Study of KRAS new predictive marker in a clinical laboratory

ABSTRACT

BACKGROUND: The presence of somatic mutations in the KRAS gene has been identified as a reliable strong negative predictor for the response to targeting the epidermal growth factor receptor (EGFR), in patients with metastatic colorectal cancer and the use of anti-EGFR monoclonal antibodies such as Cetuximab and Panitumumab is now restricted to patients with no detectable KRAS mutations. Between 30 and 40 % of colorectal cancers contain a mutated KRAS oncogene. The aim of this study was to evaluate concordance between three methods to analyze KRAS mutational status in regard to clinical testing. METHODS: We analyzed KRAS mutations in codons 12 and 13 of exon 2 in one hundred formalin-fixed paraffin-embedded (FFPE) colorectal cancer samples by three different methods: Direct Sequencing and two commercial kits on allele-specific oligonucleotide hybridization (KRAS StripAssay, Vienna Lab.) and Amplification Refractory Mutation System/Scorpions (ARMS/S; TheraScreen KRAS Mutation kit DxS) based on q-PCR. RESULTS: We have found similar frequencies of KRAS mutations by TheraScreen and Strip-Assay (44 and 48 %), with a κ value of 0.90, indicating almost perfect agreement between methods. The frequency by direct sequencing was much lower (26 %) and the κ values were 0.67 (compared to TheraScreen) and 0.57 (compared to Strip-Assay) indicating low sensitivity. CONCLUSIONS: On analyzing KRAS mutation in FFPE tumor samples, direct sequencing sensitivity is too low to be used in a clinical setting. Choosing between ARMS/S; TheraScreen KRAS Mutation kit DxS and KRAS StripAssay, Vienna Lab, will depend on laboratory facilities and expertise (AU)