Are new conditioning regimens for transplants in acute myelogenous leukemia better?

Pretransplant conditioning regimens designed to decrease leukemia relapse and increase leukemia-free survival in allotransplants in acute myelogenous leukemia (AML) were developed recently. We review studies of new regimens containing drugs like busulfan, cytarabine, melphalan or etoposide as well as novel radiation schemes. Results are compared to those achieved with cyclophosphamide and total body radiation. Some new regimens seem inferior. Others seem to decrease relapse but do not improve leukemia-free survival because of increased deaths from causes other than leukemia. In a third group of new regimens reporting improved antileukemia efficacy and increased leukemia-free survival, results are not convincingly superior to cyclophosphamide and total body radiation. This failure to detect major improvements with new conditioning regimens may indicate the relative insensitivity of current clinical trial designs to detect improvement or the absence of an effective dose-response relationship in AML.