Cyclophosphamide and Busulfan Followed by Donor Stem Cell Transplant in Treating Patients With Myelofibrosis, Acute Myeloid Leukemia, or Myelodysplastic Syndrome

This trial is studying the side effects and how well giving cyclophosphamide and busulfan followed by donor stem cell transplant works in treating patients with myelofibrosis, acute myeloid leukemia, or myelodysplastic syndrome. Giving chemotherapy, such as cyclophosphamide and busulfan, before a donor stem cell transplant helps stops the growth of cancer cells. It also helps stop the patient's immune system from rejecting the donor's stem cells. The donated stem cells may replace the patient's immune cells and help destroy any remaining cancer cells (graft-versus-tumor effect). Sometimes the transplanted cells from a donor can also make an immune response against the body's normal cells. Giving tacrolimus and methotrexate after the transplant may stop this from happening