The impact of pre-transplant extramedullary disease on the outcome of allogeneic hematopoietic cell transplantation for acute myeloid leukaemia in children- on behalf of PDWP/EBMT.

Extramedullary disease (EMD) is a rare presentation in Acute Myeloid Leukaemia (AML). On behalf of PDWP/EBMT we studied the effect of EMD compared to isolated BM involvement in the outcomes following non-TBI conditioning hematopoietic stem cell transplantation (HCT) for AML in children. Patients were grouped into three categories: BM involvement only (Group A), BM + CNS involvement only (Group B) and BM+ other EMD+/- CNS (Group C). A total of 958 patients were included, 685 (71.5%) in Group A, 135 (14.1%) in Group B and 138 (14.4%) in Group C. The median post HCT follow-up was 5.4 years. Five years LFS, OS, RI and NRM were 62%, 68.4%, 26.4% and 11.6%, respectively. Multivariate analysis showed higher RI in Group C compared to Group A (HR = 1.45 (1.01-2.06) p = 0.04). In the multivariate analysis patients with EMD had no significant difference in LFS, OS and NRM. Our findings suggest that children with AML and BM with EMD+/- CNS involvement (group C) have a higher incidence of relapse after HCT compared to those with BM only or BM + CNS only disease. However, the presence of EMD did not have an impact on overall, leukaemia-free survival or non-relapse mortality.