Comparison of Reduced Intensity Conditioning (RIC) Regimen and Myeloablative Conditioning (MAC) Regimen in Allogeneic Hematopoietic Stem Cell Transplantation (Allo-HSCT) for Adult Patients with Acute Leukemia

Introduction:The development of RIC regimens enabled HSCT also for elderly patients who had contraindications for intensive conditioning regimens. The aim of this study is to evaluate the effects of conditioning regimens on outcomes of alllo-HSCT for adult patients with acute leukemia.

Method:In this study, we retrospectively analysed 490 acute leukemia patients who underwent allo-HSCT between June 1988 to June 2015 at Ankara University School of Medicine Department of Hematology. We compared the outcomes of MAC vs RIC conditioning by Fisher's test and chi-square test. Kaplan-meier curves were used for survival. The factors that effect on survival were evaluated by univariate analysis-log-rank test and multivariate analysis-cox regression.

Results: In our study, the median age of participants was 32 with M/F ratio of 285 (57.9%) / 207 (42.1%). The patients were diagnosed as acute myeloid leukemia (AML) in 344 patients (69.9%), acute lymphoblastic leukemia (ALL) in 140 patients (28.5%) and others in 8 patients (1.6%). Pre-transplant active disease detected in 105 (22.7%) patients. Patients received grafts from related donors in 397 (80.7%) transplants. The most common stem cell source was peripheral blood in 378 patients (76.8%) followed by bone marrow in 99 patients (20.1%). MAC was used in 224 (90.4%) recipients whereas RIC was used in 47 (9.6%). The age, unrelated transplants, number of AML patients and intermediate-high risk patients were significantly higher in RIC group (44 vs 31, p<0.001; 37% vs 18%, p=0.002; 81.4% vs 43.7%, p<0.001). Both 1-year OS and 1-year RFS rate were lower in the patients treated with RIC (65.6% vs 34.9%; 44.4% vs 16.7%). Among the patients treated with MAC, 1 year-OS was higher in patients who developed chronic GVHD (78.6% vs 51.1%, p<0.05). The higher OS was related with patients who were transplanted in remission, received grafts from related donors as well as having acute and chronic graft vs host disease.

Conclusion: Lower OS and RFS were observed in the RIC conditioned patients compared to MAC in our study. In the treatment of young patients who do not have comorbidities for intense conditioning regimens, show good performance status and are high risk; the initial use of standard myeloablative conditioning regimens is feasible. However, the lower number of RIC transplants and the variations between groups in terms of patient and donor characteristics might effect the results of this study. Therefore, conducting further prospective studies with larger cohorts would be beneficial to enhance our knowledge.