The impact of FLT3 internal tandem duplication mutant level, number, size, and interaction with NPM1 mutations in a large cohort of young adult patients with acute myeloid leukemia

NPM1, FLT3, and c-KIT mutations in pediatric acute myeloid leukemia in Russian population

We evaluated frequencies of NPM1, FLT3, c-KIT mutations in childhood acute myeloid leukemia (AML) in Russia and assessed prognostic relevance of the mutations. RNA and DNA were extracted from bone marrow samples of 186 (106 male and 80 female) pediatric patients younger than 17 year with de novo AML. Mutations and chromosomal rearrangements were detected by sequencing of a corresponding gene. NPM1 mutations were found in 5.2%, FLT3 mutations in 12.1%, c-KIT mutations in 3.7% of the patients. NPM1 mutations were associated with the absence of chromosomal aberrations (P=0.007) and FLT3/ITD (P=0.018). New data on incidence of c-KIT mutations in various AML subtypes as well as new variations of c-KIT mutations in the exon 8 are presented. The results are compared to previously published studies on NPM1, FLT3, c-KIT mutations in various populations. No statistically significant differences in survival rates between groups with or without of FLT3, NPM1, c-KIT mutations were found (P>0.05). Meanwhile, 4-year overall survival rates were higher in patients having NPM1 mutations comparing with NPM1/WT patients (100% vs. 50%) and in patients having FLT3 mutations comparing with FLT3/WT patients (70% vs. 50%). The data presented contribute to knowledge on incidence and prognostic significance of the mutations in pediatric AML.

Current treatment of acute myeloid leukemia

PURPOSE OF REVIEW

The objectives of this review are to discuss standard and investigational nontransplant treatment strategies for acute myeloid leukemia (AML), excluding acute promyelocytic leukemia.

RECENT FINDINGS

Most adults with AML die from their disease. The standard treatment paradigm for AML is remission induction chemotherapy with an anthracycline/cytarabine combination, followed by either consolidation chemotherapy or allogeneic stem cell transplantation, depending on the patient's ability to tolerate intensive treatment and the likelihood of cure with chemotherapy alone. Although this approach has changed little in the last three decades, increased understanding of the pathogenesis of AML and improvements in molecular genomic technologies are leading to novel drug targets and the development of personalized, risk-adapted treatment strategies. Recent findings related to prognostically relevant and potentially 'druggable' molecular targets are reviewed.

SUMMARY

At the present time, AML remains a devastating and mostly incurable disease, but the combination of optimized chemotherapeutics and molecularly targeted agents holds significant promise for the future.

Functional pathway analysis using SCNP of FLT3 receptor pathway deregulation in AML provides prognostic information independent from mutational status

FMS-like tyrosine kinase 3 receptor (FLT3) internal tandem duplication (ITD) mutations result in constitutive activation of this receptor and have been shown to increase the risk of relapse in patients with acute myeloid leukemia (AML); however, substantial heterogeneity in clinical outcomes still exists within both the ITD mutated and unmutated AML subgroups, suggesting alternative mechanisms of disease relapse not accounted by FLT3 mutational status. Single cell network profiling (SCNP) is a multiparametric flow cytometry based assay that simultaneously measures, in a quantitative fashion and at the single cell level, both extracellular surface marker levels and changes in intracellular signaling proteins in response to extracellular modulators. We previously reported an initial characterization of FLT3 ITD-mediated signaling using SCNP. Herein SCNP was applied sequentially to two separate cohorts of samples collected from elderly AML patients at diagnosis. In the first (training) study, AML samples carrying unmutated, wild-type FLT3 (FLT3 WT) displayed a wide range of induced signaling, with a fraction having signaling profiles comparable to FLT3 ITD AML samples. Conversely, the FLT3 ITD AML samples displayed more homogeneous induced signaling, with the exception of patients with low (<40%) mutational load, which had profiles comparable to FLT3 WT AML samples. This observation was then confirmed in an independent (verification) cohort. Data from the second cohort were also used to assess the association between SCNP data and disease-free survival (DFS) in the context of FLT3 and nucleophosmin (NPM1) mutational status among patients who achieved complete remission (CR) to induction chemotherapy. The combination of SCNP read outs together with FLT3 and NPM1 molecular status improved the DFS prediction accuracy of the latter. Taken together, these results emphasize the value of comprehensive functional assessment of biologically relevant signaling pathways in AML as a basis for the development of highly predictive tests for guidance of post-remission therapy.

Genetic biomarkers in acute myeloid leukemia: will the promise of improving treatment outcomes be realized?

Recent progress in the molecular genetics of acute myeloid leukemia (AML) has shown this disease to be more heterogeneous than previously realized. Recurrent cytogenetic and mutational changes in leukemic blasts have been confirmed to have high prognostic significance. High-throughput techniques to analyze the AML genome in greater depth have revealed novel mutations with putative roles in leukemogenesis. The use of prognostic biomarkers has allowed for a more detailed categorization of AML based on risk. Despite this tremendous progress, the understanding of the mechanisms by which these changes influence leukemia growth and response to treatment is still limited, which in turn has hindered the development of rationally targeted therapies for AML. The integration of clinical, cytogenetic and molecular data will be essential to translate the current research momentum into better outcomes for patients with AML.

