The goal of this clinical research study is to learn if giving 5-aza-2 deoxycytidine (decitabine) in combination with Mylotarg (gemtuzumab ozogamicin) can help to control AML or high-risk MDS. The safety of this drug combination will also be studied.

The Study Drugs:

Gemtuzumab ozogamicin is designed to attach to Sialic acid-binding Ig-like lectin 3 (CD33), a certain protein that is often found in leukemia cells, causing them to die.

Decitabine is designed to damage the DNA (the genetic material) of cells, which may cause cancer cells to die.

Study Drug Administration:

If you are found to be eligible to take part in this study, you will receive decitabine through a needle in your vein over 1 and 1/2 hours on Days 1-5 of each cycle. You will also receive gemtuzumab ozogamicin by vein over about 1 hour after you receive decitabine on Day 5 of each 4-6 week cycle.

During Cycle 1 only, if a bone marrow test done 2 weeks after you receive your first study drug treatment shows abnormal leukemia cells, you will receive another treatment with decitabine intravenously over 1 and 1/2 hours for 5 days.

Gemtuzumab may cause allergic reactions, nausea, and vomiting. To help prevent such side effects, you will receive Benadryl (diphenhydramine) and hydrocortisone. You may receive these drugs by vein, or by mouth on the days you get gemtuzumab ozogamicin during the entire study.

Study Visits:

During Cycle 1, blood (about 2 teaspoons) will be drawn at least 1 time each week for routine tests. If the doctor thinks it is necessary, you may be asked to have additional blood drawn.

During Cycle 1, after approximately 2 weeks of your first study drug administration , you will have a bone marrow aspiration to decide whether you will receive additional decitabine in Cycle 1.

During Cycles 2-3, blood (about 2 teaspoons) will be drawn for routine tests at least 2 times each month.

During Cycles 4 and beyond, blood (about 2 teaspoons) will be drawn for routine tests at least 1 time each month.

If the doctor thinks it is necessary, you may have a bone marrow aspirate every 1 to 3 months to check the status of the disease.

Length of Study:

You may receive the combination of decitabine and gemtuzumab ozogamicin for up to 6 cycles. After this, if your doctor thinks it is in your best interest, you may continue to take decitabine alone for up to 24 cycles. You will be taken off study early if the disease gets worse, you experience intolerable side effects, or your doctor thinks that it is no longer in your best interest to receive the study drug(s).

Long-term Follow-up:

Once you are off study, you will have follow up visits every month for up to 2 years. At these visits, blood (about 2 teaspoons) will be drawn for routine tests.

This is an investigational study. Gemtuzumab ozogamicin is FDA approved and commercially available for the treatment of AML that has come back after treatment in patients over the age of 65 years. Decitabine is FDA approved and commercially available for the treatment of MDS. The use of gemtuzumab ozogamicin and decitabine in combination is investigational.

Up to 100 patients will take part in this study. All will be enrolled at M. D. Anderson.

Inclusion Criteria:

1. Understand and voluntarily sign an informed consent form.
2. Age >/= to 16 years at the time of signing the informed consent form.
3. Diagnosis of Acute myeloid leukemia (AML) [other than acute promyelocytic leukemia (APL)] with refractory/relapsed disease. Patients with newly diagnosed AML will be eligible if not a candidate for intensive chemotherapy. Patients with high-risk Intermediate-2 or high by International Prognostic Scoring System (IPSS) or >/= to 10% blasts) MDS will also be eligible. All non-hematological toxicity of previous cancer therapy should have resolved to \

Four years, six months