EORTC receptor and biomarker study group report analytical and technical evaluation of a thymidine kinase radio-enzymatic assay in breast cancer cytosols

Background: High thymidine kinase (TK) activity in cancer cells could count eract adjuvant chemotherapy directed at the inhibition of de novo DNA synth esis. TK is an independent prognostic factor in breast cancer patients rece iving adjuvant chemotherapy. Material and Methods: In this paper; we descri be the effects of extraction and dilution buffer composition on TK enzymati c activity values obtained in breast cancer cytosols with the Prolifigen se rum TK-REA kit (Sangtec Medical, Sweden). Results: The addition of MgCl2 an d ATP early in the assay, preferably during the extraction of tumor tissue, seems critical to stabilise the enzyme. Furthermore, the use of normal cal f serum to dilute both standards and samples is necessary to obtain satisfa ctory pal allelism between TK values in serial dilutions of breast cancer c ytosols. Conclusion: Based on the data reported here, the manufacturer has changed the cytosol diluent composition and is adding a specific cytosol as say insert to the Prolifigen TK-REA kit. As evidenced by the laboratory rep roducibility, these modifications to the serum assay led to an adequate, st andardized protocol for analyzing TK activity in breast tumor cytosols.