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T. Hida



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    OA 10 - Liquid Biopsy for Genomic Alterations (ID 678)

    • Event: WCLC 2017
    • Type: Oral
    • Track: Advanced NSCLC
    • Presentations: 1
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      OA 10.01 - Detection of EGFR mutations from plasma ctDNA in the osimertinib Phase III trial (AURA3): comparison of three plasma assays (ID 8984)

      11:00 - 11:10  |  Author(s): T. Hida

      • Abstract
      • Presentation
      • Slides

      Background:
      AURA3 (NCT02151981) showed osimertinib, a third-generation EGFR-TKI, significantly prolongs progression‑free survival and improves response rate vs platinum‑pemetrexed in patients with T790M-positive advanced NSCLC, whose tumors had progressed on first-line EGFR-TKI therapy. Using patient baseline samples, we report concordance between plasma circulating tumor DNA (ctDNA) and tissue for the detection of EGFR mutations (T790M, exon 19 deletions [Ex19Del], L858R) using three distinct plasma detection technologies.

      Method:
      Tumor tissue biopsy samples were taken following progression on first-line EGFR‑TKI treatment. Baseline central confirmation of EGFR mutation status was by cobas[®] EGFR Mutation Test (Roche Molecular Systems). Where possible, baseline blood samples for plasma ctDNA screening were collected from patients in the osimertinib treatment group and analyzed using allele specific (AS)‑PCR (cobas[®] EGFR Mutation Test v2), ddPCR (Biodesix) and next generation sequencing (NGS, Guardant Health).

      Result:
      Figure 1 ctDNA was undetectable (negative for all three EGFR mutations [T790M, Ex19Del, L858R]) in 51/228 (22%) patients by AS-PCR, 58/211 (27%) by ddPCR, and 54/230 (23%) by NGS. Robust correlations (Spearman’s Rank) were observed for EGFR mutant allelic fractions (AFs) between ddPCR and NGS assays: T790M R[2] 0.9129 (n=201), Ex19Del R[2] 0.9384 (n=201), L858R R[2] 0.8090 (n=200). Discordant results between ddPCR and NGS were observed in 24/201 (12%) samples for T790M, 17/201 (8%) Ex19Del and 11/200 (6%) L858R. All discordant samples had AFs ≤1% by both assays.



      Conclusion:
      Using cobas tissue test as a reference, sensitivity for the detection of plasma T790M appeared higher for ddPCR and NGS assays compared with AS-PCR. Robust correlations were observed between quantitative ddPCR and NGS assays for determination of AFs across all three mutations. About 25% of AURA3 patients did not appear to shed ctDNA, as evidenced by absence of all three EGFR mutations across the three platforms.

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