Detection of Frequent MET Exon 14 Skipping Events in Pulmonary Sarcomatoid Carcinoma and Response to Targeted Inhibition.

8020 Background: Pulmonary sarcomatoid carcinoma (PSC) represents a category of highly aggressive carcinomas associated with a poor prognosis. New therapeutic strategies based on better knowledge of the molecular pathogenesis of PSC are needed. We recently identified a high frequency of a unique type of MET alterations leading to exon 14 skipping (exon 14Δ) in PSC. Methods: Whole-exome sequencing in a discovery set and targeted MET mutation screening in an independent validation set of PSC were performed. RT-PCR and Western blotting were performed to validate MET exon 14Δ. A lung adenosquamous cell line H596 (MET exon 14Δ and PIK3CA mutated) and a gastric adenocarcinoma cell line Hs746T (MET exon 14 Δ) were used for functional studies. Ablation of MET signaling by siRNA or pharmacological inhibitor (Crizotinib) was conducted, and subsequent MTS assays and Western blotting were then performed. Simultaneous MET signaling blockade and PIK3CA signaling inhibition using PIK3CA inhibitor (GDC0941) were performed to assess synergistic effects in H596 cells. Results: Alterations affecting MET exon 14 splice sites, including deletions at the 5’ splice site (n = 3) and point mutations at the 3’ splice site (n = 5) were found in 22% (8/36) of PSC. One PSC harbored MET exon 14Δ and a concurrent PIK3CA mutation. RT-PCR and Western blotting confirmed the presence of MET exon 14Δ in tumor and in H596 and Hs746T cells. Both MET siRNA silencing and crizotinib decreased cell proliferation and inhibited downstream AKT and MAPK activation in Hs746T cells, whereas effects were modest in H596 cells and negligible in control Calu-3 and HCC827 cells. Concomitant MET and PI3K blockade had synergistic effects in H596 cells. Migration/invasion assays in H596 and Hs746T cells, as well as further functional studies utilizing specific MET exon 14 expression constructs are ongoing. Conclusions: Our study finds that MET exon 14Δ alterations are a frequent and potentially targetable event in PSC. Our studies also suggest that concurrent PIK3CA mutations require combined treatment. Clinical studies assessing biomarker-driven MET/PI3K inhibition should be explored in PSC as well as other malignancies harboring MET exon 14Δ events.