Intravenous Busulfan-Based Conditioning Prior to Allogeneic Stem Cell Transplantation in Adults Patients with AML - An ALWP-EBMT Survey.
Authors: Nagler Arnon , Labopin Myriam , Shimoni Avichai , Bunjes Donald , Pimentel Pedro , Socie Gerard , Boudjedir Karim , Zander Axel R. , Gomez A. Torres , Baccarini Michele , Goker Hakan , Fassas Athanasios , Kenzey Chantal , Samey Benedicte , Hamadi Zouabi , Rocha Vanderson 
Published: April 2020

Abstract
Oral Busulfan (Bu) is the historical backbone of pre-allogeneic stem cell transplantation (alloSCT) conditioning regimen. However, oral Bu has an erratic and unpredictable absorption with wide inter and also intra-patient (pt) variability. In contrast, I.V. Busulfan (IV Bu) is with more predictable pharmacokinetics and favorable toxicity profile. In order to assess the impact of the use of IV Bu, the ALWP of the EBMT performed a survey in AML pts who received IV-Bu as part of their pre-alloSCT conditioning regimen. 36 EBMT centers participated in this study: 9 centers performed more than 10 transplants each. Overall, 271 alloSCT were analyzed. Age was 44 (range, 16–67) years. 146 were males (54%) and 125 (46%) were females. Disease status at alloSCT was CR1-53%, CR2-16%, primary refractory-13%, Rel1-12%, Rel2-5% and untreated-1%.77% of the pts were with intermediate, 15% with poor and 8% with good risk cytogenetics, respectively. Median WBC at diagnosis was 26×109/L. Conditioning consisted of IV Bu and cyclophosphamide (IV BuCy) in 52%, IV Bu and fludarabine (IV BuFlu) in 38% and various other IV Bu containing regimens in 10% of the pts, respectively. Overall, conditioning was myeloablative in 80% and reduced-intensity (RIC) in 20% of the alloSCT, respectively. Donors were: identical siblings-59%, matched unrelated-28%, mismatched unrelated-10%, mismatched family donors-2%, syngeneic 1%. 83% of the pts were transplanted with mobilized PBSC grafts while 17% received BM grafts. GVHD prophylaxis consisted of CSA and MTX in 85% of the transplants. With median follow up of 24 (range, 1–66) months, 53% of the pts are alive while 47% have died. Day 100 mortality was 7%. The incidence of veno-occlusive disease of the liver (VOD) was 10.4%. VOD was more frequent in pts that were transplanted from unrelated donors in comparison to those who were transplanted from sibling donors (18% vs. 5%, respectively). It was also more common after myeloablative conditioning than RIC (11.5% vs. 5.5%, respectively). Median age of pts with VOD was 42(17–65) years, not different than the age of the whole group, but they had more advanced disease (primary refrectory-35%, Rel2-30%). Day of onset of VOD was +10(range, 1–162). VOD was severe in only 15% of the pts and only 6 pts died of VOD. All together 30% of the pts with VOD are alive. Overall, alloSCT transplant related mortality (TRM) was 22±4% for pts transplanted at CR1 vs 33±8% for pts transplanted at advanced disease. Similarly, leukemia free survival (LFS) for pts transplanted at CR1 was 55±4% vs. 21+5% for pts transplanted in advanced disease. In summary, IV Bu based conditioning reduced the incidence and severity of VOD post alloSCT for AML as compared to published figures for historical controls. A randomized trial assessing VOD incidence and TRM using IV BuCy vs. IV BuFlu with 2 vs. 4 days of IV Bu, respectively may be indicated.