Inclusion Criteria:

* Patients must have histologically or cytologically confirmed myeloid metaplasia with myelofibrosis (this includes all subtypes - chronic idiopathic myelofibrosis or angiogenic myeloid metaplasia, post thrombocythemic and post polycythemic myelofibrosis); patients must have anemia (hemoglobin < 11 g/dL) or palpable splenomegaly (measured in cm from costal margin - to be eligible); patients with palpable splenomegaly must have spleen size documented ultrasonographically as well; they must also meet standard diagnostic criteria for MMM
* Patients with morphologic evidence of advanced phases of the disease including accelerated (10-19% blasts) phase or with evidence of evolution to acute leukemia (>= 20% blasts) are also eligible for this study
* The Italian Diagnostic Criteria for MMM

* Necessary criteria

* Diffuse bone marrow fibrosis
* Absence of the Philadelphia chromosome or BCR-ABL rearrangement in peripheral blood cells
* Optional criteria

* Splenomegaly of any grade
* Anisopoikilocytosis with tear drop erythrocytes
* Presence of circulating immature myeloid cells
* Presence of circulating erythroblasts
* Presence of clusters of megakaryoblasts and anomalous megakaryocytes in bone marrow sections
* Myeloid metaplasia
* Diagnosis of MMM is acceptable if the following combinations are present

* The two necessary criteria plus any other two optional criteria when splenomegaly is present OR
* The two necessary criteria plus any other four optional criteria when splenomegaly is absent
* Patients may have had prior chemotherapy or radiation therapy including splenic irradiation; prior therapy with erythropoietin, granulocyte-colony stimulating factor (GCSF), other growth factors or androgenic steroids is also permitted; there is no limit to the number of prior regimens received; at least 4 weeks must have elapsed since prior chemo or radiation therapy; at least 2 weeks must have elapsed since growth factor (erythropoietin, GCSF, granulocyte-macrophage colony-stimulating factor \[GM-CSF\]) or other therapy
* Eastern Cooperative Oncology Group (ECOG) performance status =< 2 (Karnofsky >= 60%)
* Total bilirubin =< 2mg/dL

* In patients with associated hemolytic anemia; total bilirubin > 2mg/dL is permissible as long as this is as a result of predominantly unconjugated hyperbilirubinemia; such patients may be enrolled only after discussion with the study chair
* Aspartate aminotransferase (AST) (serum glutamic oxaloacetic transaminase \[SGOT\])/alanine aminotransferase (ALT) (serum glutamate pyruvate transaminase \[SGPT\]) =< 3 x institutional upper limit of normal unless due to disease
* Serum creatinine =< 2mg/dL
* Patients must not be pregnant or nursing; women of child- bearing potential and men must agree to use an effective contraceptive method; should a woman become pregnant or suspect she is pregnant while participating in this study, she should inform her treating physician immediately
* Ability to understand and the willingness to sign a written informed consent document

Exclusion Criteria:

* Prior therapy with decitabine
* Patients who have had chemotherapy or radiotherapy within 4 weeks (6 weeks for nitrosoureas or mitomycin C) prior to entering the study or those who have not recovered from adverse events due to agents administered more than 4 weeks earlier
* Patients may not be receiving any other investigational agents
* Patients with known central nervous system (CNS) disease should be excluded from this clinical trial
* History of allergic reactions attributed to compounds of similar chemical or biologic composition to decitabine
* Uncontrolled intercurrent illness including, but not limited to, ongoing or active infection, symptomatic congestive heart failure, unstable angina pectoris, cardiac arrhythmia, or psychiatric illness/social situations that would limit compliance with study requirements
* Pregnant women are excluded from this study; breastfeeding should be discontinued if the mother is treated with decitabine
* Human immunodeficiency virus (HIV)-positive patients receiving combination anti-retroviral therapy are excluded from the study