Clinical features of brain metastases in breast cancer: an implication for hippocampal-sparing whole-brain radiation therapy

OBJECTIVE: The objectives of this study were to describe the distribution of brain metastases (BM) in breast cancer patients and investigate the risk factors for perihippocampal metastases (PHM). PATIENTS AND METHODS: Retrospective analysis of the clinicopathological characteristics and patterns of BM was performed. Associations between clinicopathological characteristics and PHM (the hippocampus plus 5 mm margin) were evaluated using logistic regression analyses. RESULTS: A total of 1,356 brain metastatic lesions were identified in 192 patients. Patients with 1–3 BM, 4–9 BM, and ≥10 BM accounted for 63.0%, 18.8%, and 18.2%, respectively. There were only 7 (3.6%) patients with hippocampal metastases (HM) and 14 (7.3%) patients with PHM. On logistic regression, the number of BM was an independent risk factor for PHM. Patients with ≥10 BM had a significantly higher risk of PHM compared with those with <10 BM. Breast cancer subtype (BCS) was not associated with PHM. The number of BM was significantly correlated with various BCSs. Patients with hormone receptor (HR)+/human epidermal growth factor receptor 2 (HER2)+, HR−/HER2+, and HR−/HER2− subtypes had a higher probability of ≥10 BM, relative to patients with an HR+/HER2− subtype. CONCLUSION: Our study suggests that a low incidence of PHM may be acceptable to perform hippocampal-sparing whole-brain radiation therapy for breast cancer patients. Patients with extensive diffuse metastases (≥10 BM) were associated with higher odds of PHM.