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

Plasma KMO is a promising screening biomarker for canine neoplasia, outperforming Ki-67 with an AUC of 0.837.

This case-control study evaluated plasma kynurenine 3-monooxygenase (KMO) and Ki-67 as potential screening biomarkers for neoplasia in dogs, enrolling 162 dogs with confirmed tumors and 46 tumor-free controls. KMO concentrations were significantly elevated in neoplastic dogs (median 2.02 ng/mL) compared to controls (median 0.69 ng/mL; P < .0001), demonstrating strong discriminatory ability with an AUC of 0.837 on ROC analysis. Ki-67 concentrations were also higher in neoplastic dogs (median 4.28 ng/mL vs. 3.80 ng/mL; P < .05), though its diagnostic performance was modest with an AUC of 0.644. Importantly, no significant correlation was found between KMO and Ki-67 levels (R² = 0.003; P = .48), and approximately 50.6% of dogs showed inconsistent results between the two markers, suggesting they reflect different aspects of tumor biology. KMO demonstrated superior standalone diagnostic utility compared to Ki-67, which lacked sufficient sensitivity and specificity for independent clinical use. However, Ki-67 may still provide complementary information about systemic tumor activity when used alongside KMO. This study represents one of the first evaluations of plasma KMO activity in a clinical veterinary oncology setting and supports its potential as a minimally invasive screening tool. Limitations include the case-control design, heterogeneity of tumor types, and lack of tumor-stage stratification. Further prospective studies with larger, more homogeneous cohorts are warranted to validate these findings and define clinical cut-off values.

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