Intravenous Compared to Oral Busulfan with Cyclophophamide for Allogeneic Hematopoietic Progenitor Cell Transplant Conditioning for AML and MDS.

Abstract 3475

Busulfan (Bu) is commonly used with cyclophosphamide (Cy) as a conditioning regimen for allogeneic hematopoietic progenitor cell transplantation (HPCT). Recently, intravenous (IV) Bu has often replaced oral Bu for conditioning. We have previously reported that substituting IV for oral Bu was associated with a lower rate of relapse, and superior relapse-free and overall survivals for relapsed or refractory non-Hodgkin lymphoma patients undergoing autologous HPCT (Dean et al. Br J Haematol 2010 Jan;148(2):226-34). We retrospectively compared the outcomes of 135 consecutively treated AML and MDS patients who underwent allogeneic HPCT at our institution from 5/2001 through 10/2009 with BuCy using oral (n = 93) or IV (n = 42) Bu, without dose adjustment. The analysis included matched related (n=97) and 8/8 HLA matched unrelated donors (n=38). Oral Bu was administered as 1 mg/kg every 6 hours for 16 doses while IV Bu was administered as 0.8 mg/kg every 6 hours for 16 doses (days –8 through -4) followed by Cy 60 mg/kg/day × 2 (days –3 and –2). The IV Bu patients were older (median age 49 vs. 47 yrs, respectively, p=0.037), more commonly had unrelated donors and peripheral blood stem cells for their HPCT cell source than those treated with oral Bu. There were no significant differences between the groups with regards to patient gender, race, CIBMTR comorbidity index score, number of prior chemotherapy regimens, pre-transplant disease status (each group had 45% of patients in CR1 or CR2), donor-recipient gender relationships or nucleated cell dose infused. The IV Bu group had a higher median CD34+ cell dose infused than those who received oral Bu (3.34 vs. 2.19 ×10⁶/kg, respectively, p=0.028). The IV Bu patients experienced a significantly lower incidence of mucositis (3% vs. 55%, p<0.001) and less severe mucositis (median OMAS scores 0 vs.0.08, respectively, p<0.001). However, there were no significant differences between the IV and oral Bu groups in days until neutrophil and platelet count engraftment, length of transplant hospitalization, incidence of acute or chronic GVHD, sinusoidal obstruction syndrome, and 100 day mortality. At this time 26 (62%) of the IV Bu patients and 33 (36%) of the oral Bu patients are alive, however, the median follow-up was substantially longer for the oral Bu group (50 vs. 13 months, p<0.001). Disease relapse was the most common cause of death for both the IV and oral Bu patients accounting for approximately 50% of deaths in each group. The 1 and 2 year transplant-related mortality for the IV Bu patients was 21% for both, while that for the oral Bu group was 23% and 29%, respectively. The 1 and 2 year relapse mortality for the IV Bu patients was 21% for both, while that for the oral Bu group was 24% and 29%, respectively. Substituting IV for oral Bu reduces variability in drug exposure and potentially improves safety as suggested from our finding of significantly less severe oral mucositis in the IV Bu group. Further follow-up of the IV Bu group is required to adequately assess for a survival benefit. Whether pharmacokinetic-based Bu dosing can improve outcomes after allogeneic HPCT in this setting is worthy of further study.