Receptor Tyrosine Kinase Fusions and BRAF Kinase Fusions are Rare but Actionable Resistance Mechanisms to EGFR Tyrosine Kinase Inhibitors.

INTRODUCTION: We analyzed a large set of EGFR-mutated (EGFR+) NSCLC to identify and characterize cases with co-occurring kinase fusions as potential resistance mechanisms to EGFR tyrosine kinase inhibitors (TKIs).

METHODS: EGFR+ (del 19, L858R, G719X, S768I, L851Q) NSCLC clinical samples (formalin-fixed paraffin-embedded tumor and blood) were analyzed for the presence of receptor tyrosine kinase (RTK) and BRAF fusions. Treatment history and response were obtained from provided pathology reports and treating clinicians.

RESULTS: Clinical samples from 3505 unique EGFR+ NSCLCs were identified from June 2012 to October 2017. A total of 31 EGFR+ cases had concurrent kinase fusions detected: 10 (32%) BRAF, 7 (23%) ALK receptor tyrosine kinase (ALK), 6 (19%) ret proto-oncogene (RET), 6 (19%) fibroblast growth factor receptor 3 (FGFR3), 1 (3.2%) EGFR, and 1 (3.2%) neurotrophic receptor tyrosine kinase 1 (NTRK1), including two novel fusions (SALL2-BRAF and PLEKHA7-ALK). Twenty-seven of 31 patients had either a known history of EGFR+ NSCLC diagnosis or prior treatment with an EGFR TKI before the fusion+ sample was collected. Twelve of the 27 patients had paired pre-treatment samples where the fusion was not present before treatment with an EGFR TKI. Multiple patients treated with combination therapy targeting EGFR and the acquired fusion had clinical benefit, including one patient with osimertinib resistance due to an acquired PLEKHA7-ALK fusion achieving a durable partial response with combination of full-dose osimertinib and alectinib.

CONCLUSIONS: RTK and BRAF fusions are rare but potentially druggable resistance mechanisms to EGFR TKIs. Detection of RTK and BRAF fusions should be part of comprehensive profiling panels to determine resistance to EGFR TKIs and direct appropriate combination therapeutic strategies.