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4889 Outcomes of Allogeneic Transplantation with Clofarabine and Post-Transplant Cyclophosphamide-Based Conditioning in Patients with Very High-Risk Acute Myeloid Leukemia

Program: Oral and Poster Abstracts
Session: 721. Allogeneic Transplantation: Conditioning Regimens, Engraftment, and Acute Toxicities: Poster III
Hematology Disease Topics & Pathways:
Combination therapy, Clinical Practice (Health Services and Quality), Diseases, Treatment Considerations, Adverse Events
Monday, December 9, 2024, 6:00 PM-8:00 PM

Lucia Castilla Garcia1*, Rebeca Bailen2*, Ignacio Alberto Gomez Centurion Luna3*, Paula Fernández-Caldas4*, Pablo Silva De Tena2*, Carolina Martinez-Laperche, PhD5,6*, Javier Anguita7*, Ramon Garcia-Sanz, MD, PhD7 and Mi Kwon, MD, PhD7

1Hospital General Universitario Gregorio Marañon, Madrid, Spain
2Hospital General Universitario Gregorio Marañón, Madrid, Spain
3Hospital General universitario Gregorio Marañon, MADRID, ESP
4Hematology Department, Hospital General Universitario Gregorio Marañón, Madrid, Spain
5Department of Hematology, Hospital Universitario Gregorio Marañón, Madrid, Spain
6Instituto de Investigación Sanitaria Hospital General Universitario Gregorio Marañón, Madrid, Spain
7General University Hospital Gregorio Marañón, Madrid, Spain

Introduction: Patients undergoing allogeneic hematopoietic stem cell transplantation (HSCT) with active disease exhibit relapse rates exceeding 50% and an estimated survival of less than 25%. Among those with very adverse genetics, particularly acute myeloid leukemia (AML) with complex karyotypes and/or bi-allelic mutations in TP53, the relapse rate exceeds 80%. Clofarabine (Clo) directly induces apoptosis through caspase activation and interacts with the mitochondrial membrane, conferring superior anti-leukemic activity compared to other nucleoside analogs. Its use as part of the conditioning regimen for HSCT in AML and high-risk or active disease has been explored, particularly in the context of sequential transplantation and in some HSCT platforms utilizing matched donors with conventional prophylaxis for graft-versus-host disease (GVHD). The objective of this study was to analyze our center's experience with patients at very high risk of relapse who received Clo-based conditioning and post-transplant cyclophosphamide (PT-CY) as GVHD prophylaxis.

Patients and Methods: A unicentric retrospective study was conducted, including adult patients who underwent allogeneic HSCT with Clo-based conditioning.The criteria for using this conditioning regimen was visible-phase AML at the time of transplantation, multi-hit TP53 mutation, and/or very high-risk cytogenetics (complex/monosomal karyotye). The intermediate-intensity regimen (TCI 2.5) consisted of Clo 30 mg/m² (for 5 days) plus Melphalan 140 mg/m² on day -2, while the high-intensity regimen (TCI 4) consisted of Clo 40 mg/m² (for 5 days) plus Busulfan 3.2 mg/kg/day (for 4 days). All patients received PT-CY on days +3 and +4, followed by a calcineurin inhibitor (CNI) and mycophenolate mofetil (MMF) from day +5. No patient received antithymocyte globulin (ATG).

Results: A total of 20 HSCTs were identified between 2018 and 2024, with a median follow-up of 37.6 months (range 27-53). The ge-adjusted HCT-CI score was ≥ 3 in 60%; 25% had previously undergone an allogeneic HSCT. Disease risk index was high or very high in 90%, 4% were primary refractory, 10% presented with visible extramedullary disease at the time of transplantation, only 4 patients underwent transplantation with a negative measurable residual disease (in these patients, it was their second bone marrow transplant), and 15 of the 20 patients had very high-risk genetic alterations at diagnosis. 80% of patients received the intermediate-intensity conditioning. Stem cell source was in all cases, and 9 (45%) patients received a haploidentical HSCT. There were no cases of graft failure, with cumulative incidences of neutrophil and platelet engraftment at 28 days of 90% and 50%, respectively (median of 17 and 27 days). The most frequent complications were Grade ≥ 2 mucositis (55%), reactivation of CMV (55%), hepatotoxicity Grade 2-4 (35%), hemorrhagic cystitis (15%), cardiotoxicity (5%), clofarabine-related skin rash (15%), endotheliolopathy (10%), neuropathy (10%), and hepatic veno-occlusive disease (5%). Cumulative incidence of acute GVHD II-IV at 180 days was 16% (Grade III-IV GVHD at 5%). Cumulative incidence of chronic GVHD was 20%, with moderate-severe chronic GVHD of 11%. The combined objective of relapse and GVHD-free survival (GRFS) was 47% at 3 years, with a median of 33 months (95% CI 19-47). At 3 years, overall survival was 52%, with a median of 40 months (95% CI 27-57), and event-free survival was 49% with a median of 37 months (95% CI 24-52). Treatment-related mortality (TRM) at 2 years was 15%; there were two late events, resulting in a TRM of 26% at 3 years. The relapse incidence at three years was 26%, with no differences in subgroup analysis for higher risk (active disease at transplant and TP53 mutation).

Conclusions: In our experience, the incorporation of Clo to the conditioning regime in patients with very high relapse-risk AML, including visible disease at transplantation, using peripheral blood and post-transplant cyclophosphamide GVHD prophylaxis with both matched and haploidentical donors, offers favorable outcomes for this population, which has historically presented adverse results.

Disclosures: Garcia-Sanz: BMS/Celgene: Consultancy, Honoraria; Janssen: Consultancy, Honoraria; Novartis: Consultancy, Honoraria; Takeda Pharmaceutical: Consultancy, Honoraria; MSD: Honoraria; Amgen: Consultancy, Honoraria. Kwon: Jazz: Speakers Bureau; Sanofi: Honoraria; Pfizer: Speakers Bureau; Gilead-Kite: Honoraria, Research Funding, Speakers Bureau.

*signifies non-member of ASH