ERBB2 and breast cancer: Among all breast cancer patients, that risk is 5-10%, but the riskincreases to 15% among patients with extracranial metastases (stage IV disease) [15, 16].The risk increases further for breast cancer of specific receptor subtypes: patients withhuman epidermal growth factor receptor 2-enriched (HER2+) or triple-negative stage IV breastcancer are at a 25-45% risk of developing brain metastasis [17, 18].