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.