The evolution of hematopoietic SCT in myelodysplastic syndrome.

Allogeneic hematopoietic SCT (allo-HCT) is the only curative therapy for myelodysplastic syndrome (MDS). Numerous myeloablative (MA), nonmyeloablative SCT (NST) and reduced conditioning transplant (RIC) studies have included MDS patients. Twenty-four MA HCT studies published from 2000 and 2008 reported OS and disease-free survival (DFS) ranging from 25 and 16% at 2 years to 52 and 50% at 4 years. In these publications, the incidence of grades II-IV acute GVHD was 18-100%, chronic GVHD 13-88%, relapse risk 24% at 1 year to 54.5% at 4 years and TRM 19% at day 100 to 61% at 5 years. From 2003 to 2008, 30 publications combining RIC and NST reported OS and DFS from 22 and 20% at 2 years to 79 and 79% at 4 years. Incidence of grades II-IV acute GVHD ranged from 9 to 63%, chronic GVHD 18 to 80%, relapse risk 6 to 61% and TRM 0% at day 100 to 34% at 5 years. The wide range in the published results leaves many unanswered questions. Although no ideal transplant conditioning has emerged, many of the MA and RIC studies used BU-based regimens and used a recipient age cutoff of 50-55 years for MA HCT. Similarly, there is no agreement on the use of induction or hypomethylating therapy before HCT, but azacitidine and decitabine are gaining increasing attention as a bridge to HCT. Until recently, the International Prognostic Scoring System (IPSS) dictated the use and timing of HCT. The WHO classification and WHO Prognostic Scoring System (WPSS) may be better suited in predicting the outcomes and should probably be incorporated in transplant algorithms. Most published MDS transplant series combine matched related donors (MRD) and matched unrelated donors (MUD). Umbilical cord blood (UCB) grafts will likely broaden the population of MDS patients eligible for allografting, but outcome data for MDS are scant. At this time, it is reasonable to consider the availability of an MRD or MUD as separate from an UCB graft in the decision of transplantation for MDS. The development of RIC, improvements in supportive therapy and alternative donor selection will provide better OS for MDS patients undergoing transplantation. Simultaneously, better understanding and medical therapy of MDS are leading us to re-examine patient selection and the timing of HCT. The results of HCT for MDS continue to improve together with the outlook of patients afflicted with myelodysplasia.