A Phase II Study of Clofarabine in Patients With Relapsed or Refractory Multiple Myeloma

Inclusion Criteria: 1. Multiple myeloma diagnosed by standard criteria. 2. Measurable levels of monoclonal protein in serum (\>= 0.5 g/dL) or urine (\>= 0.2 g/24 hr). 3. At least 1 prior therapies for multiple myeloma with documented evidence of progression on the most recent treatment. 4. Age 18 years or older. 5. ECOG performance status \<= 2. 6. Acceptable organ and marrow function as defined below: * Hemoglobin \>= 8 gm/dL * Absolute neutrophil count \>= 1,000/mm3 * Platelets \>= 50,000/mm3 * Total bilirubin \<= 2.5 X institutional upper limit of normal * AST, ALT \<= 2.5 X institutional upper limit of normal * Creatinine 1.5 x institutional upper limit of normal * Normal cardiac function as determined by standard institutional methods 7. Women of child bearing potential must agree to use adequate contraception prior to study entry and for the duration of study. 8. Ability to understand and the willingness to sign a written informed consent document. Exclusion Criteria: 1. Receiving any other investigational agents. 2. Receiving concurrent steroids with a dose equivalent of prednisone of \>= 150 mg/month. 3. Pregnant or nursing. 4. Active systemic infection considered opportunistic, life threatening or clinically significant at the time of treatment. 5. Severe concurrent disease, including severe insulin-dependent diabetes, uncontrolled hypertension, transient ischemic attacks, uncontrolled symptomatic coronary artery disease, or symptomatic CNS involvement or psychiatric illness/social situations that would limit compliance with study requirements. 6. History of other malignancy except for basal cell or squamous cell carcinoma of the skin or carcinoma in situ of the cervix or breast unless the subject has been off treatment and free from disease for \>= 3 years.