Inclusion Criteria:

- Histologically/cytologically confirmed PTCL, using the Revised European American
Lymphoma (REAL) World Health Organization (WHO) disease classification:

1. T/Natural Killer (T/NK) cell leukemia/lymphoma

2. Adult T-cell lymphoma/leukemia (human T-cell leukemia virus [HTLV] 1+)

3. Angioimmunoblastic T cell lymphoma

4. Blastic Natural Killer (NK) lymphoma (with skin, lymph node, or visceral
involvement)

5. Anaplastic large cell lymphoma, primary systemic type

6. PTCL - unspecified

7. T/NK-cell lymphoma - nasal

8. Enteropathy-type intestinal lymphoma

9. Hepatosplenic T cell lymphoma

10. Extranodal peripheral T/NK-cell lymphoma - unspecified

11. Subcutaneous panniculitis T-cell lymphoma

12. Transformed mycosis fungoides

- Documented progression of disease after at least 1 prior treatment. Patients may not
have received experimental therapy as their only prior therapy. Patient has at least
1 biopsy from initial diagnosis or in the relapsed setting to confirm the diagnosis
of PTCL. Patient has recovered from the toxic effects of prior therapy. Patients
treated with monoclonal antibody therapy may be enrolled regardless of the time frame
of the therapy if they have progression of disease.

- Eastern Cooperative Oncology Group (ECOG) Performance Status ≤ 2.

- ≥ 18 years of age.

- Adequate hematological, hepatic, and renal function.

- Women of childbearing potential must agree to practice a medically acceptable
contraceptive regimen from study treatment initiation until at least 30 days after
the last administration of pralatrexate and must have a negative serum pregnancy test
within 14 days prior to the first day of study treatment. Patients who are
postmenopausal for at least 1 year or are surgically sterilized do not require this
test.

- Men who are not surgically sterile must agree to practice a medically acceptable
contraceptive regimen from study treatment initiation until at least 90 days after
the last administration of pralatrexate.

- Patient has given written informed consent.

Exclusion Criteria:

- Patient has:

1. Precursor T/NK neoplasms, with the exception of blastic NK lymphoma

2. T cell prolymphocytic leukemia (T-PLL)

3. T cell large granular lymphocytic leukemia

4. Mycosis fungoides, other than transformed mycosis fungoides

5. Sézary syndrome

6. Primary cutaneous CD30+ disorders: Anaplastic large cell lymphoma and
lymphomatoid papulosis

- Active concurrent malignancy (except non melanoma skin cancer or carcinoma in situ of
the cervix). If there is a history of prior malignancy, the patient must be disease
free for greater than or equal to 5 years.

- Congestive heart failure Class III/IV according to the New York Heart Association's
Heart Failure Guidelines.

- Uncontrolled hypertension.

- Human immunodeficiency virus (HIV)-positive diagnosis and is receiving combination
anti-retroviral therapy.

- Patient has, or history of, brain metastases or central nervous system (CNS) disease.

- Patient has undergone an allogeneic stem cell transplant.

- Patient has relapsed less than 75 days from time of an autologous stem cell
transplant.

- Active uncontrolled infection, underlying medical condition including unstable
cardiac disease, or other serious illness that would impair the ability of the
patient to receive protocol treatment.

- Major surgery within 2 weeks of study entry.

- Receipt of any conventional chemotherapy or radiation therapy (RT) within 4 weeks (6
weeks for nitrosoureas or mitomycin C) prior to study treatment or planned use during
the course of the study.

- Receipt of corticosteroids within 7 days of study treatment, unless patient has been
taking a continuous dose of no more than 10 mg/day of prednisone for at least 1
month.

- Use of any investigational drugs, biologics, or devices within 4 weeks prior to study
treatment or planned use during the course of the study.

- Previous exposure to pralatrexate.