CLAG-M or FLAG-Ida Chemotherapy and Reduced-Intensity Conditioning Donor Stem Cell Transplant for the Treatment of Relapsed or Refractory Acute Myeloid Leukemia, Myelodysplastic Syndrome, or Chronic Myelomonocytic Leukemia

This study tests an intensive chemotherapy regimen followed by a bone marrow transplant (stem cell transplant from a donor) for people with blood cancers — specifically acute myeloid leukemia (AML), myelodysplastic syndrome (MDS), or chronic myelomonocytic leukemia (CMML) — that have come back or stopped responding to treatment. It compares two chemotherapy combinations (CLAG-M and FLAG-Ida) to see which works better before transplant. **You may be eligible if...** - You are 18 or older - You have AML, MDS, or CMML that has relapsed or not responded to prior treatment - You have a suitable stem cell donor available (matched related, matched unrelated, or half-matched/haploidentical) - You are in reasonable health with adequate heart, lung, liver, and kidney function - Your overall health score (Karnofsky or ECOG) indicates you can tolerate intensive treatment **You may NOT be eligible if...** - You have active cancer in the brain or spinal fluid - You have active uncontrolled infections - You are pregnant or breastfeeding - You have an illness expected to cause death within the next year unrelated to your blood cancer - You are currently receiving other anti-leukemia treatments Talk to your doctor to see if this trial is right for you.