Sequential Use of Flamsa, FLAG, CLAG or TEC-Based Conditioning Regimen Followed By Allogeneic Hematopoietic Transplantation Results in Favorable Outcome for High Risk Acute Myeloid Leukemia, Myelodysplastic Syndrome and Myeloproliferative Neoplasia Patients: 15 Year Follow-up of the Multicenter Study in Singapore

Introduction: Allogeneic hematopoietic cell transplant (allo-HCT) is an effective consolidative treatment for patients with certain hematological malignancies and gives the best outcome when done in remission. However, patients with refractory acute myeloid leukemia (AML) or some myeloproliferative neoplasia (MPN) and myelodysplastic syndrome (MDS) deemed unable to achieve remission with standard induction are often excluded from allo-HCT with conventional conditioning regimen as pre-transplant remission could not be achieved. Recently, a sequential transplant approach, as developed by the Munich group, comprising of intensive cytoreductive chemotherapy FLAMSA (Fludarabine/Amsacrine/Cytarabine) to decrease leukemia cell burden shortly prior to conditioning regimen, has been successfully used for high-risk (HR) AML/MDS with promising results.

Methods: We studied 72 patients (median age 51 years, range 17-68) with HR AML (n=57), as defined by refractory, relapsed disease, secondary leukemia, complete remission with adverse-risk cytogenetics according to ELN criteria, or high/very risk refined Disease Risk Index (DRI), MPN (n=3) and HR MDS (n=12) according to IPSS-R, undergoing allo-HCT using the sequential transplant approach in 2 transplant centers in Singapore between January 2009 and July 2022. The sequential transplant approach combined a cytoreductive chemotherapy, which consisted of either FLAMSA (n=21), FLAG [Fludarabine/Cytarabine/Granulocyte Colony Stimulating Factor (GCSF)] +/- Idarubicin (n=30), CLAG (Clofarabine +/- Cytarabine +/- GCSF) (n=18), or TEC (Thiotepa, Etoposide, Cyclophosphamide) (n=3) followed by reduced intensity (RIC) (n=61) or myeloablative (MAC) (n=11) conditioning regimen. All patients received peripheral blood stem cell from matched related donors (MRD) (n=36), mismatched related donors (MMRD) (n=7), matched unrelated donors (MUD) (n=21), or mismatched unrelated donors (MMURD) (n=8). Post-grafting immunosuppression consisted of calcineurin inhibitor and mycophenolate mofetil (MMF) in all patients. Thymoglobulin and post-transplant cyclophosphamide were added for GVHD prophylaxis for MUD/MMURD and MMRD transplant, respectively. One MMRD had selective ex vivo T-cell depleted transplant followed by MMF as GVHD prophylaxis.

Results: The median time to neutrophil > 1000/μL was 11 days (range, 8-25). With a median follow-up duration of 51 months (range, 1-148), the Kaplan-Meier estimate of overall survival (OS) and leukemia-free survival (LFS) at 5 years were 42% (95% CI, 30-54) and 32% (95% CI 20-44), respectively. The cumulative incidence of relapse and non-relapse mortality (NRM) at 2 years were 47% (95% CI, 35-59) and 16% (95% CI, 9-26), respectively.

Patients receiving FLAG, CLAG or TEC-based sequential regimen showed a trend towards lower NRM and relapse compared to FLAMSA-based regimen, although the difference was not statistically significant. This translated into a more favorable 5-year LFS (40% vs 13%, p=0.04), but no statistically significant difference in 5-year OS (42% vs 40%, p=0.56). Patients with refractory disease (n=49) were at higher risk of relapse compared to patients whom had achieved at least a partial remission prior to sequential allo-HCT (n=17) (2-year cumulative incidence of relapse: 59.0% vs 34.0%, p=0.02). This resulted in an inferior 5-year OS (31% vs 66%; p=0.02) and LFS (20% vs 75%, p<0.01).

On multivariable analysis, only refined DRI showed significant impact on OS (p=0.01) and LFS (p=0.02) but had no significant impact on NRM and relapse. The 5-year OS for patients with intermediate/high risk and very high risk DRI were 51% and 21% (p<0.01), and the corresponding 5-year LFS were 42% and 10% (p<0.01), respectively (Figure 1 and Figure 2).

Conclusions: Sequential transplant conditioning with FLAMSA, FLAG, CLAG or TEC-based cytoreductive regimen followed by allo-HCT is an effective strategy in overcoming the dismal prognosis of HR AML, MDS and MPN, including patients with high risk DRI, and enabling favorable long-term disease-free survival. More studies on effective strategies such as optimising the conditioning regimen intensity or post-transplant maintenance therapy with prophylactic donor lymphocyte infusion, are needed to further eliminate the risk of relapse, without increasing risk of treatment-related toxicity.

No relevant conflicts of interest to declare.