Abstract 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.
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