Midostaurin in patients with acute myeloid leukemia and FLT3-TKD mutations: a subanalysis from the RATIFY trial

Tracking Response and Resistance in Acute Myeloid Leukemia through Single-Cell DNA Sequencing Helps Uncover New Therapeutic Targets

Acute myeloid leukemia (AML) is an aggressive hematologic neoplasia with a complex polyclonal architecture. Among driver lesions, those involving the FLT3 gene represent the most frequent mutations identified at diagnosis. The development of tyrosine kinase inhibitors (TKIs) has improved the clinical outcomes of FLT3-mutated patients (Pt). However, overcoming resistance to these drugs remains a challenge. To unravel the molecular mechanisms underlying therapy resistance and clonal selection, we conducted a longitudinal analysis using a single-cell DNA sequencing approach (MissionBioTapestri® platform, San Francisco, CA, USA) in two patients with FLT3-mutated AML. To this end, samples were collected at the time of diagnosis, during TKI therapy, and at relapse or complete remission. For Pt #1, disease resistance was associated with clonal expansion of minor clones, and 2nd line TKI therapy with gilteritinib provided a proliferative advantage to the clones carrying NRAS and KIT mutations, thereby responsible for relapse. In Pt #2, clonal architecture was less complex, and 1st line TKI therapy with midostaurin was able to eradicate the leukemic clones. Our results corroborate previous findings about clonal selection driven by TKIs, highlighting the importance of a deeper characterization of individual clonal architectures for choosing the best treatment plan for personalized approaches aimed at optimizing outcomes.

Perspectives and challenges of small molecule inhibitor therapy for FLT3-mutated acute myeloid leukemia

Acute myeloid leukemia (AML) is a heterogeneous clonal disease characterized overall by an aggressive clinical course. The underlying genetic abnormalities present in leukemic cells contribute significantly to the AML phenotype. Mutations in FMS-like tyrosine kinase 3 (FLT3) are one of the most common genetic abnormalities identified in AML, and the presence of these mutations strongly influences disease presentation and negatively impacts prognosis. Since mutations in FLT3 were identified in AML, they have been recognized as a valid therapeutic target resulting in decades of research to develop effective small molecule inhibitor treatment that could improve outcome for these patients. Despite the approval of several FLT3 inhibitors over the last couple of years, the treatment of patients with FLT3-mutated AML remains challenging and many questions still need to be addressed. This review will provide an up-to-date overview of our current understanding of FLT3-mutated AML and discuss what the current status is of the available FLT3 inhibitors for the day-to-day management of this aggressive disease.

The importance of protein domain mutations in cancer therapy

Cancer is a complex disease that is caused by multiple genetic factors. Researchers have been studying protein domain mutations to understand how they affect the progression and treatment of cancer. These mutations can significantly impact the development and spread of cancer by changing the protein structure, function, and signalling pathways. As a result, there is a growing interest in how these mutations can be used as prognostic indicators for cancer prognosis. Recent studies have shown that protein domain mutations can provide valuable information about the severity of the disease and the patient's response to treatment. They may also be used to predict the response and resistance to targeted therapy in cancer treatment. The clinical implications of protein domain mutations in cancer are significant, and they are regarded as essential biomarkers in oncology. However, additional techniques and approaches are required to characterize changes in protein domains and predict their functional effects. Machine learning and other computational tools offer promising solutions to this challenge, enabling the prediction of the impact of mutations on protein structure and function. Such predictions can aid in the clinical interpretation of genetic information. Furthermore, the development of genome editing tools like CRISPR/Cas9 has made it possible to validate the functional significance of mutants more efficiently and accurately. In conclusion, protein domain mutations hold great promise as prognostic and predictive biomarkers in cancer. Overall, considerable research is still needed to better define genetic and molecular heterogeneity and to resolve the challenges that remain, so that their full potential can be realized.

Hypomethylating agent monotherapy in core binding factor acute myeloid leukemia: a French multicentric retrospective study

Very few data are available about hypomethylating agent (HMA) efficiency in core binding factor acute myeloid leukemias (CBF-AML). Our main objective was to evaluate the efficacy and safety of HMA in the specific subset of CBF-AML. Here, we report the results of a multicenter retrospective French study about efficacy of HMA monotherapy, used frontline or for R/R CBF-AML. Forty-nine patients were included, and received a median of 5 courses of azacitidine (n = 46) or decitabine (n = 3). ORR was 49% for the whole cohort with a median time to response of 112 days. After a median follow-up of 72.3 months, median OS for the total cohort was 10.6 months. In multivariate analysis, hematological relapse of CBF-AML at HMA initiation was significantly associated with a poorer OS (HR: 2.13; 95%CI: 1.04-4.36; p = 0.038). Responders had a significantly improved OS (1-year OS: 75%) compared to non-responders (1-year OS: 15.3%; p < 0.0001). Hematological improvement occurred for respectively 28%, 33% and 48% for patients who were red blood cell or platelet transfusion-dependent, or who experienced grade 3/4 neutropenia at HMA initiation. Adverse events were consistent with the known safety profile of HMA. Our study highlights that HMA is a well-tolerated therapeutic option with moderate clinical activity for R/R CBF-AML and for patients who cannot handle intensive chemotherapy.

