Objective:To investigate the factors influencing the prognosis of patients with estrogen receptor (ER)-positive de novo stage Ⅳ breast cancer.Methods:The clinical data of 339 patients with ER-positive de novo stage Ⅳ breast cancer treated in Tianjin Medical University Cancer Hospital and Cangzhou Hospital of Integrated TCM-WM from February 2010 to December 2017 were retrospectively analyzed. Related factors such as age, time of chief complaint, the clinical T/N stage, site of metastasis, expressions of molecular markers and treatment mode were included. Univariate log-rank test and multivariate Cox regression model were used to analyze the effects of prognostic factors on patients' overall survival (OS).Results:Univariate analysis showed that there were statistically significant differences in the OS of patients stratified by clinical N stage at first diagnosis, metastasis sites at first diagnosis, ER expression, progesterone receptor (PR) expression, Ki-67 positive index and p53 expression, endocrine therapy, chemotherapy at first diagnosis, surgery and radiotherapy of the primary lesions (all P < 0.01). Multivariate Cox regression analysis results showed that metastasis sites at first diagnosis, Ki-67 positive index, surgery and radiotherapy of the primary lesions were all independent influencing factors of OS for breast cancer patients (all P < 0.01). Conclusions:Patients with ER-positive de novo stage Ⅳ breast cancer have a good prognosis when they have oligometastasis, Ki-67 positive index ≤ 20%, and they receive surgery and radiotherapy of the primary lesions.