Search

Introduction: FLT3 internal tandem duplication mutations are independent risk factors for worse overall survival (OS) and increased relapse risk in AML patients and thus are an attractive target fo...

Acute myeloid leukemia (AML) is an aggressive hematologic malignancy with inadequate treatment options. Approximately one-third of cases have a FLT3-ITD or FLT3-TKD mutation which leads to constitutive tyrosine kinase activation which contributes to leukemogenesis. The FLT3-ITD mutation is associated with a particularly poor prognosis. Midostaurin is a multi-kinase inhibitor active against the FLT3 receptor. Midostaurin was approved by the US FDA in April 2017 for treatment of newly diagnosed FLT3-mutant AML in combination with chemotherapy. Areas covered: Standard treatment of FLT3-mutant AML and outcomes. Early clinical development of midostaurin including pharmacokinetics and metabolism. The development of midostaurin in FLT3-mutant AML is then outlined including review of the phase I, II, and III trials of midostaurin as a single agent and in combination with chemotherapy. Expert commentary: The approval of midostaurin represents the first new therapy for AML in several decades. It is also the first targeted therapy approved for AML. Future studies will focus on defining mechanisms of resistance to midostaurin as well as establishing the role of midostaurin in combination with hypomethylating agents and as maintenance therapy. Second generation, more potent and selective FLT3 inhibitors are also in development; these agents need to be compared to midostaurin.

Dynamics of molecular response in AML patients with NPM1 and FLT3 mutations undergoing allogeneic stem cell transplant

