Effectiveness of Reduced Toxicity Conditioning Regimen with Intravenous Busulfan Plus Pentostatin (BUPENT) in Patients Older Than 50 Years with Advanced Hematologic Malignancies.
Authors: Rodriguez Tulio E. , Parthasarathy Mala , Smith Scott E. , Vesole David H. , Earley Zachary M. , Gerds Aaron T. , Toor Amir A. , Stiff Patrick J. 
Published: October 2019

Abstract
Abstract 3331
Poster Board III-219

Introduction
Current data suggests that recipient age above 50 is associated with an inferior outcome after myeloablative allogeneic stem cell transplantation (SCT). Overall survival (OS) of 31%, and transplant related mortality (TRM) of 17% at 100 days have been reported in this population (Ditchkowski, et al 2005; Yanada, et al. 2004). Encouraging results are observed with non-myeloablative conditioning regimens. However, for patients with a high relapse risk, this approach may not be sufficient to achieve long term disease control. In these cases, a reduced toxicity, yet ablative stem cell transplantation (RT-SCT) may give adequate time to the transplanted cells to mature and mount an immune-mediated antitumor response. This study evaluated the outcome after RT-SCT using a conditioning regimen consisting of intravenous busulfan (Bu) and pentostatin (Pent).

Methods
Consented adult patients up to 70 years with a fully-matched related (MRD) or unrelated donor (MUD) were screened for enrollment. Conditioning consisted of Bu 1.6 mg/kg every 12 hours days -7 to -4, and Pent 4 mg/m2 on day -3 and -2 prior to stem cell infusion on day 0. GVHD prophylaxis was methotrexate 10 mg/m2 on day 1, and 5 mg/m2 on days 3, and 6. Tacrolimus was started on day -2, and then tapered over 1 month after day +100.

Characteristics
Twenty six patients were analyzed. Male to female ratio was 1:1. Stem cell source was from MRD in 15 patients and MUD in 11. Median age was 62, with 92% of patients being older than 50 years. Indications for treatment were AML (35%), MDS (42%), Refractory CLL (23%), Relapsed NHL (12%), and Philadelphia (+) ALL (4%). All AML patients were high risk either due to poor cytogenetic, transformation, or relapse and only two of them were transplanted in first complete remission. MDS patients were RAEB (36%), secondary MDS (36%), or multilineage dysplasia (18%). Two patients had prior autologous transplants.

Results
No graft failure was observed. All patients achieved neutrophil (NEU) engraftment. Two patients expired prior to platelet (PLT) engraftment. Median engraftment days for NEU and PLT were 13 days. At a median follow up of 25 months, the OS and progression free survival for the entire group was 40% and 38% respectively. The OS in the MRD group was 58%. TRM at 100 days was seen in one patient (4%) due to veno-occlusive disease (VOD). Limited chronic GVHD was the most common observed toxicity (54%), followed by diarrhea (30%) and mucositis (23%). Mucositis was mainly grade 1 (8%) and grade 2 (8%). No grade 3 mucositis was observed. There was only one case of VOD and one case of acute GVHD.

Conclusion
To our knowledge, this is the first report of a RT-SCT using BuPent. This study demonstrates the efficacy of the regimen in patients older than 50 years. No graft failure was observed and the regimen related toxicity was acceptable in this high-risk population. The overall survival of 40% at a median follow up of 25 months compares favorably with prior reports of myeloablative allogeneic stem cell transplatation in patients older than 50 years. This regimen provides an exciting opportunity to extend the benefits of allogenic transplant to an older population, and warrants replication with larger controlled trials.

Disclosures
Rodriguez: Otsuka: Membership on an entity's Board of Directors or advisory committees, Research Funding. Vesole:Amgen: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Celgene: Speakers Bureau; Millenium: Speakers Bureau; Centocor Ortho Biotech: Speakers Bureau.