Compared with other intrinsic subtypes, HER2-positive breast cancer has a high propensity to metastasize to the brain.[26] In fact, it is estimated that 35% to 55% of patients with HER2-positive breast cancer will develop brain metastases during the course of the disease, and they are known to have a poor prognosis.[27,28]. This evidence concerns the gene ERBB2 and breast cancer.