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Reduced sensitivity for EGFR T790M mutations using the Idylla EGFR Mutation Test
  1. Eric Lee,
  2. Victoria Jones,
  3. Eleni Topkas,
  4. James Harraway
  1. Molecular Pathology, Sullivan Nicolaides Pathology, Brisbane, QLD, Australia
  1. Correspondence to Dr Eric Lee, Molecular Pathology, Sullivan Nicolaides Pathology, Brisbane, QLD 4006, Australia; eric_lee{at}


Aims Osimertinib is a third-generation EGFR (epidermal growth factor receptor) tyrosine kinase inhibitor that is effective in non-small cell lung cancer (NSCLC) harbouring the EGFR T790M mutation. The Idylla EGFR Mutation Test is a rapid cartridge-based method for detecting T790M and other EGFR mutations. However, false negative T790M results have been reported, and the sensitivity of the assay for this mutation is uncertain.

Methods Eighty NSCLC samples were tested by both Idylla and a next-generation sequencing (NGS) assay; 46 were from patients at disease progression, and 24 of these had known T790M mutations. Droplet digital PCR (ddPCR) was used to confirm NGS findings in samples with the T790M mutation.

Results Of 19 samples with T790M variant allele frequencies (VAF) higher than the stated 5% limit of detection, 14 were detected by Idylla (sensitivity 74%, 95% CI 49% to 90%). Where sufficient sample remained, ddPCR was consistent with NGS findings in all samples. False negative T790M results were associated with higher EGFR control Cq values (median 22.8 vs 19.8), presence of the EGFR Q787Q polymorphism in cis (80% vs 44%) and presence of an invalid T790M amplification curve. An EGFR exon 19 indel with VAF >5% was also not detected by the Idylla assay in two samples.

Conclusions The Idylla EGFR Mutation Test has reduced sensitivity for the T790M mutation compared with NGS and ddPCR methods. The presence of an invalid T790M amplification curve may indicate a possible false negative result that warrants further testing by an orthogonal method.

  • lung cancer
  • EGFR
  • molecular pathology

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  • Handling editor Runjan Chetty.

  • Contributors EL, VJ and JH conceived and designed the study; ET performed the experiments; EL, VJ, ET and JH analysed the data; EL wrote the manuscript.

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Competing interests None declared.

  • Patient consent for publication Not required.

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Data availability statement All data relevant to the study are included in the article or uploaded as online supplementary information.