Impact of FLT3-ITD allele ratio and ITD length on therapeutic outcome in cytogenetically normal AML patients without NPM1 mutation

The Clinical Utility of FLT3 Mutation Testing in Acute Leukemia: A Canadian Consensus

FMS-like tyrosine kinase 3 (FLT3) mutations are detected in approximately 20-30% of patients with acute myeloid leukemia (AML), with the presence of a FLT3 internal tandem duplication (FLT3-ITD) mutation being associated with an inferior outcome. Assessment of FLT3 mutational status is now essential to define optimal upfront treatment in both newly diagnosed and relapsed AML, to support post-induction allogeneic hematopoietic stem cell transplantation (alloSCT) decision-making, and to evaluate treatment response via measurable (minimal) residual disease (MRD) evaluation. In view of its importance in AML diagnosis and management, the Canadian Leukemia Study Group/Groupe canadien d'étude sur la leucémie (CLSG/GCEL) undertook the development of a consensus statement on the clinical utility of FLT3 mutation testing, as members reported considerable inter-center variability across Canada with respect to testing availability and timing of use, methodology, and interpretation. The CLSG/GCEL panel identified key clinical and hematopathological questions, including: (1) which patients should be tested for FLT3 mutations, and when?; (2) which is the preferred method for FLT3 mutation testing?; (3) what is the clinical relevance of FLT3-ITD size, insertion site, and number of distinct FLT3-ITDs?; (4) is there a role for FLT3 analysis in MRD assessment?; (5) what is the clinical relevance of the FLT3-ITD allelic burden?; and (6) how should results of FLT3 mutation testing be reported? The panel followed an evidence-based approach, taken together with Canadian clinical and laboratory experience and expertise, to create a consensus document to facilitate a more uniform approach to AML diagnosis and treatment across Canada.

Genetic mutation signature for relapse prediction in normal karyotype acute myeloid leukemia

Risk stratification for normal karyotype acute myeloid leukemia (NK-AML) remains unsatisfactory, which is reflected by the high incidence of leukemia relapse. This study aimed to evaluate the role of gene mutations and clinical characterization in predicting the relapse of patients with NK-AML. A prognostic system for NK-AML was constructed. A panel of gene mutations was explored using next-generation sequencing. A nomogram algorithm was used to build a genomic mutation signature (GMS) nomogram (GMSN) model that combines GMS, measurable residual disease, and clinical factors to predict relapse in 347 patients with NK-AML from four centers. Patients in the GMS-high group had a higher 5-year incidence of relapse than those in the GMS-low group (p < 0.001). The 5-year incidence of relapse was also higher in patients in the GMSN-high group than in those in the GMSN-intermediate and -low groups (p < 0.001). The 5-year disease-free survival and overall survival rates were lower in patients in the GMSN-high group than in those in the GMSN-intermediate and -low groups (p < 0.001) as confirmed by training and validation cohorts. This study illustrates the potential of GMSN as a predictor of NK-AML relapse.

Correlation of blood cell counts with mutant subtypes and impact prognosis in acute myeloid leukemia patients with FLT3 mutations

OBJECTIVES

Acute myeloid leukemia (AML) often presents with abnormal blood cell counts and gene mutations at diagnosis. But, the correlation between blood cell counts and gene mutations and the clinical effects on AML is unclear.

METHODS

279 AML patients with FMS-like tyrosine kinase 3(FLT3) mutations were selected. Patients with FLT3 mutations were counted by PCR amplification products direct sequencing and second-generation sequencing (NGS), and blood cell counts at the time of initial diagnosis. The relapse-free survival (RFS) and overall survival (OS) and the influence of the clinical characteristics of patients on the prognosis in different groups were analyzed.

RESULTS

The median of platelet (PLT) count was higher in the TET2 non-mutation group than mutation group and higher in the IDH1/2 mutation group than non-mutation group. The median of white blood cell (WBC) count was reduced in the poor prognosis group. The differences in levels of WBC and PLT count varied among the four groups binding sequence (JM-B), switching sequence (JM-S), zipper sequence (JM-Z), and high chain region (JM-H). The differences in PLT count varied between the insertion length ≥39 bp and <39 bp, and between ≥ 50 bp and <50 bp; The OS and RFS in 10 < WBC (×10⁹/L) < 100 group and in the 30 ≤ PLT (×109/L)<80 group were better.

