Potent Graft-versus-Leukemia Effect after Reduced-Intensity Allogeneic SCT for Intermediate-Risk AML with FLT3-ITD or Wild-Type NPM1 and CEBPA without FLT3-ITD

Clinical practice recommendation on hematopoietic stem cell transplantation for acute myeloid leukemia patients with FLT3-internal tandem duplication: a position statement from the Acute Leukemia Working Party of the European Society for Blood and Marrow Transplantation

The FMS-like tyrosine kinase 3 (FLT3) gene is mutated in 25-30% of patients with acute myeloid leukemia (AML). Because of the poor prognosis associated with FLT3-internal tandem duplication mutated AML, allogeneic hematopoietic stem-cell transplantation (SCT) was commonly performed in first complete remission. Remarkable progress has been made in frontline treatments with the incorporation of FLT3 inhibitors and the development of highly sensitive minimal/measurable residual disease assays. Similarly, recent progress in allogeneic hematopoietic SCT includes improvement of transplant techniques, the use of haploidentical donors in patients lacking an HLA matched donor, and the introduction of FLT3 inhibitors as post-transplant maintenance therapy. Nevertheless, current transplant strategies vary between centers and differ in terms of transplant indications based on the internal tandem duplication allelic ratio and concomitant nucleophos-min-1 mutation, as well as in terms of post-transplant maintenance/consolidation. This review generated by international leukemia or transplant experts, mostly from the European Society for Blood and Marrow Transplantation, attempts to develop a position statement on best approaches for allogeneic hematopoietic SCT for AML with FLT3-internal tandem duplication including indications for and modalities of such transplants and on the potential optimization of post-transplant maintenance with FLT inhibitors.

T-cell replete haploidentical stem cell transplantation attenuates the prognostic impact of FLT3-ITD in acute myeloid leukemia: A report from the Acute Leukemia Working Party of the European Society for Blood and Marrow Transplantation

Acute myeloid leukemia (AML) patients harboring the FLT3-ITD mutation are considered a high risk patient subset preferentially allocated for allogeneic stem cell transplantation in first remission. Whether FLT3-ITD retains a prognostic role in haploidentical stem cell transplantation (haplo-SCT) is unknown. To analyze the prognostic impact of FLT3-ITD in haplo-SCT, we performed a retrospective analysis of the multicenter registry of the acute leukemia working party of the European Society for Blood and Marrow Transplantation. We included all adult AML patients with known FLT3 status who underwent a first T-cell replete related haplo-HCT in first complete remission from 2005 to 2016. We evaluated 293 patients of whom 202 were FLT3^wt and 91 were FLT3-ITD mutated. FLT3-ITD patients were more likely to be NPM1 mutated as well as be in the intermediate risk cytogenetic risk category. In multivariate analysis, patients with FLT3-ITD had comparable rates of relapse incidence [Hazard ratio (HR) = 1.34, confidence interval (CI) 95%, 0.67-2.7; P = .9] and leukemia-free survival (HR = 0.99, CI 95%, 0.62-1.57; P = .9) to those of FLT3^wt patients. Overall survival, the incidence of nonrelapse mortality, and graft versus host disease-free/relapse-free survival were not significantly impacted by FLT3-ITD status. Furthermore, relapse and overall survival were comparable between FLT3-ITD patients transplanted from various donor pools, namely matched siblings, unrelated donors, haplo-SCT). Finally, subset analysis of patients with intermediate risk cytogenetics confirmed the absence of a prognostic impact of FLT3-ITD also for this patient segment. In AML patients undergoing T-cell replete haplo-SCT, the FLT3-ITD mutation possibly does not retain its prognostic significance.

