Patients receive cyclophosphamide intravenously (IV) and vincristine sulfate IV on day 1, etoposide IV on days 1-3 or orally (PO) once daily (QD) on days 2-3, and prednisone PO QD on days 1-5 (CEOP administration). Patients also receive pralatrexate IV over 3-5 minutes on days 15, 22, and 29 (P administration). Treatment repeats every 42 days for up to 6 courses in the absence of disease progression or unacceptable toxicity.