CONCLUSIONS

In AML patients with FLT3 mutations, the location of FLT3 mutations and the type of co-mutated genes may be correlated with blood cell counts, and different blood cell counts may have an impact on the prognosis.

Impact of genetic patterns on sorafenib efficacy in patients with FLT3-ITD acute myeloid leukemia undergoing allogeneic hematopoietic stem cell transplantation: a multi-center, cohort study

Sorafenib therapy improves overall survival (OS) in patients with FLT3 internal tandem duplication (ITD) acute myeloid leukemia (AML) undergoing allogeneic hematopoietic stem cell transplantation. We explored the efficacy of sorafenib therapy in this population with different concomitant genetic patterns. In this multi-center, cohort study, we enrolled patients with FLT3-ITD AML undergoing allogenic hematopoietic cell transplantation. Patients with sorafenib maintenance post-transplantation for at least four weeks were allocated to the sorafenib group, and otherwise to the control group. Endpoints were OS, disease-free survival, and relapse for the whole cohort and OS for genetic pattern subgroups. Among 613 patients enrolled, 275 were in the sorafenib and 338 the control group. Median follow-up was 36.5 (interquartile range (IQR), 25.2-44.7) months post-transplantation. The 3-year OS post-transplantation was 79.6% (95% confidential interval (CI) 74.8%-84.6%) and 65.2% (95% CI 60.3%-70.6%) (Hazard ratio (HR) 0.50, 95% CI 0.37-0.69; P < 0.0001) in both groups. Sorafenib maintenance post-transplantation improved OS in the favorable (HR 0.33, 95% CI 0.14-0.77; P = 0.011) and adverse (HR 0.56, 95% CI 0.33-0.93; P = 0.026) ELN 2017 risk subgroups. Patients with mutated NPM1, DNMT3A, co-occurring NPM1/DNMT3A, "activated signaling" and "DNA methylation" genes benefited in OS from sorafenib maintenance, while those carrying CEBPA, "tumor suppressors" and "myeloid transcription factors" genes did not. Patients with FLT3-ITDhigh and FLT3-ITDlow AML both benefited in OS from sorafenib maintenance. Our results identify the response of genetic patterns to sorafenib maintenance, providing new viewpoints for the optimal use of sorafenib in FLT3-ITD AML in the transplantation setting.

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

BACKGROUND

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

OBJECTIVE

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

STUDY DESIGN

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

RESULTS

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

CONCLUSION

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

ITDetect: a method to detect internal tandem duplication of FMS-like tyrosine kinase (FLT3) from next-generation sequencing data with high sensitivity and clinical application

Internal tandem duplication (ITD) of the FMS-like tyrosine kinase (FLT3) gene is associated with poor clinical outcomes in patients with acute myeloid leukemia. Although recent methods for detecting FLT3-ITD from next-generation sequencing (NGS) data have replaced traditional ITD detection approaches such as conventional PCR or fragment analysis, their use in the clinical field is still limited and requires further information. Here, we introduce ITDetect, an efficient FLT3-ITD detection approach that uses NGS data. Our proposed method allows for more precise detection and provides more detailed information than existing in silico methods. Further, it enables FLT3-ITD detection from exome sequencing or targeted panel sequencing data, thereby improving its clinical application. We validated the performance of ITDetect using NGS-based and experimental ITD detection methods and successfully demonstrated that ITDetect provides the highest concordance with the experimental methods. The program and data underlying this study are available in a public repository.

