Outcome of Fludarabine-Based Conditioning in High-Risk Aplastic Anemia Patients Undergoing Matched Related Donor Transplantation: A Single-Center Study from Pakistan

Despite excellent transplant outcomes of aplastic anemia (AA) in developed countries, management in developing countries is challenging because of delay in the diagnosis, use of family donors for transfusions, and higher infection risk pretransplant. These factors can lead to allo-immunization, increased risk of graft failure, graft-versus-host disease (GVHD), and transplant-related mortality, leading to unfavorable outcomes. Conventional cyclophosphamide (Cy) and antithymocyte globulin (ATG) are associated with inferior overall survival in such high-risk patients. We conducted single-center retrospective analysis of high-risk AA patients (N = 147) enrolled consecutively and undergoing matched related donor transplant from March 2002 through October 2018. We included high-risk AA patients receiving fludarabine (Flu)-based conditioning. Median patient age was 20 years (range, 3 to 52). The median time from diagnosis to transplant was 11 months (range, 3 to 63). High-risk features included age ≥ 20 years in 55.8% of patients (n = 82), disease duration more than 3 months in 95 % (n = 140), RBC concentrates transfusions > 20 in 79.6% (n = 117), random donor platelet transfusion > 50 in 64.6% of patients (n = 95), and second hematopoietic stem cell transplant (HSCT) in 7.4% (11). We divided patients into 2 groups based on different conditioning regimens. Flu group 1 (Flu1) received Flu 120 to 150 mg/m2, Cy 120 to 200 mg/kg, and ATG 20 mg/kg, and Flu group 2 (Flu2) was given Flu 150 mg/m2, Cy 300 mg/m2, and ATG 20 mg/kg. Bone marrow stem cells were used as graft source in 97% of patients (n = 144) (alone in 52% and with peripheral blood stem cells in 45%). Cyclosporine alone was used for GVHD prophylaxis in 75% (n = 110) and cyclosporine plus methotrexate in 25% (n = 37). Median total nucleated cell dose was 5 × 108/kg. Median days for neutrophil engraftment was 13 (range, 10 to 20) and platelet engraftment 20 (range, 14 to 43). Day 100 mortality was 7.5% (n = 11). Sustained successful engraftment was achieved in 87.8% of patients (n = 129). Most graft failures (40%) occurred in Flu2 conditioning (P = .000) and in patients with >2 risk factors (P = .000). Overall incidence of acute and chronic GVHD was 11.6% (n = 17) and 12.9% (n = 19), respectively, in Flu1 and Flu2 groups. Overall survival (OS), disease-free survival (DFS), and GVHD-free relapse-free survival (GRFS) was 83.7%, 78.2%, and 70.7%, respectively. A trend toward improved OS was observed in patients receiving Flu1 conditioning but was statistically nonsignificant (P = .256), whereas DFS and GRFS were significantly better in Flu1 versus Flu2 (P = .004 and .001, respectively). When stratified per number of risk factors (age > 20, RBC concentrate > 20 or platelet > 50 random, duration > 3 months, previous HSCT), OS and DFS decreased significantly with increasing number of risk factors (P = .000 and .001, respectively). Patients are able to tolerate Flu-based conditioning well with lower rates of rejection and excellent long-term survival in high-risk AA patients. Cyclosporine alone as GVHD prophylaxis and marrow source stem cells as graft source are preferable options. Use of Flu plus low-dose Cy conditioning is associated with inferior survival outcomes. A randomized trial of Flu-based versus conventional Cy-containing conditioning would be helpful in establishing a standard of care conditioning regimen in high-risk AA patients.