Detection of EGFR Variants in Plasma: A Multilaboratory Comparison of the cobas EGFR Mutation Test v2 in Europe

Molecular testing of EGFR is required to predict the response likelihood to targeted therapy in non–small-cell lung cancer. Analysis of circulating tumor DNA in plasma may complement limitations of tumor tissue. This study evaluated the interlaboratory performance and reproducibility of the cobas EGFR Mutation Test v2 to detect EGFR variants in plasma. Fourteen laboratories received two identical panels of 27 single-blinded plasma samples. Samples were wild-type or spiked with plasmid DNA to contain seven common EGFR variant s at six predefined concentrations from 50 to 5000 copies per mL. The circulating tumor DNA was extracted by the cobas cfDNA Sample Preparation kit, followed by duplicate analysis with the EGFRv2 kit (Roche Molecular Systems, Pleasanton, CA). Lowest sensitivities were obtained for the c.2156G>C p.(Gly719Ala) and c.2573T>G p.(Leu858Arg) variants for the lowest target copies. For all other variants, sensitivities varied between 96.3% and 100.0%. Specificities were all 98.8% to 100.0%. Coefficients of variation indicated good intra and interlaboratory repeatability and reproducibility, but increased for decreasing concentrations. Prediction models revealed a significant correlation for all variants between the pre-defined copy number and the observed semiquantitative index values which reflects the samples' plasma mutation load. This study demonstrates an overall robust performance of the EGFRv2 kit in plasma. Prediction models may be applied to estimate the plasma mutation load for diagnostic or research purposes.