Breast Cancer Subtypes and Mortality of Breast Cancer Patients With Brain Metastasis at Diagnosis: A Population-Based Study

Background Brain metastasis is an important cause of breast cancer-related death. Aim We evaluated the relationships between breast cancer subtype and prognosis among patients with brain metastasis at the initial diagnosis. Methods The Surveillance, Epidemiology, and End Results database was searched to identify patients with brain metastasis from breast cancer between 2010 and 2015. Multivariable Cox proportional hazard models were used to identify factors that were associated with survival among patients with initial brain metastases. The Kaplan-Meier method was used to compare survival outcomes according to breast cancer subtype. Results Among 752 breast cancer patients with brain metastasis at diagnosis, 140 patients (18.6%) underwent primary surgery and 612 patients (81.4%) did not undergo surgery, while 460 patients (61.2%) received chemotherapy and 292 patients (38.8%) did not receive chemotherapy. Multivariable analysis revealed that, relative to HR+/HER2- breast cancer, HR-/HER2- breast cancer was associated with significantly poorer overall survival (hazard ratio: 2.52, 95% confidence interval: 1.99-3.21), independent of age, sex, race, marital status, insurance status, grade, liver involvement, lung involvement, primary surgery, radiotherapy, and chemotherapy. The median overall survival intervals were 12 months for HR+/HER2-, 19 months for HR+/HER2+, 11 months for HR-/HER2+, and 6 months for HR-/HER2- (P < .0001). Relative to HR+/HER2- breast cancer, HR-/HER2- breast cancer was associated with a significantly higher risk of mortality among patients, and the association was stronger among patients who received chemotherapy (p for interaction = .005). Conclusions Breast cancer subtype significantly predicted overall survival among patients with brain metastasis at diagnosis.