Possible False Results With cobas^? EGFR Mutation Test v2 and Oncomine Dx Target Test for EGFR Mutation

Background/Aim: Disparities in the results of next-generation sequencing-based multiplex gene panel tests and those of single-gene tests when detecting epidermal growth factor receptor (EGFR) mutations in non-small-cell lung cancer (NSCLC) have been reported. However, the possible underlying causes have not been investigated. The aim of this study was to explore the possibilities and causes of false results obtained using cobas((R)) EGFR Mutation Test v2 (cobas((R)) EGFR) and Oncomine Dx Target Test (ODxTT). Patients and Methods: The data of patients with NSCLC who underwent gene assessment using both cobas((R)) EGFR and ODxTT between April 2021 and May 2022 were retrospectively reviewed. Disparate results of EGFR mutation analyses were then reviewed. Results: One hundred and sixteen patients were included in the analysis. The results of six samples were inconsistent. In four samples, exon 20 insertion mutations were detected using cobas((R)) EGFR, but not identified using ODxTT. A fragment analysis was performed on three of the four samples, and all showed negative results for exon 20 insertion. Furthermore, one false negative result was obtained in the ODxTT for both exon 19 deletion and L858R mutations. For exon 19 deletion mutation, a single nucleotide variant from adenine to thymine was identified close to the mutation site. Conclusion: False positives for exon 20 insertion may occur when using cobas((R)) EGFR, and false negatives for exon 19 deletion and L858R mutations may occur when using ODxTT.