Rare Hematologic Malignancies and Pre-Leukemic Entities in Children and Adolescents Young Adults

There are a variety of rare hematologic malignancies and germline predispositions syndromes that occur in children and adolescent young adults (AYAs). These entities are important to recognize, as an accurate diagnosis is essential for risk assessment, prognostication, and treatment. This descriptive review summarizes rare hematologic malignancies, myelodysplastic neoplasms, and germline predispositions syndromes that occur in children and AYAs. We discuss the unique biology, characteristic genomic aberrations, rare presentations, diagnostic challenges, novel treatments, and outcomes associated with these rare entities.

Therapeutic biomarkers in acute myeloid leukemia: functional and genomic approaches

Acute myeloid leukemia (AML) is clinically and genetically a heterogeneous disease characterized by clonal expansion of abnormal hematopoietic progenitors. Genomic approaches to precision medicine have been implemented to direct targeted therapy for subgroups of AML patients, for instance, IDH inhibitors for IDH1/2 mutated patients, and FLT3 inhibitors with FLT3 mutated patients. While next generation sequencing for genetic mutations has improved treatment outcomes, only a fraction of AML patients benefit due to the low prevalence of actionable targets. In recent years, the adoption of newer functional technologies for quantitative phenotypic analysis and patient-derived avatar models has strengthened the potential for generalized functional precision medicine approach. However, functional approach requires robust standardization for multiple variables such as functional parameters, time of drug exposure and drug concentration for making in vitro predictions. In this review, we first summarize genomic and functional therapeutic biomarkers adopted for AML therapy, followed by challenges associated with these approaches, and finally, the future strategies to enhance the implementation of precision medicine.

Optimal Post-Remission Consolidation Therapy in Patients with AML

BACKGROUND

Despite recent advances, 40-85% of patients with acute myeloid leukaemia (AML) achieve complete remission after intensive chemotherapy. However, without optimal treatment after remission, the risk of relapse remains high.

SUMMARY

A variable number of consolidation cycles consisting of intermediate doses of cytarabine are the most commonly used regimens in low-intermediate-risk AML, while patients at higher risk of relapse should consolidate response by proceeding to HSCT. Different post-consolidation (maintenance therapies) have demonstrated their benefit in prolonging relapse-free survival, and others are still under investigation. Careful consideration should be given to which patients benefit most from each of these interventions, considering that the risk of relapse is dynamic.

KEY MESSAGES

Patients consolidated with chemotherapy should receive either 2 courses of HDAC or no more than 3-4 cycles of IDAC with dose reduction in patients over 60 years. Patients with mutated FLT3 AML benefit from post-consolidation maintenance with FLT3 inhibitors, and selected patients not fit for adequate consolidation may benefit from CC-468 maintenance. Patients at higher risk of relapse should proceed to allogeneic SCT as soon as possible, opting for a more intensive conditioning in patients younger than 55 years. However, autologous HSCT may still have role in favourable-risk MRD-negative AML. Multiple treatment options targeting MRD are emerging, either as definitive treatment or as a bridge to allogeneic transplantation, and are likely to become increasingly relevant.

Midostaurin in addition to intensive chemotherapy in acute myeloid leukemia with t(8;21) and KIT and/or FLT3- ITD mutations: results of the SAL MIDOKIT trial

Not available.

How acute myeloid leukemia (AML) escapes from FMS-related tyrosine kinase 3 (FLT3) inhibitors? Still an overrated complication?

