Introduction

1. K-RAS mutation status associated with clinical outcome in metastatic colorectal cancer patients treated with 5-fluorouracil/oxaliplatin Wu Zhang1, Anthony El-Khoueiry1, Dongyun Yang2, Alexandra Pohll, Yan Ning1, Georg Lurje1, Phillip Manegold1, Syma Iqbal and Heinz-Josef Lenz1, 2, 1.Dept of Medical Oncology, USC/Norris Comprehensive Cancer Center, Los Angeles, CA 2.Dept of Preventive Medicine, USC/Norris Comprehensive Cancer Center, Los Angeles, CA Introduction Results Oncogenic K-RAS mutations are found in about 40% (20-50%) of colorectal cancers. Eight-six percent of these mutations occur at codons 12 and 13. Previous in vitro studies suggested that mutant ras genes may confer resistance to cytotoxic effects of platinum, possibly through up-regulation expression of ERCC1, which has been shown to be associated with platinum sensitivity. We tested the hypothesis whether the K-RAS mutation status will predict efficacy of 5-FU and oxaliplatin in patients with metastatic colorectal cancer in a phase II clinical trial. Patients and method A total of 173 patients were accrued in a phase II study of oxaliplatin in combination with continuous infusion 5-FU in patients with metastatic colorectal cancer refractory to 5-FU/CPT-11 based chemotherapy from September 2001 to August 2004. Sixty-six patients tumor tissue were available for current pharmacogenetic study. The clinical and pathological characteristics of these 66 patients were similar to the characteristic of the whole cohort of 173 patients. The dose of oxaliplatin administered was 130mg/m2 every 3 weeks and 5-FU was 200mg/m2/day CI for 10 weeks followed by 2 weeks rest. Mutational analyses of K-RAS were performed using genomic DNA isolated from microdissected tumor specimens by DNA sequencing. Primers used for K-RAS codons 12 and 13 were as follows: K-RAS forward, 5’-TGACTGAATATAAACTTGTGGTAGTTG-3’, and K-RAS reverse, 5’-TCGTCCACAAAA TGATTCTGAA-3’. PCR fragments were sequenced on an ABI 3100A Capillary Genetic Analyzer (Applied Biosystems) and analyzed in both sense and antisense directions for the presence of heterozygous mutations. DNA sequence analyzes were done by two independent investigators (G.L and W.Z.) using the ABI Sequencing Scanner v1.0(Applied Biosystems). Appropriate positive and negative controls were included for each of the codons evaluated. Univariate analysis (Fisher’s exact test for response; log-rank test for TTP and OS) was performed to examine associations between polymorphisms and clinical outcome. Conclusion K-RAS mutation status may be a potential molecular predictive marker of oxaliplatin based chemotherapy for patients with metastatic colorectal cancer Larger, prospective studies are warranted to confirm our preliminary findings.