Azacitidine: A pyrimidine analogue that inhibits DNA methyltransferase, impairing DNA methylation. It is also an antimetabolite of cytidine, incorporated primarily into RNA. Azacytidine has been used as an antineoplastic agent.Myelodysplastic Syndromes: Clonal hematopoietic stem cell disorders characterized by dysplasia in one or more hematopoietic cell lineages. They predominantly affect patients over 60, are considered preleukemic conditions, and have high probability of transformation into ACUTE MYELOID LEUKEMIA.Antimetabolites, Antineoplastic: Antimetabolites that are useful in cancer chemotherapy.Leukemia, Myelomonocytic, Chronic: A myelodysplastic-myeloproliferative disease characterized by monocytosis, increased monocytes in the bone marrow, variable degrees of dysplasia, but an absence of immature granulocytes in the blood.Chromatography, Supercritical Fluid: A CHROMATOGRAPHY method using supercritical fluid, usually carbon dioxide under very high pressure (around 73 atmospheres or 1070 psi at room temperature) as the mobile phase. Other solvents are sometimes added as modifiers. This is used both for analytical (SFC) and extraction (SFE) purposes.Compassionate Use Trials: Providing an investigational therapy to a patient who is not eligible to receive that therapy in a clinical trial, but who has a serious or life-threatening illness for which other treatments are not available. Compassionate use trials allow patients to receive promising but not yet fully studied or approved therapies when no other treatment option exists. Also called expanded access trial.Leukemia, Myeloid, Acute: Clonal expansion of myeloid blasts in bone marrow, blood, and other tissue. Myeloid leukemias develop from changes in cells that normally produce NEUTROPHILS; BASOPHILS; EOSINOPHILS; and MONOCYTES.Injections, Subcutaneous: Forceful administration under the skin of liquid medication, nutrient, or other fluid through a hollow needle piercing the skin.Anemia, Refractory: A severe sometimes chronic anemia, usually macrocytic in type, that does not respond to ordinary antianemic therapy.Consolidation Chemotherapy: Drug treatment designed to further diminish the disease toward complete remission following INDUCTION CHEMOTHERAPY. It helps to consolidate the gains during induction chemotherapy and may be followed by MAINTENANCE CHEMOTHERAPY.Induction Chemotherapy: Initial drug treatment designed to bring about REMISSION INDUCTION. It is typically a short-term and high-dose drug treatment that is followed by CONSOLIDATION CHEMOTHERAPY and then MAINTENANCE CHEMOTHERAPY.Anemia, Refractory, with Excess of Blasts: Chronic refractory anemia with granulocytopenia, and/or thrombocytopenia. Myeloblasts and progranulocytes constitute 5 to 40 percent of the nucleated marrow cells.Drug Approval: Process that is gone through in order for a drug to receive approval by a government regulatory agency. This includes any required pre-clinical or clinical testing, review, submission, and evaluation of the applications and test results, and post-marketing surveillance of the drug.DNA Methylation: Addition of methyl groups to DNA. DNA methyltransferases (DNA methylases) perform this reaction using S-ADENOSYLMETHIONINE as the methyl group donor.DNA Modification Methylases: Enzymes that are part of the restriction-modification systems. They are responsible for producing a species-characteristic methylation pattern, on either adenine or cytosine residues, in a specific short base sequence in the host cell's own DNA. This methylated sequence will occur many times in the host-cell DNA and remain intact for the lifetime of the cell. Any DNA from another species which gains entry into a living cell and lacks the characteristic methylation pattern will be recognized by the restriction endonucleases of similar specificity and destroyed by cleavage. Most have been studied in bacterial systems, but a few have been found in eukaryotic organisms.Treatment Outcome: Evaluation undertaken to assess the results or consequences of management and procedures used in combating disease in order to determine the efficacy, effectiveness, safety, and practicability of these interventions in individual cases or series.Survival: Continuance of life or existence especially under adverse conditions; includes methods and philosophy of survival.International Agencies: International organizations which provide health-related or other cooperative services.Epigenomics: The systematic study of the global gene expression changes due to EPIGENETIC PROCESSES and not due to DNA base sequence changes.United States Food and Drug Administration: An agency of the PUBLIC HEALTH SERVICE concerned with the overall planning, promoting, and administering of programs pertaining to maintaining standards of quality of foods, drugs, therapeutic devices, etc.Thalidomide: A piperidinyl isoindole originally introduced as a non-barbiturate hypnotic, but withdrawn from the market due to teratogenic effects. It has been reintroduced and used for a number of immunological and inflammatory disorders. Thalidomide displays immunosuppressive and anti-angiogenic activity. It inhibits release of TUMOR NECROSIS FACTOR-ALPHA from monocytes, and modulates other cytokine action.Drug Administration Schedule: Time schedule for administration of a drug in order to achieve optimum effectiveness and convenience.Antimetabolites: Drugs that are chemically similar to naturally occurring metabolites, but differ enough to interfere with normal metabolic pathways. (From AMA Drug Evaluations Annual, 1994, p2033)Remission Induction: Therapeutic act or process that initiates a response to a complete or partial remission level.Biological Availability: The extent to which the active ingredient of a drug dosage form becomes available at the site of drug action or in a biological medium believed to reflect accessibility to a site of action.Blood Transfusion: The introduction of whole blood or blood component directly into the blood stream. (Dorland, 27th ed)Leukemia, Myeloid: Form of leukemia characterized by an uncontrolled proliferation of the myeloid lineage and their precursors (MYELOID PROGENITOR CELLS) in the bone marrow and other sites.Tetrazolium Salts: Quaternary salts derived from tetrazoles. They are used in tests to distinguish between reducing sugars and simple aldehydes, for detection of dehydrogenase in tissues, cells, and bacteria, for determination of corticosteroids, and in color photography. (From Mall's Dictionary of Chemistry, 5th ed, p455)Cytarabine: A pyrimidine nucleoside analog that is used mainly in the treatment of leukemia, especially acute non-lymphoblastic leukemia. Cytarabine is an antimetabolite antineoplastic agent that inhibits the synthesis of DNA. Its actions are specific for the S phase of the cell cycle. It also has antiviral and immunosuppressant properties. (From Martindale, The Extra Pharmacopoeia, 30th ed, p472)Antineoplastic Combined Chemotherapy Protocols: The use of two or more chemicals simultaneously or sequentially in the drug therapy of neoplasms. The drugs need not be in the same dosage form.Maximum Tolerated Dose: The highest dose of a biologically active agent given during a chronic study that will not reduce longevity from effects other than carcinogenicity. (from Lewis Dictionary of Toxicology, 1st ed)Fatigue: The state of weariness following a period of exertion, mental or physical, characterized by a decreased capacity for work and reduced efficiency to respond to stimuli.Acute Disease: Disease having a short and relatively severe course.Retrospective Studies: Studies used to test etiologic hypotheses in which inferences about an exposure to putative causal factors are derived from data relating to characteristics of persons under study or to events or experiences in their past. The essential feature is that some of the persons under study have the disease or outcome of interest and their characteristics are compared with those of unaffected persons.Hematopoietic Stem Cell Transplantation: Transfer of HEMATOPOIETIC STEM CELLS from BONE MARROW or BLOOD between individuals within the same species (TRANSPLANTATION, HOMOLOGOUS) or transfer within the same individual (TRANSPLANTATION, AUTOLOGOUS). Hematopoietic stem cell transplantation has been used as an alternative to BONE MARROW TRANSPLANTATION in the treatment of a variety of neoplasms.Recurrence: The return of a sign, symptom, or disease after a remission.