Taylor SS, Dodkin S, Papasouliotis K, et al. Serum thymidine kinase activity in clinically healthy and diseased cats: a potential biomarker for lymphoma. J Feline Med Surg. 2013; 15: 142-7.
Researchers at the University of Bristol, UK and collaborators investigated the utility of serum thymidine kinase-1 (sTK1) as a biomarker for feline lymphoma. Thymidine kinase-1 is a cytoplasmic salvage enzyme involved in phosphorylation of deoxythymidine to deoxythymidine monophosphate, one of the key steps in the synthesis of DNA and thereby in cell division and proliferation. Its action is markedly increased only during the DNA synthesis phase (S-phase) of the cell cycle. This association with DNA synthesis and correlation with cell proliferation is particularly high in hematopoietic malignancies like feline lymphoma. The aim of this study was to determine a reference level for sTK1 in clinically healthy cats and then to evaluate the potential use of sTK1 as a biomarker for feline lymphoma by comparing levels in cats with lymphoma, inflammatory disease, and non-hematopoietic neoplasia (NHPN).
Forty-nine serum samples were collected from clinically healthy cats and sTK1 activity was determined using a radioenzyme technique which has a linear measurement range of 1-100 U/l. Based on these healthy cats, a reference interval of sTK1 < 5.5 U/l was established. The lymphoma group comprised 33 cats with a median age of 9 years, the inflammatory disease group comprised 55 cats with a median age of 7 years, and the NHPN group comprised of 34 cats with a median age of 10 years. Stringent criteria were used for inclusion in each group. The majority of cats in each group were non-pedigree cats. Cats in the lymphoma group had significantly higher mean sTK1 activity level (17.5 U/l) than clinically healthy cats (2.2 U/l), cats with inflammatory disease (3.4 U/l), or cats with NHPN (4.3 U/l). However, the lymphoma group showed a wide variability in the sTK1 activity (<1 to >100 U/l) and a receiver-operator curve (ROC) revealed a low sensitivity for this test. The researchers suggest a cut-off point of 8.9 U/l based on the ROC is highly suggestive of a lymphoma diagnosis, while there is a low predictability for cats with low sTK1 values. In addition, the number of cats in the study was too low to draw conclusions regarding lymphoma anatomical location and sTK1 activity. [GO]