Allogeneic stem cell transplantation benefits for patients ≥ 60 years with acute myeloid leukemia and FLT3 internal tandem duplication: a study from the Acute Leukemia Working Party of the European Society for Blood and Marrow Transplantation

Intermediate-risk cytogenetic acute myeloid leukemia with an internal tandem duplication of FLT3 (FLT3-ITD) is associated with a high risk of relapse, and is now a standard indication for allogeneic stem cell transplantation. Nevertheless, most studies supporting this strategy have been performed in young patients. To address the benefit of allogeneic transplantation in the elderly, we made a selection from the European Society for Blood and Marrow Transplantation registry of de novo intermediate-risk cytogenetic acute myeloid leukemia harboring FLT3-ITD in patients aged 60 or over and transplanted from a related or unrelated donor between January 2000 and December 2015. Two hundred and ninety-one patients were identified. Most patients received a reduced-intensity conditioning (82%), while donors consisted of an unrelated donor in 161 (55%) patients. Two hundred and twelve patients received their transplantation in first remission, 37 in second remission and 42 in a more advanced stage of the disease. The 2-year leukemia-free survival rate was 56% in patients in first remission, 22% in those in second remission and 10% in patients with active disease, respectively (P<0.005). Non-relapse mortality for the entire cohort was 20%. In multivariate analysis, disease status at transplantation was the most powerful predictor of worse leukemia-free survival, graft-versus-host disease and relapse-free survival, and overall survival. In this elderly population, age was not associated with outcome. Based on the current results, allogeneic transplantation translates into a favorable outcome in fit patients ≥ 60 with FLT3-ITD acute myeloid leukemia in first remission, similarly to current treatment recommendations for younger patients.

Midostaurin approved for FLT3-mutated AML

Midostaurin was recently approved by the US Food and Drug Administration for the treatment of FLT3-mutant acute myeloid leukemia (AML). This is the first drug to receive regulatory approval for AML in the United States since the year 2000. Midostaurin is a small-molecule kinase inhibitor with activity against the receptor tyrosine kinase FLT3, and its approval will hopefully mark the beginning of an era of targeted agents for the treatment of molecularly defined subtypes of AML.

Pharmacologic maintenance strategies following allogeneic hematopoietic cell transplantation for acute myeloid leukemia

The use of pharmacologic agents to maintain remission following allogeneic hematopoietic cell transplantation (HCT) is a topic of increasing interest and exploration for patients with high-risk acute myeloid leukemia (AML). This review details published and ongoing studies focused on post-transplant pharmacologic maintenance for AML. While early phase studies have demonstrated the safety and tolerability of various maintenance approaches following HCT, the results of several ongoing randomized prospective studies will be required to determine the clinical efficacy needed to expand this approach from experimental to standard of care.

Molecular therapy for acute myeloid leukaemia

Acute myeloid leukaemia (AML) is a heterogeneous disease that is, in general, associated with a very poor prognosis. Multiple cytogenetic and molecular abnormalities that characterize different forms of AML have been used to better prognosticate patients and inform treatment decisions. Indeed, risk status in patients with this disease has classically been based on cytogenetic findings; however, additional molecular characteristics have been shown to inform risk assessment, including FLT3, NPM1, KIT, and CEBPA mutation status. Advances in sequencing technology have led to the discovery of novel somatic mutations in tissue samples from patients with AML, providing deeper insight into the mutational landscape of the disease. The majority of patients with AML (>97%) are found to have a clonal somatic abnormality on mutational profiling. Nevertheless, our understanding of the utility of mutation profiling in clinical practice remains incomplete and is continually evolving, and evidence-based approaches to application of these data are needed. In this Review, we discuss the evidence-base for integrating mutational data into treatment decisions for patients with AML, and propose novel therapeutic algorithms in the era of molecular medicine.

Outcome of patients with distinct molecular genotypes and cytogenetically normal AML after allogeneic transplantation

In AML with normal cytogenetics, age, response to induction, and FLT3-ITD allow for an estimate of outcome after allogeneic HSCT in CR1. Neither variation of classical transplant techniques nor development of chronic GVHD outweighs the negative impact of FLT3-ITD.

Reduced-intensity conditioning with fludarabine and busulfan for allogeneic hematopoietic cell transplantation in elderly or infirm patients with advanced myeloid malignancies

