Safety and efficacy of clofarabine for preconditioning intervention in patients undergoing allogeneic hematopoietic stem cell transplantation for relapsed/refractory acute lymphoblastic leukemia.

Previous studies have suggested that intensive chemotherapy to induce bone marrow hypoplasia before allogeneic hematopoietic stem cell transplantation (HSCT) may improve outcomes in relapsed/refractory acute lymphoblastic leukemia. In this retrospective single-center study, we analyzed 14 patients who received clofarabine (CLO) as a preconditioning intervention (PCI) before HSCT between 2019 and 2024. PCI was defined as initiation of conditioning within 2 weeks after CLO. The median age was 34 years, and seven patients were not in remission at the time of CLO. CLO (30 mg/m for 5 days) was given in one or two cycles. WBC and bone marrow nucleated cells significantly decreased after CLO. The 1-year overall survival, relapse incidence, and non-relapse mortality rates were 67.5%, 32.2%, and 21.6%, respectively. Neutrophil engraftment was achieved in all patients. Acute and chronic graft-versus-host disease occurred in four and two patients, respectively. Bloodstream infections within 100 days after HSCT were observed in nine patients. Thrombotic microangiopathy (n = 2), sinusoidal obstruction syndrome/veno-occlusive disease (n = 2), drug-induced cardiomyopathy (n = 1), and organizing pneumonia (n = 1) were also observed but were clinically manageable. Considering the high-risk nature of this cohort, CLO-based PCI followed by HSCT appears to be a feasible treatment strategy with acceptable toxicity, warranting further investigation.