Reduced sensitivity for T790M mutations using the Idylla EGFR Mutation Test.

AIMS

Osimertinib is a third-generation (epidermal growth factor receptor) tyrosine kinase inhibitor that is effective in non-small cell lung cancer (NSCLC) harbouring the T790M mutation. The Idylla EGFR Mutation Test is a rapid cartridge-based method for detecting T790M and other 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 control Cq values (median 22.8 vs 19.8), presence of the Q787Q polymorphism in cis (80% vs 44%) and presence of an invalid T790M amplification curve. An 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.