• CBC, platelet count, Creatinine, bilirubin, SGPT. [ Time Frame: CBC, platelet count 1-2 x weekly course 1, every 2-4 weeks while on therapy. Creatinine, bilirubin, SGPT weekly course 1, every 2-4 weeks while on therapy. ] [ Designated as safety issue: No ]
  

• Bone marrow aspiration to document remission then every 1-3 courses. Cytogenetics at remission if abnormal pretherapy. [ Time Frame: Bone marrow aspiration to document remission then every 1-3 courses. ] [ Designated as safety issue: No ]
  

Treatment: Methylation is a change that occurs to DNA that has an effect on gene usage in human cells. Abnormal methylation is very common in leukemias. Decitabine is a new drug that blocks DNA methylation.

Before treatment starts, a physical exam, blood tests (between 4-6 tablespoons), and a bone marrow study will be done. To collect a bone marrow sample, an area of the hip or chest bone is numbed with anesthetic and a small amount of bone marrow is withdrawn through a large needle. Women able to have children must have a negative blood or urine pregnancy test.

When this study began, participants were randomly assigned (as in the toss of a coin) to one of 3 treatment groups. The assignment to one of the 3 schedules was adjusted according to how well patients respond to treatment. About 17 patients were assigned to each group for the first 50 patients.

Participants in the first group received decitabine intravenously (IV--through a needle in their vein) over one hour, once a day, for 10 days. Treatment was given every 4 to 8 weeks depending on how well their blood counts recovered. Participants in the second group received decitabine as an IV infusion over one hour, once a day, for 5 days. Treatment was given every 4 to 8 weeks. Participants who received decitabine by vein got the same total dose per course. Participants in the third group received decitabine by subcutaneous (SQ) injections (injections given under the skin) twice a day for 5 days. As in the first and second group, treatment was given every 4 to 8 weeks.

After 65 patients were enrolled on this study, it was decided that the 5-day IV schedule was the best of the 3 schedules. The study will now continue with all new patients receiving the 5 -day IV decitabine treatment. If you are now enrolling on the study, you will be placed in this treatment group, instead of being randomly assigned to a treatment group.

Participants who are already on study and who are receiving the 5-day SQ schedule or the 10-day IV schedule, will be given the option to change to the 5-day IV schedule at the start of their next course of study drug treatment, since this is considered the new "standard" schedule on this particular study.

If you choose to take part in this study and begin receiving the study treatment described above, your response to treatment will be checked after completing 8 weeks of therapy. If the response to treatment is good, treatment with decitabine will continue. Decitabine treatment may be continued for up to 24 courses, or as long as it is judged best to control the leukemia.

During this study, you will need to visit your doctor for a physical exam and vital signs. The frequency of doctor visits will vary depending on your physical condition, but will be required at least once a month.

Blood tests (about 2 teaspoons) will be done about every week during the first 6-8 weeks of treatment, then every 1 to 2 weeks for the length of the study. The blood samples will be used for routine lab tests. Periodic bone marrow samples will also be taken to check cells related to the disease before, during, and after completion of this study.

Patients will be taken off study if the disease gets worse or intolerable side effects occur.

This is an investigational study. Decitabine is not yet FDA approved.Up to 133 participants will be treated in this study. All will be enrolled at M. D. Anderson.