Pediatric Acute Leukemia (PedAL) Screening Trial: Developing New Therapies for Relapsed Leukemias.

Inclusion Criteria: - Patients must be less than 22 years of age at the time of study enrollment - Patient must have one of the following at the time of study enrollment: - Patient has known or suspected relapsed/refractory (including primary refractory) AML as defined in protocol - This includes isolated myeloid sarcoma - Patient has known or suspected relapsed/refractory (including primary refractory) myeloid leukemia of Down syndrome (ML-DS) - Patient has known or suspected relapsed ALL as defined in protocol that meets one of the following criteria: - Second or greater B-ALL medullary relapse, excluding KMT2Ar - Any first or greater B-ALL medullary relapse involving KMT2Ar - Any first or greater T-ALL medullary relapse with or without KMT2Ar - Patient has known or suspected relapsed/refractory (including primary refractory) mixed phenotype acute leukemia (MPAL) as defined in protocol - Patient has known or suspected de novo or relapsed/refractory (including primary refractory) treatment-related AML (t-AML) - Patient has known or suspected de novo or relapsed/refractory (including primary refractory) myelodysplastic syndrome (MDS) or treatment-related myelodysplastic syndrome (t-MDS) - Note: Relapsed/refractory disease includes stable disease, progressive disease, and disease relapse. - Patient has known or suspected de novo or relapsed/refractory (including primary refractory) juvenile myelomonocytic leukemia (JMML) - Note: Relapsed/refractory disease includes stable disease, progressive disease, and disease relapse. - All patients and/or their parents or legal guardians must sign a written informed consent - All institutional, Food and Drug Administration (FDA), and National Cancer Institute (NCI) requirements for human studies must be met