Microtransplantation improves the outcome of older patients with newly diagnosed acute myeloid leukemia: a single-center study with long-term follow-up

Background Microtransplantation (MST) combines chemotherapy with infusion of HLA-mismatched granulocyte colony-stimulating factor-mobilized peripheral blood stem cells (G-PBSCs) without graft-versus-host disease (GVHD) prophylaxis, offering a potential therapeutic alternative for older acute myeloid leukemia (AML) patients. Methods In this single-center study, 29 patients aged ≥60 years with newly diagnosed non-acute promyelocytic leukemia (AML) received MST between April 2008 and June 2021. Patients were stratified into two age cohorts: 60–70 years ( n = 20) and >70 years ( n = 9). Each MST course comprised induction or consolidation chemotherapy followed by G-PBSC infusion. Donor chimerism was monitored by the InDels assay. Endpoints included complete remission (CR), overall survival (OS), leukemia-free survival (LFS), relapse, non-relapse mortality (NRM), and safety. Competing risk analysis (Fine–Gray model) was used to evaluate the cumulative incidence of relapse and NRM. Transcriptomic profiling was performed in a subset of long-term survivors. Results The median follow-up was 148.5 months (range 52.96–219.12). The CR rate was 86.2% (25/29), with no significant difference between age groups (90.0% vs. 66.7%, p = 0.290). The median OS was 20.00 months (range 1.00–205.00). Patients aged 60–70 years had significantly better OS than those >70 years (50.0% vs. 10.0%, p = 0.002). Similarly, LFS was higher in the younger group (45.0% vs. 10.0%, p = 0.015). Receiving >3 MST courses was associated with longer OS and LFS (both p < 0.001). Competing risk analysis showed a significantly higher cumulative incidence of relapse in the >70-year group (66.7% vs. 45.0%, p = 0.048). NRM did not differ significantly between groups ( p = 0.13). GVHD occurred in one patient (3.4%). Transcriptomic analysis of four survivors revealed distinct gene expression profiles enriched in immune and hematopoietic pathways. Conclusion MST is an effective and tolerable treatment for older AML patients, particularly those aged 60–70 years and those receiving more than three treatment courses. These results support MST as a viable alternative for older patients ineligible for intensive transplantation.