A Study of 5-Azacitidine (Vidaza®) in Patients With Chronic Myelomonocytic Leukemia

Inclusion Criteria: 1. Diagnosis of CMML as defined by the WHO criteria 1. Persistent peripheral blood monocytosis of more than 1 x 109/L for at least 3 months and 2. No Philadelphia chromosome or BCR-ABL fusion gene and 3. Less than 20% blasts in the blood or bone marrow and 4. Dysplasia in one or more of the myeloid lineages\* \* In the absence of dysplasia in one or more of the myeloid lineages, the diagnosis of CMML can still be made if a) - c) are met AND an acquired clonal chromosomal abnormality is present in the bone marrow cells, the monocytosis has been present for more than 3months AND all other causes of monocytosis have been ruled out. 2. Age of 18 years or older. Both men and women and members of all races and ethnic groups will be included. 3. ECOG performance status \<3 4. Adequate organ function defined as: 1. Total bilirubin \<2.5 x upper limit of normal (ULN) 2. Direct bilirubin \<2 x ULN 3. Creatinine \<2 mg/dL 4. ALT and AST \<2.5 x ULN 5. Ability to understand and the willingness to sign a written informed consent document 6. Willingness to use adequate contraception for the duration of the study Exclusion Criteria: 1. Progression to acute myeloid leukemia (defined by at least 20% blasts in the blood or bone marrow). In the unlikely event that progression to acute leukemia is demonstrated in the "screening" bone marrow biopsy, it is at the discretion of the investigator to enroll the patient after adequate discussion of the findings and alternative therapies. Enrollment of such a patient must be reported to the HCI PI. 2. Presence of activating mutations of the platelet derived growth factor receptors alpha or beta, which would suggest likely benefit from imatinib treatment (these mutations will usually be obvious from karyotyping and fluorescence in situ hybridization studies) 3. Known or suspected hypersensitivity to 5-azacitidine or mannitol 4. Clinically significant heart disease (New York Heart Association Class III or IV) or other serious intercurrent illnesses or psychiatric illness/social situations that would limit compliance with study requirements 5. Major surgery within 28 days before registration (exception: central venous line placement), or lack of full recovery from prior major surgery 6. Prior therapy with a hypomethylating agent 7. Cytotoxic chemotherapy less than 2 weeks prior to starting study medication (exception: hydroxyurea and/or anagrelide) 8. Erythropoietin or darbepoietin, G-CSF, GM-CSF, thalidomide or lenalidomide less than 2 weeks from day 1 of cycle 1 9. Concomitant cytotoxic chemotherapy (exception: hydroxyurea for up to 1 week per cycle) 10. Concomitant therapy with other investigational agents 11. Other active malignancies except basal cell carcinoma of the skin and carcinoma in situ of the cervix. 12. Pregnancy or breastfeeding (possible risk to the fetus or infant)