1 Introduction The brain is one of the most common sites for metastasis from lung cancer, and patients with brain metastases (BM) have a poorer prognosis than those without BM[1] Lung cancer is pathologically classified into: non-small cell lung cancer (NSCLC), accounting for 80–85% of cases, and small cell lung cancer (SCLC), accounting for 15–20% of cases.[2] Among patients with non-metastatic NSCLC, the risk of developing BM is 11% for lung adenocarcinoma, 6% for squamous cell carcinoma...