Prognostic implication of MET overexpression in myxofibrosarcomas: an integrative array comparative genomic...

It remains obscure in myxofibrosarcoma about the basis of tumorigenesis, progression, and metastasis. Chromosome 7 gains are common in some sarcomas, including myxofibrosarcoma, whereas the specific oncogenes are yet to be characterized. We performed an integrative study of MET gene at 7q31.2 to elucidate its implication in myxofibrosarcoma. Focused on candidate oncogenes on chromosome 7, 385K array comparative genomic hybridization was used to profile DNA copy number alterations of 12 samples. MET transcript was successfully quantified by real-time RT-PCR for 16 laser-microdissected tumors and two myxofibrosarcoma cell lines (NMFH-1, OH931). MET immunoexpression was assessable in 86 primary localized tumors with follow-up. To analyze endogenous MET expression and activation, NMFH-1 and OH931 cells, both with wild-type MET gene, were subjected to Western blotting and hepatocyte growth factor-treated NMFH-1 cells were evaluated for the kinetics of MET tyrosine phosphorylation. Non-random large-scale gains on 7q were detected in five cases, delineating three recurrent amplicons, 7q21.11-7q21.3, 7q22.1-22.3, and 7q31.1-7q32.3, in which the locus of MET displayed increased copy number, among others. MET mRNA was upregulated in OH931, NMFH-1, and nine tumors (56%), whereas neither gene dosage nor mRNA expression of MET was associated with clinicopathological factors. In contrast, MET protein overexpression, present in 67% of cases, was highly related to deep location (P=0.004), higher grades (P=0.001), and more advanced stages (P<0.001). Importantly, MET overexpression independently portended inferior metastasis-free survival (P=0.004) and overall survival (P=0.0221). Expressing activating phospho-MET at Tyr(1234)/Tyr(1235), OH931 cells had more abundant total MET than NMFH-1 cells, whereas the latter became promptly phosphorylated on stimulation of hepatocyte growth factor. In primary myxofibrosarcomas, MET overexpression, as a frequent event, is likely driven by 7q gains with mRNA upregulation, associated with important prognosticators, and independently predictive of worse outcomes, highlighting its possible causative function in tumor aggressiveness and potentiality as a therapeutic target.