Thymidine kinase and cancer monitoring.

Thymidine kinases (TK) have a key function in the synthesis of DNA. Two isoenzymes have been characterized: TK1 is cell cycle-dependent and present in the cytoplasm whereas TK2--located in mitochondria--is cell cycle-independent. The diagnostic and prognostic role of TK1 has recently been investigated. TK1 might be helpful for screening and monitoring of human malignancies. TK1 may also serve as a prognostic factor for progression. Herein, we summarize the status of TK1 for cancer monitoring and point out its use as a proliferation marker. A comprehensive overview about the association of TK-1 with various entities is given.