Impact of FLT3 internal tandem duplication and NPM1 mutations in acute myeloid leukemia treated with allogeneic hematopoietic cell transplantation

Understanding mechanisms of resistance to FLT3 inhibitors in adult FLT3-mutated acute myeloid leukemia to guide treatment strategy

The presence of FLT3 mutations, including the most common FLT3-ITD (internal tandem duplications) and FLT3-TKD (tyrosine kinase domain), is associated with an unfavorable prognosis in patients affected by acute myeloid leukemia (AML). In this setting, in recent years, new FLT3 inhibitors have demonstrated efficacy in improving survival and treatment response. Nevertheless, the development of primary and secondary mechanisms of resistance poses a significant obstacle to their efficacy. Understanding these mechanisms is crucial for developing novel therapeutic approaches to overcome resistance and improve the outcomes of patients. In this context, the use of novel FLT3 inhibitors and the combination of different targeted therapies have been studied. This review provides an update on the molecular alterations involved in the resistance to FLT3 inhibitors, and describes how the molecular monitoring may be used to guide treatment strategy in FLT3-mutated AML.

The FLT3-ITD allelic ratio and NPM1 mutation do not impact outcomes in AML patients with FLT3-ITD after allo-HSCT: a retrospective propensity-score matching study

BACKGROUND

FLT3-ITD mutation has consistently been correlated with poor outcomes in AML patients. Allo-HSCT (allogeneic hematopoietic stem cell transplantation) plays a major role in curing blood diseases. Whether allo-HSCT can eliminate the detrimental effects of FLT3-ITD mutation in AML patients remains debatable. In addition, studies showed that FLT3-ITD allelic ratio (AR) and NPM1 mutation appear to further influence the prognostic utility of FLT3-ITD in patients with FLT3-ITD-mutated AML. The influence of NPM1 mutation and AR on FLT3-ITDmut patients remains unclear in our database.

OBJECTIVE

To compare the survival outcomes following allo-HSCT between FLT3-ITDmut and FLT3-ITDwt patients and further analyze the influence of NPM1 and AR on outcomes.

STUDY DESIGN

118 FLT3-ITDmut patients and 497 FLT3-ITDwt patients with allo-HSCT were matched 1:3 on the propensity score using a nearest-neighbor matching with a caliper size of 0.2. 430 AML patients were considered, including 116 FLT3-ITDmut patients and 314 FLT3-ITDwt patients.

RESULTS

OS (overall survival) and LFS (leukemia-free survival) of FLT3-ITDmut patients were similar to FLT3-ITDwt (2-year OS:78.5% vs 82.6%, P=0.374; 2-year LFS: 75.1% vs 80.8%, P= 0.215). A cut-off of 0.50 was applied to define subgroups with a low or high AR of FLT3-ITD, no significant CIR (cumulative incidence of relapse) and LFS differences were observed between the low AR and high AR groups (2-year CIR: P=0.617; 2-year LFS: P=0.563). CIR and LFS were comparable when patients were grouped according to the presence or absence of NPM1 and FLT3-ITD (2-year CIR: P=0.356; 2-year LFS: P=0.159). Additionally, the CIR and LFS of FLT3-ITDmut and FLT3-ITDwt patients tended to be different after MSD-HSCT (matched-sibling donor hematopoietic stem cell transplantation) (2-year CIR: P= 0.072; 2-year LFS: P= 0.084), however, the differences were not observed in patients with haplo-HSCT (2-year CIR: P= 0.59; 2-year LFS: P= 0.794). The presence of MRD before transplantation and non-CR1 were risk factors related to inferior outcomes in a multivariate analysis, regardless of FLT3-ITD or NPM1 status.

CONCLUSION

Our results suggested that allo-HSCT, especially haplo-HSCT, may overcome the adverse effect of FLT3-ITD mutation, regardless of the NPM1 status or AR. Allo-HSCT could be an ideal option for AML patients with FLT3-ITD.

Adverse impact of a high allelic burden FLT3-ITD mutation on allogeneic hematopoietic stem cell transplantation in patients with cytogenetically normal AML

Risks associated with the FLT3-ITD mutation in patients receiving chemotherapy alone for cytogenetic normal acute myeloid leukemia (CN-AML) depend on the allelic ratio (AR) and concomitant NPM1 mutation. Nevertheless, their prognostic ability after allogeneic hematopoietic cell transplantation (allo-HCT) remains undetermined. Moreover, previous studies have revealed that haploidentical transplantation improves outcomes of FLT3-ITD patients. To elucidate whether this alteration also impacts prognosis of myeloablative allo-HCT upon first remission, we retrospectively reviewed the prognostic ability of FLT3-ITD mutations in 205 CN-AML patients. Our analysis demonstrated that FLT3-ITD AR was closely related to pretransplant MRD and induction response. Multivariate analysis showed that high-AR FLT3-ITD, pretransplant MRD and induction response were independent risk factors for CN-AML. In addition, we presented evidence that the high-AR FLT3-ITD patient prognosis was not overcome by haploidentical transplantation, but was markedly improved by cGVHD. More importantly, among patients with negative pretransplant MRD, high-AR FLT3-ITD patients did not have increased relapse risk, compared to low-AR FLT3-ITD and wild-type FLT3 patients. Our findings will aid in accurate prognostic stratification of FLT3-ITD patients. We also recommend further targeted and coordinated approaches to sustain durable remission following induction chemotherapy and allo-HCT in this high-risk patient population.