Efficacy of a Second Allogeneic Hematopoietic Cell Transplant in Relapsed Acute Myeloid Leukemia: Results of a Systematic Review and Meta-Analysis.

Allogeneic hematopoietic cell transplantation (allo-HCT) remains the only known treatment modality that can offer the possibility of cure for acute myeloid leukemia (AML). Unfortunately, relapse and disease progression still occur in more than one third of cases even when patients are allografted in complete hematologic remission (CR). Treatment of AML relapsing after a first allo-HCT is particularly challenging. A second allo-HCT is offered to patients considered fit for the procedure, but reported outcomes have been conflicting. To perform a systematic review and meta-analysis to assess the totality of evidence on the role of a second allo-HCT in patients with AML, we performed a comprehensive literature search using PUBMED/MEDLINE and EMBASE on August 25, 2021, and extracted clinical outcome data relating to benefits (CR, overall survival [OS], and progression-free/disease-free survival [PFS/DFS]) and harms (acute and chronic graft-versus-host disease, non-relapse mortality [NRM], and relapse). The search identified 821 studies. Only 20 studies (n = 2772 patients) met our inclusion criteria. A second allo-HCT resulted in pooled CR, OS, PFS/DFS, NRM and relapse rates of 67%, 34%, 30%, 27%, and 51%, respectively. OS was 2-fold higher when the second allo-HCT was performed in CR (38% versus 17%) and 3-fold higher in patients who had a later relapse from the first allo-HCT (34% versus 10%). There was no apparent difference in pooled OS (hazard ratio = 1.01; 95% confidence interval, 0.78-1.31; P = .94) whether the same original donor or a different one was used. Notwithstanding several limitations apart from the high heterogeneity among included studies, this analysis shows that a second allo-HCT is a reasonable treatment option for relapsed AML. The procedure appears to be more effective when performed in CR and in patients who had a later relapse from the first allo-HCT. The high pooled relapse rates exceeding 50%, even when receiving the second allo-HCT in CR is worrisome and emphasizes the need to incorporate new therapies whether as post-transplantation maintenance or consolidation to mitigate relapse risk. This analysis was limited to patients receiving a second allo-HCT for the sole purpose of treating AML relapse. Accordingly, we caution against extrapolating these findings to other indications such as treatment of graft failure, poor graft function, or mixed donor chimerism.