NK-Cell Leukemia

Patients are in 2 cohorts: Cohort 1: dexamethasone, methotrexate, ifosfamide, pegaspargase, and etoposide (modified SMILE) chemotherapy regimen alone and pembrolizumab in children, adolescents, and young adults with advanced stage NK lymphoma and leukemia Cohort 2: combining pralatrexate (PRX) (Cycles 1, 2, 4, 6) and brentuximab vedotin (BV) (Cycles 3, 5) to cyclophosphamide, doxorubicin, and prednisone in children, adolescent, and young adults with advanced peripheral T-cell lymphoma (non-anaplastic large cell lymphoma or non-NK lymphoma/leukemia) . Both groups proceed to allogeneic stem cell transplant with disease response.