A Phase 1, Open-Label, Dose-Escalation & Expanded Cohort, Continuous IV Infusion, Multi-center Study of the Safety, Tolerability,PK & PD of EPZ-5676 in Treatment Relapsed/Refractory Patients With Leukemias Involving

Inclusion Criteria: 1. Male and female patients aged ≥ 18 years. 2. Patients with relapsed /refractory AML, ALL, or MLL with rearrangement of the MLL gene, including 11q23 or PTD, are eligible for the expanded cohort: * At least one prior therapy; * Refractory disease on most recent therapy, or disease recurrence following remission on most recent therapy; * Received and failed all known effective therapies for their disease; * Not a candidate for allogeneic stem cell transplantation * \> 10% blasts or biopsy-documented leukemia cutis or myeloid sarcoma. 3. Eastern Cooperative Oncology Group (ECOG) performance status of 0-2. 4. Patients must have the following clinical laboratory values: * Serum creatinine ≤2 mg/dL or creatinine clearance \> 60 mL/minute; * Total bilirubin ≤2.0 times the ULN for the institution, unless considered due to Gilbert's syndrome; * ALT or AST ≤ twice the upper limit of normal (ULN), unless considered due to organ leukemic involvement; * Absolute neutrophil count ≥1,000/µL (unless due to documented leukemic involvement of the bone marrow at the time of study entry) * Platelets ≥100,000/µL (unless due to documented leukemic involvement of the bone marrow at the time of study entry). * PT or aPTT \< 1.5 times the ULN 5. Able and willing to give written informed consent. 6. Life expectancy of at least 3 months Exclusion Criteria: 1. Uncontrolled intercurrent illness or psychiatric illness/social situations that would limit compliance with study requirements. 2. Active heart disease 3. Receiving any other standard treatment for their hematologic malignancy. 4. Receiving strong CYP3A4 inhibitors/ inducers. 5. Known history of cerebrovascular accident in the past 6 months. 6. Known bleeding diathesis. 7. Known, active (symptomatic) involvement of the central nervous system by leukemia. 8. On immunosuppressive therapy. 9. Known active infection. 10. Pregnant or nursing females.