Study of KRAS new predictive marker in a clinical laboratory

Abstract

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. 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. 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. 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.