Acute myeloid leukaemia in adults

The outlook for patients with acute myeloid leukaemia has improved in the past 30 years. Unlike other cancers, much of this progress is attributable to refinement of supportive treatment, rather than the introduction of new drugs. New antibacterial and antifungal agents, antiemetics, and improved transfusion support have decreased the rate of early death, and morbidity and mortality from allogeneic stem cell transplantation has been substantially reduced. However, more than half of young adult patients and about 90% of older patients still die from their disease. Refractoriness to initial induction treatment and, more frequently, relapse after complete remission, are still the main obstacles to cure. Accordingly, new treatment approaches with mechanisms of action different from those of conventional chemotherapy are needed. Our knowledge of the various chromosomal and molecular abnormalities implicated in the pathogenesis of the many subtypes of the disease has greatly expanded; as a result, clinical research is moving towards the investigation of new non-cytotoxic agents in combination with chemotherapy. The goal is to target the molecular abnormalities identified at diagnosis; however, several aberrations can coexist in subclones of acute myeloid leukaemia, making the disease less likely to be inhibited by a single agent.

Identification of a 24-gene prognostic signature that improves the European LeukemiaNet risk classification of acute myeloid leukemia: an international collaborative study

PURPOSE

To identify a robust prognostic gene expression signature as an independent predictor of survival of patients with acute myeloid leukemia (AML) and use it to improve established risk classification.

PATIENTS AND METHODS

Four independent sets totaling 499 patients with AML carrying various cytogenetic and molecular abnormalities were used as training sets. Two independent patient sets composed of 825 patients were used as validation sets. Notably, patients from different sets were treated with different protocols, and their gene expression profiles were derived using different microarray platforms. Cox regression and Kaplan-Meier methods were used for survival analyses.

RESULTS

A prognostic signature composed of 24 genes was derived from a meta-analysis of Cox regression values of each gene across the four training sets. In multivariable models, a higher sum value of the 24-gene signature was an independent predictor of shorter overall (OS) and event-free survival (EFS) in both training and validation sets (P < .01). Moreover, this signature could substantially improve the European LeukemiaNet (ELN) risk classification of AML, and patients in three new risk groups classified by the integrated risk classification showed significantly (P < .001) distinct OS and EFS.

CONCLUSION

Despite different treatment protocols applied to patients and use of different microarray platforms for expression profiling, a common prognostic gene signature was identified as an independent predictor of survival of patients with AML. The integrated risk classification incorporating this gene signature provides a better framework for risk stratification and outcome prediction than the ELN classification.

Favorable outcome of patients with acute myeloid leukemia harboring a low-allelic burden FLT3-ITD mutation and concomitant NPM1 mutation: relevance to post-remission therapy

Risk associated to FLT3 internal tandem duplication (FLT3-ITD) in patients with acute myeloid leukemia (AML) may depend on mutational burden and its interaction with other mutations. We analyzed the effect of FLT3-ITD/FLT3 wild-type (FLT3wt) ratio depending on NPM1 mutation (NPM1mut) in 303 patients with intermediate-risk cytogenetics AML treated with intensive chemotherapy. Among NPM1mut patients, FLT3wt and low ratio (<0.5) subgroups showed similar overall survival, relapse risk, and leukemia-free survival, whereas high ratio (≥0.5) patients had a worse outcome. In NPM1wt AML, FLT3-ITD subgroups showed a comparable outcome, with higher risk of relapse and shortened overall survival than FLT3wt patients. Allogeneic stem cell transplantation in CR1 was associated with a reduced relapse risk in all molecular subgroups with the exception of NPM1mut AML with absent or low ratio FLT3-ITD. In conclusion, effect of FLT3 burden is modulated by NPM1 mutation, especially in patients with a low ratio.

Acute myeloid leukemia with normal cytogenetics

Acute myeloid leukemia (AML) is proving to be a heterogeneous disease process that is driven by various genetic mutations and aberrant protein expression. As our population ages, the incidence of AML is likely to increase, with approximately a third of adult cases categorized with normal cytogenetics. Advances in technology are now allowing us to explore the genetic expression and protein transcription patterns of AML, providing more information that must find its place in the prognosis and the therapeutic algorithm of this disease. As we learn more, we hope to further categorize patients with normal karyotype AML into discrete risk categories that will help in treatment decision making and further elucidate the necessity for hematopoietic cell transplantation. However, at this time, many of the identified mutations and expression patterns are still experimental, requiring further analysis to determine their exact role in AML.

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.

High-risk acute myelogenous leukemia: treatment today ... and tomorrow

High-risk acute myelogenous leukemia (AML) constitutes a distinct subset of disease based on clinical and biological characteristics and comprises a significant percentage of all cases of adult AML. Biologic features such as distinct clonal cytogenetic and molecular abnormalities identify a subgroup of AML patients characterized by poor response to induction chemotherapy and poor long-term survival after treatment with consolidation chemotherapy. Clinical variables that predict for poor response include AML relapsed after less than 1 year of remission and AML characterized by resistance to conventional agents. We review here our understanding of the defining biologic subtypes of AML and discuss how adequate initial evaluation can be used to inform the choice of treatment. By defining high-risk biologic and clinical variables, a strong case can be made for treating patients with investigational agents, with treatment directed at distinct cytogenetic or molecular abnormalities. Allogeneic transplantation is the only form of therapy available outside of the setting of a clinical trial that may offer a chance for long-term survival for patients with high-risk AML.

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.

