Abstract: Objective:To investigate the clinicopathologic characteristics and prognosis of primary invasive breast can -cer patients with ER/PR single-positive status. Methods:A total of1,054 patients with primary invasive breast cancer with different ER or PR status seen in our hospital between October1998and May 2004were analyzed. Patients were stratified according to ER and PR expression. The study was focused on the single-positive groups (ER+/PR-and ER /PR+) and as-sessed their main characteristics and evaluated the prognostic difference between the double positive and negative tu-mors. The survival rate of breast cancer was calculated by Kaplan-Meier analysis and log-rank test. COX multivariate analy-sis was conducted to determine the independent risk factors of prognosis. Results: The prognosis of double-positive tumors was best in different receptor groups and was better in single-positive group than in double-negative group. The majority of ER+/PR- tumors were small and well-differentiated. They were more frequently seen in elder and postmenopausal women. The survival analysis showed no difference in overall survival between the two groups ( P=0.890 ). However, disease-free survival was better in ER +/PR- patients than in ER-/PR + patients (P=0.035 ). Compared with the double-negative pheno-type, ER+/PR- group was associated with better outcome. In patients with single-positive receptor who received adjuvant hormone therapy, different ER or PR positive status was an independent risk factor for disease-free survival (P=0.023 ). Conclusion:ER +/PR- and ER-/PR + tumors were two distinct groups of breast cancer in clinicopathologic characteristics and prognosis. ER-/PR+ breast cancer patients might need active treatment because of its aggressive behaviors