Comprehensive cross-platform comparison of methods for non-invasive EGFR mutation testing: Results of the RING observational trial.

Several platforms for non-invasive EGFR testing are currently used in the clinical setting with sensitivities ranging from 30% to 100%. Prospective studies evaluating agreement and sources for discordant results remain lacking. Herein, 7 methodologies including two next-generation sequencing (NGS)-based methods, three high-sensitivity PCR-based platforms and two FDA-approved methods were compared using 72 plasma samples, from EGFR-mutant non-small cell lung cancer (NSCLC) patients progressing on a first-line tyrosine kinase inhibitor (TKI). NGS platforms as well as high-sensitivity PCR-based methodologies showed excellent agreement for EGFR-sensitizing mutations (K=0.80 to 0.89) and substantial agreement for T790M testing (K=0.77 and 0.68, respectively). Mutant allele frequencies (MAFs) obtained by different quantitative methods showed an excellent reproducibility (intraclass correlation coefficients 0.86-0.98). Among other technical factors, discordant calls mostly occurred at mutant allele frequencies (MAFs) ≤0.5%. Agreement significantly improved when discarding samples with MAF≤0.5%. EGFR mutations were detected at significantly lower MAFs in patients with brain metastases, suggesting that these patients risk for a false positive result. Our results support the use of liquid biopsies for non-invasive EGFR testing and highlight the need to systematically report MAFs.