Role of autologous hematopoietic stem cell transplantation according to the NPM1/FLT3-ITD molecular status for cytogenetically normal AML patients: a GOELAMS study

The choice of postremission therapy for acute myeloid leukemia (AML) patients is now based on the blasts' cytogenetic and molecular profile. However, the potential benefit of autologous hematopoietic stem cell transplantation (auto-HSCT) according to the NPM1/FLT3-ITD status has been poorly studied in AML patients with a normal karyotype (NK). Therefore, we evaluated the NPM1/FLT3-ITD molecular status in 135 NK-AML patients treated by allogeneic HSCT (allo-HSCT), auto-HSCT, or chemotherapy as consolidation therapy within the GOELAMS LAM-2001 trial. In univariate analyzes, 4-year leukemia-free survival (LFS) and overall survival (OS) were significantly higher for NPM1+/FLT3-ITD- patients compared with patients presenting another molecular profile (61 vs. 43% and 72 vs. 48%, P = 0.02 and P = 0.01, respectively). In the NPM1+/FLT3-ITD- subgroup, there was no benefit for allo-HSCT or auto-HSCT vs. chemotherapy (4-year LFS: 71, 56, and 60%; 4-year OS: 73, 71, and 60%, respectively; P = NS). For patients with other NPM1/FLT3-ITD molecular profiles, allo-HSCT was found to be the best consolidation therapy, whereas auto-HSCT was associated with a better outcome when compared with chemotherapy (allo-HSCT-, auto-HSCT-, and chemotherapy-related 4-year LFS: 68, 44, and 36%, P = 0.004; 4-year OS: 68, 52, and 29%, respectively, P = 0.02). Our study indicates that allo-HSCT and auto-HSCT provide similar outcomes compared with chemotherapy as consolidation for NPM1+/FLT3-ITD- NK-AML patients. For NK-AML patients with an adverse molecular profile, auto-HSCT could represent an alternative therapeutic approach when no human leukocyte antigen-matched allogeneic donor is available.

Multiplex high-throughput gene mutation analysis in acute myeloid leukemia

Classification of acute myeloid leukemia increasingly depends on genetic analysis. However, the number of known mutations in acute myeloid leukemia is expanding rapidly. Therefore, we tested a high-throughput screening method for acute myeloid leukemia mutation analysis using a multiplex mass spectrometry-based approach. To our knowledge, this is the first reported application of this approach to genotype leukemias in a clinical setting. One hundred seven acute myeloid leukemia cases were screened for mutations using a panel that covers 344 point mutations across 31 genes known to be associated with leukemia. The analysis was performed by multiplex polymerase chain reaction for mutations in genes of interest followed by primer extension reactions. Products were analyzed on a Sequenom MassARRAY system (San Diego, CA). The multiplex panel yielded mutations in 58% of acute myeloid leukemia cases with normal cytogenetics and 21% of cases with abnormal cytogenetics. Cytogenetics and routine polymerase chain reaction-based screening of NPM1, CEBPA, FLT3-ITD, and KIT was also performed on a subset of cases. When combined with the results of these standard polymerase chain reaction-based tests, the mutation frequency reached 78% in cases with normal cytogenetics. Of these, 42% harbored multiple mutations primarily involving NPM1 with NRAS, KRAS, CEBPA, PTPN11, IDH1, or FLT3. In contrast, cases with abnormal cytogenetics rarely harbored more than 1 mutation (1.5%), suggesting different underlying biology. This study demonstrates the feasibility and utility of broad-based mutation profiling of acute myeloid leukemia in a clinical setting. This approach will be helpful in defining prognostic subgroups of acute myeloid leukemia and contribute to the selection of patients for enrollment into trials with novel inhibitors.

Molecular diagnostics of acute myeloid leukemia: it's a (next) generational thing

This commentary highlights the article by Spencer et al that outlines a novel next-generation sequencing-based method for the detection of FLT3 mutations.

A phase I/II study of sorafenib in combination with low dose cytarabine in elderly patients with acute myeloid leukemia or high-risk myelodysplastic syndrome from the National Cancer Institute of Canada Clinical Trials Group: trial IND.186

Sorafenib is active in patients with acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS). The National Cancer Institute of Canada (NCIC) Clinical Trials Group initiated a phase I/II study of the combination of sorafenib with cytarabine in older patients with AML or high-risk MDS who were unsuitable for intensive chemotherapy. FLT3 mutational status was determined in all patients. Twenty-one patients were enrolled (four MDS, 17 AML) with a median age of 77 years. The recommended phase II dose (RP2D) was cytarabine 10 mg bid days 1-10 and sorafenib 600 mg/day days 2-28. Dose-limiting toxicities were fatigue, sepsis and skin rash. Of 15 evaluable patients treated at the RP2D, two patients responded. The overall response rate for eligible patients was 10%. FLT3 mutations were found in only three patients. We conclude that this combination of sorafenib and cytarabine has limited activity in this unselected cohort of elderly patients with AML/MDS in which FLT3 mutations seemed underrepresented.

Detection of FLT3 internal tandem duplication in targeted, short-read-length, next-generation sequencing data

A recurrent somatic mutation frequently found in cytogenetically normal acute myeloid leukemia (AML) is internal tandem duplication (ITD) in the fms-related tyrosine kinase 3 gene (FLT3). This mutation is generally detected in the clinical laboratory by PCR and electrophoresis-based product sizing. As the number of clinically relevant somatic mutations in AML increases, it becomes increasingly attractive to incorporate FLT3 ITD testing into multiplex assays for many somatic mutations simultaneously, using next-generation sequencing (NGS). However, the performance of most NGS analysis tools for identifying medium-size insertions such as FLT3 ITD mutations is largely unknown. We used a multigene, targeted NGS assay to obtain deep sequence coverage (>1000-fold) of FLT3 and 26 other genes from 22 FLT3 ITD-positive and 29 ITD-negative specimens to examine the performance of several commonly used NGS analysis tools for identifying FLT3 ITD mutations. ITD mutations were present in hybridization-capture sequencing data, and Pindel was the only tool out of the seven tested that reliably detected these insertions. Pindel had 100% sensitivity (95% CI = 83% to 100%) and 100% specificity (95% CI = 88% to 100%) in our samples; Pindel provided accurate ITD insertion sizes and was able to detect ITD alleles present at estimated frequencies as low as 1%. These data demonstrate that FLT3 ITDs can be reliably detected in panel-based, next-generation sequencing assays.