Background: Despite widespread interest in pain management and opioid use across the United States, information on pain and opioid utilization in patients with relapsed or refractory acute myeloid leukemia (R/R AML) is lacking. Better understanding of patient-reported outcomes (PROs) specific to pain could be used to identify strategies to improve the quality of life in patients with R/R AML. Aim/Objective: To describe pain and opioid use in patients with FLT3 mutation-positive (FLT3mut+)R/R AML receiving either gilteritinib or salvage chemotherapy (SC) using PRO data collected from the ADMIRAL study (NCT02421939). Methods: ADMIRAL was a phase 3, open-label, multicenter, active-controlled randomized study comparing the efficacy and safety of gilteritinib to SC in patients with FLT3mut+ R/R AML. Pain was assessed using selected items from the Functional Assessment of Cancer Therapy - Leukemia (FACT-Leu; GP4 item: "I have pain") and the EuroQol 5-Dimension 5-Level Questionnaire (EQ-5D-5L; Pain/Discomfort domain). Data for these instruments were collected at baseline (BL), Day 1 of every treatment cycle, and end of treatment (EOT). A modified EOT (mEOT) was defined as the last PRO assessment before patient discontinuation, study data cut-off date, or patient death. Patients on high-intensity chemotherapy (HIC) were treated for up to two cycles depending on treatment response; as such, only changes from BL to Cycle 2 were evaluated. Opioid utilization, including percentage of patients using any opioid medication, specific medications, duration of use, and use by transfusion dependence, was also described. Analyses of the intention-to-treat population using analysis of covariance, including BL score, response to first-line AML therapy, and investigator-preselected SC as covariates, were conducted to estimate least squares mean (LSM) and compare the differences in pain question responses between treatment arms. Descriptive statistics were used to describe opioid utilization. Results: Of 371 eligible patients, 247 were randomized to gilteritinib and 124 to SC. The median age for both groups was 62 years and slightly more patients were female (gilteritinib, 53.0%; SC, 56.5%). Improvements at the mEOT from BL in the Fact-Leu GP4 item were observed in both gilteritinib (LSM -0.3) and SC (LSM -0.1). Scores also changed on the EQ-5D-5L at the mEOT from BL for both groups (gilteritinib, LSM 0.2; SC, LSM 0.3). No treatment differences were observed between gilteritinib vs SC on the change from BL to Cycle 2 or mEOT on the Fact-Leu GP4 item (LSM [95% CI] of -0.1 [-0.65, 0.38]; P=0.6016 and -0.2 [-0.53, 0.21]; P=0.3902, respectively) or on the EQ-5D-5L Pain/Discomfort domain (LSM [95% CI] of 0.2 [-0.21, 0.62]; P=0.3255 and -0.1 [-0.38, 0.23]; P=0.6288, respectively). During Cycles 1 and 2, no differences were identified between gilteritinib or SC on the percentage of patients using opioids (Cycle 1: 49.8% vs 55.6%; Cycle 2: 58.9% vs 62.7%, respectively) or the time-averaged duration of use (Cycle 1: 12.4 days vs 14.1 days; Cycle 2: 15.0 days vs 17.2 days, respectively). Patients on gilteritinib were less likely to use opioids during the first two cycles compared with patients on HIC, when stratified by chemotherapy intensity (Cycle 1: 49.0% vs 72.0%, P Conclusions: Patients with FLT3mut+ R/R AML receiving gilteritinib or SC demonstrated modest changes in responses to pain-related assessments at EOT compared with BL values. Opioids were used more frequently by patients receiving HIC regimens and transfusion-dependent patients receiving gilteritinib. These data suggest that treatments for FLT3mut+ R/R AML may impact opioid use; further study should be done to determine the relationships between these factors and their potential impact on overall quality of life. Disclosures Cella: DSI: Consultancy, Research Funding; Evidera: Consultancy; Ipsen: Consultancy, Research Funding; Mei Pharma: Consultancy; Oncoquest: Consultancy; ASAHI KASEI PHARMA CORP.: Consultancy; BMS: Consultancy, Research Funding; IDDI: Consultancy; Kiniksa: Consultancy; Novartis: Consultancy; Pfizer: Consultancy, Research Funding; Apellis: Consultancy; Alexion: Research Funding; Clovis: Research Funding; Janssen: Research Funding; Pled Pharma: Research Funding; PROMIS Health Org: Membership on an entity's Board of Directors or advisory committees, Other; BlueNote: Consultancy; Astellas: Consultancy, Honoraria; FACIT.org: Membership on an entity's Board of Directors or advisory committees, Other: President; Abbvie: Consultancy, Research Funding. Ritchie:Abbvie: Honoraria; Sierra Oncology: Honoraria; Novartis: Honoraria; Pfizer: Honoraria, Research Funding; Jazz pharmaceuticals: Honoraria, Research Funding; Incyte: Speakers Bureau. Kanda:Pfizer: Honoraria, Research Funding; Astellas Pharma: Honoraria, Research Funding; Janssen: Honoraria; Shionogi: Research Funding; Chugai Pharma: Honoraria, Research Funding; Otsuka: Honoraria, Research Funding; Celgene: Honoraria; Sumitomo Dainippon Pharma: Honoraria; Eisai: Honoraria, Research Funding; Novartis: Honoraria; Kyowa Kirin: Honoraria, Research Funding; Bristol-Myers Squibb: Honoraria; Takeda Pharmaceuticals: Honoraria; Alexion Pharmaceuticals: Honoraria; Shire: Honoraria; Daiichi Sankyo: Honoraria; Ono Pharmaceutical: Honoraria; Nippon Shinyaku: Honoraria, Research Funding; Mochida Pharmaceutical: Honoraria; Mundipharma: Honoraria; Sanofi: Honoraria, Research Funding; Meiji Seika Kaisha: Honoraria; Merck Sharp & Dohme: Honoraria. Ivanescu:Astellas: Other: IQVIA employee which is a contracted by Astellas. Pandya:Astellas Pharma, Inc.: Current Employment. Shah:Astellas: Current Employment.

Biologically, Acute myeloid leukemia (AML) is highly heterogenous. AML with cup-like blast morphology variant has been reported to have important role in risk group stratification and treatment implications. In pediatric age group, this morphology and its clinical implication is rarely discussed. Although this morphology variant is not stated in World Health Organization (WHO) classification of Tumours of Haematopoietic and Lymphoid Tissues, it is associated with poor outcome from the association with other features. A 10- year old girl diagnosed to have AML with this morphology variant is reported in this study. Her laboratory features were hyperleucocytosis, high D-dimer, and blasts morphology of cup-like cells and few mimic the bilobed features of acute promyelocytic leukemia (APML). Further investigation showed clinical and laboratory features similar to what had been reported before in adults, including the presence of adverse marker of Fms-like tyrosine kinase 3 (FLT3) mutation. She was treated with chemotherapy, following which the bone marrow examination documented marrow in remission. Unfortunately, she succumbed to the disease complication from sepsis and marrow failure after few months of diagnosis. Haemato-morphologists might consider this unique morphological recognition and correlate it with other findings, including molecular testing for proper clinical evaluation. The blast feature and haematological findings could predict the clinical behaviour of this type of AML and guide the patient management. This morphological variant serves an important role especially if molecular testing is not available in some parts of the world or at the time of presentation when the result is still pending.

