Azacitidine monotherapy versus combination regimens as post-allogeneic transplantation maintenance in high-risk myeloid malignancies: A retrospective cohort Study

Abstract Introduction: Post-transplant relapse remains the leading cause of failure in high-risk acute myeloid leukemia (AML) and myelodysplastic syndromes (MDS), where azacitidine (AZA) monotherapy demonstrates efficacy but combination strategies lack comparative evidence. This study addresses a critical knowledge gap by conducting the first direct evaluation of AZA monotherapy versus AZA combined with immunotherapy (interferon-α, IFN-α) or molecularly targeted agents (sorafenib/venetoclax) within a minimal residual disease (MRD)-negative cohort post allogeneic hematopoietic stem cell transplantation (allo-HSCT). Methods: We conducted a retrospective cohort analysis of 59 consecutive high-risk AML/MDS patients (AML=56, MDS=3) undergoing allo-HSCT at our institution between 2019-2023, all receiving protocolized AZA-based maintenance therapy initiated at a median of 120 days post-transplant. Patients were stratified into three groups: AZA monotherapy (75 mg/m² days 1-5/28-day cycle; n=33); AZA + IFN-α (300 IU subcutaneously every other day for two weeks; n=15); AZA + targeted agents (sorafenib 400mg BID for FLT3-ITD+ [n=8] or venetoclax 400mg daily for TP53mut [n=3]). Primary endpoints were relapse-free survival (RFS) and overall survival (OS). Continuous and categorical variables were compared using Student's t test and chi-square test, respectively. Survival analyses employed Kaplan-Meier methodology (OS) and competing risk analysis (RFS). Results: The cohort had a median age of 41 years (range, 9-65) and received a median of 4 pre-transplant therapy cycles. The median number of CD34+ cell in peripheral blood hematopoietic stem cells was 6.16 × 10^6/kg (range, 2.13-34.17), and the median time of neutrophil and platelet engraftment were 11 (range, 10-25) and 12 days (range, 8-33), respectively. At a median follow-up of 31 months (range, 7-63), the 3-year OS was 84.4% (95% CI, 78.9-89.9%). Relapse rates did not differ significantly between groups: 9.1% (3/33) with AZA monotherapy vs. 13.3% (2/15) with AZA+IFN-α vs. 9.1% (1/11) with AZA+targeted agents (P=0.850). Considering that two patients had already died before the recurrence of the disease, a competing risk analysis was done. Competing risk analysis confirmed no association between therapy type and relapse (P=0.736). Notably, survival analysis confirmed non-inferiority of monotherapy against combinations (RFS HR 1.01, P=0.975; OS HR 0.91, P=0.770), and comparable hematologic toxicity (grade ≥3 cytopenia: 36.4% monotherapy vs 60.0% IFN-α vs 18.2% targeted, P=0.087). Subgroup analyses revealed biomarker-specific advantages: zero relapses in FLT3-ITD-positive patients receiving AZA+sorafenib (0/8), while the AZA+venetoclax subgroup experienced one relapse in a TP53 mutation patient (1/3). Critically, AZA+IFN-α demonstrated potent graft-versus-leukemia activity in haploidentical recipients with 13.3% relapse. Conclusion: This study established that AZA-based maintenance therapy achieves exceptional 3-year survival in rigorously selected MRD-negative high-risk myeloid malignancy patients post-allo-HSCT. AZA monotherapy demonstrates non-inferior efficacy to combination regimens with comparable toxicity, supporting its role as a foundational strategy. While limited by retrospective design and subgroup sizes, these findings provide a clinically actionable framework for personalizing post-transplant maintenance and clues for subsequent clinical trials on post-transplant maintenance regimen selection.