FLT3 mutation status is a predictor of early death in pediatric acute promyelocytic leukemia: a report from the Children's Oncology Group

BACKGROUND

FLT3 mutations (FLT3/Mut) are prevalent in de novo AML and are associated with early relapse. The prevalence and prognostic significance of FLT3/Mut have not been well defined in childhood acute promyelocytic leukemia (APL).

PROCEDURE

Diagnostic specimens from 104 pediatric APL patients were screened for FLT3/Mut (FLT3/ITD or FLT3/ALM). FLT3/Mut status was correlated with disease characteristics and clinical outcome for patients treated on CALGB C9710 (n = 50).

RESULTS

Forty-two of the 104 patients (40%) had either FLT3/ITD (n = 28, 27%) or FLT3/ALM (n = 15, 14%). Median diagnostic WBC count was 23,400 cells/µl vs. 3,600 cells/µl for those with and without FLT3/Mut (P < 0.001), and similar results for the cohort of 50 patients treated on C9710 (P < 0.001). In patients treated on C9710, presence of a FLT3 mutation was highly correlated with diagnostic WBC count >10,000 (P = 0.004), microgranular variant histology (P = 0.035), and a lower remission rate (P = 0.009). In patients who received ATRA (C9710 or CCG-2911, n = 8), those with FLT3/Mut had an induction death rate of 30% (7/23) compared to 3% (1/35) in FLT3/WT patients (P = 0.005). In patients with high WBC counts (>10,000), those with FLT3/Mut had a significantly higher risk of induction death versus FLT3/WT patients (47% vs. 0%, P = 0.05). FLT3/Mut was not associated with adverse outcome in those who survived induction therapy.

CONCLUSIONS

FLT3/Mut are prevalent in pediatric APL and are associated with high WBC count and increased induction death. This study provides further evidence for testing APL patients for FLT3/Mut and the potential role for FLT3 inhibitors in this disease.

Prognostic significance of the European LeukemiaNet standardized system for reporting cytogenetic and molecular alterations in adults with acute myeloid leukemia

PURPOSE

To evaluate the prognostic significance of the international European LeukemiaNet (ELN) guidelines for reporting genetic alterations in acute myeloid leukemia (AML).

PATIENTS AND METHODS

We analyzed 1,550 adults with primary AML, treated on Cancer and Leukemia Group B first-line trials, who had pretreatment cytogenetics and, for cytogenetically normal patients, mutational status of NPM1, CEBPA, and FLT3 available. We compared complete remission (CR) rates, disease-free survival (DFS), and overall survival (OS) among patients classified into the four ELN genetic groups (favorable, intermediate-I, intermediate-II, adverse) separately for 818 younger (age < 60 years) and 732 older (age ≥ 60 years) patients.

RESULTS

The percentages of younger versus older patients in the favorable (41% v 20%; P < .001), intermediate-II (19% v 30%; P < .001), and adverse (22% v 31%; P < .001) genetic groups differed. The favorable group had the best and the adverse group the worst CR rates, DFS, and OS in both age groups. Both intermediate groups had significantly worse outcomes than the favorable but better than the adverse group. Intermediate-I and intermediate-II groups in older patients had similar outcomes, whereas the intermediate-II group in younger patients had better OS but not better CR rates or DFS than the intermediate-I group. The prognostic significance of ELN classification was confirmed by multivariable analyses. For each ELN group, older patients had worse outcomes than younger patients.

CONCLUSION

The ELN classification clearly separates the genetic groups by outcome, supporting its use for risk stratification in clinical trials. Because they have different proportions of genetic alterations and outcomes, younger and older patients should be reported separately when using the ELN classification.

Molecular analysis of different FLT3-ITD mutations in acute myeloid leukemia

Mutation of the FMS-like tyrosine kinase-3 (FLT3) gene occurs with a frequency of 20-25% in acute myeloid leukemia (AML). Different studies have reported conflicting results, stating the importance of the length, position and number of internal tandem duplications (ITDs) for prognostic significance. In the present study, FLT3-ITD mutations were found in 51 (23%) of 218 patients with AML. Using sequence analysis we categorized ITD integration sites according to functional regions of the FLT3 receptor. Median ITD size was 61 bp. The insertion site was strongly correlated with ITD size: more C-terminal located inserted fragments were significantly bigger. Our data confirm that FLT3-ITD mutations identify a subset of young patients with AML with normal cytogenetics but with inferior outcome. Patients with AML with mutation localization outside the juxtamembrane domain showed no correlation with worse prognosis. A high mutant/wild-type ratio appears to have a major impact on the prognostic relevance.

Prognostic impact of NPM1 mutations in Serbian adult patients with acute myeloid leukemia

Based on current findings, the presence of NPM1 mutations in acute myeloid leukemia (AML) patients is associated with an increased probability of complete remission (CR) and better overall survival (OS). We determined the incidence and prognostic relevance of NPM1 mutations, their association with FLT3 and IDH mutations, and other clinical characteristics in Serbian adult AML patients. Samples from 111 adult de novo AML patients, including 73 AML cases with a normal karyotype (NK-AML), were studied. NPM1, FLT3, and IDH mutations were detected by PCR and direct sequencing. NPM1 mutations were detected in 22.5% of patients. The presence of NPM1 mutations predicted a low CR rate and shorter OS. NPM1 mutations showed an association with both FLT3 and IDH mutations. Survival analysis based on NPM1/FLT3 mutational status revealed a lower OS for NPM1(+)/FLT3(-) compared to the NPM1(-)/FLT3(-) group in NK-AML patients. The lack of impact or unfavorable prognostic effect of NPM1 mutations found in this study can be assigned to a small cohort of analyzed AML patients, as can the presence of FLT3 and IDH mutations or other genetic lesions that cooperate with NPM1 mutations influencing prognosis.

