Author of

• 18975

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  P3.01 - Advanced NSCLC (ID 621)

  • Event: WCLC 2017
  • Type: Poster Session with Presenters Present
  • Track: Advanced NSCLC
  • Presentations: 1
  • Moderators:
  • Coordinates: 10/18/2017, 09:30 - 16:00, Exhibit Hall (Hall B + C)

  • 23905

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    P3.01-046 - Longitudinal Analysis of Plasma CtDNA in EGFR-Mutant NSCLC: SWOG S1403 Trial of Afatinib with or Without Cetuximab (ID 9535)

    09:30 - 09:30  |  Author(s): D. Dix
    • Abstract

    Background:
    Detection of actionable mutations using circulating tumor DNA (ctDNA) isolated from patient plasma is now accepted as clinical practice in NSCLC. Nevertheless, the full extent to which longitudinal plasma analysis can be utilized to guide clinical decision-making has yet to be realized. We prospectively incorporated serial next-generation sequencing (NGS) of ctDNA into the ongoing SWOG S1403 clinical trial (NCT02438722) of afatinib+cetuximab vs afatinib in treatment-naïve NSCLC patients with EGFR-mutant tumors.
    
    Method:
    Time points for specimen collection were pre-treatment, after two months of therapy on Cycle 3 Day1 (C3D1) and at progression. Objectives were to: 1) determine the prognostic and predictive significance the EGFR mutant allele frequency (MAF) at each time point; 2) correlate changes in MAF over time with regard to patient outcome, and 3) identify putative emergent resistance mechanisms and companion mutations. Specimen analysis was conducted using the Guardant360 73-gene digital NGS panel.
    
    Result:
    To date, 53 patients with advanced EGFR-mutant NSCLC have contributed baseline samples. Of these, 46 had ctDNA detectable at baseline (87%). 39 of these 46 (85%) had detectable, tissue-identical EGFR mutations, for an overall EGFR detection rate of 74% (39/53). A positive finding for EGFR amplification (Amp) in plasma correlated with high ctDNA MAF: median for Amp 16.9 vs nonAmp 0.9 (range/n: 11.6-43.7/10 vs 0.11-7.7/17; p<0.0001). Of patients with detectable EGFR mutation at baseline, 27 had analyzable ctDNA collected at C3D1. Of these, 26/27 showed decreasing MAFs on-treatment (mean for baseline: 9.8 vs C3D1: 0.14; p<0.0001), with 20 cases having no detectable EGFR mutation at C3D1 (mean of 7 positives at C3D1: 0.55). At progression, samples were collected from 14 patients and 10 had EGFR mutations detectable, with T790M present in 3. Another patient had an FGFR3 fusion at PD, but no previous draws were available to determine if it was emergent.
    
    Conclusion:
    Longitudinal analysis of plasma ctDNA in S1403 patients demonstrated significant treatment-induced changes in mutation burden and identified resistance mechanisms at progression. EGFR gene amplification, as assessed in plasma, was significantly associated with increased ctDNA MAFs. Patients showed a significant, one-to-two orders of magnitude decline in EGFR MAF after two months of therapy, with 74% dropping below detectable levels. At progression, EGFR mutation detection rates increased, often concomitantly with a putative emergent resistance factor. Accrual to S1403 is ongoing and patient treatment and outcomes remain blinded. The prognostic and predictive utility of baseline and therapy-induced changes in ctDNA MAF kinetics will be determined at study unblinding.