Busulfan Dosing May Affect Survival Following Reduced Intensity Stem Cell Transplantation in Patients with Acute Myelogeneous Leukemia.
Authors: Ballen Karen K , McAfee Steven L , Dey Bimalangshu R , Dube Christine , Attar Eyal C , Chen Yi-Bin , Amrein Philip C , Spitzer Thomas R 
Published: October 2019

Abstract
Abstract 4328
The prognosis for patients with acute myelogeneous leukemia over age 60 is poor, with a 5 year survival of less than 10%. Reduced intensity allogeneic transplantation has been employed in an attempt to improve survival. We report 23 patients who received reduced intensity allogeneic transplantation after a conditioning regimen of busulfan and fludarabine. Fifteen patients received a transplant from a matched sibling donor,1 patient from a 5/6 matched child and 7 patients from a fully matched (10/10) unrelated donor. We treated 10 patients with the reduced intensity conditioning regimen of busulfan IV 0.8 mg/kg daily Days -6, -5, -4, -3 (total dose 3.2 mg/kg) and fludarabine IV 30 mg/m2 Days -6,-5, -4, -3 (total dose 120mg/kg). After November, 2007, 10 patients were treated with twice daily busulfan IV 0.8mg/kg (total dose 6.4 mg/kg) with the same dose of fludarabine. Three patients were treated on a national protocol in which the same dose of busulfan (6. 4 mg/kg) was administered but given at 0.8 mg/kg four times daily for 2 days on Days -4 and -3 with fludarabine. GVHD prophylaxis was cyclosporine or tacrolimus with either cellcept or (after July, 2008) methotrexate. Seven recipients of unrelated donor or mismatched transplants also received rabbit antithymocyte globulin 1.5 mg/kg Days -3, -2, -1 (total dose 4.5 mg/kg) as part of their GVHD prophylaxis. Median age was 65 years (range 46-70 years). Fourteen patients were in 1st complete remission, 8 were in 2nd complete remission, and one patient had active disease at the time of transplant. Two patients had received a prior autologous stem cell transplant and 2 patients had received a prior allogeneic transplant. The median days to neutrophil (ANC >500) and platelet engraftment (plt >20K) were 15 and 14 respectively. The median length of stay was 25 days (range 13-40 days). Median follow-up was 12 months among the 10 patients still alive. The incidence of acute GVHD Grades II-IV and chronic GVHD were 44% and 35% respectively. Transplant related (non relapse) mortality at 100 days and at 6 months was 0. The overall non-relapse mortality was 4%. Relapse rate was 67% in the daily busulfan group and 46% in the higher dose busulfan group. The one-year overall and disease-free survivals for all patients were 44% and 25% respectively. Causes of death were relapse in 12 patients and in one patient sepsis six years after transplant. In multivariate analysis, disease status, age, and GVHD did not predict for survival, perhaps due to the small sample size. There was a trend to improved survival in the higher dose busulfan group but the follow up was shorter for these patients. In summary, 1) Reduced intensity transplantation is tolerated well in an older population with acute myelogeneous leukemia, with no transplant related mortality at Day 100 or at 6 months post transplant; 2) Relapse rermains the most common cause of death; 3) There was a trend to improved survival with a twice daily busulfan dosing. Future studies will address the outcomes of twice daily busulfan dosing in a larger cohort of older patients with AML in complete remission.

Disclosures:
Spitzer: Genzyme: Consultancy.