Prognostic importance of thymidine kinase in colorectal and breast cancer

Background: Thymidine kinase (TK) plays an essential role in the processing of thymidine within the cell and therefore it is an important marker of proliferation, particularly in tumor cells. The aim of our study was to determine the diagnostic, prognostic and predictive importance of TK measurement in cancer. Patients and Methods: TK was measured using radioreceptor analysis (RRA) with Immunotech assay kits. The serum level of TK was measured in 1087 patients with malignant disease (355 patients with hematology malignancies and 732 patients with solid tumors). Results: Serum levels of TK were significantly elevated in inflammatory and immunological diseases in comparison with healthy individuals. Malignant diseases were associated with elevated serum levels of TK only in particular cases (e.g. hematological malignancies, cervical cancer). This marker has a high sensitivity for use as a primary diagnostic tool. It also has a high sensitivity during the follow-up period in breast and colorectal cancer for the prediction of relapse at the time of primary diagnosis and 3 months earlier than the diagnosis of relapse by imaging methods. Conclusion: TK represents a secondary tumor marker which is particularly useful for cancer disease monitoring. Interpretation of this marker must be performed only in association with evaluation of clinical status since all other possible non-specific causes (inflammatory or immunological diseases) of elevated serum levels must be excluded.