We report a retrospective single-center analysis of 112 consecutive patients that underwent allogeneic hematopoietic cell transplantation (HCT) after reduced-intensity conditioning (RIC) with fludarabine (FLU) and busulfan (BU) for the treatment of acute myeloid leukemia (AML), myelodysplastic syndrome (MDS) and myeloproliferative syndrome (MPS) from 2005 to 2014. Three-year event-free survival (EFS) and overall survival (OS) were 46 and 58 %, respectively. Patients ≥60 years of age showed a similar outcome compared to younger patients (3-year OS 55 vs. 61 %, p = 0.96; 3-year EFS 46 vs. 46 %, p = 0.82). Cumulative incidence of non-relapse mortality (NRM) at 3 years adjusted for relapse as competing risk was 25 % for patients aged <60 years and 15 % for older patients (p = 0.15). Infusions of higher CD34(+) blood stem cell doses were associated with a significantly better outcome in the elderly subgroup (3-year OS 82 vs. 39 %, p = 0.007). Moreover, complete donor chimerism at day +100 was associated with a significantly improved survival (3-year OS 69 vs. 23 %, p = 0.003). In conclusion, our data suggest that RIC with FLU/BU enables long-term disease-free survival even in an elderly patient population. Age has no negative impact on the outcome of allogeneic HCT, and decision for transplant should be based on disease risk and performance status rather than age alone.

Is it time to change conventional consolidation chemotherapy for acute myeloid leukemia in CR1?

PURPOSE OF REVIEW

Choosing the most appropriate postremission therapy (PRT) for a patient with acute myeloid leukemia (AML) in first complete remission remains a challenging task. Factors such as risk for disease relapse, nonrelapse mortality associated with different PRT approaches, donor availability, prospects for salvage should disease relapse, and patient preference all affect PRT choice.

RECENT FINDINGS

New genetic markers refine AML risk stratification and identify patients within the 'classical' risk groups who may benefit from transplant-based or chemotherapy-based PRT. The use of minimal residual disease in first remission to guide PRT choice and the application of novel, targeted therapies have the potential to alter PRT approaches across AML risk groups. The advent of alternative donor sources, use of reduced intensity regimens, and improved supportive care all affect the availability and safety of transplant-based PRT and challenge the relevance of the older legacy 'donor/no-donor' genetically randomized trials.

SUMMARY

Genetic risk assessment, monitoring of minimal residual disease in first remission, use of targeted agents, and the newer transplant strategies all have the potential to 'personalize' PRT choice in the AML patient. The clinical value of these novel interventions awaits validation in prospective, risk-adapted clinical trials.

FLT3 mutational status is an independent risk factor for adverse outcomes after allogeneic transplantation in AML

Allogeneic HCT has been increasingly used in the setting of FLT3 mutated AML. However, its role in conferring durable relapse-free intervals remains in question. Herein, we sought to investigate FLT3 mutational status on transplant outcomes. We conducted a retrospective cohort study of 262 consecutive AML patients who underwent first-time allogeneic HCT (2008-2014), of whom 171 had undergone FLT3-ITD mutational testing. FLT3 mutated AML was associated with nearly twice the relapse risk (RR) compared with those without FLT3 mutation 3 years post-HCT (63% vs. 37%, P<0.001), and with a shorter median time to relapse (100 vs. 121 days). FLT3 mutational status remained significantly associated with this outcome after controlling for patient, disease, and transplant-related risk factors (P<0.05). Multivariate analysis showed a significant association of FLT3 mutation with increased 3-year RR (HR 3.63, 95% CI: 2.13, 6.19, P<0.001), and inferior disease-free survival (HR 2.05, 95% CI: 1.29, 3.27, P<0.01) and overall survival (HR 1.92, 95% CI: 1.14, 3.24, P<0.05). These data demonstrate high risk of early relapse after allogeneic HCT for FLT3 mutated AML that translates into adverse disease-free and overall survival outcomes. Additional targeted and coordinated interventions are needed to maintain durable remission after allogeneic HCT in this high-risk population.

Immunotherapy in acute myeloid leukemia

Despite the remarkable progress made in some leukemias such as CML and CLL, cytotoxic treatment for AML remains essentially unchanged over the last 4 decades. Several lines of evidence, including the graft versus leukemia effect associated with allogeneic hematopoietic stem cell transplantation (HSCT), suggest that immunotherapy is an active modality in AML. Given the lack of progress for chemotherapy in this disease, many novel immunologic treatment approaches have been explored. The goals of non-transplant-based immune approaches have largely consisted of the stimulation or restoration of endogenous immune responses or the targeting of specific tumor antigens by immune cells. These strategies have been associated with less toxicity than allogeneic HSCT but typically have inferior efficacy. Allogeneic HSCT exploits major and minor histocompatibility differences between the donor and recipient in order to recognize and eradicate malignancy. With the recognition that the immune system itself provides a basis for treating AML, immunotherapy continues to be an attractive modality to exploit in the treatment of this disease.

