Clinical relevance of MRD in children undergoing allogeneic stem cell transplantation for ALL

The toxicity and expense of allogeneic stem cell transplantation (ASCT) is such that it is currently reserved for the treatment of children deemed to be at unacceptable risk of relapse when treated with chemotherapy alone. Although ASCT carries at least 10% treatment-related mortality, the commonest cause of death in transplant recipients is relapse of the original disease. This chapter reviews the literature pertaining to the clinical significance of minimal residual disease (MRD) in ASCT. Particular emphasis is placed on the strong correlation between pre-transplant minimal residual disease burden and clinical outcome. Recommendations for the design of MRD-based therapeutic trials are given.