Sequential Conditioning With FLAMSA Does Not Improve Outcomes of Allogeneic Stem Cell Transplantation in Chronic Myelomonocytic Leukemia Patients

As with myelodysplastic syndromes (MDS), effective treatment options for chronic myelomonocytic leukemia (CMML) are limited, and the optimal treatment approach remains undefined. Allogeneic stem cell transplantation (allo-SCT) is potentially curative therapy for patients with CMML. Sequential conditioning with FLAMSA was initially developed for refractory acute myeloid leukemia and has since been applied in the treatment of MDS and CMML. Data on optimal allo-SCT conditioning in CMML Patients is scarce. This retrospective study from the Department of Stem Cell Transplantation at the University Medical Center Hamburg, Germany, compared allo-SCT outcomes in CMML patients across three conditioning regimes: Thiotepa-busulfan (TB), sequential FLAMSA-busulfan fludarabine (FLAMSA-FB), and treosulfan-fludarabine (Treo-Flu). Sixty-nine consecutive patients with CMML who underwent allo-SCT between the years 2006 and 2022 were included in the study. Twenty-two received TB, 27 received FLAMSA-FB, and 20 received Treo-Flu conditioning. Transplant sources included matched related donors (8 patients), mismatched related donors (8 all in the TB group), matched unrelated donors (31), and mismatched unrelated donors (22) with significant group variations (P < .001). Most patients received anti-T lymphocyte Globulin for graft versus host disease (GVHD) prophylaxis (TB 68%, FLAMSA-FB 93%, Treo-Flu 85%, P = .08). CPSS-Molecular score was comparable between the groups. One TB patient experienced primary graft failure, but engraftment times were comparable across the groups. Although not statistically significant, the TB group showed a trend toward improved 3-year overall survival (OS) rates (80%) compared to FLAMSA-FB (37%) and Treo-Flu (55%) (P = .05). The TB group also displayed significantly higher 3-year progression-free survival (PFS) rates (80%) compared to FLAMSA-FB (33%) and Treo-Flu (both 39%), (P = .02). No significant differences were observed in 3-year non-relapse mortality across the TB (20%), FLAMSA-FB (30%), and Treo-Flu (26%) groups (P = .8). Interestingly, no TB patients relapsed at 3 years, contrasting with the FLAMSA-FB (41%) and Treo-Flu groups (30%, P = .02). Lastly, cumulative incidences of acute and chronic GVHD were similar across groups. Our analysis suggests FLAMSA-FB does not improve transplant outcomes, however, TB represents the preferred conditioning regimen for CMML patients undergoing allo-SCT. It demonstrates notable advantages in relapse prevention and leads to improved OS and PFS compared to FLAMSA-FB and Treo-Flu protocols.