Acute myeloid leukemia (AML) with FLT3-mutation carries a poor prognosis, and allogeneic stem cell transplantation (allo-SCT) is recommended at first complete remission (CR1). We assessed 462 adults (median age 50 years) with FLT3-mutated AML allografted between 2010 and 2015 from a matched related (40%), unrelated (49%), or haploidentical donor (11%). The median follow-up of alive patients was 39 months. Day-100 acute graft versus host disease (GVHD) grades II-IV and III-IV were encountered in 26% and 9%, whereas the 2-year incidence of chronic and extensive chronic GVHD were 34% and 16%, respectively. The 2-year incidences of relapse and nonrelapse mortality were 34% and 15%, respectively. The 2-year leukemia-free survival, overall survival (OS), and GVHD relapse-free survival (GRFS) were 51%, 59%, and 38%, respectively. In multivariate analysis, NPM1-mutation, transplantation in CR1, in vivo T-cell depletion, and posttransplant sorafenib improved OS, whereas more than one induction (late CR1) negatively affected OS. Similarly, NPM1-mutation, a haploidentical donor, T-cell depletion, and sorafenib maintenance improved GRFS, whereas late CR1 or persistent disease negatively affected it. In conclusion, FLT3-mutated AML remains a challenge even following allo-SCT. In vivo T-cell depletion and posttransplant sorafenib significantly improve OS and GRFS, and may be considered as standard of care. ispartof: Clin Hematol Int vol:1 issue:1 pages:58-74 ispartof: location:United States status: Published online

A 53-years old man with FLT3-ITD-mutant Acute Myeloid Leukemia relapsed ten months after hemopoietic allogeneic stem cell transplant as multiple cutaneous Myeloid Sarcomas. Molecular testing was performed on the core-needle biopsy of the lesion and since positive for the FLT3 mutation, a targeted-therapy with the tyrosine kinase inhibitor sorafenib as single agent was started, obtaining a sustained complete response. After 18 months of therapy patient relapsed on the previously involved sites, because of acquisition of sorafenib-resistant mutation and switched to systemic therapy. Sorafenib proved to be able to distribute in skin and subcutaneous tissues and could be safely used. Molecular testing on Myeloid Sarcoma can be therefore an innovative and effective approach in the management of extra medullary leukemia.

7020 Background: The advent of genomic sequencing technologies has revealed underlying genetic alterations, such as FLT3 mutations, that can be targeted in acute myeloid leukemia (AML). However, development of resistance limits the durability of response. Recent data has implicated that factors from the bone marrow microenvironment mediate initial resistance to FLT3 inhibitors (FLT3i) in AML. We combined high dimensional characterization techniques, time-of-flight mass cytometry (CyTOF) and RNA sequencing, to examine sequential marrow stromal samples from a subset of patients with FLT3 mutated AML treated with the FLT3i gilteritinib. Here, we report on the heterogeneity and evolution of cell surface and secreted factors over time. Methods: RNA sequencing of primary FLT3-ITD stromal samples (N = 29) from pre-study and on-treatment patients enabled prioritization of candidate targets for CyTOF. Target-specific purified antibodies were purchased pre-conjugated to metal lanthanides or conjugated in house according to manufacturer protocols (after validation via traditional flow cytometry). Primary stromal cells were cultured ex vivo until confluent and were harvested and stained according to a standardized protocol, and subsequently run on a Helios (Fluidigm) mass cytometer. A computational approach was employed to compensate and visualize data via the CATALYST R package. A total of four pre-treatment and four post-gilteritinib timepoint isolates (N = 8) were analyzed. Results: A 36-target mass cytometry panel revealed protein level differences in patients before and after gilteritinib therapy. Dimensional reduction techniques such as MDS and UMAP showed that samples taken from later timepoints clustered together compared to their earlier counterparts with respect to global protein expression. Inflammatory mediators such as IL1-beta and MCP-1 were upregulated in patient stroma soon after gilteritinib treatment and therefore potentially contribute to early resistance. Novel markers previously implicated in early resistance to targeted therapies in AML such as FGF2 and FGFR1 similarly peaked earlier in treatment, mimicking the clinical course of expression observed in marrow stroma of patients treated with another FLT3 inhibitor quizartinib (Traer et al. Cancer Res. 2016). Conclusions: Our findings show that primary marrow stroma evolves during gilteritinib treatment, and that stromal proteins previously reported to promote early resistance to FLT3i are also upregulated during gilteritinib resistance. The heterogeneity of stromal cell isolates detected by mass cytometry highlights the utility of high dimensional tracking of disease course in patients, and may enable a better understanding of how the temporal evolution of the marrow microenvironment contributes to development of resistance to targeted therapies such as gilteritinib and other FLT3i over time.

