Study of Forodesine Hydrochloride in Patients With Relapsed/Refractory Precursor T-Lymphoblastic Leukemia/Lymphoma Who Have Failed Two or More Prior Treatment Regimens

Inclusion Criteria: * Patients with an unequivocal histologic diagnosis of precursor T-lymphoblastic leukemia/lymphoma (World Health Organization \[WHO\] classification). * Failure to have responded to or relapsed after two or more treatment regimens for their disease, one of which could be HSCT. * Performance status of 2 by Eastern Cooperative Oncology Group (ECOG) criteria (see Appendix A). * Eighteen years of age and older. * Life expectancy of at least three months. * Adequate liver function (aspartate aminotransferase \[AST\] and/or alanine aminotransferase \[ALT\] ≤3 times upper limit of normal), unless related to the underlying leukemia. * Negative serum or urine pregnancy test within two to seven days prior to the start of study treatment in females of childbearing potential. * Females of childbearing potential and males must be willing and able to use an adequate method of contraception to avoid pregnancy for the duration of the study in such a manner that the risk of pregnancy is minimized. Acceptable contraceptives include intra-uterine devices (IUDs), hormonal contraceptives (oral, depot, patch, or injectable), and double-barrier methods such as condoms or diaphragms with spermicidal gel or foam. * Signed informed consent form (ICF) prior to start of any study-specific procedures. * Willing and able to provide authorization for the use and disclosure of personal health information in accordance with Health Insurance Portability and Accountability Act (HIPAA) policy (U.S. patients only). Exclusion Criteria: * Patients with known human immunodeficiency virus (HIV) infection or human T lymphotrophic virus 1 (HTLV-1). * Patients with active hepatitis B or C infection. * Patients with clinical evidence of active central nervous system (CNS) leukemia. * Active serious infection not controlled by oral or intravenous antibiotics. * Patients with a calculated creatinine clearance of \<50 mL/min. * Prior treatment with any investigational antileukemic or chemotherapy agent within seven days prior to study entry or lack of full recovery from side effects due to prior therapy, independent of when that therapy was given. * Rapidly progressive disease with compromised organ function judged to be life threatening by the Investigator. * Concurrent treatment with other antileukemia agents (CNS prophylaxis \[e.g., intrathecal methotrexate, cytarabine, or hydrocortisone\] and corticosteroid use will not be excluded, but must first be approved by the Medical Monitor) (see Sections 9.2.1 and 9.2.2). * Pregnant and/or lactating female. * Patients who cannot swallow or who have chronic gastrointestinal disease or conditions that may hamper compliance and/or absorption of the product. * Hypersensitive or intolerant to any component of the study drug formulations. * Patients who have received prior forodesine treatment.