Inclusion Criteria:

- Patients must have pathologically documented precursor T-cell acute lymphoblastic
leukemia/lymphoma (T-ALL), relapsed or refractory to standard therapy, or not be a
candidate for standard myelosuppressive chemotherapy due to age or comorbid disease.

- Patient must have performance status <2 on the ECOG performance status for patients
>16 years old; Lansky performance level >50 for patients 12 months to less than or
equal to 16 years old.

- Patient must have adequate renal and liver function as indicated by the laboratory
values performed within 14 days of receiving the first dose of study drug.

- Patient must have fully recovered from any chemotherapy and be greater than 2 weeks
from radiotherapy, immunotherapy, or systemic steroid therapy with the exception of
hydroxyurea, intrathecal therapy, or immunosuppressant therapy for chronic
graft-versus-host disease prophylaxis following allogeneic bone marrow transplant.

- Patient must be greater than 2 months following bone marrow or peripheral blood stem
cell transplantation and off all immunosuppressant therapy (with the exception of
patients taking immunosuppressant therapy for chronic graft-versus-host disease
prophylaxis following allogeneic bone marrow transplant).

- Men and women of reproductive potential must use an effective contraceptive method
while enrolled in the study.

- Patient or the patient's legal representative must be able to understand the study
and give written informed consent.

Exclusion Criteria:

- Patient has had treatment with any investigational therapy during the preceding 30
days.

- Patient has uncontrolled congestive heart failure, angina, or had a myocardial
infarction in the preceding 3 months.

- Patient has known hypersensitivity to the components of study drug, its analogs, or
to allopurinol.

- Patient has active or uncontrolled infection.

- Patient has known psychiatric or substance abuse disorders that would interfere with
cooperation with the requirements of the trial.

- Patient is pregnant or lactating.

- Patient has any other severe concurrent disease which would make the patient
inappropriate for entry into this study.

- Patient is known to be HIV positive or who has an AIDS-related illness.

- Patients with a "currently active" second malignancy, other than non-melanoma skin
cancer should not be enrolled.

- Patient has isolated CNS disease.