Thiotepa, busulfan and fludarabine compared to busulfan and cyclophosphamide as conditioning regimen for allogeneic stem cell transplant from matched siblings and unrelated donors for acute myeloid leukemia

Busulfan plus cyclophosphamide (BuCy) is the traditional conditioning regimen for allogeneic stem cell transplant (allo-SCT) for young, fit patients with acute myeloid leukemia (AML). The thiotepa-busulfan-fludarabine (TBF) protocol has recently demonstrated promising outcome in cord blood and haploidentical SCT; however, there is limited evidence about this regimen in transplant from matched siblings (MSD) and unrelated donors (UD). We retrospectively compared outcomes of 2523 patients aged 18-50 with AML in remission, undergoing transplant from MSD or UD prepared with either TBF or BuCy conditioning. A 1:3 pair-matched analysis was performed: 146 patients receiving TBF were compared with 438 patients receiving BuCy. Relapse risk was significantly lower in the TBF when compared with BuCy group (HR 0.6, P = .02), while NRM did not differ. No significant difference was observed in LFS and OS between the two regimens. TBF was associated with a trend towards higher risk of grades III-IV aGVHD (HR 1.8, P = .06) and inferior cGVHD (HR 0.7, P = .04) when compared with BuCy. In patients undergoing transplant in first remission, the advantage for TBF in terms of relapse was more evident (HR 0.4, P = .02), leading to a trend for better LFS in favor of TBF (HR 0.7, P = .10), while OS did not differ between the two cohorts. In conclusion, TBF represents a valid myeloablative conditioning regimen providing significantly lower relapse and similar survival when compared with BuCy. Patients in first remission appear to gain the most from this protocol, as in this subgroup a tendency for better LFS was observed when compared with BuCy.