Combined Targeting of EGFR and BRAF Triggers Regression of Osimertinib Resistance by Using Osimertinib and Vemurafenib Concurrently in a Patient with Heterogeneity Between Different Lesions.

Abstract Acquired BRAF V600E mutation can occur in tumors with EGFR mutation and is suspected as a resistance mechanism to third‐generation EGFR‐tyrosine kinase inhibitors (TKIs). However, the treatment strategy for the coexistence of EGFR and acquired BRAF mutation with heterogeneity in lung cancer has not been systematically established. Here, we report a patient in whom BRAF V600E and EGFR 19del mutation in a metastatic lesion followed by disease progression on osimertinib was detected. Treatment with single‐agent vemurafenib was effective for treatment of the metastatic lesion in this patient but the primary lesion progressed. A concurrent combination of vemurafenib and osimertinib was therefore administered and a partial response of both primary and metastatic lesions was achieved with progression‐free survival (PFS) of 7 months. The concurrent combination treatment was well tolerated by the patient through dosing modification and supportive medical care. This case highlights the consideration of heterogeneity between different lesions and provides a successful example of the concurrent therapy with vemurafenib and osimertinib for triggering regression of osimertinb resistance induced by BRAF mutation.