FMS-related tyrosine kinase 3 (FLT3) mutations, present in about 25%-30% of acute myeloid leukemia (AML) patients, constitute one of the most frequently detected mutations in these patients. The binding of FLT3L to FLT3 activates the phosphatidylinositol 3-kinase (PI3K) and RAS pathways, producing increased cell proliferation and the inhibition of apoptosis. Two types of FLT3 mutations exist: FLT3-ITD and FLT3-TKD (point mutations in D835 and I836 or deletion of codon I836). A class of drugs, tyrosine-kinase inhibitors (TKI), targeting mutated FLT3, is already available with 1^st and 2^nd generation molecules, but only midostaurin and gilteritinib are currently approved. However, the emergence of resistance or the selection of clones not responding to FLT3 inhibitors has become an important clinical dilemma, as the duration of clinical responses is generally limited to a few months. This review analyzes the insights into mechanisms of resistance to TKI and poses a particular view on the clinical relevance of this phenomenon. Has resistance been overlooked? Indeed, FLT3 inhibitors have significantly contributed to reducing the negative impact of FLT3 mutations on the prognosis of AML patients who are no longer considered at high risk by the European LeukemiaNet (ELN) 2022. Finally, several ongoing efforts to overcome resistance to FLT3-inhibitors will be presented: new generation FLT3 inhibitors in monotherapy or combined with standard chemotherapy, hypomethylating drugs, or IDH1/2 inhibitors, Bcl2 inhibitors; novel anti-human FLT3 monoclonal antibodies (e.g., FLT3/CD3 bispecific antibodies); FLT3-CAR T-cells; CDK4/6 kinase inhibitor (e.g., palbociclib).

Epigenomic machinery regulating pediatric AML: clonal expansion mechanisms, therapies, and future perspectives

Acute myeloid leukemia (AML) is a heterogeneous disease with a genetic, epigenetic, and transcriptional etiology mainly presenting somatic and germline abnormalities. AML incidence rises with age but can also occur during childhood. Pediatric AML (pAML) accounts for 15-20% of all pediatric leukemias and differs considerably from adult AML. Next-generation sequencing technologies have enabled the research community to "paint" the genomic and epigenomic landscape in order to identify pathology-associated mutations and other prognostic biomarkers in pAML. Although current treatments have improved the prognosis for pAML, chemoresistance, recurrence, and refractory disease remain major challenges. In particular, pAML relapse is commonly caused by leukemia stem cells that resist therapy. Marked patient-to-patient heterogeneity is likely the primary reason why the same treatment is successful for some patients but, at best, only partially effective for others. Accumulating evidence indicates that patient-specific clonal composition impinges significantly on cellular processes, such as gene regulation and metabolism. Although our understanding of metabolism in pAML is still in its infancy, greater insights into these processes and their (epigenetic) modulation may pave the way toward novel treatment options. In this review, we summarize current knowledge on the function of genetic and epigenetic (mis)regulation in pAML, including metabolic features observed in the disease. Specifically, we describe how (epi)genetic machinery can affect chromatin status during hematopoiesis, leading to an altered metabolic profile, and focus on the potential value of targeting epigenetic abnormalities in precision and combination therapy for pAML. We also discuss the possibility of using alternative epidrug-based therapeutic approaches that are already in clinical practice, either alone as adjuvant treatments and/or in combination with other drugs.

An Update on FLT3 in Acute Myeloid Leukemia: Pathophysiology and Therapeutic Landscape

PURPOSE OF REVIEW

This review aims to summarize the pathophysiology, clinical presentation, and management of acute myeloid leukemia (AML) with FMS-like tyrosine kinase-3 (FLT3) mutations.

RECENT FINDINGS

The recent European Leukemia Net (ELN2022) recommendations re-classified AML with FLT3 internal tandem duplications (FLT3-ITD) as intermediate risk regardless of Nucleophosmin 1 (NPM1) co-mutation or the FLT3 allelic ratio. Allogeneic hematopoietic cell transplantation (alloHCT) is now recommended for all eligible patients with FLT3-ITD AML. This review outlines the role of FLT3 inhibitors in induction and consolidation, as well as for post-alloHCT maintenance. It outlines the unique challenges and advantages of assessing FLT3 measurable residual disease (MRD) and discusses the pre-clinical basis for the combination of FLT3 and menin inhibitors. And, for the older or unfit patient ineligible for upfront intensive chemotherapy, it discusses the recent clinical trials incorporating FLT3 inhibitors into azacytidine- and venetoclax-based regimens. Finally, it proposes a rational sequential approach for integrating FLT3 inhibitors into less intensive regimens, with a focus on improved tolerability in the older and unfit patient population. The management of AML with FLT3 mutation remains a challenge in clinical practice. This review provides an update on the pathophysiology and therapeutic landscape of FLT3 AML, as well as a clinical management framework for managing the older or unfit patient ineligible for intensive chemotherapy.

