Children with acute leukemia who relapse after hematopoietic cell transplant (HCT) have few therapeutic options. We studied 251 children and young adults with acute myeloid or lymphoblastic leukemia who underwent a second HCT for relapse after their first HCT. The median age at second HCT was 11 years and the median interval between first and second HCT, 17 months. Most
(n=187; 75%) were in remission, received myeloablative conditioning regimen (n=157; 63%) and unrelated donor HCT (n=230; 92%). The 2-year probability of leukemia-free survival (LFS) after transplantation in remission was 33% compared to 19% for transplantations that were not in remission (p=0.02). The corresponding 8-year probabilities were 24% and 10% (p=0.003). Higher relapse contributed to the difference in leukemia-free survival. The 2-year probability of relapse for transplantations in remission was 42% compared to 56% for transplantations in relapse (p=0.05). The corresponding 8-year probabilities were 49% and 64% (p=0.04). These data extend the findings of others in that those with low disease burden are more likely to benefit from second transplantation. Late relapse led to a 10% decrement in LFS beyond the second year after second HCT. This differs from first HCT were most relapses occur within 2 years after HCT.