A Prospective Phase III Trial for Comparing Cyclophosphamide and Fludarabine Conditioning Regimen in Severe Idiopathic Aplastic Anemia

Our previous study showed that a less toxic regimen comprising reduced cyclophosphamide (Cy), fludarabine and anti-thymocyte globulin (ATG) (Cy-Flu-ATG), was less toxic for allogeneic hematopoietic cell transplantation (alloHCT) compared with standard Cy-ATG in patients with adult severe aplastic anemia (AA). We postulated that replacing Cy with Flu (Flu-ATG) would be more beneficial. Therefore, we performed a randomized phase III study to compare the regimen-related toxicities (RRTs) of two different conditioning regimens: Cy-ATG vs. Flu-ATG. Pre-defined RRTs were defined as pulmonary complications, hepatic sinusoidal obstruction syndrome (SOS), hemorrhagic cystitis and death of any causes. We present the final analysis. Patients in the Cy-ATG arm received Cy at 200 mg/kg. Those in the Flu-ATG arm received fludarabine (Flu) at 180 mg/m2. Bone marrow (BM) as allowed when the donor was matched sibling donor and otherwise stem cell source was mobilized peripheral blood (PB). Regimen for graft-versus-host disease (GvHD) was cyclosporine and short-course methotrexate. A total of 63 patients (31 patients in Cy-ATG and 32 patients in Flu-ATG) were enrolled. The basic patients'characteristics were similar between both arms in terms of gender, age, prior immune suppression therapy history, stem cell source, stem cell dose, donor type and HLA-matching. There were 36 unrelated donors in each arm (p=1.000). All predefined RRTs were similar between Cy-ATG and Flu-ATG (33.3% vs. 21.9%; p=0.691). There was no difference between Cy-ATG and Flu-ATG in terms of pulmonary complications (12.9% vs. 3.1%; p=1.000), SOS (0% vs. 3.1%; p=1.000), hemorrhagic cystitis (6.5% vs. 3.1%; p=0.607) and death of any causes (23.3% vs. 15.6%; p=0.443). Primary engraftment failure was not found in Flu-ATG arm but 2 patients in Cy-ATG (p = 0.230), one of which died of treatment-related hepatic toxicity before engraftment. However, there was higher secondary engraftment failure inFlu-ATG arms compared with Cy-ATG (2nd GF; 21.9% vs. 6.9%; p=0.098). Therefore, any engraftment failure was not different between Cy-ATG vs. Flu-ATG (13.3% vs. 21.9%; p=0.379). The incidence of all grades acute GvHD was significantly higher in Cy-ATG arm (35.7% vs. 9.4%; p=0.013). The incidence of chronic GvHD was lower in Cy-ATG arm but was not statistically significant (11.5% vs. 23.1%; p=0.271). Any significant treatment-related toxicities including RRTs were similar between Cy-ATG and Flu-ATG arms (43.3% vs. 43.8%; p=0.974). The 3-year survival rate did not differ between Cy-ATG and Flu-ATG (72.9% vs. 79.3%; p=0.329). In conclusion, Flu-ATG can be comparable with Cy-ATG in terms of RRT and survival.