Clinical Implications of the FLT3-ITD Allelic Ratio in Acute Myeloid Leukemia in the Context of an Allogeneic Stem Cell Transplantation

Although the presence of FLT3-ITD, as well as levels of the FLT3-ITD allelic ratio, have been described as prognostic factors in acute myeloid leukemia (AML), little is known about how the FLT3-ITD allelic ratio impacts patients' outcomes when receiving an allogeneic hematopoietic stem cell transplantation (HSCT). We analyzed 118 patients (median age at diagnosis 58.3, range 14.3-82.3 years) harboring FLT3-ITD, of whom 94 patients were consolidated with an allogeneic HSCT and included in outcome analyses. A high FLT3-ITD allelic ratio was associated with a higher white blood cell count, higher blood and bone marrow blasts, and worse ELN2017 risk at diagnosis. Patients with a high FLT3-ITD allelic ratio more often had NPM1 mutations, while patients with a low allelic ratio more often had FLT3-TKD mutations. Patients with a high FLT3-ITD allelic ratio were less likely to achieve a measurable residual disease (MRD)-negative remission prior to allogeneic HSCT and had a trend for a shorter time to relapse. However, there was no distinct cumulative incidence of relapse, non-relapse mortality, or overall survival according to the FLT3-ITD allelic ratio in transplanted patients. While co-mutated FLT3-TKD was associated with better outcomes, the MRD status at HSCT was the most significant factor for outcomes. While our data indicates that an allogeneic HSCT may mitigate the adverse effect of a high FLT3-ITD allelic ratio, comparative studies are needed to evaluate which FLT3-ITD mutated patients benefit from which consolidation strategy.

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.

FLT3-ITD allelic ratio and HLF expression predict FLT3 inhibitor efficacy in adult AML

FLT3 internal tandem duplication (FLT3-ITD) is a frequent mutation in acute myeloid leukemia (AML) and remains a strong prognostic factor due to high rate of disease recurrence. Several FLT3-targeted agents have been developed, but determinants of variable responses to these agents remain understudied. Here, we investigated the role FLT3-ITD allelic ratio (ITD-AR), ITD length, and associated gene expression signatures on FLT3 inhibitor response in adult AML. We performed fragment analysis, ex vivo drug testing, and next generation sequencing (RNA, exome) to 119 samples from 87 AML patients and 13 healthy bone marrow controls. We found that ex vivo response to FLT3 inhibitors is significantly associated with ITD-AR, but not with ITD length. Interestingly, we found that the HLF gene is overexpressed in FLT3-ITD⁺ AML and associated with ITD-AR. The retrospective analysis of AML patients treated with FLT3 inhibitor sorafenib showed that patients with high HLF expression and ITD-AR had better clinical response to therapy compared to those with low ITD-AR and HLF expression. Thus, our findings suggest that FLT3 ITD-AR together with increased HLF expression play a role in variable FLT3 inhibitor responses observed in FLT3-ITD⁺ AML patients.

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

BACKGROUND AIMS

The internal tandem duplication of FLT3 (FLT3^ITD) and NPM1 mutations (NPM1^mut) are well-established prognostic factors in cytogenetically intermediate-risk acute myeloid leukemia (AML) when treated with chemotherapy alone. However, their prognostic value in the setting of allogeneic hematopoietic cell transplantation (HCT) is controversial.

METHODS

FLT3 and NPM1 mutational status was determined at diagnosis using single-gene polymerase chain reaction or next-generation sequencing in 247 adult patients with cytogenetically intermediate-risk AML who underwent myeloablative HCT. Multivariate Fine-Gray and Cox regression was used to analyze the cumulative incidence of relapse (CIR), relapse-free survival (RFS) and overall survival (OS).

RESULTS

FLT3^ITD and NPM1^mut were present in 74 of 247 (30%) and 79 of 247 (32%) patients, respectively. There was no significant difference between patients without a FLT3^ITD or NPM1^mut (FLT3^NONITD/NPM1^WT) and patients with a FLT3^ITD mutation alone (FLT3^ITD/NPM1^WT) with regard to CIR (P = 0.60), RFS (P = 0.91) or OS (P = 0.66). Similarly, there was no significant difference between FLT3^NONITD/NPM1^WT and FLT3^NONITD/NPM1^mut patients with regard to CIR (P = 0.70), RFS (P = 0.75) or OS (P = 0.95). The presence of a concurrent mutation in NPM1 did not appear to modify the impact of having a FLT3^ITD mutation.