Update on current treatments for adult acute myeloid leukemia: to treat acute myeloid leukemia intensively or non-intensively? That is the question

For several decades, the treatment for acute myeloid leukemia (AML) has been a dichotomous choice between intensive chemotherapy strategies with curative intent and non-intensive options including supportive care. Patients' age and fitness, as well as comorbidities, primarily influenced this choice. However, the therapeutic armamentarium is evolving, so that there are highly effective and increasingly specific drugs, fitting the mutational profile of a patient's leukemia. There is now a spectrum of treatment options that are less intense and can be administered in an outpatient setting and to a substantial extent are equally or even more effective than standard intensive therapy. We are, therefore, witnessing a radical change in the treatment landscape of AML. In this review, we examine the current treatment options for patients with AML, considering the molecular spectrum of the disease on the background of patient-related factors.

The evolution of targeted therapy in pediatric AML: gemtuzumab ozogamicin, FLT3/IDH/BCL2 inhibitors, and other therapies

Despite the maximum intensification of chemotherapy and the increased use of hematopoietic stem cell transplantation (HCT) in pediatric patients with acute myeloid leukemia (AML), nearly 40% of patients still experience relapse, and cure in this setting remains a significant challenge. Recent improvements in AML characterization, including advances in flow cytometry and comprehensive genomic sequencing, have led to a better understanding of AML biology and the identification of multiple potential therapeutic targets. Novel agents targeting genomic lesions, cell surface antigens, and other mechanisms that permit oncogenesis or immune escape are being incorporated into current treatment strategies or are under investigation in efforts to improve outcomes and decrease the toxicities and late effects associated with traditional intensive chemotherapeutic and HCT treatment. However, multiple challenges still exist, including the biologic and immunophenotypic heterogeneity of childhood AML, the differences in underlying biology as compared to adult AML, and the significant potential for on-target/off-tumor toxicity associated with therapies directed at targets common to myeloid cells, both leukemic and normal. This article reviews the current landscape of genomic and cell surface targets for children with AML with a focus on the currently available targeted therapeutic agents, those in active clinical investigation, and those still in development.

Therapeutic Targeting of FLT3 in Acute Myeloid Leukemia: Current Status and Novel Approaches

FMS-like tyrosine kinase 3 (FLT3) is mutated in approximately 30% of acute myeloid leukemia (AML) patients. The presence of FLT3-ITD (internal tandem duplication, 20-25%) mutation and, to a lesser extent, FLT3-TKD (tyrosine kinase domain, 5-10%) mutation is associated with poorer diagnosis and therapy response since the leukemic cells become hyperproliferative and resistant to apoptosis after continuous activation of FLT3 signaling. Targeting FLT3 has been the focus of many pre-clinical and clinical studies. Hence, many small-molecule FLT3 inhibitors (FLT3is) have been developed, some of which are approved such as midostaurin and gilteritinib to be used in different clinical settings, either in combination with chemotherapy or alone. However, many questions regarding the best treatment strategy remain to be answered. On the other hand, various FLT3-dependent and -independent resistance mechanisms could be evolved during FLT3i therapy which limit their clinical impact. Therefore, identifying molecular mechanisms of resistance and developing novel strategies to overcome this obstacle is a current interest in the field. In this review, recent studies of approved FLT3i and knowledge about major resistance mechanisms of clinically approved FLT3i's will be discussed together with novel treatment approaches such as designing novel FLT3i and dual FLT3i and combination strategies including approved FLT3i plus small-molecule agents targeting altered molecules in the resistant cells to abrogate resistance. Moreover, how to choose an appropriate FLT3i for the patients will be summarized based on what is currently known from available clinical data. In addition, strategies beyond FLT3i's including immunotherapeutics, small-molecule FLT3 degraders, and flavonoids will be summarized to highlight potential alternatives in FLT3-mutated AML therapy.

Prognostic impact of NPM1 and FLT3 mutations in patients with AML in first remission treated with oral azacitidine