Based upon the clinical behavior of three patients, we suggest that the combination of low-dose Ara-C and all-trans retinoic acid may potentially be effective in some elderly patients, unfit for intensive chemotherapy, affected with NPM1-mutated acute myeloid leukemia without FLT3 mutations, warranting perspective clinical studies in these selected patients.

Whether or not FLT3 mutations are present and expressed within a leukemic hematopoietic stem cell has engendered some controversy. New evidence has now been presented on this issue that could change the way we manage the disease in the future.

Background: Conventional treatments for follicular thyroid cancer (FTC) can be ineffective, leading to poor prognosis. The aim of this study was to identify mutations associated with FTC that would serve as novel molecular markers of the disease and its outcome and could potentially identify new therapeutic targets. Methods: FLT3 mutations were first detected in a 29-year-old White female diagnosed with metastasized, treatment-refractory FTC. Analyses of FLT3 mutational status through next-generation sequencing of formalin-fixed, paraffin-embedded FTC specimens were subsequently performed in 35 randomly selected patients diagnosed with FTC. Results: FLT3 mutations were found in 69% of patients. FLT3 mutation-positive patients were significantly older than those that were FLT3 mutation-negative [median age at diagnosis 54 (36–82) versus 45 (27–58) ( p = 0.023)]. Patients over 60 years were 23 times more likely to be FLT3 mutation-positive ( p = 0.006). However, the number of FLT3 mutations did not correlate with age ( r-Pearson: –0.244, p-value: 0.25). A total of 26 mutations were identified in the FLT3 gene with 2–16 FLT3 mutations in each FLT3 mutation-positive patient (mean: 5.6 mutations/patient). Tyrosine kinase domain (TKD) mutations in the FLT3 gene were detected in 58% of FLT3 mutation-positive patients. All FLT3 mutation-positive patients with a disease stage of pT2N1 or worse harbored at least one mutation in the TKD of FLT3. Conclusions: There is a wide spectrum and high frequency of FLT3 mutations in FTC. The precise role of FLT3 mutations in the genesis of FTC, as well as its potential role as a therapeutic target, requires further investigation.

To perform a retrospective analysis of the prognostic relevance of clinicopathologic parameters in a well-documented cohort of patients treated with all-trans-retinoic acid (ATRA)-based induction regimens in order to discover which indicators can predict a high risk of early death (ED) and patient survival.We analyzed data of 288 newly diagnosed adult acute promyelocytic leukemia patients in Hangzhou, China. The median follow-up time was 32 months (range, 6-78 months).The 3-year disease-free and overall survival rates were 90.83% and 91.69%, respectively. In the multivariable analysis, older age (≥ 60 years) was the only independent risk factor for ED (hazard ratio [HR] = 15.057; P = .004). High white blood cell count was not a risk factor for ED (P = .055), but it was for relapse (HR = 2.7; P = .009). FLT3 mutation (HR = 3.9; 95% confidence interval, 1.4 to 10; P = .007) and older age (≥ 60 years) (HR = 5.3; 95% confidence interval, 2.4 to 11; P .001) were prognostic factors for poorer disease-free and overall survival. Interestingly, CD15 negativity (HR = 0.23; P = .049) was a prognostic factor for relapse. The ED rate was 5.9% (17/288 patients).The perceived impact of the identification of these high-risk factors should be described in order to decide whether any modifications to treatment strategy should be entertained.

