Potential predictive markers of chemotherapy for advanced gastric cancer: Biomarker study in GC0301/TOP-002, randomized phase III study of irinotecan plus S-1 versus S-1.

55 Background: Irinotecan plus S-1(IRI-S) achieved longer median survival than S-1 monotherapy and was well tolerated for patients with advanced gastric cancer (AGC) in GC0301/TOP-002, but it did not show significant superiority (Gastric Cancer 2011). According to subset analyses, IRI-S may have extra survival benefit in some group of patients, prompting to explore prognostic or predictive markers.We correlated expression of 5 genes related to DNA and anticancer drug metabolism (TS, DPD, Topo-I, ERCC1, TP) with outcome of patients in each arm. Methods: Paraffin-embedded primary tumor specimens before chemotherapy were available from 126 of 326 patients. mRNA expression in microdissected tumors was measured by real-time RT-PCR, and categorized into low and high using the median as a cut-off. Multivariate analysis for overall survival (OS) adjusting baseline factors, gene expression and treatment (S-1/IRI-S) was performed with a Cox regression model. Interaction tests were also carried out between gene expr...