The novel tyrosine kinase inhibitor AKN-028 has significant antileukemic activity in cell lines and primary cultures of acute myeloid leukemia

Aberrantly expressed tyrosine kinases have emerged as promising targets for drug development in acute myeloid leukemia (AML). We report that AKN-028, a novel tyrosine kinase inhibitor (TKI), is a potent FMS-like receptor tyrosine kinase 3 (FLT3) inhibitor (IC₅₀=6 nℳ), causing dose-dependent inhibition of FLT3 autophosphorylation. Inhibition of KIT autophosphorylation was shown in a human megakaryoblastic leukemia cell line overexpressing KIT. In a panel of 17 cell lines, AKN-028 showed cytotoxic activity in all five AML cell lines included. AKN-028 triggered apoptosis in MV4-11 by activation of caspase 3. In primary AML samples (n=15), AKN-028 induced a clear dose-dependent cytotoxic response (mean IC₅₀ 1 μℳ). However, no correlation between antileukemic activity and FLT3 mutation status, or to the quantitative expression of FLT3, was observed. Combination studies showed synergistic activity when cytarabine or daunorubicin was added simultaneously or 24 h before AKN-028. In mice, AKN-028 demonstrated high oral bioavailability and antileukemic effect in primary AML and MV4-11 cells, with no major toxicity observed in the experiment. In conclusion, AKN-028 is a novel TKI with significant preclinical antileukemic activity in AML. Possible sequence-dependent synergy with standard AML drugs and good oral bioavailability has made it a candidate drug for clinical trials (ongoing).

FLT3 inhibition: a moving and evolving target in acute myeloid leukaemia

Internal tandem duplication (ITD) of the fms-like tyrosine kinase 3 (FLT3) gene is a gain-of-function mutation common in acute myeloid leukaemia (AML). It is associated with inferior prognosis and response to chemotherapy. Single base mutations at the FLT3 tyrosine kinase domain (TKD) also leads to a gain of function, although its prognostic significance is less well defined because of its rarity. The clinical benefits of FLT3 inhibition are generally limited to AML with FLT3-ITD. However, responses are transient and leukaemia progression invariably occurs. There is compelling evidence that leukaemia clones carrying both ITD and TKD mutations appear when resistance to FLT3 inhibitors occurs. Interestingly, the emergence of double ITD and TKD mutants can be recapitulated in vitro when FLT3-ITD+ leukaemia cell lines are treated with mutagens and FLT3 inhibitors. Furthermore, murine xenotransplantation models also suggest that, in some cases, the FTL3-ITD and TKD double mutants actually exist in minute amounts before treatment with FLT3 inhibitors, expand under the selection pressure of FLT3 inhibition and become the predominant resistant clone(s) during the drug-refractory phase. On the basis of this model of clonal evolution, a multipronged strategy using more potent FLT3 inhibitors, and a combinatorial approach targeting both FLT3-dependent and FLT3-independent pathways, will be needed to improve outcome.

Molecular markers in acute myeloid leukaemia

An increasing number of cytogenetic and molecular genetic aberrations have been identified in acute myeloid leukaemia (AML), highlighting the biological heterogeneity of the disease. Moreover, the characterisation of specific molecular abnormalities provides the basis for targeted therapies, such as all trans retinoic acid (ATRA) and arsenic trioxide treatment in acute promyelocytic leukaemia or tyrosine kinase inhibitors in AML with FLT3 mutations. Several cytogenetic and molecular genetic changes have been shown to be prognostically relevant and have been acknowledged in the latest WHO classification of AML as separate entities. A detailed marker assessment at diagnosis is crucial for risk-stratification of AML patients, allowing the identification of those at high risk of relapse, who may benefit from early allogeneic stem cell transplantation. Finally, molecular markers are important for the detection of minimal residual disease after initial therapy and during long-term follow-up, which enables a more tailored treatment approach for individual AML patients.

Influence of FLT3-internal tandem duplication allele burden and white blood cell count on the outcome in patients with intermediate-risk karyotype acute myeloid leukemia

BACKGROUND

In patients with acute myeloid leukemia (AML), testing for fms-like tyrosine kinase-3 (FLT3)-internal tandem duplication (FLT3-ITD) and nucleophosmin-1 (NPM1) mutations can allow for further prognostic subclassification, but less is known about the effects of FLT3-ITD allele burden and presenting white blood cell count (WBC) within molecular subgroups.

METHODS

The authors retrospectively assessed 206 adult patients who had AML with an intermediate-risk karyotype and who received treatment on a uniform induction and consolidation chemotherapy regimen.

RESULTS

The presenting WBC was a prognostic factor for survival only in patients who had an FLT3-ITD mutation. On multivariate analysis, after correcting for age, WBC, secondary AML, and blast percentage, nucleophosmin-1 (NPM1)-mutated/FLT3-ITD-negative patients had superior overall survival compared with patients in the other molecular subgroups. Patients who had FLT3-ITD mutations had an inferior overall survival compared with patients who had NPM1 wild-type/FLT3-negative disease, and patients who had low or intermediate levels of the FLT-ITD of mutant allele had overall and disease-free survival similar to those in patients who had high-level mutations.

