The incidence of breast cancer brain metastasis (BM) has increased in recent years, particularly in the subpopulation of triple-negative breast cancer (TNBC) (estrogen receptor <ER>-/progesterone receptor <PR>-/human epidermal growth factor receptor 2 <Her2>-, ER-/PR-/Her2-).1–3 TNBC, which accounts for 15–25% of all breast cancers,4,5 has problematic diagnosis because patients with TNBC do not respond to hormone or HER2-targeted therapies due to the lack of expression of ER, PR, and HER2.4 Moreover, the exact pathologic process of BM in the TNBC subset is poorly understood up to now. The gene discussed is ESR1; the disease is breast cancer.