ERBB2 and breast cancer: In the Systemic Therapies for HER2-positive Metastatic Breast Cancer study of 977 patients with ERBB2-positive MBC, 87 (8.9%) had evidence of BRM at initial diagnosis of metastatic disease while 212 (21.7%) subsequently developed intracranial metastatic disease, but any difference in incidence over time was not recorded.21 BRM incidence rates for each subtype are similarly lacking in the Breast Cancer Network Registry study of 1712 MBC patients with BRM,22 but detailed data regarding their survival patterns were well documented.