CONCLUSIONS

In contrast to chemotherapy-only treatment, FLT3 and NPM1 mutational status does not appear to predict outcomes in patients with cytogenetically intermediate-risk AML following HCT. These results suggest that HCT may ameliorate the poor prognostic effect of FLT3^ITD mutation and that HCT should be considered over chemotherapy-only treatment in FLT3^ITD-mutated AML.

The consensus from The Chinese Society of Hematology on indications, conditioning regimens and donor selection for allogeneic hematopoietic stem cell transplantation: 2021 update

The consensus recommendations in 2018 from The Chinese Society of Hematology (CSH) on indications, conditioning regimens and donor selection for allogeneic hematopoietic stem cell transplantation (allo-HSCT) facilitated the standardization of clinical practices of allo-HSCT in China and progressive integration with the world. There have been new developments since the initial publication. To integrate recent developments and further improve the consensus, a panel of experts from the CSH recently updated the consensus recommendations, which are summarized as follows: (1) there is a new algorithm for selecting appropriate donors for allo-HSCT candidates. Haploidentical donors (HIDs) are the preferred donor choice over matched sibling donors (MSDs) for patients with high-risk leukemia or elderly patients with young offspring donors in experienced centers. This replaces the previous algorithm for donor selection, which favored MSDs over HIDs. (2) Patients with refractory/relapsed lymphoblastic malignancies are now encouraged to undergo salvage treatment with novel immunotherapies prior to HSCT. (3) The consensus has been updated to reflect additional evidence for the application of allo-HSCT in specific groups of patients with hematological malignancies (intermediate-risk acute myeloid leukemia (AML), favorable-risk AML with positive minimal residual disease, and standard-risk acute lymphoblastic leukemia). (4) The consensus has been updated to reflect additional evidence for the application of HSCT in patients with nonmalignant diseases, such as severe aplastic anemia and inherited diseases. (5) The consensus has been updated to reflect additional evidence for the administration of anti-thymocyte globulin, granulocyte colony-stimulating factors and post-transplantation cyclophosphamide in HID-HSCT.

Molecular characterisation of NPM1 and FLT3-ITD mutations in a central South African adult de novo acute myeloid leukaemia cohort

Background

Recognition of molecular abnormalities in acute myeloid leukaemia (AML) has improved our understanding of its biology. NPM1 and FLT3-ITD mutations are recurrent in AML and clinically significant. NPM1 mutations are associated with a favourable prognosis, while FLT3-ITD mutations are an independent poor prognostic factor in AML.

Objective

This study described the prevalence and molecular characteristics of the NPM1 and FLT3-ITD mutations in a newly diagnosed AML patient cohort in central South Africa.

Methods

The study included 40 de novo AML patients. An NPM1 and FLT3-ITD multiplex polymerase chain reaction assay was optimised to screen patients for the respective mutations and were confirmed using Sanger sequencing. The prevalence of the NPM1 and FLT3-ITD mutations were determined, and mutation-specific characteristics were described in relation to patients' demographic information and AML classifications.

Results

The patients' median age was 38.5 years, with 77.5% (n = 31) of patients being self-proclaimed Black Africans. AML with recurrent genetic abnormalities was most prevalent (57.5%; n = 23), of which acute promyelocytic leukaemia (APL) was most common (40.0%; n = 16). None of the patients had the NPM1 mutation. FLT3-ITD was present in 37.5% (6/16) of APL patients and in one (20.0%) of five AML patients with a t(8;21) translocation. Most patients had an FLT3-ITD allele ratio of ≥ 50% and ITD lengths of > 39 bp.

Conclusion

FLT3-ITD mutations were mainly found in APL cases at a similar prevalence as reported in the literature. High FLT3-ITD allele ratios and long ITD lengths predominated. No NPM1 mutations were detected.

FLT3-ITD Allele Frequency Is an Independent Prognostic Factor for Poor Outcome in FLT3-ITD-Positive AML Patients

BACKGROUND

FMS-like tyrosine kinase 3 internal tandem duplication (FLT3-ITD) is a molecular genetic alteration significantly affecting the clinical outcome in patients with acute myeloid leukemia (AML). FLT3-ITD mutations are characterized by variable mutant-to-wild allelic ratios (ARs) and sizes of the duplicated sequences. The size of the inserted sequence may vary from a few to hundreds of nucleotides. The aim of this work was to determine the impact of FLT3-ITD ARs, FLT3-ITD allelic frequency (AF), and allele size in de novo AML.

