MET exon 14 mutations in advanced lung adenocarcinoma: Frequency and coexisting alterations.

e20656 Background: In lung cancer the evaluation of MET, a tyrosine kinase receptor involved in tumor growth and invasiveness, for copy number amplification and point mutations is relevant for prognosis and therapy. In lung adenocarcinoma (ADC) MET amplification is observed in 1-2% and MET mutations in 3-4% of cases. Mutations mainly occur in exon 14 (ex14), which encodes for the juxtamembrane negative regulatory domain, including splice site alterations and missense mutations within the exon.Commonly, MET ex14 alterations, in particular splice site ones, are mutually exclusive with other driver mutations, but co-occurrence with MET and MDM2 amplification and KRAS mutations was described. We evaluated METex14 mutation frequency and coexistence with additional driver alterations in a prospective cohort of Italian ADC patients. Methods: 315 ADC patients were tested (January-December 2016) for MET ex14 alterations by Sanger Sequencing on formalin-fixed paraffin-embedded tissues and cytological smears (tumor cells > 40%). MET positive cases were screened also for other oncogenes, among which KRAS, BRAF and PIK3CA, using a MALDI-TOF platform, and for ROS1 translocations and MET amplification by FISH. Results: 16 patients (5%) were MET positive: 7 splice site mutations (43%) and 9 (57%) other alterations within ex14. Among splice site mutations 1 co-occurred with ROS1 translocation and 1 with MET amplification. Among other mutations we found 5 T1010I missense mutations: 3 co-occurring with G12D/G13C/Q61H KRAS, 1 with G469A BRAF and 1 with a MET intron 13 point mutation; 2 R988C mutations: 1 with G13C KRAS and 1 with G13C KRAS plus ROS1 translocation; 1 P1026S mutation and 1 frameshift deletion (p.A991del;R992fs*999), both with G12C KRAS. Conclusions: Splice site mutations cause MET activation by exon skipping and increase sensitivity to tyrosine-kinase inhibitors, whereas how other ex14 mutations affect MET function is not fully understood. In our cohort we found a high rate of METex14 mutations together with alterations in other oncogenes, mostly KRAS. The interaction of MET with cancer signaling pathways deserve further investigation in order to better define the role of ex14 mutations in the context of target therapy.