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J.C. Barrett
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MINI 16 - EGFR Mutant Lung Cancer 2 (ID 130)
- Event: WCLC 2015
- Type: Mini Oral
- Track: Treatment of Advanced Diseases - NSCLC
- Presentations: 1
- Moderators:G.J. Riely, M.C. Garassino
- Coordinates: 9/08/2015, 16:45 - 18:15, Four Seasons Ballroom F3+F4
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MINI16.09 - Design, Execution, and Preliminary Biomarker Results from Paired Tumor Biopsy Cohorts of the AZD9291 AURA Trial (ID 941)
17:30 - 17:35 | Author(s): J.C. Barrett
- Abstract
Background:
Epidermal growth factor receptor (EGFR)-mutant non-small cell lung cancer (NSCLC) exhibits sensitivity to EGFR tyrosine kinase inhibitors (TKIs) such as erlotinib and gefitinib; however, acquired resistance eventually develops in most patients. The most common mechanism of TKI resistance is a second-site mutation in the EGFR kinase domain, T790M. AZD9291 is an oral, potent, irreversible EGFR-TKI with potency against both T790M resistance and sensitizing EGFR mutations. In the ongoing Phase I AURA study (NCT01802632), AZD9291 induced durable responses in patients with acquired resistance to EGFR-TKIs. We report results of paired biopsy cohorts of the AURA trial, reviewing modulation of key molecular biomarkers of AZD9291 activity in patient tumor samples.
Methods:
Two cohorts of patients on the AURA trial were consented for collection of paired tumor biopsies. These patients had a pre-study tumor biopsy with T790M positive tumor status confirmed by central laboratory EGFR testing (Cobas™ EGFR Mutation Test). Following 8 to 15 days of once daily AZD9291 treatment (80 or 160 mg), a post-dose tumor biopsy was obtained. Baseline and post-dose tumor tissue was processed for routine histology and pathologic evaluation. More than 100 viable tumor cells per sample were required for subsequent biomarker scoring. Formalin-fixed paraffin-embedded tumor biopsies were profiled by immunohistochemistry with a suite of key pathway and tumor-relevant markers (phospho[p]-EGFR, pERK, pAKT, pS6, PD-L1, CD8). Matching plasma pharmacokinetic samples were also obtained for PK-PD correlations.
Results:
As of February 2015, 58 potential patients with an evaluable baseline biopsy were identified as candidates for post-dose biopsy collection. Sixteen of these patients did not proceed to an on-study biopsy as the identified lesions had regressed too substantially or were no longer considered suitable for re-biopsy, one patient was medically excluded from re-biopsy, and one patient’s sample was not available. In total, 40 patients supplied matched pre- and on-treatment biopsies. As of March 2015, paired tumor samples were available for QC from 26 of these 40 patients. Ten of these 26 biopsy specimens subsequently failed QC due to inadequate tumor content, leaving 16 paired tumor samples available for biomarker analyses, of which five have thus far been evaluated. AZD9291 treatment resulted in the inhibition of EGFR pathway components in the majority of post-treatment tumor biopsies. Tissue biomarker analyses are ongoing and updated data on evaluable biopsy pairs will be reported at the time of the congress.
Conclusion:
The completion of a paired biopsy cohort within the AURA trial was challenging due to the rapid onset of anti-tumor effects of AZD9291. Approximately 29% (17/58) of potentially eligible patients were unsuitable for the post-dose biopsy procedure due to tumor regression and 38% (10/26) of available post-dose biopsies were found to contain too little tumor for analysis. In the evaluable tumor pairs, pharmacodynamic modulation of the EGFR pathway was evident. Further biomarker analyses, including evidence of modulation of immune system markers, may help inform future combination strategies.
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ORAL 17 - EGFR Mutant Lung Cancer (ID 116)
- Event: WCLC 2015
- Type: Oral Session
- Track: Treatment of Advanced Diseases - NSCLC
- Presentations: 1
- Moderators:P. Meldgaard, E. Felip
- Coordinates: 9/08/2015, 10:45 - 12:15, Four Seasons Ballroom F3+F4
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ORAL17.07 - Mechanisms of Acquired Resistance to AZD9291 in EGFR T790M Positive Lung Cancer (ID 1365)
11:50 - 12:01 | Author(s): J.C. Barrett
- Abstract
Background:
AZD9291 is an irreversible, mutant-selective epidermal growth factor receptor tyrosine kinase inhibitor (EGFR-TKI) developed to have potency against both EGFR-sensitizing mutations and T790M. In the ongoing Phase I study of AZD9291 (AURA, NCT01802632), the response rate in patients with T790M positive lung cancer with disease progression on previous EGFR-TKI was >60%, with a preliminary median progression-free survival of >10 months. The molecular mechanisms underlying acquired resistance to AZD9291 are currently under investigation.
Methods:
Plasma genotyping was performed on patients from AURA who had progressed on AZD9291 if they had detectable T790M pre-AZD9291, as assessed by tumor or plasma genotyping, and if they had plasma collected at progression available for analysis. Cell-free DNA (cfDNA) was extracted from plasma taken at progression. Droplet digital PCR (ddPCR) was performed for EGFR exon 19 deletions, L858R, T790M, and C797S. For further exploration, next-generation sequencing (NGS) of an amplicon panel was performed on available progression cfDNA. Lastly, targeted NGS was performed on available resistance biopsy specimens.
Results:
Plasma specimens were available following disease progression on AZD9291 from 40 patients with tumors positive for T790M through tumor (33) or plasma genotyping (7). Twenty-six progression cfDNA specimens were positive for an EGFR-sensitizing mutation by ddPCR, and were deemed eligible for initial resistance analysis. Of these, 12 (46%) had no detectable T790M in plasma despite presence of the EGFR-sensitizing mutation, suggesting overgrowth of an alternate resistance mechanism. Seven patients had detectable C797S on ddPCR (27%), all with detectable T790M; of 14 with detectable T790M at resistance, C797S was only detected with EGFR exon 19 deletions (7/9) and not L858R (0/5, p=0.02). Plasma NGS was performed on 12 cases with acquired resistance that were T790M positive pretreatment. Exon 19 deletion/T790M/C797S were detected in four cases, with two of these harboring two different DNA mutations encoding for C797S. One case lost T790M and exhibited HER2 copy number gain (6.3 copies); a tumor biopsy from a separate case underwent aCGH at Institute Gustave Roussy and was also found to have focal HER2 amplification with loss of T790M. Targeted NGS was performed on resistance biopsies from a total of 10 patients from four centers with T790M positive biopsies pre-AZD9291. Six cases maintained T790M, with three harboring exon 19 del/T790M/C797S. In four cases with loss of T790M, one harbored BRAF V600E and one harbored PIK3CA E545K.
Conclusion:
Complementary genomic analysis of plasma and tumor DNA provides insight into the diverse molecular mechanisms of acquired resistance to AZD9291 in EGFR-mutant lung cancer. Our studies show that a majority of cases maintained T790M at resistance, at times acquiring a new C797S mutation in those with EGFR exon 19 deletion. Loss of T790M at progression may be mediated by overgrowth of cells harboring HER2 amplification, BRAF V600E, or PIK3CA mutations. These data highlight the need for investigation of combination therapies to effectively prevent or treat the complexity of drug resistance in EGFR-mutant lung cancer.
