Chemopredictive diagnostic project in patients (pts) receiving capecitabine (X) or 5-FU/leucovorin (LV) as first-line chemotherapy for metastatic colorectal cancer (MCRC).

9652 Background X (Xeloda®) is a tumor-activated oral fluoropyrimidine, with superior response rate and improved safety compared to bolus 5-FU/LV in 1st-line MCRC. Variation in tumor expression levels of thymidine phosphorylase (TP), thymidylate synthase (TS) and dihydropyrimidine dehydrogenase (DPD) may impact efficacy or toxicity of X-containing regimen. We are retrospectively evaluating the relationship of the expression of these enzymes to outcomes in a 1st-line MCRC phase III trial of X vs 5-FU/LV (Hoff, JCO 2001). 9 Canadian sites participated in the trial (N=164). Methods Pts were eligible if they received at least one dose of chemotherapy. We obtained informed consent through next-of-kin or Ethics Committee waiver. We obtained formalin-fixed, paraffin-embedded tissue from primary tumors +/- synchronous metastases. We analyzed TP, DPD and TS expression levels using immunohistochemistry (IHC) and quantitative reverse transcriptase - polymerase chain reaction (RT-PCR) kits, both from Roche Diagnostic...