Abstract: Previous case reports have demonstrated the effectiveness of combination therapy involving EGFR TKI, BRAF inhibitor dabrafenib, and MEK inhibitor trametinib in metastatic non-small-cell lung cancer (NSCLC) patients with acquired BRAF V600E and EGFR mutations. However, the current literature does not provide any reports on the presence of resistant mutations in response to the administration of three-drug combination therapy. Exploring the resistance mechanism of targeted therapy is helpful to optimize the subsequent treatment strategy of patients. Herein, we report a case of a patient with advanced EGFR positive lung adenocarcinoma harboring an acquired BRAF V600E mutation who responded to the combination of furmonertinib, dabrafenib, and trametinib therapy. Unexpectedly, a MAP2K1 K57N acquired mutation was identified by NGS (Next-generation sequencing) analysis of re-biopsy tumor tissue after the patient was resistant to three-drug therapy. As far as we know, this is the first report demonstrating that the efficacy of using combination of furmonertinib and BRAF/MEK inhibitors and the MAP2K1 K57N mutation serves as a resistant mechanism to the three-drug therapy. This novel finding not only revealed a new resistant mutation but also had important implications for the identification of effective patients to EGFR/BRAF/MEK combination therapy.

Keywords: MAP2K1, furmonertinib, lung adenocarcinoma, EGFR, mutation