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.

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.