PATIENTS AND METHODS

We studied 117 patients with FLT3-ITD gene mutation-positive AML, dividing them into those with low ARs and those with high ARs (>0.64) and examined their prognostic impact.

RESULTS

High FLT3-ITD AR ≥ 0.64 and AF ≥ 0.5 were significantly associated with a lower overall survival compared with lower AR (median 0.625 vs. 1.020 months, respectively; P = .041) and AF (median 0.493 vs. 0.954 months, respectively; P = .009). NPM1 mutation had no favorable impact on the low-level FLT3-ITD group.

CONCLUSION

Initial high total leukocyte count, FLT3-ITD AF, and splenomegaly are independent prognostic factors for poor outcome in FLT3-ITD-positive AML.

Potential targeting of FLT3 acute myeloid leukemia

Aberrant FLT3 receptor signaling is common in acute myeloid leukemia (AML) and has important implications for the biology and clinical management of the disease. Patients with FLT3-mutated AML frequently present with critical illness, are more likely to relapse after treatment, and have worse clinical outcomes than their FLT3 wild type counterparts. The clinical management of FLT3-mutated AML has been transformed by the development of FLT3 inhibitors, which are now in use in the frontline and relapsed/refractory settings. However, many questions regarding the optimal approach to the treatment of these patients remain. In this paper, we will review the rationale for targeting the FLT3 receptor in AML, the impact of FLT3 mutation on patient prognosis, the current standard of care approaches to FLT3-mutated AML management, and the diverse array of FLT3 inhibitors in use and under investigation. We will also explore new opportunities and strategies for targeting the FLT3 receptor. These include targeting the receptor in patients with non-canonical FLT3 mutations or wild type FLT3, pairing FLT3 inhibitors with other novel therapies, using minimal residual disease (MRD) testing to guide the targeting of FLT3, and novel immunotherapeutic approaches.

De novo adult acute myeloid leukemia with two new mutations in juxtatransmembrane domain of the FLT3 gene: a case report

Background

Approximately 30% of adult acute myeloid leukemia (AML) acquire within fms-like tyrosine kinase 3 gene (FLT3) internal tandem duplications (FLT3/ITDs) in their juxtamembrane domain (JMD). FLT3/ITDs range in size from three to hundreds of nucleotides, and confer an adverse prognosis. Studies on a possible relationship between of FLT3/ITDs length and clinical outcomes in those AML patients were inconclusive, yet.

Case presentation

Here we report a 54-year-old Arab male diagnosed with AML who had two FLT3-ITD mutations in addition to NPM1 mutation. Cytogenetic approaches (banding cytogenetics) and fluorescence in situ hybridization (FISH) using specific probes to detect translocations t(8;21), t(15;17), t(16;16), t(12;21), and deletion del(13q)) were applied to exclude chromosomal abnormalities. Molecular genetic approaches (polymerase chain reaction (PCR) and the Sanger sequencing) identified a yet unreported combination of two new mutations in FLT3-ITDs. The first mutation induced a frameshift in JMD, and the second led to a homozygous substitution of c.1836T>A (p.F612L) also in JMD. Additionally a NPM1 type A mutation was detected. The first chemotherapeutic treatment was successful, but 1 month after the initial diagnosis, the patient experienced a relapse and unfortunately died.

Conclusions

To the best of our knowledge, a combination of two FLT3-ITD mutations in JMD together with an NPM1 type A mutation were not previously reported in adult AML. Further studies are necessary to prove or rule out whether the size of these FLT3-ITDs mutations and potential other double mutations in FLT3-ITD are correlated with the observed adverse outcome.

Outcomes of pediatric acute myeloid leukemia patients with FLT3-ITD mutations in the pre-FLT3 inhibitor era

Background

Acute myeloid leukemia (AML) with internal tandem duplication in FMS-like tyrosine kinase 3 (FLT3-ITD) is associated with poor outcomes. This study aimed to analyze the outcomes of pediatric AML patients with FLT3-ITD mutations in the pre-FLT3 inhibitor era.

