Transplant Conditioning Regimens and Outcomes After Allogeneic Hematopoietic Cell Transplantation (HCT) In Children and Adolescents with Acute Lymphoblastic Leukemia (ALL)

Abstract

AbstractAbstract 3506Recurrent disease is the most important cause of treatment failure after HCT. Total body irradiation (TBI)-containing conditioning regimens are associated with fewer relapses and longer leukemia-free survival (LFS) in children and adolescents with ALL. While TBI <13 Gy + cyclophosphamide (Cy) is considered standard, attempts to lower relapse rates have led to addition of a second chemotherapeutic agent (etoposide) or higher dose TBI (≥13 Gy) with or without addition of etoposide. TBI dosing (<13 Gy vs. ≥13 Gy) or the addition of etoposide to TBI + Cy regimen has not been examined in children. We report on 765 patients aged <18 years, who received either an HLA-matched sibling (n=160) or an unrelated donor (URD, n=605) HCT between 1998 and 2007. Seventy percent of patients were in 2nd complete remission (CR), 20% were in 3rd CR, and the remaining 10%, in relapse at HCT. The median age of the study population is 9 years and the median follow-up of surviving patients is 4 years. Transplant outcomes were examined in four treatment groups: 1) TBI <13 Gy + Cy (n=304), 2) TBI <13 Gy + Cy + etoposide (n=108), 3) TBI ≥13 Gy + Cy (n=327), and 4) TBI ≥13 Gy + Cy + etoposide (n=26). Ninety-six percent of patients in the TBI <13 Gy group received 12 Gy and 4%, 10 Gy. Irradiation doses in the TBI ≥13 Gy group were 13.2 Gy (24%), 13.5 Gy (41%) and 14 Gy (35%). Patient and disease characteristics (performance score, disease status, NCI-risk score, duration of first remission and cytogenetic risk) were similar among the treatment groups. The 3-year probabilities (95% confidence interval) of treatment-related mortality (TRM), relapse, and LFS in the four treatment groups are shown in the Table below. Neither higher dose TBI (≥13 Gy) nor the addition of etoposide regardless of TBI dose was associated with lower risks of leukemia recurrence or longer LFS after HCT. In the absence of an advantage for leukemia control, further intensification of the conditioning regimen TBI <13 Gy + Cy is not recommended.TRMRelapseLFS1) TBI dose <13 Gy + Cy25 (21–31)%30 (24–35)%45 (39–51)%2) TBI dose <13 Gy + Cy + etoposide29 (21–38)%26 (18–34)%45 (35–54)%3) TBI dose ≥13 Gy + Cy23 (19–28)%33 (28–39)%43 (38–49)%4) TBI dose ≥13 Gy + Cy + etoposide35 (17–52)%31 (15–69)%35 (17–52)% Disclosures:No relevant conflicts of interest to declare.