LAUSR

9030 Background: MET mutations ( MET∆ex14), amplifications or translocations can activate oncogenic signaling in lung cancer and are sensitive to MET inhibition. Acquired resistance to therapy with MET tyrosine kinase inhibitors (TKI) occurs inevitably. Methods: Between 2015 and 2018, eighteen patients with MET-driven NSCLC were treated with capmatinib or crizotinib as single agent at our site. Rebiopsy samples from five patients were analyzed by NGS and fluoreszenz-in-situ hybridization (FISH) at time of progression. Results: Of the five patients with rebiopsy samples at time of progression, two had initially a MET amplification (one patient with low-level and one patient with high-level amplification), two patients had a MET∆ex14 and one patient had a KIF5B-MET fusion. Patient 1 (low-level MET amplification) showed a partial response to crizotinib. The rebiopsy revealed an acquired KRAS mutation as a potential mechanism of resistance. Patient 2 (high-level MET amplification) showed stable disease as best response to capmatinib and patient 3 (MET∆ex14) showed a partial response to capmatinib. Both patients developed acquired HER2 amplifications. Patient 4 ( MET∆ex14) showed initially a partial response to crizotinib. The rebiopsy sample revealed an acquired MET kinase domain mutation (p.D1246N). As preclinical findings suggested that D1246N confers resistance to type I MET inhibitors but remains sensitive to type II inhibitors, cabozantinib was started. A CT six weeks after therapy initiation showed progressive disease. Patient 5 ( KIF5B-MET) had a partial response to crizotinib. An acquired MET p.Y1248H mutation was found at time of progression. Therapy was changed to cabozantinib. A new CT scan is pending. Conclusions: Resistance to MET inhibition is heterogeneous with on- and off-target-mechanisms occurring. We found HER2 amplification as a potential new bypass mechanism. The MET mutation D1246N conferred resistance to type I and type II inhibitors. We describe the first case of an acquired mutation of the MET tyrosine kinase domain in a patient with an oncogenic MET fusion. Further investigations are needed to collect comprehensive data to understand resistance mechanisms in MET inhibition and to develop novel therapeutic strategies.