Is allogeneic transplantation really the best treatment for FLT3/ITD-positive acute myeloid leukemia? A systematic review

Fetal liver tyrosine kinase 3 (FLT3)-internal tandem duplications (ITDs) has been used as a powerful adverse prognostic indicator for acute myeloid leukemia (AML) in any age group. Evidence is mixed regarding the effects of allogeneic transplantation (allo-HSCT) in first complete remission (CR) for patients with FLT3/ITD AML. To fill this gap, this study provides a systematic review and meta-analysis of patients with FLT3/ITD AML receiving HSCT. A search of PubMed, Embase, and OVID yielded 1706 abstracts, two researchers screening the trials based on inclusion and exclusion criteria, and assessed the methodology quality independently. Meta-analysis showed that compared with chemotherapy, both allo-HSCT and autologous hematopoietic cell transplantation (auto-HSCT) can reduce the relapse rate (p < 0.01) and improve both the OS (p < 0.01) and DFS (p < 0.01). But when compared allo-HSCT with auto-HSCT, the OS (p = 0.27) and DFS (p = 0.19) have no statistical significance, and only the relapse indicator has statistical significance, p < 0.01. Based on the results, we can conclude that allo-HSCT is an efficient therapy approach for patients with FLT3/ITD AML. Chemotherapy cannot change the poor prognosis. Auto-HSCT can improve OS and DFS, but it cannot reduce the relapse rate.

Phase I trial of maintenance sorafenib after allogeneic hematopoietic stem cell transplantation for fms-like tyrosine kinase 3 internal tandem duplication acute myeloid leukemia

The fms-like tyrosine kinase 3 internal tandem duplication (FLT3-ITD) mutation is associated with a high relapse rate for patients with acute myeloid leukemia (AML) even after allogeneic hematopoietic stem cell transplantation (HSCT). Sorafenib is a tyrosine kinase inhibitor, which inhibits the FLT3 tyrosine kinase and has shown encouraging activity in FLT3-ITD AML. We conducted a phase I trial of maintenance sorafenib after HSCT in patients with FLT3-ITD AML (ClinicalTrials.govNCT01398501). Patients received a variety of conditioning regimens and graft sources. A dose escalation 3 + 3 cohort design was used to define the maximum tolerated dose (MTD), with an additional 10 patients treated at the MTD. Sorafenib was initiated between days 45 and 120 after HSCT and continued for 12 28-day cycles. Twenty-two patients were enrolled (status at HSCT: first complete remission [CR1], n = 16; second complete remission [CR2], n = 3; refractory, n = 3). The MTD was established at 400 mg twice daily with 1 dose-limiting toxicity (DLT) observed (pericardial effusion). Two patients died of transplantation-related causes, both unrelated to sorafenib. Two patients stopped sorafenib after relapse and 5 stopped because of attributable toxicities after the DLT period. Median follow-up for surviving patients is 16.7 months after HSCT (range, 8.1 to 35.0). There was 1 case of grade II acute graft-versus-host disease (GVHD) after starting sorafenib and the 12-month cumulative incidence of chronic GVHD was 38% (90% confidence interval [CI], 21% to 56%). For all patients, 1-year progression-free survival (PFS) was 85% (90% CI, 66% to 94%) and 1-year overall survival (OS) was 95% (90% CI, 79% to 99%) after HSCT. For patients in CR1/CR2 before HSCT (n = 19), 1-year PFS was 95% (90% CI, 76% to 99%) and 1-year OS was 100%, with only 1 patient who relapsed. Sorafenib is safe after HSCT for FLT3-ITD AML and merits further investigation for the prevention of relapse.

