PRIMARY OBJECTIVES: I. To evaluate the feasibility of using the combination of oral metronomic cyclophosphamide and oral dexamethasone for treatment of men with metastatic castration -resistant prostate Cancer (mCRPC) who have progressed on 2 or more prior treatments. II. To assess the safety of cyclophosphamide + dexamethasone in men with mCRPC who have progressed on 2 or more prior treatments. SECONDARY OBJECTIVE:I. To evaluate prostate specific antigen (PSA) response and progression free survival and time to event outcome in participants with mCRPC treated with cyclophosphamide and dexamethasone. EXPLORATORY OBJECTIVE: I. To analyze serial blood samples for PSA monitoring and tumor tissue for pRb (encoded by the RB1 gene) and p53 (encoded by the TP53 gene) mutations. OUTLINE: Patients receive cyclophosphamide orally (PO) once daily (QD) and dexamethasone PO QD on days 1-28 of each cycle. Cycles repeat every 28 days in the absence of disease progression or unacceptable toxicity. After completion of study treatment, patients are followed up at 30 days and then every 3 months thereafter.
This phase I trial tests the safety and side effects of cyclophosphamide given together with dexamethasone in treating patients with castration resistant prostate cancer that has spread to other places in the body (metastatic). Chemotherapy drugs, such as cyclophosphamide, work in different ways to stop the growth of tumor cells, either by killing the cells, by stopping them from dividing, or by stopping them from spreading. Giving low doses of cyclophosphamide daily may reduce side effects. Dexamethasone is a corticosteroid drug that is used to treat some of the problems caused by chemotherapy treatment. The combination of cyclophosphamide and dexamethasone may work better in treating patients with castration resistant prostate cancer.