Serum thymidine kinase activity: an alternative to histologic markers of cellular proliferation in canine lymphoma.

Thymidine kinase (TK) is a cellular enzyme which is involved in a 'salvage pathway' of DNA synthesis. It is activated in the G1/S phase of the cell cycle, and its activity has been shown to correlate with the proliferative activity of tumor cells.... Clinical studies have reported high serum TK concentrations in a variety of neoplasias. The majority of these studies concerned hematological malignancies. TK seems to be a useful marker in non-Hodgkin's lymphoma, where it correlates with clinical staging and provides marked prognostic information on (progression-free) survival.