Overexpression of MET receptor tyrosine kinase and its ligand hepatocyte growth factor (HGF) and MET gene amplification have been well-documented in non–small-cell lung cancer (NSCLC). Activated MET signaling plays an important role in human cancer tumorigenesis, metastasis, and drug resistance. However, the deregulation of MET/HGF pathway in NSCLC harboring ALK gene rearrangement (ALK[+]), which is sensitive to dual ALK and MET inhibitor Crizotinib, has not been reported.
We performed systematic analysis of MET/HGF expression by immunohistochemistry (IHC) and MET gene amplification by dual color, dual hapten bright field in situ hybridization in 19 ALK(+) and 73 ALK(−) NSCLC tumor tissues from those who had clinical ALK rearrangement test done at the Cleveland Clinic from August 2010 to January 2013. IHC scoring was interpreted on a standard four-tier system.
The percentage of MET IHC score 0, 1+, 2+, and 3+ were 5.5%, 27.8%, 50.0%, and 16.7% in ALK(+) group, compared with 28.8%, 33.9%, 23.7%, and 13.6% in ALK(−) group, respectively. The MET high expression (IHC score 2 or 3) was significantly higher in ALK(+) group statistically (66.7% versus 37.3%, p = 0.03). HGF-high expression (IHC score 2 or 3) was 33.3% in ALK(+) and 15.8% in ALK(−) (p = 0.17). We identified eight cases in ALK(−) and one case in ALK(+) tumor who had MET gene amplification (18.4% versus 7.1%, p = 0.43) by dual color, dual hapten bright field in situ hybridization. No significant correlation between MET protein receptor expression and gene amplification was identified.
Our study demonstrated for the first time that MET receptor expression, but not MET gene amplification, is significantly increased in ALK(+) NSCLC. MET gene amplification is a relatively rare event in this unique population compared with ALK(−) NSCLC.