Concordance of KRAS mutation detection between Illumina next generation gene sequencing (NGS) and CLIA-approved, clinical assays in metastatic colorectal cancer (mCRC)

345 Background: It is well known that KRAS mutations limit the efficacy of anti-EGFR therapy in patients with mCRC. Therefore, accurate testing of KRAS is needed to ensure that appropriate patients receive anti-EFGR therapy. Most clinical institutions conduct KRAS testing in CLIA approved labs using standard DNA sequencing methods. The purpose of this study is to correlate KRAS mutation detection by Illumina KRAS gene sequencing to standard KRAS testing performed with CLIA. Methods: We analyzed tumor samples collected from 471 patients between 1998-2010. Patients were chosen randomly based on availability of sufficient tissue for DNA extraction. We performed targeted exome sequencing using an Illumina NGS platform with 50-100X coverage of KRAS. The BWA/GATK pipeline was used to identify variants and indels. Because matched normal samples were not available for comparison to identify somatic mutations, filtering of normal variants was performed using 1000 Genomes. Variants identified in 1000 Genomes with an MAF < 0.01 were filtered. Results: Out of 471 patients, 83 pts had KRAS testing done both by exome sequencing & CLIA approved labs. The concordance rate between the two testing methods was 89%. 39 pts (47%) were KRAS mutation negative (wild type) and 35 pts (46%) harbored KRAS mutation as determined by both methods. Of these, 31 pts had codon 12 mutations and 4 pts had codon 13 mutations. However, 6 pts (7%) were found to have no KRAS mutation using CLIA but were found to have KRAS mutations by NGS (two had A146V mutations, the others had Q61 mutations). In addition, 3 pts (4%) were KRAS mutants using CLIA but wild type by NGS. Thus, 10% of samples tested showed a discrepancy in outcome between the NGS & CLIA testing. Conclusions: Standard DNA sequencing methods (CLIA) was able to identify a majority of the KRAS mutants detected by NGS. However 10% of patients had either false positive or false negative results. The main explanation for this discrepancy is that CLIA approved labs generally only test for codons 12 & 13. The clinical role for NGS in tumor KRAS mutation detection should be further investigated to ensure that patients with mCRC receive appropriate therapy.