Risk factors for outcome in refractory acute myeloid leukemia patients treated with a combination of fludarabine, cytarabine, and amsacrine followed by a reduced-intensity conditioning and allogeneic stem cell transplantation.

INTRODUCTION: Hematopoietic stem cell transplantation (HCT) is considered a standard treatment for high-risk acute myeloid leukemia (AML) in first or second complete remission (CR). Unfortunately, not all patients achieve complete remission prior to HCT. We sought to establish predictive factors for survival after HCT for refractory AML after FLAMSA-RIC.

PATIENTS AND METHODS: We analyzed the outcome of 44 consecutive patients aged between 21 and 65 years transplanted at the University Hospitals of Jena and Leipzig for refractory AML between 2006 and January 2013. Conditioning for HCT was performed with chemotherapy consisting of fludarabine, cytarabine, and amsacrine followed by total body irradiation or busulfan combined with cyclophosphamide. Antithymocyte globulin was given when transplanting from unrelated donors (FLAMSA-RIC).

RESULTS: Estimated overall survival (OS) and event-free survival (EFS) at 3 years after a median follow-up of 34 (range 6-71) months were 15 and 12 %, respectively. Causes of death were relapse in 66 %, infection in 11 %, and graft-versus-host disease (GvHD) in 7 % of all patients. Twenty-five from 42 evaluable patients (60 %) achieved CR 4 weeks after HCT, while eight patients had partial remission (PR), and nine patients had stable disease (SD). Another six patients with PR and SD achieved CR (overall CR rate 74 %) from 4 weeks to day 90 after HCT following reduction in immunosuppression. The strongest favorable factors in univariate analysis for OS, EFS, and RI were ≥98 % total donor chimerism 2-4 weeks after HCT and <3 lines of pretreatment prior to HCT. In addition, better OS was detected in patients with <20 % bone marrow blasts alone (32 vs. 5 % at 3 years) and in combination with <3 lines of pretreatment (38 vs. 4 % at 3 years). Only a trend for better EFS and lower RI was observed in patients with limited chronic GvHD. In addition, a lower RI was seen in patients with <5 % blasts 4 weeks after HCT. Multivariate analysis revealed that ≥98 % donor chimerism 2-4 weeks after HCT for OS, EFS, and RI and <3 lines of pretreatment for OS and EFS are the strongest predictors for better outcome.

CONCLUSION: FLAMSA-RIC shows long-term survival in refractory AML patients. Factors for favorable outcome are <20 % bone marrow blasts prior to HCT, <3 lines of pretreatment and complete donor chimerism after HCT.