This text contains seven chapters, five of which are original articles. One of them deals with the invention and development of cyclophosphamide, mechanisms of action and side effects while a separate chapter deals with the management of hemorrhagic cystitis, the most important and serious side effect after using the drug at high doses. Other chapters deal with the clinical application in metastatic breast cancer and the role of cyclophosphamide in improving breast cancer microenvironment through mobilization of mesenchymal stem cells from bone marrow. The idea of metronomic chemotherapy in combination with Aromatase inhibitors (AI) in breast cancer with bone metastasis is also explained in this book. Cyclophosphamide may replace Ifosfamide in case of an Ifosfamide shortage in metastatic soft tissue sarcoma. Finally, the drug that forms one of the back bones of the ACEP protocol used to treat the aggressive Peripheral T-cell non-Hodgkin's lymphoma is described by the authors.