Author of

• 25918

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  MA26 - New Therapies and Emerging Data in ALK, EGFR and ROS1 (ID 930)

  • Event: WCLC 2018
  • Type: Mini Oral Abstract Session
  • Track: Targeted Therapy
  • Presentations: 1
  • Moderators:
  • Coordinates: 9/26/2018, 13:30 - 15:00, Room 201 BD

  • 27924

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    MA26.03 - Activity of Osimertinib and the Selective RET Inhibitor BLU-667 in an EGFR-Mutant Patient with Acquired RET Rearrangement (ID 14731)

    13:40 - 13:45  |  Author(s): D Dias-Santagata
    • Abstract
    • Presentation
    • Slides

    Background
    The spectrum of acquired resistance (AR) to osimertinib is not yet fully characterized. We present a single-center cohort of osimertinib AR biopsies and results of a patient with RET-mediated AR treated with the investigational RET-specific TKI BLU-667 and osimertinib.
    a9ded1e5ce5d75814730bb4caaf49419 Method
    We assayed tissue via SNaPshot or Foundation One next-generation sequencing (NGS) and plasma via Guardant360 NGS under an IRB-approved protocol. In vitro studies assessed implications of RET fusions in EGFR-mutant cancers. We treated one patient with osimertinib/BLU-667 using an IRB and FDA-approved compassionate use protocol.
    4c3880bb027f159e801041b1021e88e8 Result
    41 EGFR-mutant patients with AR to osimertinib were assessed histologically and queried by tissue NGS (n=22), plasma NGS (n=9) or both (n=10). Key AR findings: SCLC transformation (2/32 tissue); EGFR C797S (5/32 tissue, 5/19 plasma, all cis with T790M); MET amplification (7/32 tissue, 3/19 plasma); BRAF rearrangement (2/32 tissue) and CCDC6-RET rearrangement (1/32 tissue, 1/19 plasma [distinct case]).
    CCDC6-RET was expressed in PC9 (EGFR del19) and MGH134 (EGFR L858R/T790M) cells, which maintained MAPK signaling and conferred resistance to osimertinib and afatinib. Inhibition of RET by BLU-667 or cabozantinib resensitized cells expressing CCDC6-RET to EGFR inhibition.
    A 60-year-old woman with EGFR del19 progressed on afatinib (T790M+), then osimertinib. Tissue biopsy at osimertinib AR showed acquired CCDC6-RET (T790-wt). She began osimertinib 80mg/BLU-667 200mg daily x2 weeks, then BLU-667 was increased to 300mg daily. Her dyspnea improved within days of initiation. Scans after 8 weeks revealed a marked response with RECIST tumor shrinkage of 78% (Figure). She experienced only grade 1 toxicities of fatigue, leukopenia, hypertension, dry mouth, and elevated transaminases.
    8eea62084ca7e541d918e823422bd82e Conclusion
    RET rearrangements are rare but recurrent in EGFR-mutant patients with AR to osimertinib. In vivo models suggest they mediate AR and this patient provides proof-of-concept that combination EGFR+RET inhibition with osimertinib/BLU-667 is a well-tolerated and effective regimen for RET-mediated AR. Further study is ongoing.
    
    
    
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