For patients with human epidermal growth factor receptor 2– (HER2–) positive breast cancer or epidermal growth factor receptor mutation–positive non–small cell lung cancer, the brain remains a frequent site of disease recurrence regardless of disease control for primary tumors by systemic treatment with molecularly targeted agents such as trastuzumab or gefitinib, respectively [4, 5]. This evidence concerns the gene ERBB2 and lung cancer.