Evaluation of plasma kynurenine 3-monooxygenase and Ki-67 as screening biomarkers for neoplasia in dogs.

BACKGROUND: Early detection of tumors might prolong the survival of dogs. Kynurenine 3-monooxygenase (KMO) and Ki-67 are tumor biomarkers, but few studies have described the clinical value of KMO and Ki-67 in veterinary medicine. HYPOTHESIS/OBJECTIVES: This study aims to compare the activity of KMO and the concentration of Ki-67 between healthy dogs and dogs with neoplasms. ANIMALS: A total of 162 dogs with different types of tumors were included. Forty-six tumor-free individuals were included as the control group. METHODS: This is a case-control study. Dogs with neoplasms, confirmed through medical record review, were recruited. The primary outcomes were the plasma concentrations of KMO and Ki-67, along with their diagnostic efficacy. RESULTS: Expression levels of KMO were significantly higher in dogs with neoplasms (median, 2.02 ng/mL; IQR, 1.03-3.65) than in tumor-free individuals (median, 0.69 ng/mL; IQR, 0.23-1.18; P < .0001). The values of Ki-67 were higher in dogs with neoplasms (median, 4.28 ng/mL; IQR, 3.75-4.84) than in the control group (median, 3.80 ng/mL; IQR, 3.31-4.43; P < .05). No significant correlation was found between KMO and Ki-67 concentrations (R2 = 0.003, P = .48) in the tested samples and 50.6% (82/162) of dogs exhibited inconsistent results. The area under the ROC curve for KMO and Ki-67 were 0.837 and 0.644. CONCLUSIONS AND CLINICAL IMPORTANCE: This study presents that KMO is an effective biomarker and Ki-67 is an adjunctive marker. While lacking standalone diagnostic utility, Ki-67 reflects systemic tumor biology and complements biomarkers such as KMO.