Conditioning with fludarabine and treosulfan compared to FLAMSA-RIC in allogeneic stem cell transplantation for myeloid malignancies: a retrospective single-center analysis

Sequential conditioning with FLAMSA does not improve outcomes of allogeneic stem cell transplantation in CMML patients

BACKGROUND

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 (AML) and has since been applied in the treatment of MDS and CMML. Data on optimal allo-SCT conditioning in CMML Patients is scarce.

METHODS

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).

RESULTS

Sixty-nine consecutive patients with CMML who underwent allo-SCT between the years 2006-2022 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 (MRD, 8 patients), mismatched related donors (MMRD, 8 all in the TB group), matched unrelated donors (MUD, 31), and mismatched unrelated donors (MMUD, 22) with significant group variations (p<0.001). Most patients received anti-T lymphocyte Globulin (ATLG) for graft versus host disease (GVHD) prophylaxis (TB 68%, FLAMSA-FB 93%, Treo-Flu 85%, p=0.08). 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 towards improved 3-year OS rates (80%) compared to FLAMSA-FB (37%) and Treo-Flu (55%) (p=0.05). The TB group also displayed significantly higher 3-year PFS rates (80%) compared to FLAMSA-FB (33%) and Treo-Flu (both 39%), (p=0.02). No significant differences were observed in 3-year non-relapse mortality (NRM) across the TB (20%), FLAMSA-FB (30%), and Treo-Flu (26%) groups (p=0.8). Interestingly, no TB patients relapsed at 3 years, contrasting with the FLAMSA-FB (41%) and Treo-Flu groups (30%, p=0.02). Lastly, cumulative incidences of acute and chronic GVHD were similar across groups.

CONCLUSION

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.

Current challenges in conditioning regimens for MDS transplantation

Myelodysplastic syndrome (MDS) is a very heterogeneous clonal disorder. Patients with "higher-risk" MDS, defined by specific recurrent genetic abnormalities, have a poor prognosis because of a high risk of progression to secondary acute myeloid leukemia with low chemosensitivity. Allogeneic hematopoietic stem cell transplantation remains the only treatment that offers durable disease control because the donor immune system allows graft-versus-MDS effects. In terms of preparation steps before transplantation, targeting the malignant clone by increasing the conditioning regimen intensity is still a matter of intense debate. MDS is mainly diagnosed in older patients, and high toxicity related to common myeloablative conditioning regimens has been reported. Efforts to include new drugs in the conditioning regimen to achieve the best malignant clone control without increasing toxicity have been made over the past 20 years. We summarized these retrospective and prospective studies and evaluated the limitations of the available evidence to delineate the ideal conditioning regimen.

Treosulfan-Versus Melphalan-Based Reduced Intensity Conditioning in HLA-Haploidentical Transplantation for Patients ≥ 50 Years with Advanced MDS/AML

Relapse and regimen-related toxicities remain major challenges in achieving long-term survival, particularly among older patients with high-risk myelodysplastic syndrome (MDS) or acute myeloid leukemia (AML) undergoing allogeneic hematopoietic stem cell transplantation (allo-HSCT). Previous studies have demonstrated the feasibility of treosulfan-based conditioning, noting stable engraftment and low non-relapse mortality (NRM) in patients undergoing HLA-matched allo-HSCT. However, data on treosulfan-based conditioning in the HLA-haploidentical transplantation (HaploT) setting are limited. We retrospectively compared conditioning with fludarabine-cyclophosphamide (FC)-melphalan (110 mg/m2) and FC-treosulfan (30 g/m2) prior to HaploT using post-transplantation cyclophosphamide (PTCy) in patients with high-risk MDS/AML patients ≥ 50 years, transplanted from 2009-2021 at our institution (n = 80). After balancing patient characteristics by a matched-pair analysis, we identified twenty-one matched pairs. Two-year OS and LFS were similar among the groups (OS 66% and LFS 66%, p = 0.8 and p = 0.57). However, FC-melphalan was associated with a significantly lower probability of relapse compared to FC-treosulfan (0% vs. 24%, p = 0.006), counterbalanced by a higher NRM (33% vs. 10%, p = 0.05). Time to engraftment and incidences of acute and chronic graft-versus-host disease (GvHD) did not differ significantly. In conclusion, HaploT using FC-treosulfan in combination with PTCy in patients aged ≥50 years with MDS/AML appears safe and effective, particularly in advanced disease stages. We confirm the favorable extramedullary toxicity profile, allowing for potential dose intensification to enhance antileukemic activity.

Hematopoietic cell transplantation (HCT) in MDS patients of older age

Hematopoietic cell transplantation (HCT) has evolved to an essential treatment in younger and more recently in elderly patients with myelodysplastic syndrome (MDS), the age group with the highest incidence. Less intense conditioning regimens and improvements in supportive therapy have reduced considerably transplant related mortality and in the same time increased the access to this curative treatment. Timing of HCT in the course of the disease assumes a crucial role. Detection of disease progression, geriatric assessment, comorbidity evaluation, and identification of transplant-specific risks are becoming increasingly important in this context. Novel statistical methods, molecular biomarkers, and quantification of tumor burden pre- and post-HCT will play an essential role in years to come. More effective and less toxic treatments to reduce the tumor burden before and/or after HCT are expected to improve the outcome. In this review article we discuss the current views and what we can expect.