Early outcomes after allogeneic hematopoietic SCT in pediatric patients with hematologic malignancies following single fraction TBI.

Fractionated TBI (FTBI) followed by allogeneic hematopoietic SCT results in donor engraftment and improves survival in children with high-risk hematologic malignancies. However, acute toxicities (skin, lung and mucosa) are common after FTBI. Late complications include cataracts, endocrine dysfunction, sterility and impaired neurodevelopment. Instead of FTBI, we used low-dose single fraction TBI (550 cGy) with CY as transplant conditioning for pediatric hematologic malignancies. GVHD prophylaxis included CYA and short-course MTX; methylprednisolone was added for unrelated donor transplants. A total of 55 children in first (40%) or second remission and beyond (60%) underwent transplantation from BM (65%) or peripheral blood; 62% from unrelated donors; 22% were mismatched. Median follow-up was 18.5 months (1-68). Overall survival and disease-free survival at 1 year were 60 and 47%, respectively. Acute toxicities included grade 3-4 mucositis (18%), invasive infections (11%), multiorgan failure/shock (11%), hemolytic anemia (7%), veno-occlusive disease (4%) and renal failure (4%). TRM was 11% at 100 days. Non-relapse mortality was 6% thereafter. Graft rejection occurred in 2%. Three patients (5%) died of GVHD. The regimen was well tolerated even in heavily pretreated children and supported donor cell engraftment; long-term follow up is in progress.