Dose Escalation Study of Clofarabine in Patients With Relapsed or Refractory Low Grade or Intermediate-Grade B-Cell Lymphoma

Inclusion Criteria: * Adult patients who are at least 18 years old * Histologically confirmed low grade or intermediate-grade B-cell lymphoma * Relapsed or refractory to at least one standard chemotherapy regimen. Patients who have received Rituximab alone without having received a cytotoxic agent are not eligible. * Measurable disease, defined by the Cheson lymphoma criteria. * Eastern Cooperative Oncology Group (ECOG) performance status of 0, 1, or 2 * Life expectancy greater than 12 weeks * Laboratory values obtained ≤2 weeks prior to entry * Absolute neutrophil count (ANC) ≥ 1000 x 10 9/L * White blood cell (WBC) count \> 2.5 x 10 9/L * Platelets ≥ 75 x 10 9/L * Hemoglobin (Hg) \> 9.0 g/dL * Total bilirubin ≤2.0 mg/dL * Aspartate transaminase (AST)/alanine transaminase (ALT) ≤3 × upper limit of normal (ULN) * Serum creatinine ≤2.0 mg/dL * Normal cardiac function, defined as an ejection fraction ≥45% determined by pretreatment radionuclide ventriculography (RVG) or echocardiogram. * Capable of understanding the investigational nature, potential risks and benefits of the study, and able to provide valid informed consent. * Female patients of childbearing potential must have a negative serum pregnancy test within 2 weeks prior to enrollment. * Male and female patients must use an effective contraceptive method during the study and for a minimum of 6 months after study treatment. Exclusion Criteria: * Previously untreated B-cell lymphoma. * Received previous treatment with clofarabine. * Patients with known AIDS-related or HIV-positive lymphoma. * Autologous bone marrow or stem cell transplant within 6 months of study entry. * Prior radiotherapy to the only site of measurable disease. * Any medical condition that requires chronic use of oral high-dose corticosteroids greater than 20 mg/day prednisone. * Active autoimmune thrombocytopenia. * Use of investigational agents within 30 days or any anticancer therapy within 3 weeks before study entry. The patient must have recovered from all acute toxicities from any previous therapy. * Patients with an active, uncontrolled systemic infection considered to be opportunistic, life threatening, or clinically significant at the time of treatment or with a known or suspected fungal infection (ie, patients on parenteral antifungal therapy). * Active secondary malignancy. * Pregnant or lactating patients. * Any significant concurrent disease, illness, or psychiatric disorder that would compromise patient safety or compliance, interfere with consent, study participation, follow up, or interpretation of study results. * Patients with active or untreated central nervous system (CNS) lymphoma.