Methods

We retrospectively reviewed and identified 18 patients diagnosed with non-M3 AML with FLT3-ITD mutations at Seoul National University Children’s Hospital between May 2008 and August 2019.

Results

The median age was 13 years (range, 6‒19 yr). The median follow-up time was 43 months (range, 6‒157 mo). Fourteen patients received BH-AC-based (N4-Behenoy1-1-b-D-arabinofuranosy1cytosine) and 4 received cytarabine-based induction chemotherapy. Complete remission (CR) was achieved in 72.2% of the patients after the first induction chemotherapy and 80% of the patients achieved CR after salvage therapy. The overall CR rate was 94% (17/18 patients). These 17 patients underwent hematopoietic stem cell transplantation (9 matched unrelated donors, 5 matched related donors, and 3 haploidentical donors). Relapse occurred in 22% of the patients. Event free survival and overall survival rates were 53.8±12.1% and 53.6±12.1%, respectively, and they were not significantly different according to the type of induction chemotherapy (P=0.690) or the type of donor (P=0.102).

Conclusion

This study outlines the outcomes of pediatric AML patients with FLT3-ITD-mutations in one institution over a decade. Outcomes were significantly improved in this study compared to our previous report in 2004, where RFS and EFS were 0%. This study can provide baseline data for pediatric patients in the pre-FLT3 inhibitor era.

Digital Polymerase Chain Reaction Paired with High-Speed Atomic Force Microscopy for Quantitation and Length Analysis of DNA Length Polymorphisms

DNA length polymorphisms are found in many serious diseases, and assessment of their length and abundance is often critical for accurate diagnosis. However, measuring their length and frequency in a mostly wild-type background, as occurs in many situations, remains challenging due to their variable and repetitive nature. To overcome these hurdles, we combined two powerful techniques, digital polymerase chain reaction (dPCR) and high-speed atomic force microscopy (HSAFM), to create a simple, rapid, and flexible method for quantifying both the size and proportion of DNA length polymorphisms. In our approach, individual amplicons from each dPCR partition are imaged and sized directly. We focused on internal tandem duplications (ITDs) located within the FLT3 gene, which are associated with acute myeloid leukemia and often indicative of a poor prognosis. In an analysis of over 1.5 million HSAFM-imaged amplicons from cell line and clinical samples containing FLT3-ITDs, dPCR-HSAFM returned the expected variant length and variant allele frequency, down to 5% variant samples. As a high-throughput method with single-molecule resolution, dPCR-HSAFM thus represents an advance in HSAFM analysis and a powerful tool for the diagnosis of length polymorphisms.

Novel agents targeting leukemia cells and immune microenvironment for prevention and treatment of relapse of acute myeloid leukemia after allogeneic hematopoietic stem cell transplantation

Relapse remains the worst life-threatening complications after allogeneic hematopoietic stem cell transplantation (allo-HSCT) in patients with acute myeloid leukemia (AML), whose prognosis has been historically dismal. Given the rapid development of genomics and immunotherapies, the interference strategies for AML recurrence have been changing these years. More and more novel targeting agents that have received the U.S. Food and Drug Administration (FDA) approval for de novo AML treatment have been administrated in the salvage or maintenance therapy of post-HSCT relapse. Targeted strategies that regulate the immune microenvironment of and optimize the graft versus leukemia (GVL) effect of immune cells are gradually improved. Such agents not only have been proven to achieve clinical benefits from a single drug, but if combined with classic therapies, can significantly improve the poor prognosis of AML patients who relapse after allo-HSCT. This review will focus on currently available and promising upcoming agents and also discuss the challenges and limitations of targeted therapies in the allogeneic hematopoietic stem cell transplantation community.