Differential impact of allelic ratio and insertion site in FLT3-ITD-positive AML with respect to allogeneic transplantation

The objective was to evaluate the prognostic and predictive impact of allelic ratio and insertion site (IS) of internal tandem duplications (ITDs), as well as concurrent gene mutations, with regard to postremission therapy in 323 patients with FLT3-ITD-positive acute myeloid leukemia (AML). Increasing FLT3-ITD allelic ratio (P = .004) and IS in the tyrosine kinase domain 1 (TKD1, P = .06) were associated with low complete remission (CR) rates. After postremission therapy including intensive chemotherapy (n = 121) or autologous hematopoietic stem cell transplantation (HSCT, n = 17), an allelic ratio ≥ 0.51 was associated with an unfavorable relapse-free (RFS, P = .0008) and overall survival (OS, P = .004); after allogeneic HSCT (n = 93), outcome was significantly improved in patients with a high allelic ratio (RFS, P = .02; OS, P = .03), whereas no benefit was seen in patients with a low allelic ratio (RFS, P = .38; OS, P = .64). Multivariable analyses revealed a high allelic ratio as a predictive factor for the beneficial effect of allogeneic HSCT; ITD IS in TKD1 remained an unfavorable factor, whereas no prognostic impact of concurrent gene mutations was observed. The clinical trials described herein were previously published or are registered as follows: AMLHD93 and AMLHD98A, previously published; AML SG 07-04, ClinicalTrials.gov identifier #NCT00151242.

Targeting FLT3 to treat leukemia

INTRODUCTION

Approximately 23% of acute myeloid leukemia (AML) patients younger than 60 years of age carry a mutation in the transmembrane domain of the FMS-like tyrosine kinase-3 (FLT3) gene (FLT3/internal tandem duplications [ITD]). In normal karyotype AML, the presence of a FLT3/ITD mutation is associated with poor prognosis, as mirrored by a high risk of relapse even after allogeneic stem cell transplantation. The poor prognostic impact along with the observation that FLT3 is frequently overexpressed in the majority of AML cases has formed the platform for the development of FLT3-targeted strategies. To date, several FLT3 kinase inhibitors have been investigated in preclinical and clinical studies. However, as of yet, none of the studied FLT3 inhibitors has received FDA approval for routine clinical use in AML. This is in part due to the 'off target' effects observed with most inhibitors when administered at concentrations needed to achieve sustained levels of FLT3 inhibition, which are required to exhibit substantial cytotoxic effects against leukemic blasts. Furthermore, the development of resistance mutations has emerged as a clinical issue posing a threat to successful FLT3 inhibitor therapy.

AREAS COVERED

In this review, the authors provide a brief summary of FLT3 inhibitors investigated thus far, and discuss current treatment approaches and strategies how to best incorporate FLT3 tyrosine kinase inhibitors (TKIs) into therapy.

EXPERT OPINION

The combination of a FLT3 inhibitor with conventional chemotherapeutic regimens, epigenetic modifiers or inhibitors of FLT3 downstream and collateral effectors has emerged as a promising strategy to improve treatment outcome. The future of a tailored, molecular-based treatment approach for FLT3-mutated AML demands novel clinical trial concepts based on harmonized and aligned research goals between clinical and research centers and industry.

Role of genotype-based approach in the clinical management of adult acute myeloid leukemia with normal cytogenetics

Acute myeloid leukemia (AML) is the most common form of acute leukemia affecting adults. Although it is a complex disease driven by numerous genetic and epigenetic abnormalities, nearly 50% of patients exhibit a normal karyotype (CN-AML) with an intermediate cytogenetic risk. However, a widespread genomic analysis has recently shown the recurrence of genomic aberrations in this category (mutations of FLT3, CEBPA, NPM1, RUNX1, TET2, IDH1/2, DNMT3A, ASXL1, MLL and WT1) thus revealing its marked genomic heterogeneity. In this perspective, a global gene expression analysis of AML patients provides an independent prognostic marker to categorize each patient into clinic-pathologic subgroups based on its molecular genetic defects. Consistently such classification, taking into account the uniqueness of each AML patient, furnishes an individualized treatment approach leading a step closer to personalized medicine. Overall the genome-wide analysis of AML patients, by providing novel insights into biology of this tumor, furnishes accurate prognostic markers as well as useful tools for selecting the most appropriate treatment option. Moreover it provides novel therapeutic targets useful to enhance efficacy of the current anti-AML therapeutics. Here we describe the prognostic relevance of such new genetic data and discuss how this approach can be used to improve survival and treatment of AML patients.

