title: Incidence and relapse risk of intracranial metastases within the perihippocampal region in 314 patients with breast cancer.
abstract: OBJECTIVE
  The safe prerequisite of hippocampal-sparing whole brain radiotherapy (HS-WBRT) for patients with breast cancer is unclear. This study investigated the risk and relapse of perihippocampal (PH) metastases in breast cancer.
  
  
  METHODS
  Consecutive breast cancer patients with brain metastasis (BM) were reviewed. Metastases and hippocampi were contoured in cranial magnetic resonance imaging (MRI). The closest distance from metastasis to hippocampus was calculated. Clinical and radiographic variables were correlated with PH (in or within 5mm around the hippocampus) metastasis. The risk of post-treatment PH recurrence was estimated.
  
  
  RESULTS
  Three hundred and fourteen patients with 1678 metastases exhibited a median breast cancer-specific overall survival (OS) and OS after BM (BMOS) of 75.4 and 14.3 months, respectively. Hippocampal metastases were identified in 1.2% of metastases and 4.1% of patients. PH lesions comprised 3.5% of lesions in 11.1% of patients. The number and aggregated volume of BM were associated with PH disease probability (univariate). Only the number of BM significantly correlated with PH disease in the multivariate analysis. The patients with PH lesions exhibited more non-oligometastatic disease, increased tumor volume, and poor BMOS. One hundred and eleven patients without original PH lesions developed intracranial progression post-treatment. The risks of PH metastasis recurrence were 4.6% for WBRT and 6.8% for sub-therapeutic irradiation in the PH region. The increase in the absolute risk of PH recurrence with hippocampal-sparing irradiation was approximately 2%.
  
  
  CONCLUSIONS
  These novel findings indicate that BM from breast cancer exhibits low risks of metastases and relapse within the hippocampal avoidance region. Non-oligometastatic disease is associated with PH metastasis. Thus, HS-WBRT is considered safe and suitable for breast cancer.
authors.affiliation: Department of Radiotherapy, Affiliated Hospital of Academy of Military Medical Sciences, Beijing, China. Electronic address: sunice116@163.com.
authors.forename: Bing
authors.initials: B
authors.lastname: Sun
authors.affiliation: Department of Radiotherapy, Affiliated Hospital of Academy of Military Medical Sciences, Beijing, China. Electronic address: 632509397@qq.com.
authors.forename: Zhou
authors.initials: Z
authors.lastname: Huang
authors.affiliation: Department of Radiotherapy, Affiliated Hospital of Academy of Military Medical Sciences, Beijing, China. Electronic address: skywu4923@sina.com.
authors.forename: Shikai
authors.initials: S
authors.lastname: Wu
authors.affiliation: Department of Radiotherapy, Affiliated Hospital of Academy of Military Medical Sciences, Beijing, China. Electronic address: shenge219@126.com.
authors.forename: Ge
authors.initials: G
authors.lastname: Shen
authors.affiliation: Department of Science and Technology, Academy of Military Medical Sciences, Beijing, China. Electronic address: leicha@bmi.ac.cn.
authors.forename: Lei
authors.initials: L
authors.lastname: Cha
authors.affiliation: Department of Radiotherapy, Affiliated Hospital of Academy of Military Medical Sciences, Beijing, China. Electronic address: kzmxy@163.com.
authors.forename: Xiangying
authors.initials: X
authors.lastname: Meng
authors.affiliation: Department of Radiotherapy, Affiliated Hospital of Academy of Military Medical Sciences, Beijing, China. Electronic address: ding31788@sina.com.
authors.forename: Lijuan
authors.initials: L
authors.lastname: Ding
authors.affiliation: Department of Radiotherapy, Affiliated Hospital of Academy of Military Medical Sciences, Beijing, China. Electronic address: wjl1000@tom.com.
authors.forename: Junliang
authors.initials: J
authors.lastname: Wang
authors.affiliation: Department of Breast Cancer, Affiliated Hospital of Academy of Military Medical Sciences, Beijing, China. Electronic address: songsantai2006@163.com.
authors.forename: Santai
authors.initials: S
authors.lastname: Song
mesh_terms: D000328:Adult; D000368:Aged; D001932:Brain Neoplasms / Q000556:secondary*; D001943:Breast Neoplasms / Q000401:mortality / Q000473:pathology*; D005260:Female; D006624:Hippocampus / Q000473:pathology*; D006801:Humans; D015994:Incidence; D008279:Magnetic Resonance Imaging; D008875:Middle Aged; D012306:Risk; D047368:Tumor Burden
keywords: Brain metastasis; Breast cancer; Hippocampal avoidance; Whole brain radiotherapy