Total body irradiation, thiotepa, and cyclophosphamide as a conditioning regimen for children with acute lymphoblastic leukemia in first or second remission undergoing bone marrow transplantation with HLA-identical siblings

Purpose: Allogeneic hematopoietic stem-cell transplantation (HSCT) from HLA-identical siblings can be used to treat children with acute lymphoblastic leukemia (ALL). However, a significant proportion of patients with ALL who undergo HSCT relapse. For this reason, we prospectively evaluated a preparative regimen that included total body irradiation (TBI), thiotepa (TT), and cyclophosphamide (CY) in patients with high-risk ALL in first complete remission (CR) and in children with ALL in second CR. Patients and Methods: Forty children (median age, 9 years; range, 1 to 18 years) with ALL in first or second CR who underwent allogeneic HSCT from HLA-identical siblings were conditioned with a combination of fractionated TBI, TT (10 mg/kg), and CY (120 mg/kg over 2 days). Graft-versus-host disease (GVHD) prophylaxis consisted of cyclosporine administered intravenously at a dose of 1 to 3 mg/kg/d for the first 21 days and subsequently orally at a dose of 6 mg/kg/d. Results: All assessable patients were engrafted, with a median time of 11 and 24 days for neutrophil and platelet recovery, respectively. The preparative regimen was well tolerated. Only one patient died as a result of regimen-related causes. Eight patients relapsed at a median time of 8 months after transplantation (range, 3 to 9 months), and this determined a cumulative probability of relapse of 23%. Twenty-six of 40 patients (65%) are alive and in complete hematologic remission, with a median observation time of 36 months (range, 14 to 57 months), which results in a disease-free survival (DFS) at 3 years of 65%. The 13 patients who underwent transplantation in first CR had a DFS of 85%, whereas the 27 patients who underwent HSCT in second CR had a DFS of 56%. Conclusion: These data suggest that TT is an effective cytotoxic drug that can be safely added to the classical TBI-CY regimen. Because of its cell cycle-independent action, good CHS diffusion, and limited extramedullary toxicity, TT may contribute to increasing the percentage of children with ALL who are successfully cured with allogeneic BMT.