CONCLUSIONS

NPM1 and FLT3-ITD status, age, WBC, and secondary AML were identified as important prognostic variables that can help to risk stratify patients with AML who have intermediate-risk cytogenetics. FLT3 allele burden had no significant influence on outcomes after correcting for other variables.

Diversity of the juxtamembrane and TKD1 mutations (exons 13-15) in the FLT3 gene with regards to mutant load, sequence, length, localization, and correlation with biological data

In acute myeloid leukemia (AML) mutations in the juxtamembrane and tyrosine kinase 1 domain (exons 13-15) of the FLT3 gene (FLT3-ITD/LM) are heterogeneous with respect to mutation load, size, and localization. We characterized length and structure of these mutations by fragment analysis and sequencing in 689 AML which were identified among 3,365 (20.5%) newly diagnosed AML (1,803 males, 1,562 females; 15.8-91.8 years). Mutations were heterogeneous in length (median: 63, range: 3-1,236 nucleotides; nt). Most frequent were sizes of 21 (8.4%) or 24 nt (6.0%). Ninety-one different insertion sites were observed (between nt 1,788 and 1,934, according to accession "FLT3 [Ensembl/Havana merge: ENSG00000122025]" with nt 1,856 (n = 41) and 1,863 (n = 35) being most frequent. In addition, 89 different insertion end points were observed between nt 1,790 and 1,994. FLT3-mutation/wild-type ratio was available in 615 patients (median, 0.80; range 0.03-181.73). 128 Patients (20.8%) had ratios <0.3, 334 (54.3%) had ratio ≥0.3 <1, 118 (19.2%) ≥1, and 35 (5.7%) showed complete loss of the FLT3-wild-type allele. Overall (OS) and event-free (EFS) survival were better for FLT3-negative than FLT3mut normal karyotype patients (P = 0.078 and P = 0.004, respectively) and patients with low level FLT3-mutations had significantly longer OS and EFS compared with high level mutations (FLT3-mutation/wild-type ratio ≥1) (P < 0.001 and P = 0.002, respectively). The length of the mutation had no prognostic impact. Mutations localized more 5' were associated with better outcome than more 3'mutations, but no strict association to certain functional domains was detected. In conclusion, FLT3-mutations are extremely heterogenous with mutation load being the most relevant parameter.

Impact of numerical variation in FMS-like tyrosine kinase receptor 3 internal tandem duplications on clinical outcome in normal karyotype acute myelogenous leukemia

BACKGROUND

The impact of single versus multiple fms-like tyrosine kinase receptor 3 internal tandem duplication (FLT3-ITD) mutations on the clinical outcome of patients with acute myelogenous leukemia has not been well studied, and particularly has not been investigated while simultaneously accounting for the quantitative mutation burden.

METHODS

The authors conducted a multivariate analysis of overall survival, event-free survival, and complete remission duration, including numeric variation (single vs multiple) and quantitative mutant burden of FLT3-ITD as variables among other clinically relevant factors.

RESULTS

An analysis of a cohort of 1043 patients with AML demonstrated that, among patients with normal-karyotype acute myelogenous leukemia and FLT3-ITD mutation, overall survival and event-free survival were not affected by the number of FLT3-ITD mutations, but complete remission duration was significantly longer in patients who had multiple FLT3-ITD mutations (median, 86 weeks vs 34 weeks; P = .03).

CONCLUSIONS

The current results indicated that time-to-event analyses of patients with normal-karyotype acute myelogenous leukemia and FLT3-ITD mutation should take into account the number of mutations and the mutant burden, among other factors.

Patient-specific analysis of FLT3 internal tandem duplications for the prognostication and monitoring of acute myeloid leukemia

OBJECTIVES

Internal tandem duplications (ITDs) of the fms-like tyrosine kinase 3 ( FLT3) gene occur in 13-35% of patients with acute myeloid leukemia (AML). FLT3-ITD is associated with poor clinical outcome and is an indication for allogeneic stem cell transplantation (allo-SCT).

METHODS

To investigate FLT3-ITD length, position, and mutational load in AML cases, we developed patient-specific quantitative real-time reverse transcription polymerase chain reaction (qRT-PCR) assays and correlated the results with established sensitive minimal residual disease (MRD) parameters and clinical outcome.

RESULTS

In 409 patients with AML, FLT3-ITDs could be detected in 54 cases (13%). Within our cohort, patients with FLT3-ITD ≥ 45 base pairs had significantly higher relapse rates (P = 0.03) and a worse overall survival (P = 0.03). Our method could be applied to 97% of FLT3-ITD-positive patients and was as sensitive as other MRD parameters such as PML-RARA , NPM1 mutations, or MLL -PTD (correlation: r = 0.63; 0.99, and 0.99, respectively). MRD negativity predicted lasting remission independent of allo-SCT (N = 7) or non-allo-SCT (N = 9). All paired diagnostic/relapsed samples showed FLT3-ITD positivity. Compared with bone marrow samples, FLT3-ITD analyses appeared to be equivalently sensitive in peripheral blood.

CONCLUSIONS

We conclude that individualized monitoring of FLT3-ITD in patients with AML may guide treatment decisions and should be evaluated for the indication for allo-SCT.

Prognostic factors in adult acute leukemia

The prognostic factors in acute leukemia have undergone a major change over the past decade and are likely to be further refined in the coming years. While age is the single most important prognostic factor in both AML and in ALL, recurring cytogenetic abnormalities and molecular markers have become crucial for the prognosis of patients and for new directions in the development of targeted therapies. No less important is the development of a personalized approach for therapy as determined by the response to therapy using increasingly sensitive technologies. The assessment of MRD is rapidly superseding other prognostic factors in ALL and, somewhat lacking behind, coming into its own in AML. The next decade should see further refinement of response-driven prognostication, to include epigenetics as well as pharmacogenetics and pharmacodynamics of individual drugs used and the responses to them. It is hoped that these refinements and better predictors of response will also lead to a significantly improved overall outcome of patients with both AML and ALL.

