Matched and mismatched unrelated donor transplantation: is the outcome the same as for matched sibling donor transplantation?

The outcome of allogeneic stem cell transplantation has improved over the past decades due to a significant reduction of nonrelapse mortality, whereas our ability to control underlying malignant diseases has remained unchanged. Reduction of nonrelapse mortality has been achieved in matched sibling donor transplantation, but perhaps more so with unrelated donor transplantation, in part due to the advances in HLA matching between donor and recipient, but also as a result of improved supportive care, better GVHD prophylaxis, and tailored conditioning regimens. Therefore, over the past decade, results of matched sibling donor and unrelated donor grafts have grown more similar, and the difference in 1-year survival for patients with leukemia has gone from 21% in 1988 in favor of MSD to 9% in 2008. However, due to the significant and combined effect of patient, transplantation, and donor variables, comparisons are made here in the context of defined subsets of patients and specific diseases and in some circumstances also looking at separate studies in children and adults.