Efficacy of Cord Blood Transplantation for the Management of Chronic Myelomonocytic Leukemia: A Registry-Based Study in Japan
Authors: Kurosawa Shuhei , Shimomura Yoshimitsu , Ishiyama Ken , Fuse Kyoko , Shimazu Yutaka , Doki Noriko , Uchida Naoyuki , Tanaka Masatsugu , Takahashi Satoshi , Sakurai Masatoshi , Kobayashi Hikaru , Katayama Yuta , Takada Satoru , Ozeki Kazutaka , Nakamae Hirohisa , Ishimaru Fumihiko , Kanda Yoshinobu , Ichinohe Tatsuo , Atsuta Yoshiko , Itonaga Hidehiro 
Published: December 2023

Introduction
Chronic myelomonocytic leukemia (CMML) is a challenging malignancy that shares characteristics with myelodysplastic syndromes and myeloproliferative neoplasms. Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is the only curative option for CMML. Numerous studies have examined transplant outcomes and prognostic factors; however, the focus has primarily been on bone marrow transplantation (BMT) and peripheral blood stem cell transplantation, while cord blood transplantation (CBT) is understudied. To address this knowledge gap, we conducted a nationwide retrospective study to comprehensively compare the outcomes of unrelated BMT and single-unit umbilical CBT in patients with CMML.
Methods
Data were collected from the Transplant Registry Unified Management Program 2 of the Japanese Data Center for Hematopoietic Cell Transplantation. The inclusion criteria were as follows: age of 16 years or higher, a diagnosis of CMML, and receipt of the first allo-HSCT between 2013 and 2019 through unrelated BMT from a human leukocyte antigen (HLA) 8/8-matched donor (UBMT group) or single-unit umbilical CBT (CBT group). The primary endpoint was overall survival (OS) after allo-HSCT, and the secondary endpoints included progression-free survival (PFS), cumulative incidences of relapse and non-relapse mortality (NRM), neutrophil engraftment, and graft-versus-host (GVHD)-free, relapse-free survival (GRFS).
The impact of CBT versus unrelated BMT on outcomes was evaluated using inverse probability of treatment weighting (IPTW) analysis. In this analysis, the Cox proportional hazards regression model for OS, PFS, and GRFS and the Fine-Gray proportional hazards regression model for relapse, NRM, engraftment, and GVHD were used. Hazard ratios (HRs) and 95% confidence intervals (CIs) were calculated for all outcomes. The propensity score (PS) was calculated via logistic regression by using the following factors: age at allo-HSCT, sex, cytogenetic risk, disease status, days from diagnosis to allo-HSCT, and year of allo-HSCT. For the CBT group, the stabilized weights were calculated by dividing CBT prevalence by each individual's PS. Conversely, for the UBMT group, the weights were calculated by dividing the 1 minus prevalence of CBT by 1 minus each individual's PS.
Results
Between 2013 and 2021, 238 patients with CMML underwent their first allo-HSCT. Among them, 50 underwent HLA 8/8 allele-matched unrelated BMT (UBMT group) and 68 underwent single-unit umbilical CBT (CBT group). The median age at allo-HSCT was 58.5 (range: 26-75) years; the median follow-up period for survivors was 1,329.5 (range: 100-1,967) days. Intergroup differences in age at allo-HSCT, recipient sex, hematopoietic cell transplantation-specific comorbidity index, Eastern Cooperative Oncology Group performance status, cytogenetic risk, pre-transplant treatment, disease status at allo-HSCT, conditioning intensity, GVHD prophylaxis, and year of allo-HSCT were not significant.
The transplantation outcomes are shown in Figure 1. There were no significant differences in the 3-year OS rate (UBMT: 51.0% [95% CI: 34.1-65.5%] vs CBT: 46.2% [95% CI: 33.2-58.1%]; P = 0.60; Figure 1A). IPTW analysis revealed no significant differences between the CBT and UBMT groups (HR: 1.21, 95% CI: 0.69-2.10, P = 0.51). PFS, relapse, NRM, and GRFS were not significantly different between the groups (Figure 1B-E). The neutrophil engraftment rate at 30 days was significantly higher in the UBMT group than in the CBT group (UBMT: 92.0% [95% CI: 78.9-97.1%] vs CBT: 79.4% [95% CI: 67.5-87.4%]; P &lt; 0.01; Figure 1F). These observations associated with the secondary endpoints were concurrently corroborated by the IPTW analysis.
Conclusion
Our study suggests that CBT can serve as a viable treatment option, demonstrating efficacy comparable to that of unrelated BMT for patients with CMML. These findings underscore the improved outcomes over time after CBT in patients with CMML, which is a treatment previously perceived as inferior to other donor sources (Itonaga et al., Biol Blood Marrow Transplant. 2018;24:840-48). Further investigations are warranted to optimize transplantation strategies and improve outcomes in patients with CMML.