Study of Combination Ruxolitinib and Decitabine Treatment for Accelerated Phase MPN or Post-MPN AML

Inclusion Criteria:

* Accelerated phase MPN as defined by 10%-19% blasts in the peripheral blood or bone marrow and evidence of dysplastic marrow features with a concomitant diagnosis of essential thrombocythemia (ET), polycythemia vera (PV) or primary myelofibrosis (PMF) or a diagnosis of acute myelogenous leukemia as defined by 20% blasts in the blood or bone marrow following a previous diagnosis of ET, PV or PMF.
* \>18 years of age
* Eastern Cooperative Oncology Group (ECOG) Performance status of 0-2. Patients with ECOG performance status of 3 will be eligible if the lower performance status is deemed by the investigator to be due entirely to accelerated or blastic phase MPN and not due to another comorbidity.
* Acceptable pre-study organ function during screening as defined as: Total bilirubin \< 1.5 times the upper limit of normal (ULN) unless due to Gilbert's disease or hemolysis, Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) ≤ 2.5 times ULN, Serum creatinine ≤ 1.5 x ULN
* Women of childbearing potential and males must agree to use adequate contraception (i.e., hormonal or barrier method of birth control; abstinence) prior to study entry and for the duration of study participation. Should a female subject become pregnant or suspect she is pregnant while participating in this study, she should inform the treating physician immediately.
* Patients who are not candidates for or have declined an allograft.
* Ability to understand and willingness to sign a written informed consent document.

Exclusion Criteria:

* Have had chemotherapy or investigational therapy, with the exception of hydroxyurea, within 4 weeks of study entry. Previous treatment with either ruxolitinib or decitabine as single agents will not exclude eligibility. Previous stem cell transplant will also not exclude eligibility as long as other inclusion/exclusion criteria have been met.
* Patients with acute myelofibrosis are excluded.
* Uncontrolled intercurrent illness including, but not limited to hepatitis, human immunodeficiency virus (HIV)-positive subjects receiving combination antiretroviral therapy, ongoing or active infection, symptomatic congestive heart failure, unstable angina pectoris, ventricular arrhythmia, or psychiatric illness/social situations that would limit compliance with study requirements.
* Other medications, severe acute/chronic medical or psychiatric conditions, or laboratory abnormalities that may increase the risk associated with study participation or study drug administration, or may interfere with the interpretation of study results, that in the judgment of the Investigator would make the subject inappropriate for entry into this study.