Serum TK1 protein and C-reactive protein correlate to treatment response and predict survival in dogs with...

Thymidine kinase 1 (TK1), involved in DNA precursor synthesis, is used as a serum biomarker in cancer diagnostics in both human and veterinary medicine. We investigated the utility of serum TK1 protein (TK1p) and TK1 activity (TK1a) determinations for prognosis and monitoring of canine hematological malignancies. The combination of TK1p or TK1a with canine C-reactive protein (CRP) determinations was also investigated. Serum samples from 51 client-owned dogs with naive hematological malignancies and from 149 healthy subjects were included. Serum TK1p levels were determined using a prototype TK1-ELISA, TK1a using the [³H]-dThd phosphorylation assay, and CRP using an immunoturbidimetric assay. Mean TK1p in sera from dogs with tumors was significantly higher than from healthy dogs (mean ± SD = 3.9 ± 5.9 vs. 0.45 ± 0.15 ng/mL). Similarly, TK1a in hematological malignancies was significantly higher than in healthy dogs (mean ± SD = 15.1 ± 31.3 vs. 0.96 ± 0.33 pmol/min/mL). The receiver-operating characteristic indicated that a combination of TK1p or TK1a with CRP gave higher sensitivity than either biomarker alone for the prognosis of hematological malignancies. Median pretreatment TK1p and TK1a levels were significantly higher than in dogs in remission and correlated with clinical outcome. Kaplan-Meier curve analysis showed that naive dogs with high TK1p, TK1a, and CRP had significantly shorter survival. This study present two new polyclonal antibodies used in an ELISA system to determine TK1p. The study also show that combining TK1p or TK1a with CRP gave higher sensitivity than either biomarker alone. Monitoring patients in the study while undergoing chemotherapy, suggests that the TK1 + CRP combination could be useful in a biomarker panel, possibly aiding the prognosis and therapy monitoring of hematological malignancies in dogs.