Clofarabine for Relapsed or Refractory T-Cell or B-Cell Non-Hodgkin Lymphoma (NHL)

Inclusion Criteria: * Adult patients who are at least 18 years old with histology confirmed diffuse large cell B-cell NHL who have failed prior systemic chemotherapy with or without monoclonal antibody-based therapies. * Measurable disease determined by Ct or PET scans or bone marrow involvement, defined as lesions that can be accurately measured in two dimensions by CT or PET scan with the longest diameter accurately as greater than or equal to 1.0 cm or palpable lesions with both diameters greater than or equal to 2.0 cm. PET scan measurable disease is defined based on SUV value as determined by nuclear medicine evaluation. * Eastern Cooperative Oncology Group (ECOG) performance status of 0,1,or 2. * Life expectancy greater than 12 weeks. * Laboratory values obtained less than or equal to 14 days prior to registration: * Absolute neutrophil count (ANC) greater than or equal to 1500. * White blood cell (WBC) count greater than 3.0. * Platelets greater than or equal to 100. * Hemoglobin (HG) greater than 9.0 g/dL. * Total bilirubin less than or equal to 2.0 mg/dL. * Aspartate transaminase (AST)/alanine transaminase (ALT) less than or equal to 3 times the upper limit of normal (ULN). Higher values are acceptable if it is deemed that they are related to liver involvement with NHL. * Serum creatinine less than or equal to 2.0 mg/dL. * Cardiac function on pretreatment MUGA scan or echocardiogram that is considered normal by institutional standards. * 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 minium of 6 months after study treatment. Exclusion Criteria: * Previously untreated NHL. * Received previous treatment with clofarabine. * History of T-cell lymphoma. * Bulky disease (ie, any single mass greater than 10 cm or circulating malignant cells greater than or equal to 24,000 cells/ul. * Patients with known AIDS-related or HIV-positive lymphoma. * Autologous bone marrow or stem cell transplant within 3 months of study entry. * History of allogeneic bone marrow transplant or organ transplant. * Prior radiotherapy to the only site of measurable disease. * Any medical condition that requires chronic use of oral high-dose corticosteroids. ( in excess of 1 mg/kg/day). * Autoimmune thrombocytopenia. * Use if 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 of parenteral antifungal therapy). * HIV-positive status. * 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 lymphoma (CNS) lymphoma.