The randomized, placebo-controlled, phase 3 QUAZAR AML-001 trial (ClinicalTrials.gov identifier: NCT01757535) evaluated oral azacitidine (Oral-AZA) in patients with acute myeloid leukemia (AML) in first remission after intensive chemotherapy (IC) who were not candidates for hematopoietic stem cell transplantation. Eligible patients were randomized 1:1 to Oral-AZA 300 mg or placebo for 14 days per 28-day cycle. We evaluated relapse-free survival (RFS) and overall survival (OS) in patient subgroups defined by NPM1 and FLT3 mutational status at AML diagnosis and whether survival outcomes in these subgroups were influenced by presence of post-IC measurable residual disease (MRD). Gene mutations at diagnosis were collected from patient case report forms; MRD was determined centrally by multiparameter flow cytometry. Overall, 469 of 472 randomized patients (99.4%) had available mutational data; 137 patients (29.2%) had NPM1 mutations (NPM1mut), 66 patients (14.1%) had FLT3 mutations (FLT3mut; with internal tandem duplications [ITD], tyrosine kinase domain mutations [TKDmut], or both), and 30 patients (6.4%) had NPM1mut and FLT3-ITD at diagnosis. Among patients with NPM1mut, OS and RFS were improved with Oral-AZA by 37% (hazard ratio [HR], 0.63; 95% confidence interval [CI], 0.41-0.98) and 45% (HR, 0.55; 95% CI, 0.35-0.84), respectively, vs placebo. Median OS was improved numerically with Oral-AZA among patients with NPM1mut whether without MRD (48.6 months vs 31.4 months with placebo) or with MRD (46.1 months vs 10.0 months with placebo) post-IC. Among patients with FLT3mut, Oral-AZA improved OS and RFS by 37% (HR, 0.63; 95% CI, 0.35-1.12) and 49% (HR, 0.51; 95% CI, 0.27-0.95), respectively, vs placebo. Median OS with Oral-AZA vs placebo was 28.2 months vs 16.2 months, respectively, for patients with FLT3mut and without MRD and 24.0 months vs 8.0 months for patients with FLT3mut and MRD. In multivariate analyses, Oral-AZA significantly improved survival independent of NPM1 or FLT3 mutational status, cytogenetic risk, or post-IC MRD status.

Prognostic Relevance of NPM1 and FLT3 Mutations in Acute Myeloid Leukaemia, Longterm Follow-Up-A Single Center Experience

The prognosis of acute myeloid leukemia depends on genetic aberrations, particularly NPM1 and FLT3-ITD mutations. The targeted drugs’ availability has renewed interest in FLT3 mutations, but the impact of these genetic alterations using these treatments is yet to be confirmed. Our objective was to evaluate the results obtained with the intensified NILG-AML 01/00 protocol (ClinicalTrials.gov Identifier: NCT 00400673) in 171 unselected patients (median age, 54.5 years, range 15−74) carrying the FLT3 (ITD or TKD) and/or NPM1 mutations. The CR rate and 5-y survival were 88.3% and 58% +/− 4, respectively, significantly higher in the NPM1-mutated (CR 93.9%, p: 0.0001; survival 71% +/− 6, p: 0.0017, respectively). In isolated ITD patients, the CR was lower (66.7%, p: 0.0009), and the 3 years-relapse-free survival worse (24%, p: <0.0002). The presence of ITD, irrespective of the allelic ratio, or TKD mutation, did not significantly affect the survival or relapse-free survival among the NPM1-co-mutated patients. Our data indicate that a high dose of ARAC plus idarubicin consolidation exerts a strong anti-leukemic effect in NPM1-mutated patients both with the FLT3 wild-type and mutated AML, while in the NPM1 wild-type and FLT3-mutated, the therapeutic effect remains unsatisfactory. New strategies incorporating target therapy with second-generation inhibitors will improve these results and their addition to this aggressive chemotherapeutic program merits testing.

"FLipping" the Story: FLT3-Mutated Acute Myeloid Leukemia and the Evolving Role of FLT3 Inhibitors

The treatment of many types of cancers, including acute myeloid leukemia (AML), has been revolutionized by the development of therapeutics targeted at crucial molecular drivers of oncogenesis. In contrast to broad, relatively indiscriminate conventional chemotherapy, these targeted agents precisely disrupt key pathways within cancer cells. FMS-like tyrosine kinase 3 (FLT3)-encoding a critical regulator of hematopoiesis-is the most frequently mutated gene in patients with AML, and these mutations herald reduced survival and increased relapse in these patients. Approximately 30% of newly diagnosed AML carries an FLT3 mutation; of these, approximately three-quarters are internal tandem duplication (ITD) mutations, and the remainder are tyrosine kinase domain (TKD) mutations. In contrast to its usual, tightly controlled expression, FLT3-ITD mutants allow constitutive, "run-away" activation of a large number of key downstream pathways which promote cellular proliferation and survival. Targeted inhibition of FLT3 is, therefore, a promising therapeutic avenue. In April 2017, midostaurin became both the first FLT3 inhibitor and the first targeted therapy of any kind in AML to be approved by the US FDA. The use of FLT3 inhibitors has continued to grow as clinical trials continue to demonstrate the efficacy of this class of agents, with an expanding number available for use as both experimental standard-of-care usage. This review examines the biology of FLT3 and its downstream pathways, the mechanism of FLT3 inhibition, the development of the FLT3 inhibitors as a class and uses of the agents currently available clinically, and the mechanisms by which resistance to FLT3 inhibition may both develop and be overcome.

