Methotrexate or Pentostatin for Graft-versus-host Disease Prophylaxis in Risk-adapted Allogeneic Bone Marrow Transplantation for Hematologic Malignancies

The purpose of the study is to determine if participants who receive the GVHD prophylaxis medication pentostatin will have less severe hepatic toxicities than those receiving MTX. The study is estimated to have sufficient statistical power to ascertain at least a 20% improvement in day 42 NCI CTC grade 2 or above hepatic toxicity-free survival in pentostatin recipients.