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.