Comparable outcome after haploidentical and HLA-matched allogeneic stem cell transplantation for high-risk acute myeloid leukemia following sequential conditioning—a matched pair analysis

In acute myeloid leukemia (AML), primary refractory or relapsed disease, secondary AML, and leukemia with unfavorable genetics are considered high-risk AML (hrAML), with allogeneic stem cell transplantation (SCT) representing the standard treatment. Sequential conditioning has been successfully used for SCT in hrAML in HLA-matched transplants, and found its way into HLA-haploidentical SCT (haplo-SCT) later on. Hence, sequential conditioning had become standard for all patients with hrAML in our two centers, regardless of donor type. Thereby, HLA-matched family or unrelated transplants were first/second choice, post-transplant cyclophosphamide (PTCY)-based haplo-SCT was chosen in patients missing matched donors or requiring urgent transplantation. To compare the outcome after HLA-matched and haplo-SCT for hrAML following sequential conditioning, we performed a retrospective, matched-pair comparison, using disease stage, genetic subgroups and age as matching criteria. Thirty-four well-matched pairs were identified. At SCT, patients (median age 54 years) were untreated (9%), had remission (13%), or active disease (78%). Three-year overall and leukemia-free survival (OS/LFS) of the entire cohort was 56 ± 7%/49 ± 7%, without significant differences between donor types (OS after HLA-matched/haplo-SCT 62 ± 10%/52 ± 9% ( p = 0.21), LFS 53 ± 10%/46 ± 9% ( p = 0.26)). Similarly, the cumulative incidence of relapse, non-relapse-mortality and chronic GvHD, as well as GvHD-free, relapse-free survival (GRFS), and chronic GvHD-free, relapse-free survival (cGRFS), were comparable. However, a higher incidence of acute GvHD ≥ II° was observed after HLA-matched SCT (15 ± 1% versus 50 ± 2%, p = 0.001). In conclusion, sequential conditioning SCT achieved remarkable results in hrAML, independently from donor type. PTCY-based haplo-SCT produced results that were comparable to HLA-matched SCT and can be used as an alternative option.