Thiotepa-busulfan-fludarabine compared to clofarabine-based conditioning for haploidentical transplant with posttransplant cyclophosphamide in patients with myeloid malignancies: a retrospective study from the SFGM-TC.

The optimal reduced-intensity conditioning (RIC) regimen for haploidentical hematopoietic stem cells transplantation (haplo-HSCT) using post-transplant cyclophosphamide as graft-versus-host disease (GVHD) prophylaxis has yet to be determined. Potential RIC regimen for haplo-HSCT in myeloid malignancies include Clofarabine-Baltimore (CloB) and TBF (thiotepa-busulfan-fludarabine). This multicenter retrospective study compared 297 adult patients receiving CloB (n = 59) or TBF (n = 238). The main diagnoses were acute myeloid leukemia (63%), 36% having adverse risk features. Median follow-up was 22.7 months. No significant differences were observed in overall (OS), progression-free (PFS), or GVHD-free relapse-free survival. However, 2-year non-relapse mortality (NRM) was higher after TBF (34% vs 21%, HR: 0.38; 95%CI: 0.20-0.75, p = 0.005), although the relapse incidence was lower (13% vs 23%, HR: 1.94; 95%CI: 0.98-3.87, p = 0.059). A 1:1 propensity score matching allowed the comparison of 53 CloB with 53 TBF. CloB was associated with improved 2-year OS (63% vs 44%, p = 0.02) due to a higher 2-year NRM in the TBF group (48% vs 19%, p = 0.002). By multivariate analysis, CloB remained associated with better OS (HR 0.52, 95% I 0.28-0.99, p = 0.045) and TBF with higher NRM (HR 3.43, 95%CI 1.59-7.41, p = 0.002). These results suggest that CloB is superior to TBF as a RIC regimen prior to haplo-HSCT.