Diagnostic and prognostic value of cytogenetics in acute myeloid leukemia

The last 4 decades have seen major advances in understanding the genetic basis of acute myeloid leukemia (AML), and substantial improvements in survival of children and young adults with the disease. A key step forward was the discovery that AML cells harbor recurring cytogenetic abnormalities. The identification of the genes involved in chromosomal rearrangements has provided insights into the regulation of normal hematopoiesis and how disruption of key transcription factors and epigenetic modulators promote leukemic transformation. Cytogenetics has been widely adopted to provide the framework for development of risk-stratified treatment approaches to patient management.

Genetic and epigenetic similarities and differences between childhood and adult AML

BACKGROUND

The biology of acute myeloid leukemia (AML) is complex and includes both genetic and epigenetic aberrations. We addressed the combined consequences of promoter hypermethylation of p15, CDH1, ER, MDR1, and RARB2 and mutation of NPM1, CEBPA, FLT3, and WT1 in a Danish cohort of 70 pediatric and 383 adult AML patients.

PROCEDURE

Mutation analysis was done by fragment analysis followed by sequencing or by sequencing alone. Methylation status was determined using methylation-sensitive melting curve analysis (MS-MCA) after initial bisulfite modification.

RESULTS

Among pediatric AMLs, we found promoter hypermethylation in p15 (47%), CDH1 (64%), ER (62%), MDR1 (8%), and RARB2 (22%) and mutations in NPM1 (11%), CEBPA (3%), FLT3ITD (4%), FLT3D835 (7%), and WT1 (7%). Promoter hypermethylation was significantly more frequent in core binding factor leukemias (CBF) compared to AMLs with abnormalities involving 11q23 (P = 0.024). Compared to adult AML we found a significant difference in p15 (47% vs. 73%, P < 0.001) and RARB2 (22% vs. 42%, P = 0.003) methylation, as well as in NPM1 (11% vs. 31%, P = 0.001) and FLT3ITD (4% vs. 26%, P < 0.001) mutation.

CONCLUSION

Age-related differences exist in the frequency of mutations and it appears that promoter hypermethylation occurs in a non-random pattern in childhood AML accompanying specific genetic aberrations, and might represent an important step in the leukemogenic transformation.

Sorafenib treatment of FLT3-ITD(+) acute myeloid leukemia: favorable initial outcome and mechanisms of subsequent nonresponsiveness associated with the emergence of a D835 mutation

Internal tandem duplication (ITD) of the fms-related tyrosine kinase-3 (FLT3) gene occurs in 30% of acute myeloid leukemias (AMLs) and confers a poor prognosis. Thirteen relapsed or chemo-refractory FLT3-ITD(+) AML patients were treated with sorafenib (200-400 mg twice daily). Twelve patients showed clearance or near clearance of bone marrow myeloblasts after 27 (range 21-84) days with evidence of differentiation of leukemia cells. The sorafenib response was lost in most patients after 72 (range 54-287) days but the FLT3 and downstream effectors remained suppressed. Gene expression profiling showed that leukemia cells that have become sorafenib resistant expressed several genes including ALDH1A1, JAK3, and MMP15, whose functions were unknown in AML. Nonobese diabetic/severe combined immunodeficiency mice transplanted with leukemia cells from patients before and during sorafenib resistance recapitulated the clinical results. Both ITD and tyrosine kinase domain mutations at D835 were identified in leukemia initiating cells (LICs) from samples before sorafenib treatment. LICs bearing the D835 mutant have expanded during sorafenib treatment and dominated during the subsequent clinical resistance. These results suggest that sorafenib have selected more aggressive sorafenib-resistant subclones carrying both FLT3-ITD and D835 mutations, and might provide important leads to further improvement of treatment outcome with FLT3 inhibitors.

Allogeneic stem cell transplantation in first complete remission

PURPOSE OF REVIEW

The optimal postremission therapy of acute myeloid leukemia (AML) in first complete remission (CR1) is uncertain. This review summarizes the recent developments in the clinical research and therapeutic applications defining the role of allogeneic hematopoietic stem cell transplantation (allo-HCT) in CR1.

RECENT FINDINGS

Molecular markers in combinations with cytogenetics have improved the risk stratification and informed decision-making in patients with AML in CR1. In parallel, several important advances in the transplant field, such as better supportive care, improved transplant technology, increased availability of alternative donors, and reduced-intensity conditioning, have improved the safety as well as access of allo-HCT for a larger number of patients.

SUMMARY

The progress in risk stratification and in transplant technology dictate that early donor identification search should be initiated for all eligible AML patients in CR1.

Acute myeloid leukemia: 2012 update on diagnosis, risk stratification, and management

DISEASE OVERVIEW

Acute myeloid leukemia (AML) results from accumulation of abnormal immature cells in the marrow. These cells interfere with normal hematopoiesis can escape into the blood and infiltrate lung and CNS. The most common cause of death is bone marrow failure. It is likely that many different mutations and/or epigenetic aberrations can produce the same disease, with these differences responsible for the very variable response to therapy, which is AML's principal clinical feature.

DIAGNOSIS

This rests on demonstration that the marrow or blood has >20% blasts of myeloid lineage. Blast lineage is assessed by multiparameter flow cytometry with CD33 and CD13 being surface markers typically expressed by myeloid blasts. It should be realized that clinical/prognostic considerations, not the blast % per se, should be the main factor determining how a patient is treated.

