The Sequence of Cyclophosphamide and Myeloablative Total Body Irradiation in Hematopoietic Cell Transplantation for Patients with Acute Leukemia

• The sequence of cyclophosphamide and myeloablative doses of total body irradiation does not affect post-transplantation survival in acute leukemia.
• Post-transplantation complications are similar regardless of the sequence of cyclophosphamide and total body irradiation in the conditioning.

Limited clinical data are available to assess whether the sequencing of cyclophosphamide (Cy) and total body irradiation (TBI) changes outcomes. We evaluated the sequence in 1769 (CyTBI, n = 948; TBICy, n = 821) recipients of related or unrelated hematopoietic cell transplantation who received TBI (1200 to 1500 cGY) for acute leukemia from 2003 to 2010. The 2 cohorts were comparable for median age, performance score, type of leukemia, first complete remission, Philadelphia chromosome–positive acute lymphoblastic leukemia, HLA-matched siblings, stem cell source, antithymocyte globulin use, TBI dose, and type of graft-versus-host disease (GVHD) prophylaxis. The sequence of TBI did not significantly affect transplantation-related mortality (24% versus 23% at 3 years, P = .67; relative risk, 1.01; P = .91), leukemia relapse (27% versus 29% at 3 years, P = .34; relative risk, .89, P = .18), leukemia-free survival (49% versus 48% at 3 years, P = .27; relative risk, .93; P = .29), chronic GVHD (45% versus 47% at 1 year, P = .39; relative risk, .9; P = .11), or overall survival (53% versus 52% at 3 years, P = .62; relative risk, .96; P = .57) for CyTBI and TBICy, respectively. Corresponding cumulative incidences of sinusoidal obstruction syndrome were 4% and 6% at 100 days (P = .08), respectively. This study demonstrates that the sequence of Cy and TBI does not impact transplantation outcomes and complications in patients with acute leukemia undergoing hematopoietic cell transplantation with myeloablative conditioning.