Objective:To determine the high-risk population of breast cancer brain metastasis accompanied with severe peritumoral brain edema, and to probe into the effects of peritumoral brain edema degree on the prognosis for breast cancer patients with brain metastasis.Methods:The clinical features of the breast cancer patients with brain metastasis accompanied with peritumoral brain edema in our department were retrospectively analyzed, and the edema index (EI) was adopted to represent the peritumoral edema degree, the calculation formula of which was EI=(Vedema+Vtumor) / Vtumor.EI was treated as the dependent variable, and rank sum test was conducted on factors such as age, diameter of the metastasis,reinforcing features of the metastasis, position of the metastasis in the brain, whether the lesion was regular,duration from diagnosis of breast cancer to brain metastasis, ER, PR and Her-2, so as to analyze the influence factors of EI.Kaplan-Meier method was adopted to analyze the effects of EI on the prognosis for breast cancer patients with brain metastasis, and the Coxs proportional hazard model was applied in multivariate analysis.Results:Altogether 58 cases of breast cancer patients with single brain metastasis were enrolled in this research in accordance with the inclusion and exclusion criteria, with the median age of 44 years old (range: 26 to 61 years old), and the median EI of 3.01.Patients with negative ER, those with the age of≥45 years old, and those with irregular lesions were the independent factors that influenced EI (Mann-Whitney rank sum test, p<0.05).The univariate and multivariate analysis indicated that EI was not related to the prognosis for breast cancer patients with brain metastasis.Conclusion:Breast cancer patients with brain metastasis who have negative ER, the age of≥45 years old, and irregular brain metastases are the high risk population of severe peritumoral brain edema;and the EI is not related to the prognosis for breast cancer patients with brain metastasis.