Abstract: Metronomic Low-dose Oral Cyclophosphamide Plus Endocrine Therapy as SystemicTreatment for 23 Metastatic Breast Cancer PatientsHanfang JIANG, Guohong SONG, Li CHE, Lijun DI, Jun RENCorrespondence to: Jun REN, E-mail: renjun9688@yahoo.comDepartment of Breast Medical Oncology, Key Laboratory of Carcinogenesis and Translational Research (Ministry of Education ), Pe-king University School of Oncology, Beijing Cancer Hospital & Institute, Beijing 100142, ChinaAbstract Objective: To evaluate the efficacy and safety of metronomic low-dose oral cyclophosphamide plus endocrine therapyas systemic treatment for 23 metastatic breast cancer patients. Methods: Cyclophosphamide was taken orally, 50 mg/d daily, with orwithout endocrine therapy including letrozole, exemestane, or megestrol acetate until disease progression or intolerable toxicity oc-curred. If the disease was stable, cyclophosphamide was administered for 1 year. Tumor response was evaluated by RECIST criteria,and adverse events were evaluated by NCI-CTC AE v3.0. Results: Twenty-three cases of metastatic breast cancer were retrospectivelyanalyzed. One of the 23 patients had complete response (CR 4.3%), 13 showed stable disease (SD 56.5%) and 9 had progression of dis-ease (PD 39.5%), with an objective response rate of 4.3% (CR + PR) and disease control rate of 60.8% (CR + PR + SD). Median pro-gression-free survival (PFS) was 5.0 months (95% CI 0.31-9.70 months), and mean PFS was 7.65 months (95% CI 4.93-10.38 months).Median survival time was 29 months. The 1- and 2-year survival rates were 67.9% and 50.9%, respectively. Adverse effects were mild,and the main adverse effects were leucopenia and fatigue (13%). Conclusion: Metronomic low-dose oral cyclophosphamide plus endo-crine therapy is effective in treating metastatic breast cancer and can be well tolerated. It is worthy of further study on a large scale.Keywords Metastatic breast neoplasms; Metronomic chemotherapy; Cyclophosphamide