Brain metastases (BM) increase morbidity and mortality in cancer patients1 and breast cancer (BC) is today the second most common cause of BM among solid malignancies.2,3 Over the last 2 decades, an increase in BM incidence was reported, mainly attributed to prolonged overall survival (OS) in patients with metastatic HER2-positive disease.4 In addition, the brain parenchyma acts as a sanctuary site for cancer cells protected from systemic therapy by the blood-brain barrier (BBB). The gene discussed is ERBB2; the disease is breast carcinoma.