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A. Das-Gupta
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ORAL 37 - Novel Targets (ID 146)
- Event: WCLC 2015
- Type: Oral Session
- Track: Biology, Pathology, and Molecular Testing
- Presentations: 1
- Moderators:S.S. Ramalingam, E. Thunnissen
- Coordinates: 9/09/2015, 16:45 - 18:15, Mile High Ballroom 4a-4f
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ORAL37.05 - Prevalence and Clinical Association of MET Gene Amplification in Patients with NSCLC: Results from the ETOP Lungscape Project (ID 444)
17:28 - 17:39 | Author(s): A. Das-Gupta
- Abstract
Background:
The reported prevalence of MET gene amplification in non-small cell lung cancer (NSCLC) varies from 0-21% and clinical correlations are emerging slowly. In a well-defined NSCLC cohort of the ETOP Lungscape program, we explore the epidemiology, the natural history of MET amplification and its association with MET overexpression, overall survival (OS), relapse-free survival (RFS) and time to relapse (TTR).
Methods:
Resected stage I-III NSCLC, identified based on the quality of clinical data and FFPE tissue availability, were assessed for MET gene copy number (GCN) and expression analysis using silver in-situ hybridization (SISH) and immunohistochemistry (IHC), respectively, on TMAs (MET and centromere-specific probes; anti total c-MET antibody, clone SP44; Ventana immunostainer). MET amplification was defined as MET/centromere ratio ≥2 with average MET GCN ≥4, high MET GCN at two levels as ≥median CGN and ≥5 (irrespective of amplification) and MET IHC+ as 2+ or 3+ intensity in ≥50% of tumor cells. Sensitivity analysis to define the amplification’s thresholds was also performed. All cases were analysed at participating pathology laboratories using the same protocol, after successful completion of an external quality assurance (EQA) program.
Results:
Currently 2709 patients are included in the Lungscape iBiobank (median follow-up 4.8 years, 53.3% still alive). So far, 1547 (57%) have available results for MET GCN with amplification detected in 72 (4.7%; 95%CI: 3.6%, 5.7%) and high MET GCN (≥5) in 65 (4.2%; 95%CI: 3.2%, 5.2%). The median value of average MET GCN per cell is 2.3. IHC MET expression is available for 1515 (98%) of these cases, 350 (23%) of which are MET IHC positive [170 cases (49%) 3+, 180 (51%) 2+]. The median age, for the cohort of 1547 patients, is 66.2 years, with 32.8% women, and 13.5%, 29.7%, 54% never, current, former smokers, respectively. Stage distribution is: IA 23.6%, IB 24.6%, IIA 17%, IIB 12.1%, IIIA 20.9%, IIIB 1.8%, while 52.7%, are of adenocarcinoma and 40.0% of squamous histology. MET amplification and high MET GCN (≥5) are not significantly associated with any histological tumor characteristics or stage (multiplicity adjusted alpha: 0.005). High MET GCN (≥2.3) is less frequent in current smokers (38.3% vs. 55.6% for former or non-smokers, p<0.001). MET amplification and high MET GCN are significantly associated with IHC MET positivity (p<0.001 in all cases). MET amplification is present in 9.7% of IHC MET+ vs 3.1% of IHC MET- patients and high MET GCN (≥5) in 8.6% of IHC MET+ vs 2.8% of IHC MET- patients. MET amplification ranges from 0 to 16% between centers, while high MET GCN (≥5) and (≥2.3) from 0% to 12%, and 11.8% to 98.9%, respectively. MET amplification and both levels of high MET GCN are not associated with OS, RFS or TTR.
Conclusion:
The preliminary results for this large, predominantly European, multicenter cohort demonstrate that MET amplification assessed by SISH prevails in 4.7% of NSCLC, is associated with strong MET expression, and has no influence on prognosis. The large inter-laboratory variability in GCN despite EQA efforts may highlight a critical challenge of MET SISH analysis in routine practice.
