Cyclophosphamide is an anticancer drug used to treat various types of cancer such as breast cancer, ovarian cancer, leukemias, malignant lymphomas, multiple myeloma, neuroblastoma, and retinoblastoma. Cyclophosphamide is a chemotherapy drug that works by stopping the growth of malignant cells. Cyclophosphamide also suppresses the immune system and thus treats various immune-related diseases such as lupus and rheumatoid arthritis. This Cyclophosphamide medicine may also be used to treat other conditions as determined by your doctor.