Retrospective comparison of hematopoietic stem cell transplantation following reduced-intensity conditioning with fludarabine/low-dose melphalan plus 4 Gy TBI versus fludarabine/ busulfan plus 4 Gy TBI.

Fludarabine with intravenous busulfan (6.4 mg/kg; FB2) and fludarabine with intermediate-dose melphalan (140 mg/m2; FM140) are the most widely used reduced-intensity conditioning (RIC) regimens for allogeneic hematopoietic stem cell transplantation. FM140 generally has a lower relapse rate and higher non-relapse mortality (NRM), resulting in overall survival (OS) comparable to that seen with FB2. To evaluate the effect of reducing the melphalan dose, we retrospectively compared transplant outcomes in 156 patients who received FB2 (n = 103) or FM80 (n = 53) at our center (median age: 63 years; range 27-72 years). All patients received 4-Gy total body irradiation. Three-year OS, the cumulative incidence of relapse, and NRM were comparable between groups (FB2 vs. FM80, 58% vs. 47%, p = 0.24; 30% vs. 36%, p = 0.57; 17% vs. 21%, p = 0.44, respectively). There was no significant difference in the cumulative incidence of graft-versus-host disease (GVHD) at day 100, chronic GVHD at 3 years, or the 3-year GVHD-free/relapse-free survival rate. In the high-risk disease group, patients receiving FM80 tended to have lower 3-year OS (FB2 vs. FM80, 48% vs. 17%, p = 0.06). In summary, transplant outcomes following FB2 or FM80 were comparable except in patients with high-risk disease.