Concurrent driver mutations in non-small cell lung cancer (NSCLC) patients (p) on targeted therapy uncovered by comprehensive molecular profiling.

11004 Background: NSCLC p with EGFR mutations respond initially to EGFR tyrosine kinase inhibitors (TKIs) but invariably develop acquired EGFR TKI resistance. Prior studies identified the EGFR T790M mutation and activation of MET, PI3K, AXL, HER2 and the MAPK pathway as drivers of acquired EGFR TKI resistance. To date, comprehensive molecular profiling to identify actionable modifiers of EGFR TKI response has not been conducted in NSCLC p on therapy. Methods: We performed next generation sequencing (NGS) using a 263-gene Nimblegen custom cancer panel on DNA isolated from primary patient lung adenocarcinoma FFPE specimens prior to initiating standard erlotinib treatment and upon the development of acquired erlotinib resistance after only 3 months of therapy. Results: In the pretreatment sample, we confirmed the presence of the EGFRL858R mutation in 95% of the sequencing reads and discovered a concurrent BRAF V600E mutation with a frequency of ~ 6%. NGS performed on the acquired erlotinib resistance sample revealed acquisition of the EGFR T790M mutation with a frequency of ~ 14%. Notably, the frequency of the BRAF V600E mutation increased 10-fold upon acquired erlotinib resistance from ~ 6% in the pretreatment tumor to ~ 60% in the recurrent tumor. We found that overexpression of BRAF V600E in H3255 human NSCLC, which harbor EGFR L858R (but not BRAF V600E) and are erlotinib sensitive, caused resistance to erlotinib treatment (10-fold increase in erlotinib IC50). BRAF V600E-mediated erlotinib resistance was reversed by treatment with the BRAF inhibitor vemurafenib. Additional functional studies are ongoing and the complete dataset will be presented. Conclusions: These results indicate that EGFR-mutant NSCLC can harbor additional oncogenic driver mutations in BRAF at low frequencies prior to therapy. EGFR TKI treatment can lead to expansion of BRAF V600E expressing tumor cells, resulting in acquired EGFR TKI resistance that can be reversed by BRAF inhibitor treatment. The data demonstrate the utility of routine molecular profiling of NSCLC p on targeted therapy and offer unprecedented insight into the genetic basis of therapeutic resistance.