Fludarabine/Busulfan versus Fludarabine/Melphalan Conditioning in Patients Undergoing Reduced-Intensity Conditioning Hematopoietic Stem Cell Transplantation for Lymphoma

- Patients with lymphoma who received FluBu for allogeneic stem cell transplant conditioning had significantly lower nonrelapse mortality when compared with patients receiving FluMel conditioning.
- The increased nonrelapse mortality seen with FluMel appears to be due to increased rates of mucositis and acute GVHD.
- Despite similar disease-free survival between the conditioning regimens, patients who received FluBu conditioning had a better overall survival when compared with FluMel conditioning, particularly for low or intermediate disease risk index.

There is at present little data to guide the choice of conditioning for patients with lymphoma undergoing reduced-intensity conditioning (RIC) allogeneic stem cell transplantation (SCT). In this study, we compared the outcomes of patients undergoing RIC SCT who received fludarabine and melphalan (FluMel), the standard RIC regimen used by the Spanish Group of Transplantation, and fludarabine and busulfan (FluBu), the standard RIC regimen used by the Dana-Farber Cancer Institute/Brigham and Women's Hospital. We analyzed 136 patients undergoing RIC SCT for lymphoma with either FluBu (n = 61) or FluMel (n = 75) conditioning between 2007 and 2014. Median follow-up was 36 months. The cumulative incidence of grades II to IV acute graft-versus-host disease (GVHD) was 13% with FluBu and 36% with FluMel (P = .002). The cumulative incidence of nonrelapse mortality (NRM) at 1 year was 3.3% with FluBu and 31% with FluMel (P < .0001). The cumulative incidence of relapse at 1 year was 29% with FluBu and 10% with FluMel (P = .08). The 3-year disease-free survival rate was 47% with FluBu and 36% with FluMel (P = .24), and the 3-year overall survival rate was 62% with FluBu and 48% with FluMel (P = .01). In multivariable analysis, FluMel was associated with a higher risk of acute grades II to IV GVHD (HR, 7.45; 95% CI, 2.30 to 24.17; P = .001) and higher risk of NRM (HR, 4.87; 95% CI, 1.36 to 17.44; P = .015). The type of conditioning was not significantly associated with relapse or disease-free survival in multivariable models. However, conditioning regimen was the only factor significantly associated with overall survival: FluMel conditioning was associated with a hazard ratio for death of 2.78 (95% CI, 1.23 to 6.27; P = .014) compared with FluBu. In conclusion, the use of FluBu as conditioning for patients undergoing SCT for lymphoma was associated with a lower risk of acute GVHD and NRM and improved overall survival when compared with FluMel in our retrospective study. These results confirm the differences between these RIC regimens in terms of toxicity and efficacy and support the need for comparative prospective studies.