PD-L1-negative non-small cell lung cancer harbouring a rare BRAF mutation with successful treatment of first-line pembrolizumab plus chemotherapy: A case report and review the literature.

BRAF mutations are uncommon in non-small cell lung cancer (NSCLC), accounting for less than 5% of all NSCLC cases. The utilization of targeted therapies in non-V600E BRAF mutant NSCLC is considered controversial, although non-V600E genotype is reported in ~50% of all BRAF mutant patients. We document the case of a 63-year-old patient with NSCLC harbouring a rare BRAF E501Q mutation, who had prolonged response to immunotherapy combined with chemotherapy in Vietnam. The patient was diagnosed with metastatic PD-L1-negative lung adenocarcinoma and received pembrolizumab plus chemotherapy as first-line treatment. After completing 35 cycles of pembrolizumab and pemetrexed, his disease has remained stable during the treatment-free follow-up period, and he is alive 38 months after treatment initiation at the latest follow-up. Immune-based therapy is an appropriate option for lung adenocarcinoma with rare non-V600E BRAF mutation. Further clinical studies are necessary to determine the effectiveness of using immune-based therapy in this specific population.