogs and dogs with malignant tumours revealed that serum Ki-67 concentrations above 1.9 ng/mL indicate a malignant tumour in the organism, and are associated with a sensitivity of 0.63 and a specificity of 0.62, with an AUC of 0.66. The gene discussed is MKI67; the disease is cancer.