Molecular-Targeted Therapy of Pediatric Acute Myeloid Leukemia

Acute myeloid leukemia (AML) accounts for approximately 15–20% of all childhood leukemia cases. The overall survival of children with acute myeloid leukemia does not exceed 82%, and the 5-year event-free survival rates range from 46% to 69%. Such suboptimal outcomes are the result of numerous mutations and epigenetic changes occurring in this disease that adversely affect the susceptibility to treatment and relapse rate. We describe various molecular-targeted therapies that have been developed in recent years to meet these challenges and were or are currently being studied in clinical trials. First introduced in adult AML, novel forms of treatment are slowly beginning to change the therapeutic approach to pediatric AML. Despite promising results of clinical trials investigating new drugs, further clinical studies involving greater numbers of pediatric patients are still needed to improve the outcomes in childhood AML.

The FLT3 Y842D mutation may be highly sensitive to midostaurin: a case report

A Y842D mutation within the activation loop of fms-like tyrosine kinase 3 (FLT3) has been shown to confer strong resistance to sorafenib in vitro. Whether this type of mutation exerts clinically significant effects in patients with acute myeloid leukaemia (AML) remains unclear. Here, a novel Y842D activating mutation within the kinase domain of FLT3, in a pregnant patient with de novo hyperleucocyte acute myeloid leukaemia, is described. Following induction failure with standard dose idarubicin and cytarabine (IA), the patient received re-induction combined with midostaurin, a promising agent targeting mutant-FLT3, and IA regimen. Fortunately, morphological remission was achieved. During the period of midostaurin treatment, the patient exhibited a symptom that was characteristic of differentiation syndrome, which disappeared following treatment with methylprednisolone. The present case revealed that Y842D, an uncommon activating mutation in the activation loop of FLT3, may be a midostaurin-sensitive mutation type in patients with acute myeloid leukaemia.

Increasing Role of Targeted Immunotherapies in the Treatment of AML

Acute myeloid leukemia (AML) is the most common acute leukemia in adults. The standard of care in medically and physically fit patients is intensive induction therapy. The majority of these intensively treated patients achieve a complete remission. However, a high number of these patients will experience relapse. In patients older than 60 years, the results are even worse. Therefore, new therapeutic approaches are desperately needed. One promising approach in high-risk leukemia to prevent relapse is the induction of the immune system simultaneously or after reduction of the initial tumor burden. Different immunotherapeutic approaches such as allogenic stem cell transplantation or donor lymphocyte infusions are already standard therapies, but other options for AML treatment are in the pipeline. Moreover, the therapeutic landscape in AML is rapidly changing, and in the last years, a number of immunogenic targets structures eligible for specific therapy, risk assessment or evaluation of disease course were determined. For example, leukemia-associated antigens (LAA) showed to be critical as biomarkers of disease state and survival, as well as markers of minimal residual disease (MRD). Yet many mechanisms and properties are still insufficiently understood, which also represents a great potential for this form of therapy. Therefore, targeted therapy as immunotherapy could turn into an efficient tool to clear residual disease, improve the outcome of AML patients and reduce the relapse risk. In this review, established but also emerging immunotherapeutic approaches for AML patients will be discussed.

Which FLT3 Inhibitor for Treatment of AML?

OPINION STATEMENT

Treatment options in acute myeloid leukemia (AML) have improved significantly over the last decade with better understanding of disease biology and availability of a multitude of targeted therapies. The use of FLT3 inhibitors (FLT3i) in FLT3-mutated (FLT3^mut) AML is one such development; however, the clinical decisions that govern their use and dictate the choice of the FLT3i are evolving. Midostaurin and gilteritinib are FDA-approved in specific situations; however, available data from clinical trials also shed light on the utility of sorafenib maintenance post-allogeneic stem cell transplantation (allo-SCT) and quizartinib as part of combination therapy in FLT3^mut AML. The knowledge of the patient's concurrent myeloid mutations, type of FLT3 mutation, prior FLT3i use, and eligibility for allo-SCT helps to refine the choice of FLT3i. Data from ongoing studies will further precisely define their use and help in making more informed choices. Despite improvements in FLT3i therapy, the definitive aim is to enable the eligible patient with FLT3^mut AML (esp. ITD) to proceed to allo-SCT with regimens containing FLT3i incorporated prior to SCT and as maintenance after SCT.

