Clinical and Preclinical Activity of EGFR Tyrosine Kinase Inhibitors in Non-Small-Cell Lung Cancer Harboring BRAF Class 3 Mutations

Purpose: Patients with tumors harboring BRAF class 3 mutations lack targeted therapies. These mutations are characterized by low/absent BRAF kinase domain activation and are believed to amplify already active RAS signaling, potentially triggered by receptor tyrosine kinases like EGFR. Materials and methods: Two patients with BRAF class 3-mutated metastatic non-small-cell lung cancer (NSCLC) were treated with erlotinib at our Institution after failure of standard therapies. Two cell lines were established from patients with BRAF class 3-mutated NSCLC, and their sensitivity to EGFR tyrosine kinase inhibitors (EGFR-TKIs) was assessed using EGFR-mutated, BRAF class 1 and 2-mutated, and KRAS-mutated NSCLC cell lines as controls. Results: Patient 1, a 60-year-old male with BRAFD594N-mutated NSCLC, achieved complete response to erlotinib after progression on first- and second-line chemotherapy. Patient 2, a 60-year-old female with BRAFD594G-mutated NSCLC, achieved partial response to erlotinib after progression on first-line chemoimmunotherapy. High baseline phosphorylated EGFR values and reduced EGFR activation following erlotinib were observed in BRAF class 3-mutated and EGFR-mutated cell lines, but not in BRAF class 1-mutated, BRAF class 2-mutated, or KRAS-mutated lines. Erlotinib inhibited 2-dimensional growth in BRAF class 3-mutated cell lines (IC50 6.33 and 7.11 µM) and in the BRAF class 2-mutated cell line (IC50 5.51 µM), albeit at higher concentrations than in EGFR-mutated lines, whereas it showed no effect on BRAF class 1-mutated (IC50, >25 µM) or KRAS-mutated (IC50, >25 µM) lines. These findings were corroborated by 3-dimensional and sphere formation assays. In the Cancer Cell Line Encyclopedia, BRAF class 3-mutated NSCLC cell lines showed greater sensitivity to EGFR-TKIs compared with BRAF class 2-mutated and KRAS-mutated lines. Conclusion: BRAF class 3 mutations in NSCLC may identify a novel targetable population sensitive to EGFR-TKIs.