Hematopoietic transplantation for acute myeloid leukemia with internal tandem duplication of FLT3 gene (FLT3/ITD)

PURPOSE OF REVIEW

Patients with acute myeloid leukemia (AML) traditionally classified as having an intermediate cytogenetic risk [mostly cytogenetically normal AML (CN-AML)] really include a significant proportion of cases with a poor outcome. This is based on the molecular findings at diagnosis, mainly the presence of internal tandem duplication in the FMS-like tyrosine kinase 3 gene(s) (FLT3/ITD). Optimal postremission therapy for these high-risk molecular cases is not well established; as the prognosis is adverse hematopoietic cell transplantation (HCT), mainly allogeneic HCT (allo-HCT), is the most widely accepted strategy.

RECENT FINDINGS

As a rule, patients with FLT3/ITD have a poor outcome with conventional chemotherapy alone. Only patients with an associated nucleophosmin 1 (NPM1) mutation and those with a low mutated-to-wild-type allelic ratio of FLT3/ITD have less unfavorable outcome. Most studies show an advantage of allo-HCT in first complete remission (CR1), with higher 3-5 year disease-free survival and lower relapse risk than with chemotherapy or autologous transplantation (auto-HCT). Regarding allo-HCT proceeding early after reaching CR1 seems to improve survival, rather than after several courses of consolidation chemotherapy.

SUMMARY

Patients with intermediate-risk cytogenetics AML and FLT3/ITD, especially NPM1-wild cases and those NPM1 mutated with a high allelic ratio, should proceed to allo-HCT if possible early after achieving CR1.

FLT3 tyrosine kinase inhibitors in acute myeloid leukemia: clinical implications and limitations

Internal tandem duplications of the FMS-like tyrosine kinase 3 (FLT3) gene are one of the most frequent gene mutations in acute myeloid leukemia (AML) and are associated with poor clinical outcome. The remission rate is high with intensive chemotherapy, but most patients eventually relapse. During the last decade, FLT3 mutations have emerged as an attractive target for a molecularly specific treatment strategy. Targeting FLT3 receptor tyrosine kinases in AML has shown encouraging results in the treatment of FLT3 mutated AML, but in most patients responses are incomplete and not sustained. Newer, more specific compounds seem to have a higher potency and selectivity against FLT3. During therapy with FLT3 tyrosine kinase inhibitors (TKIs) the induction of acquired resistance has emerged as a clinical problem. Therefore, optimization of the targeted therapy and potential treatment options to overcome resistance is currently the focus of clinical research. In this review we discuss the use and limitations of TKIs as a therapeutic strategy for the treatment of FLT3 mutated AML, including mechanisms of resistance to TKIs as well as possible novel strategies to improve FLT3 inhibitor therapy.

FLT3 mutations in acute myeloid leukemia: what is the best approach in 2013?

Patients with acute myeloid leukemia who harbor an FMS-like tyrosine kinase 3 (FLT3) mutation present several dilemmas for the clinician. The results of an FLT3 mutation test, which can be influenced by several variables, need to be interpreted according to the clinical setting and there is a need for internationally standardized FLT3 mutation assays. Because of the lack of prospective studies, the role of allogeneic transplantation as consolidation therapy is still somewhat controversial, but the preponderance of evidence suggests that transplantation in first remission, if possible, is probably the best option. Clinically useful FLT3 inhibitors are hopefully on the near horizon and are being studied in the context of current treatment paradigms.

Mutational landscape of AML with normal cytogenetics: biological and clinical implications

Acute myeloid leukemia (AML) is a molecularly heterogeneous disease. Based on cytogenetics and FISH, AML patients are stratified into three major risk categories: favourable, intermediate and unfavourable. However, prognostic stratification and treatment decision for the intermediate risk category, that mostly comprises AML patients with normal cytogenetics (CN-AML), has been difficult due to the clinical heterogeneity and scarce knowledge of the molecular alterations underlying this large AML subgroup. During the past decade, the identification of several mutations associated with CN-AML has resulted into important advances in the AML field. In this review, we address the biological features of the main mutations associated with CN-AML and the impact of next generation sequencing studies in expanding our knowledge of the molecular landscape of CN-AML. In addition, we outline the prognostic value of mutations for risk stratification of CN-AML patients and discuss the potential of mutations discovery process for developing new molecular targeted therapies.