MET exon 14 skipping mutation, amplification and overexpression in pulmonary sarcomatoid carcinoma: A multi-center study

High frequency of MNNG HOS transforming (MET) exon 14 skipping mutation (MET exon 14Δ) has been reported in pulmonary sarcomatoid carcinomas (PSCs). However, the frequencies differ greatly. Our study aims to investigate the frequency of MET alterations and the correlations among MET exon 14Δ, amplification, and protein overexpression in a large cohort of PSCs. MET exon 14Δ, amplification, and protein overexpression were detected in 124 surgically resected PSCs by using Sanger sequencing, fluorescent in situ hybridization (FISH), and immunohistochemistry (IHC) respectively. MET exon 14Δ was identified in 9 (7.3%) of 124 cases, including 6 pleomorphic carcinomas, 2 spindle cell carcinomas and 1 carcinosarcoma. MET amplification and protein overexpression were detected in 6 PSCs (4.8%) and 25 PSCs (20.2%), respectively. MET amplification was significantly associated with overexpression (P < 0.001). However, MET exon 14Δ has no correlation with MET amplification (P = 0.370) and overexpression (P = 0.080). Multivariable analysis demonstrated that pathologic stage (hazard ratio [HR], 2.78; 95% confidence interval [CI], 1.28–6.01; P = 0.010) and MET amplification (HR, 4.71; 95% CI, 1.31–16.98; P = 0.018) were independent prognostic factors for poor median overall survival (mOS). MET alterations including MET exon 14Δ and amplification should be recommended as routine clinical testing in PSCs patients who may benefit from MET inhibitors. MET IHC appears to be an efficient screen tool for MET amplification in PSCs.