Ruxolitinib Phosphate and Decitabine in Treating Patients With Relapsed or Refractory or Post Myeloproliferative Acute Myeloid Leukemia

PRIMARY OBJECTIVES: I. To determine the tolerability of the combination of decitabine and ruxolitinib phosphate (ruxolitinib \[DI\]) in patients with leukemia. (Phase I) II. To determine the efficacy of ruxolitinib in increasing and prolonging response induced by decitabine alone in patients with post myeloproliferative neoplasm acute myeloid leukemia (AML) (post MPN-AML) alternatively referred to as (myeloproliferative neoplasm - blast phase; MPN-BP). (Compared to historical response rate with decitabine alone) (Phase II) SECONDARY OBJECTIVES: I. To compare whether there is a difference in response rate patients with post-MPN AML with janus kinase 2 (JAK2) mutations and patients without JAK2 mutations. OUTLINE: This is a phase I, dose-escalation study of ruxolitinib phosphate followed by a phase II study. Patients receive ruxolitinib phosphate orally (PO) twice daily (BID) on days 1-28 and decitabine intravenously (IV) over 1-2 hours on days 1-5. Treatment repeats every 4-6 weeks for up to 24 courses in the absence of disease progression or unacceptable toxicity.