High levels of inactive thymidine kinase 1 polypeptide detected in sera from dogs with solid tumours by immunoaffinity methods: implications for in vitro diagnostics.

Determination of serum thymidine kinase 1 (STK1) activity has been used as a proliferation marker for neoplastic diseases in both human and veterinary medicine. The purpose of this study was to determine STK1 activity and enzyme levels in different dog tumours. Serum samples from three dogs with leukaemia, five with lymphoma, 21 with solid tumours and 18 healthy dogs were analyzed for STK1 activity, using an optimized [3H]-deoxythymidine (dThd) phosphorylation assay, and for STK1 protein levels using an immunoaffinity/western blot assay.