Participants considered an adult according to local regulations at the time of signing informed consent will be randomized in a 1:1 ratio to receive ASP2215 or salvage chemotherapy. Participants will enter the screening period up to 14 days prior to the start of treatment. Prior to randomization, the investigator will preselect a salvage chemotherapy regimen for each participant; options will include low-dose cytarabine (LoDAC), mitoxantrone, etoposide and intermediate-dose cytarabine (MEC) or fludarabine, high-dose cytarabine and granulocyte colony-stimulating factor (FLAG). The randomization will be stratified by response to first-line therapy and preselected salvage chemotherapy. Participants will be administered treatment over continuous 28-day cycles.