There are two patient subgroups: 1) those who were in complete remission (CR) at the time of transplant, and 2) those who were not in complete remission (NCR) at the time of transplant. Start of crenolanib therapy at 100 mg TID is intended at the earliest time no sooner than 30 days but no later than 90 days after allogeneic stem cell transplantation. Patients may take crenolanib continuously for up to 728 days or until one of the criteria for study discontinuation is fulfilled.