The role of TP, TS, and DPD as potential predictors of outcome following capecitabine plus oxaliplatin (XELOX) versus bolus 5-fluorouracil/leucovorin (5-FU/LV) as adjuvant therapy for stage III colon cancer: Biomarker findings from study NO16968 (XELOXA).

3578 Background: In NO16968, XELOX was superior in terms of disease-free survival (DFS) and overall survival (OS) to bolus 5-FU/LV as adjuvant therapy for stage III colon cancer (Schmoll et al. ASCO GI 2012). Three key enzymes appear to have the potential to predict efficacy and/or safety of fluoropyrimidine-based treatment: thymidine phosphorylase (TP), thymidylate synthase (TS), and dihydropyrimidine dehydrogenase (DPD). We evaluated the association between baseline TP, TS and DPD and outcome (DFS and OS). Methods: Pts with stage III colon cancer received either XELOX (8 cycles, 24w) or bolus 5-FU/LV (Mayo Clinic, 6 cycles, 24w; Roswell Park, 4 cycles, 32w). The primary study endpoint was DFS; secondary endpoints included OS. TP, TS and DPD expression levels were determined in formalin-fixed, paraffin-embedded tissues by RT-PCR, and the median used as a cut-off point: high (above median) vs. low (below median). Results: The biomarker population included 498 (26%) of 1886 pts entered (XELOX, n=242; 5-FU/...