Investigation of serum Ki-67 as a biomarker in tumor-bearing dogs

Because of the limited number of tumor markers in veterinary medicine, there is need for identifying new markers. Ki-67 has been investigated as a tissue marker of malignant alterations. We hypothesized that Ki-67 would also be measurable in serum and should therefore be elevated in cases of malignancy. The purpose of this prospective study was to measure Ki-67 in clinically healthy dogs, dogs with nonmalignant diseases, and dogs with malignant tumors. Samples from 8 healthy dogs, 13 dogs with nonmalignant diseases, and 20 dogs with malignant tumors were collected. Ki-67 was measured using the commercially available canine-specific ELISA. Results demonstrated undetectable Ki-67 serum concentrations in healthy dogs. Dogs with nonmalignant diseases displayed low Ki-67 serum concentrations. In contrast, dogs with malignancies showed significantly increased serum Ki-67 concentrations compared with the healthy (p<0.001) or nonmalignant diseased dogs (p<0.001). The degree of malignancy had a positive influence on serum Ki-67 levels. In contrast, no influence of tumor size on Ki-67 serum concentration was observed (p>0.05). Comparing healthy dogs and tumor bearing dogs a sensitivity of 0.75 and a specificity of 1.0 can be calculated using a Ki-67 cut-off value of 5.5pg/mL. When dogs with a low degree of malignancy were compared with dogs of moderate-to-severe degree malignant tumors a sensitivity of 1.0 and a specificity of 1.0 can be observed at a Ki-67 cut-off value of 19.25pg/mL. In conclusion, our results demonstrate an association of malignancies with elevated Ki-67 serum concentrations in dogs.