Clinical Outcomes in Patients with FLT3-ITD-Mutated Relapsed/Refractory Acute Myelogenous Leukemia Undergoing Hematopoietic Stem Cell Transplantation after Quizartinib or Salvage Chemotherapy in the QuANTUM-R Trial

Despite the substantial clinical activity of fms-related tyrosine kinase 3 (FLT3) inhibitors in relapsed or refractory (R/R) FLT3-ITD‒positive acute myelogenous leukemia (AML), durable remissions and prolonged survival in this population require allogeneic hematopoietic stem cell transplantation (allo-HSCT). Quizartinib, a once-daily oral, highly potent, and selective FLT3 inhibitor, significantly prolonged overall survival (OS) and improved clinical benefit compared with salvage chemotherapy (median OS, 6.2 months versus 4.7 months; hazard ratio [HR], .76; 95% confidence interval [CI], .58 to .98; P = .018; composite complete remission [CRc] rate, 48% versus 27%; median duration of CRc, 2.8 months versus 1.2 months; mortality rate, .8% versus 14% by day 30, 7% versus 24% by day 60) in patients with R/R FLT3-ITD AML in the phase 3 QuANTUM-R trial. In this post hoc analysis, we described the characteristics of and clinical outcomes in patients who underwent on-study HSCT in QuANTUM-R at the investigator's discretion and institutional practices. Of 367 randomized patients, 78 (32%) in the quizartinib arm and 14 (11%) in the salvage chemotherapy arm underwent on-study allo-HSCT without any intervening therapy for AML after quizartinib or study-specified salvage chemotherapy. Pooled data of patients from both treatment arms showed a longer median overall survival (OS) in transplant recipients versus those treated without allo-HSCT (12.2 months versus 4.4 months; HR, .315; 95% CI, .233 to .427). Pooled data also showed a longer median OS in patients with a last recorded response of CRc before allo-HSCT versus patients without a CRc (20.1 months versus 8.8 months; HR, .506; 95% CI, .296 to .864). By treatment arm, the median OS was 25.1 months with quizartinib and 20.1 months with salvage chemotherapy in patients with a last recorded response of CRc before allo-HSCT. Forty-eight patients in the quizartinib arm continued quizartinib treatment after allo-HSCT. In the 31 patients with a last recorded response of CRc before allo-HSCT who continued quizartinib after allo-HSCT, the median OS was 27.1 months. Continuation of quizartinib after allo-HSCT was tolerable, and no new safety signals were identified. These results suggest that post-transplantation survival following salvage chemotherapy and quizartinib treatment are similar. However, quizartinib response occurs more frequently than with salvage chemotherapy, potentially allowing more patients to undergo transplantation and achieve durable clinical benefit. In addition, post-transplant quizartinib was found to be tolerable and may be associated with prolonged survival in some patients, highlighting its potential value in the management of patients with FLT3-ITD R/R AML.

Advances in targeted therapy for acute myeloid leukemia

Acute myeloid leukemia (AML) is a clonal malignancy characterized by genetic heterogeneity due to recurrent gene mutations. Treatment with cytotoxic chemotherapy has been the standard of care for more than half of a century. Although much progress has been made toward improving treatment related mortality rate in the past few decades, long term overall survival has stagnated. Exciting developments of gene mutation-targeted therapeutic agents are now changing the landscape in AML treatment. New agents offer more clinical options for patients and also confer a more promising outcome. Since Midostaurin, a FLT3 inhibitor, was first approved by US FDA in 2017 as the first gene mutation-targeted therapeutic agent, an array of new gene mutation-targeted agents are now available for AML treatment. In this review, we will summarize the recent advances in gene mutation-targeted therapies for patients with AML.

Nanopore Sequencing in Blood Diseases: A Wide Range of Opportunities

The molecular pathogenesis of hematological diseases is often driven by genetic and epigenetic alterations. Next-generation sequencing has considerably increased our genomic knowledge of these disorders becoming ever more widespread in clinical practice. In 2012 Oxford Nanopore Technologies (ONT) released the MinION, the first long-read nanopore-based sequencer, overcoming the main limits of short-reads sequences generation. In the last years, several nanopore sequencing approaches have been performed in various "-omic" sciences; this review focuses on the challenge to introduce ONT devices in the hematological field, showing advantages, disadvantages and future perspectives of this technology in the precision medicine era.