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RESEARCH PRODUCT

Comprehensive cross-platform comparison of methodologies for noninvasive EGFR mutation testing: Results of the RING observational trial.

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e21518 Background: Several platforms for non-invasive EGFR testing are currently used in the clinical setting, with sensitivities ranging from 30 to 100%. Comparison studies in prospective cohorts remain limited and reports evaluating mutant allelic fractions (MAFs) are particularly scarce. The RING observational trial (ClinicalTrials.gov identifier NCT03363139) was designed to comprehensively analyze the concordance between methodologies for EGFR mutation detection in blood. Methods: Seventy-two EGFR mutant NSCLC patients were enrolled in the trial. Plasma samples were prospectively collected at progression to first line Tyrosine Kinase Inhibitor and tested for EGFR mutations by 7 methodologies; cobas EGFR Mutation Test v2, Therascreen EGFR Plasma RGQ PCR Kit, QuantStudio 3D Digital PCR System, a 5-nuclease real-time PCR assay in presence of PNA, OncoBEAM EGFR and NGS with two different gene panels, Ion Torrent Oncomine and GeneRead QIAact Lung DNA UMI Cancer Panel. Results: The agreement between all methodologies for was almost perfect for the detection of deletions in exon 19 (K = 0.86; 95%CI: 0.76-0.96) and substantial for exon 21 point mutations (K = 0.76; 95%CI: 0.63-0.89). Regarding the p.T790M resistance mutation, concordance was lower but still substantial (K = 0.68; 95%CI: 0.57-0.79). If only NGS-based technologies were considered, the agreement was almost perfect for sensitizing mutations and substantial for the resistance mutation (K = 0.84; 95%CI: 0.68-1.00, K = 0.86; 95%CI: 0.69-1.00 and K = 0.77; 95%CI: 0.60-0.95 for exon 19, exon 21 and p.T790M, respectively). Most discordant samples between methodologies had mutant allele fractions (MAFs) ≤0.5%. Sensitizing mutations were always present at higher MAFs than concomitant p.T790M, explaining the lower concordance observed for this variant. MAFs obtained by different methodologies showed an excellent reproducibility (intraclass correlation coeficients 0.85-0.97). Similarly, Passing–Bablok regression analysis showed a high correlation between methodologies when assessing MAFs. Conclusions: Our results support the use of liquid biopsies for non-invasive EGFR testing in the clinical setting and highlight the need to systematically report MAFs.