Korean J Pediatr 2012;55(3):100-106 • http://dx.doi.org/10.3345/kjp.2012.55.3.100 105 No one factor had a significant impact on the 29% cumulative relapse rate, although a previous study has shown that HSCT from an MUD leads to a lower rate of relapse17). With regards to 1-year TRM, both donor type and HLA compatibility were significant factors individually, but none proved to be important on multivariate study, possibly due to data multicollinearity between the 2 variables. However, it is important to note that donor type, which was the only significant factor for DFS, was also important in terms of 1-year TRM. We draw attention to the limitations of our study. First, as mentioned previously, the lengthy span of time during which the HSCTs took place led to heterogeneity in HLA typing methods, from low to high resolution typing, posing problems for patient classification according to HLA compatibility. Decision as to whether a patient was matched or mismatched was, therefore, based on time-appropriate HLA methodology. Survival analyses with subclassification of MUD HSCT according to HLA typing method, for example high resolution HLA- MUD versus low resolution HLA-MUD, would have given some insight into the importance of typing accuracy. However, the number of patients in each subgroup then proved to be too few to allow for accu- rate analysis. Lack of specific cytogenetic data for each patient is also conspicuous and was due to many patients transplanted in the early period not having accurate cytogenetic characterization. Cytogenetic studies and minimal residual disease monitoring pre-transplant based on such studies have since gained importance18), and should be incorpo- rated into future studies of more recent cohorts. Also, the potential efficacy of HSCT, especially in the MSD setting as shown by our results, should be tempered by the substantial risk for late effects in children who undergo HSCT. The number of physical organs and functions that are susceptible to delayed complications of transplantation are considerable, with 1 recent report indicating a 78% incidence of late effects amongst HSCT treated childhood cancer survivors19). In conclusion then, with less than half the overall cohort surviving disease free, donor type had a significant impact on survival, possibly due to increased TRM resulting from unrelated donors. Survival rates for MSD HSCTs were comparable to previous studies, but those of unrelated HSCTs tended to be lower. Recognizing that many of the patients in our study underwent HSCT more than a decade ago, and understanding the major improvements in supportive care and HLA typing methods that have taken place since then, similar studies with more recently treated cohorts should be undertaken to conclude upon possible improvements in unrelated donor HSCT results. With more than half of childhood ALL patients in second CR failing to be cured by HSCT, both means of optimizing HSCT treatment through recognition of new prognostic factors and research into other novel therapeutic options remain necessary. References 1. Gaynon PS. Treatment of pediatric acute lymphoblastic leukemia: pro- gress achieved and challenges remaining. Curr Hematol Malig Rep 2007; 2:193-201. 2. Barrett AJ, Horowitz MM, Pollock BH, Zhang MJ, Bortin MM, Buchanan GR, et al. Bone marrow transplants from HLA-identical siblings as com- pared with chemotherapy for children with acute lymphoblastic leukemia in a second remission. 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