A review of FLT3 inhibitors in acute myeloid leukemia

FLT3 mutations are the most common genetic aberrations found in acute myeloid leukemia (AML) and associated with poor prognosis. Since the discovery of FLT3 mutations and their prognostic implications, multiple FLT3-targeted molecules have been evaluated. Midostaurin is approved in the U.S. and Europe for newly diagnosed FLT3 mutated AML in combination with standard induction and consolidation chemotherapy based on data from the RATIFY study. Gilteritinib is approved for relapsed or refractory FLT3 mutated AML as monotherapy based on the ADMIRAL study. Although significant progress has been made in the treatment of AML with FLT3-targeting, many challenges remain. Several drug resistance mechanisms have been identified, including clonal selection, stromal protection, FLT3-associated mutations, and off-target mutations. The benefit of FLT3 inhibitor maintenance therapy, either post-chemotherapy or post-transplant, remains controversial, although several studies are ongoing.

Genomic landscape of patients with FLT3-mutated acute myeloid leukemia (AML) treated within the CALGB 10603/RATIFY trial

The aim of this study was to characterize the mutational landscape of patients with FLT3-mutated acute myeloid leukemia (AML) treated within the randomized CALGB 10603/RATIFY trial evaluating intensive chemotherapy plus the multi-kinase inhibitor midostaurin versus placebo. We performed sequencing of 262 genes in 475 patients: mutations occurring concurrently with the FLT3-mutation were most frequent in NPM1 (61%), DNMT3A (39%), WT1 (21%), TET2 (12%), NRAS (11%), RUNX1 (11%), PTPN11 (10%), and ASXL1 (8%) genes. To assess effects of clinical and genetic features and their possible interactions, we fitted random survival forests and interpreted the resulting variable importance. Highest prognostic impact was found for WT1 and NPM1 mutations, followed by white blood cell count, FLT3 mutation type (internal tandem duplications vs. tyrosine kinase domain mutations), treatment (midostaurin vs. placebo), ASXL1 mutation, and ECOG performance status. When evaluating two-fold variable combinations the most striking effects were found for WT1:NPM1 (with NPM1 mutation abrogating the negative effect of WT1 mutation), and for WT1:treatment (with midostaurin exerting a beneficial effect in WT1-mutated AML). This targeted gene sequencing study provides important, novel insights into the genomic background of FLT3-mutated AML including the prognostic impact of co-mutations, specific gene-gene interactions, and possible treatment effects of midostaurin.

Management of Acute Myeloid Leukemia: Current Treatment Options and Future Perspectives

Treatment of acute myeloid leukemia (AML) has improved in recent years and several new therapeutic options have been approved. Most of them include mutation-specific approaches (e.g., gilteritinib for AML patients with activating FLT3 mutations), or are restricted to such defined AML subgroups, such as AML-MRC (AML with myeloid-related changes) or therapy-related AML (CPX-351). With this review, we aim to present a comprehensive overview of current AML therapy according to the evolved spectrum of recently approved treatment strategies. We address several aspects of combined epigenetic therapy with the BCL-2 inhibitor venetoclax and provide insight into mechanisms of resistance towards venetoclax-based regimens, and how primary or secondary resistance might be circumvented. Furthermore, a detailed overview on the current status of AML immunotherapy, describing promising concepts, is provided. This review focuses on clinically important aspects of current and future concepts of AML treatment, but will also present the molecular background of distinct targeted therapies, to understand the development and challenges of clinical trials ongoing in AML patients.

Prevalence and Clinical Outcome of FMS-Like Tyrosine Kinase Mutations Among Patients With Core Binding Factor-Acute Myeloid Leukemia: Systematic Review and Meta-Analysis

BACKGROUND

Core binding factor acute myeloid leukemia (CBF-AML) belongs to favorable risk group in AML. However, approximately 50% of patients with CBF-AML remain incurable and their outcomes are also determined by the various co-occurring mutations. Though, FMS-like tyrosine kinase-3(FLT3) mutation in AML is associated with poor survival, the prevalence and prognostic significance of FLT3 mutations among CBF-AML is unknown.

PATIENTS AND METHODS

We performed a systematic review and meta-analysis to assess the prevalence of FLT3 mutations (ITD and TKD) among patients with CBF-AML. The pooled prevalence of FLT3 mutations was estimated for patients with CBF-AML, t(8;21) and Inv(16). Pooled odds ratio was calculated to compare the prevalence of various FLT3 mutations within the 2 subsets of CBF-AML. A random effects model was adopted for analysis when heterogenicity existed (P_{heterogenicity}< 0.05 or I² > 50%). Otherwise, a fixed effects model was used.

