Tailored Treatment in Metastatic Colorectal Cancer

The TS and MTHFR polymorphism has been investigated in a new study based on analysis of normal tissue. The results indicated that protein with a 3/3 TS polymorphism or a MTHFR T polymorphism had a significantly higher response rate and a longer time to progression than the other groups when treated with bolus 5-FU. Capecitabine is metabolised to 5-FU through a number of enzymatic steps. It is the first rationally designed drug that is based upon the high concentration of thymidine phosphorylase (TP) in many human tumors compared to normal tissue. TP is the last step in the conversion of capecitabine to 5-FU and seems to be the limiting factor for the activation. Capecitabine may to some extent mimic continues 5-FU infusion as opposed to bolus 5-FU. A number of small investigations have indicated that patients with 2R/2R TS polymorphism have a higher response rate than heterozygous patients. The TS and MTHFR polymorphism analysis can easily be performed on sputum, which means an easy collection and sending of the samples. At present single agent chemotherapy is based on three drugs (5-FU, capecitabine, and Irinotecan) with almost the same overall activity. It seems rational to investigate if improvement can be obtained by tailoring the treatment according to gene polymorphism.