GCF has funded Dr Nuala Helsby and her team at the University of Auckland, a year's part time salary for a clinical trial manager to support the following research. THYmine2 is an observational study to assess whether the thymine loading test can prospectively categorise patients who cannot tolerate 5-FU treatment (e.g. FOLFOX, CapeOx, FLOX). This treatment is commonly used in GI and breast cancer treatment. Reactions occur in approximately 10% of patients and can result in life threatening events. Despite extensive research it is still difficult to determine who is at risk of life-threatening toxicity related to 5-FU. This study aims to examine whether the ratio of thymine to its metabolite in urine can discriminate between patients who tolerate 5-FU and those who experience severe 5-FU related toxicity. If successful then it could be a simple and inexpensive way to identify susceptible patients before they start treatment and allow for dose adjustments or alternative treatment. This is partly funded by the David Levene Foundation.