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S. Nanjo
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OA08 - Targeted Therapies in Brain Metastases (ID 381)
- Event: WCLC 2016
- Type: Oral Session
- Track: Advanced NSCLC
- Presentations: 1
- Moderators:D. Ball, B. Perin
- Coordinates: 12/05/2016, 16:00 - 17:30, Schubert 1
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OA08.03 - MET Copy Number Gain Associates with Gefitinib Resistance in Leptomeningeal Carcinomatosis of EGFR Mutant Lung Cancer (ID 4364)
16:20 - 16:30 | Author(s): S. Nanjo
- Abstract
- Presentation
Background:
Central nervous system (CNS) metastasis, such as brain metastasis and leptomeningeal carcinomatosis (LMC), occurs frequently in EGFR mutant lung cancer. EGFR-TKIs are generally effective to CNS metastasis in EGFR mutant lung cancer patients who are naïve to TKI treatment. Nevertheless, progression of CNS lesions are frequently observed during EGFR-TKI treatment. Brain metastases are manageable by concomitant use of EGFR-TKI and local intervention, including whole brain irradiation and stereotactic radiotherapy. There is, however, no established therapy for LMC, which is resistant to first and second generation EGFR-TKIs. Therefore, novel and effective therapies need to be developed for managing LMC in EGFR mutant lung cancer patients who become refractory to these EGFR-TKIs. The purpose of this study is to clarify the mechanism of EGFR-TKI resistance in LMC and establish novel therapeutic strategy.
Methods:
We examined EGFR mutations, including T790M gatekeeper mutation, in 32 re-biopsy specimens from 12 LMC and 20 extracranial lesions (e.c., lung metastasis and malignant pleural effusions) of EGFR mutant lung cancer patients who became refractory to EGFR-TKI treatment. To clarify molecular mechanisms of acquired EGFR-TKI resistance in LMC, we utilized in vivo imaging model of LMC with EGFR mutant lung cancer cell line PC-9/ffluc and induced acquired resistance to gefitinib by continuous oral treatment.
Results:
We found that all 32 re-biopsy specimens had the same baseline EGFR mutations and that T790M was less frequent in LMC specimens than extracranial specimens (8% vs 55%). Compared with subcutaneous tumors, T790M was less frequent in LMC which acquired resistance to gefitnib. We further established PC-9/LMC-GR cells from the gefitinib-resistant LMC model and found that PC-9/LMC-GR cells were intermediately resistant to gefitinib and osimertinib (3[rd] generation EGFR-TKI). While EGFR-T790M was negative, MET copy number gain associated MET activation was involved in the gefitinib resistance in PC-9/LMC-GR cells. Moreover, combined use of EGFR-TKI and crizotinib, having inhibitory activity against MET, dramatically regressed LMC which already acquired resistance to gefitinib or osimertinib.
Conclusion:
These findings suggest that combined use of MET inhibitors may be promising for controlling LMC which acquires resistance to EGFR-TKIs including osimertinib.
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