RISK STRATIFICATION

Two features determine risk: the probability of treatment-related mortality (TRM) and, more important, even in patients aged >75 with Zubrod performance status 1, the probability of resistance to standard therapy despite not incurring TRM. The chief predictor of resistance is cytogenetics with a monosomal karyotype (MK) denoting the disease is essentially incurable with standard therapy even if followed by a standard allogeneic transplant (HCT). The most common cytogenetic finding is a normal karyotype (NK) and those of such patients with an NPM1 mutation but no FLT3 internal tandem duplication (ITD), or with a CEBPA mutation, have a prognosis similar to that of patients with the most favorable cytogenetics [inv(16) or t(8;21)] (60-70% cure rate). In contrast, NK patients with a FLT3 ITD have only a 30-40% chance of cure even after HCT. Accordingly analyses of NPM1, FLT3, and CEBPA should be part of routine evaluation, much as is cytogenetics. Risk is best assessed considering several variables simultaneously rather than, for example, only age.

RISK-ADAPTED THERAPY

Patients with inv(16) or t(8;21) or who are NPM1+/FLT3ITD- can receive standard therapy (daunorubicin + cytarabine) and should not receive HCT in first CR. It seems likely that use of a daily daunorubicin dose of 90 mg/m(2) will further improve outcome in these patients. There appears no reason to use doses of cytarabine > 1 g/m(2) (for example, bid × 6 days), as opposed to the more commonly used 3 g/m(2) . Patients with an unfavorable karyotype (particularly MK) are unlikely to benefit from standard therapy (even with dose escalation) and are thus prime candidates for clinical trials of new drugs or new approaches to HCT; the latter should be done in first CR. Patients with intermediate prognoses (for example, NK and NPM and FLT3ITD negative) should also receive HCT in first CR and can plausibly receive either investigational or standard induction therapy, with the same prognostic information about standard therapy leading one patient to choose the standard and another an investigational option.

Prognostic implications of genetic aberrations in acute myelogenous leukemia with normal cytogenetics

Acute myelogenous leukemia (AML) is a genetically heterogeneous disease in which somatic mutations, that disturb cellular growth, proliferation, and differentiation, accumulate in hematopoietic progenitor cells. Cytogenetic findings, at diagnosis, have been proven to be one of the most important prognostic indicators in AML. About half of the patients with AML are found to have "normal" cytogenetic analysis by standard culture techniques. These patients are considered as an intermediate risk group. Cytogenetically normal AML (CN-AML) is the largest cytogenetic risk group, and the variation in clinical outcome of patients in this group is greater than in any other cytogenetic group. Besides mutation testing, age and presenting white blood cell count are important predictors of overall survival, suggesting that other factors independent of cytogenetic abnormalities, contribute to the outcome of patients with AML. The expanding knowledge at the genetic and molecular levels is helping define several subgroups of patients with CN-AML with variable prognosis. In this review, we describe the clinical and prognostic characteristics of CN-AML patients as a group, as well as the various molecular and genetic aberrations detected in these patients and their clinical and prognostic implications.

Patterns of molecular response to and relapse after combination of sorafenib, idarubicin, and cytarabine in patients with FLT3 mutant acute myeloid leukemia

BACKGROUND

FMS-like tyrosine kinase 3 (FLT3) is a class III receptor tyrosine kinase involved in hematopoietic progenitor cell development. Mutations of FLT3 have been reported in about a third of patients with acute myeloid leukemia (AML), and inhibitors of FLT3 are of clinical interest. Sorafenib is an orally active multikinase inhibitor with potent activity against FLT3 and the Raf/ERK/MEK kinase pathway.

METHODS

We studied the patterns of molecular response and relapse in 18 patients with mutated FLT3 treated with the combination of sorafenib, idarubicin, and cytarabine.

RESULTS

The median follow-up was 9 months. Sixteen patients achieved complete remission (CR), and the other 2 patients achieved CR but lacked platelet recovery for an overall response rate of 100%. Ten patients had their FLT3-mutated clone eradicated, with 6 patients who showed some residual FLT3-mutated cells, and 2 patients who showed persistent FLT3-mutated cells. The elimination of FLT3-mutated population at the time of morphologic CR, however, was not predictive of relapse. After a median follow-up of 9 months (range, 1-16 months), 10 (55%) patients had relapsed, with a median CR duration of 8.8 months (range, 1-9.5 months). By DNA sequencing, there was no evidence of an acquired FLT3 point mutation at the time of relapse in 7 patients tested, which suggested the presence of other mechanisms of sorafenib resistance.

CONCLUSION

Sorafenib, combined with chemotherapy, is effective in attaining CR, but relapses still occur.

Acute myeloid leukaemia: optimal management and recent developments

The current treatment of patients with acute myeloid leukaemia yields poor results, with expected cure rates in the order of 30-40% depending on the biological characteristics of the leukaemic clone. Therefore, new agents and schemas are intensively studied in order to improve patients' outcomes. This review summarizes some of these new paradigms, including new questions such as which anthracycline is most effective and at what dose. High doses of daunorubicin have shown better responses in young patients and are well tolerated in elderly patients. Monoclonal antibodies are promising agents in good risk patients. Drugs blocking signalling pathways could be used in combination with chemotherapy or in maintenance with promising results. Epigenetic therapies, particularly after stem cell transplantation, are also discussed. New drugs such as clofarabine and flavopiridol are reviewed and the results of their use discussed. It is clear that many new approaches are under study and hopefully will be able to improve on the outcomes of the commonly used '7+3' regimen of an anthracycline plus cytarabine with daunorubicin, which is clearly an ineffective therapy in the majority of patients.