Clofarabine versus fludarabine-based reduced-intensity conditioning regimen prior to allogeneic transplantation in adults with AML/MDS

We have retrospectively compared survivals between acute myeloid leukemia (AML)/myelodysplastic syndrome (MDS) patients who received either a clofarabine/busulfan (CloB2A2) or a fludarabine/busulfan (FB2A2) RIC regimen for allogeneic stem cell transplantation. Between 2009 and 2014, 355 allotransplanted cases were identified from the SFGM-TC registry as having received either the FB2A2 (n = 316, 56% males, median age: 59.2 years, AML 78.5%, first complete remission [CR1] 72%, median follow-up: 20 months) or the CloB2A2 (n = 39, 62% males, median age: 60.8 years, AML 62%, CR1 69%, median follow-up: 22.4 months) RIC regimen. In multivariate analysis, FB2A2 was associated with significant lower overall survival (OS, HR: 2.14; 95% CI: 1.05-4.35, P = 0.04) and higher relapse incidence (RI, HR: 2.17; 95% CI: 1.02-4.61, P = 0.04) and a trend for lower leukemia-free survival (LFS, HR: 1.75; 95% CI: 0.94-3.26, P = 0.08). These results were confirmed using a propensity score-matching strategy. However, when considering AML and MDS patients separately, the benefit of the CLOB2A2 regimen was restricted to AML patients (2-year OS FB2A2: 38% [14.5-61.6] vs. CloB2A2: 79.2% [62.9-95.4], P = 0.01; 2-year LFS FB2A2: 38% [16-59.9] vs. CloB2A2: 70.8% [52.6-89], P = 0.03). The better survivals were due to the lower risk of relapse in this CloB2A2 AML subgroup (2-year RI FB2A2: 41.2% [19-62.4] vs. CloB2A2: 16.7% [5-34.2], P = 0.05). This retrospective comparison suggests that the CloB2A2 RIC regimen can likely provide longer survival than that awarded by a FB2A2 RIC regimen and may become a new standard of care RIC regimen for allotransplanted AML patients. A prospective phase 3 randomized study is warranted.