Donor Stem Cell Transplant After Busulfan, Fludarabine, and Antithymocyte Globulin in Treating Patients With Hematologic Cancer or Myelodysplastic Syndrome

DISEASE CHARACTERISTICS:

* Diagnosis of 1 of the following hematological malignancies:

  * Acute leukemia, including any of the following:

    * Refractory acute leukemia
    * Acute leukemia beyond first remission
    * Acute leukemia in first remission with intermediate to poor prognostic features as suggested by chromosomal findings
  * Chronic myelogenous leukemia (CML)

    * Second chronic phase
    * Accelerated phase
    * Blastic phase
  * Myelodysplastic syndrome (MDS)

    * High-risk MDS (refractory anemia with excess blasts \[RAEB\], RAEB in transformation, and chronic myelomonocytic leukemia) can be transplanted without prior therapy or after prior therapy failure with hypomethylating agents
    * Low-risk MDS can be considered for transplantation after prior therapy failure with immunosuppressive or hypomethylating agents
* No willing, suitable HLA-matched donor in family or in donor registries

  * Patients with active hematologic malignancy, who are felt to be in urgent need of allogeneic hematopoietic cell transplantation, can enroll without a search for HLA-matched unrelated donors
* Related donor with HLA-haploidentical mismatch at 3 or less of 6 loci available

PATIENT CHARACTERISTICS:

* Karnofsky performance status 70-100%
* Bilirubin \< 2.0 mg/dL
* Creatinine \< 2.0 mg/dL
* AST \< 3 times upper limit of normal
* Ejection fraction \> 40% by MUGA

PRIOR CONCURRENT THERAPY:

* See Disease Characteristics