Abstract: Background: Early detection of tumors prolongs the lifespan of affected dogs. Though tumor biomarkers have been used, single detection provided limited information in clinical oncology. Kynurenine 3-monooxygenase (KMO) is reported as a tumor-related antigen, and Ki67 is strongly associated with tumor cell proliferation. However, few studies explore the combined evaluation of KMO and Ki67 in canine cancer diagnosis. Objective: This study aimed to investigate the diagnostic values of KMO and Ki67 in canine plasma. Methods: KMO and Ki67 concentrations in plasma were determined through a commercial enzyme-linked immunosorbent assay (ELISA) from 180 cancer dogs and 56 tumor-free individuals. Results: KMO levels were significantly higher in cancer dogs (2.31 µg/ml ± 0.88 µg/ml) than those in tumor-free individuals (0.74 µg/ml ± 0.70 µg/ml, p < 0.0001). The values of Ki67 increased in cancer dogs (4.65 ng/ml ± 1.13 ng/ml) compared with those in controls (4.07 ng/ml ± 0.78 ng/ml, p < 0.05). We further defined the tumor dogs into tumor-positive or negative groups with the cut-off values of 0.99 µg/ml (KMO) and 4.10 ng/ml (Ki67). Notably, 31.8% of tumor cases exhibited inconsistent KMO and Ki67 increase, which might imply that simultaneously determining KMO and Ki67 can potentiate the diagnostic power. Conclusions and clinical importance: The results show that KMO and Ki67 were effective biomarkers in discriminating tumor-bearing dogs from normal ones. Furthermore, we also established a dual-screening platform with practical diagnostic ability in cancer dogs.
