Is there a best transplant conditioning regimen for acute myeloid leukemia?

The outcome of marrow transplantation is largely determined by the effectiveness of the transplant preparative regimen. Nonetheless, there have been startlingly few randomized trials attempting to identify optimal regimens for specific conditions and, at present, no single approach has emerged as superior for the treatment of acute myeloid leukemia (AML) in the few trials that have been performed. Newer approaches that appear encouraging in phase II studies include substituting etoposide for cyclophosphamide, adding thiotepa to the traditional cyclophosphamide plus total body irradiation combination in the setting of T cell depletion, and using antibody-based targeted radiotherapy as part of the transplant regimen. The ability to obtain allogeneic engraftment with nonablative regimens may open the door to additional innovative approaches, combining very specific antileukemia therapy with relatively nontoxic measures to ensure engraftment.