RESULTS

The pooled prevalence of any FLT3 mutations among patients with CBF-AML was available from 18 studies and was 13% (95% CI: 10%-16%; I² = 79%). Comparison of prevalence of FLT3 mutations between the 2 subgroups of CBF-AML showed that patients with t(8;21) had a higher prevalence of FLT3-ITD [pooled odds ratio(OR): 2.23 (95% CI:1.41-3.53, P < .01)] and lower prevalence of FLT3-TKD [pooled OR: 0.29 (95% CI:0.19-0.44; P < .01)] compared to patients with Inv(16). Additionally, we have discussed the prognostic significance of FLT3 mutations in CBF-AML patients.

CONCLUSION

The prevalence of FLT3-TKD mutation was commoner among Inv(16) AML while FLT3-ITD mutation was commoner among t(8;21) AML. Uniform reporting of outcomes is essential to understand the prognostic significance of FLT3 mutations among CBF-AML.

Towards precision medicine for AML

With rapid advances in sequencing technologies, tremendous progress has been made in understanding the molecular pathogenesis of acute myeloid leukaemia (AML), thus revealing enormous genetic and clonal heterogeneity, and paving the way for precision medicine approaches. The successful development of precision medicine for patients with AML has been exemplified by the introduction of targeted FLT3, IDH1/IDH2 and BCL-2 inhibitors. When used as single agents, these inhibitors display moderate antileukaemic activity. However, augmented clinical activity has been demonstrated when they are administered in combination with drugs with broader mechanisms of action targeting epigenetic and/or other oncogenic signalling pathways or with conventional cytotoxic agents. The development of immunotherapies has been hampered by the expression of antigens that are expressed by both leukaemic and non-malignant haematopoietic progenitor cells; nonetheless, a diverse range of immunotherapies are now entering clinical development. This myriad of emerging agents also creates challenges, such as how to safely combine agents with different mechanisms of action, the need to circumvent primary and secondary resistance, and new challenges in future clinical trial design. In this Review, we discuss the current state of precision medicine for AML, including both the potential to improve patient outcomes and the related challenges.

Midostaurin reduces relapse in FLT3-mutant acute myeloid leukemia: the Alliance CALGB 10603/RATIFY trial

The prospective randomized, placebo-controlled CALGB 10603/RATIFY trial (Alliance) demonstrated a statistically significant overall survival benefit from the addition of midostaurin to standard frontline chemotherapy in a genotypically-defined subgroup of 717 patients with FLT3-mutant acute myeloid leukemia (AML). The risk of death was reduced by 22% on the midostaurin-containing arm. In this post hoc analysis, we analyzed the cumulative incidence of relapse (CIR) on this study and also evaluated the impact of 12 4-week cycles of maintenance therapy. CIR analyses treated relapses and AML deaths as events, deaths from other causes as competing risks, and survivors in remission were censored. CIR was improved on the midostaurin arm (HR = 0.71 (95% CI, 0.54-0.93); p = 0.01), both overall and within European LeukemiaNet 2017 risk classification subsets when post-transplant events were considered in the analysis as events. However, when transplantation was considered as a competing risk, there was overall no significant difference between the risks of relapse on the two randomized arms. Patients still in remission after consolidation with high-dose cytarabine entered the maintenance phase, continuing with either midostaurin or placebo. Analyses were inconclusive in quantifying the impact of the maintenance phase on the overall outcome. In summary, midostaurin reduces the CIR.

Diagnostic and therapeutic pitfalls in NPM1-mutated AML: notes from the field

Mutations of Nucleophosmin (NPM1) are the most common genetic abnormalities in adult acute myeloid leukaemia (AML), accounting for about 30% of cases. NPM1-mutated AML has been recognized as distinct entity in the 2017 World Health Organization (WHO) classification of lympho-haematopoietic neoplasms. WHO criteria allow recognition of this leukaemia entity and its distinction from AML with myelodysplasia-related changes, AML with BCR-ABL1 rearrangement and AML with RUNX1 mutations. Nevertheless, controversial issues include the percentage of blasts required for the diagnosis of NPM1-mutated AML and whether cases of NPM1-mutated myelodysplasia and chronic myelomonocytic leukaemia do exist. Evaluation of NPM1 and FLT3 status represents a major pillar of the European LeukemiaNet (ELN) genetic-based risk stratification model. Moreover, NPM1 mutations are particularly suitable for assessing measurable residual disease (MRD) since they are frequent, stable at relapse and do not drive clonal haematopoiesis. Ideally, combining monitoring of MRD with the ELN prognostication model can help to guide therapeutic decisions. Here, we provide examples of instructive cases of NPM1-mutated AML, in order to provide criteria for the appropriate diagnosis and therapy of this frequent leukaemia entity.