To evaluate the efficacy and safety of midostaurin in combination with standard cytarabine and daunorubicin induction and cytarabine consolidation in newly diagnosed FLT3-mutated acute myeloid leukemia (AML).A literature search of PubMed and MEDLINE (September 2017) was performed using the terms midostaurin, PKC412, FLT3 gene, and acute myeloid leukemia.Clinical trials evaluating the efficacy and safety of midostaurin in combination with standard cytarabine and daunorubicin induction and cytarabine consolidation were reviewed for the treatment of newly diagnosed FLT3-mutated AML. All peer-reviewed articles with clinically relevant information were evaluated for inclusion.Midostaurin is a multikinase inhibitor also targeting FLT3 indicated for the treatment of newly diagnosed FLT3-mutated AML. A phase III trial illustrated that midostaurin in combination with standard chemotherapy improved event-free survival, disease-free survival, and overall survival in patients with newly diagnosed FLT3-mutation-positive AML compared with standard chemotherapy alone. However, midostaurin did not show a difference in the rate of patients who proceeded to receive an allogeneic stem cell transplant compared with placebo. There was no significant difference in toxicity between the midostaurin and placebo groups, except that more patients experienced grade 3 to 5 anemia and rash with midostaurin.Midostaurin in combination with standard induction and consolidation is safe and efficacious in newly diagnosed FLT3-mutated AML.

Allogeneic hematopoietic cell transplantation (HCT) has been increasingly used in the setting of FMS-like tyrosine kinase-3 (FLT3)-mutated AML. However, its role in conferring durable relapse-free intervals remains in question. Herein we sought to investigate FLT3 mutational status on transplant outcomes. We conducted a retrospective cohort study of 262 consecutive AML patients who underwent first-time allogeneic HCT (2008-2014), of whom 171 had undergone FLT3-ITD (internal tandem duplication) mutational testing. FLT3-mutated AML was associated with nearly twice the relapse risk (RR) compared with those without FLT3 mutation 3 years post-HCT (63% vs 37%, P

Background: A considerable number of patients with metastatic colorectal cancer progress after exhausting all approved standard therapies but maintain an adequate performance status and could be candidates for further treatment. We aim at reviewing our experience with sorafenib treatment of a patient with FLT3 mutation in refractory metastatic colorectal cancer. Methods: Treatment with sorafenib of a patient with metastatic colorectal cancer and FLT3 translocation who had previously been heavily treated. Results: The patient with metastatic colorectal cancer, aged 51 years, showed significant symptomatic and laboratory improvement with sorafenib treatment (400 mg twice daily). Conclusion: The presented case illustrates how an aggressive and refractory colorectal tumor may respond well to targeted therapy.

Dr Mead earned his medical degree from the University of Oxford and trained in hematology at St Bartholomew's Hospital and University College London. In 2007, he earned his PhD at UCL, which focused on the analysis of FLT3 mutations in acute myeloid leukemia. He is now Associate Professor of Hematology and MRC Senior Clinical Fellow at the WIMM, University of Oxford. His research group focuses on myeloid diseases and normal blood stem-cell biology. Dr Mead is the lead clinician for myeloproliferative neoplasms (MPN) and chronic myeloid leukemia in the Thames Valley Strategic Clinical Network and is the chief investigator for several chronic myeloid leukemia and MPN clinical trials. Additionally, Dr Mead has helped shape the diagnostic and treatment guidelines for MPNs in the UK and serves as the chair of the MPN clinical study subgroup of the National Cancer Research Institute.

The FMS-like tyrosine kinase 3 (FLT3) pathway has an important role in cellular proliferation, survival, and differentiation. Acute myeloid leukemia (AML) patients with mutated FLT3 have a large disease burden at presentation and a dismal prognosis. A number of FLT3 inhibitors have been developed over the years. The first-generation inhibitors are largely non-specific, while the second-generation inhibitors are more specific and more potent. These inhibitors are used to treat patients with FLT3-mutated AML in virtually all disease settings including induction, consolidation, maintenance, relapse, and after hematopoietic cell transplantation (HCT). In this article, we will review the use of FLT3 inhibitors in AML.

Two distinct forms of FMS-like tyrosine kinase 3 (FLT3) mutations, internal tandem duplication (ITD) in the juxtamembrane domain and point mutation within the activation loop of the tyrosine kinase domain (TKD), have been identified in considerable number of patients with AML. This study was aimed to analyze the impacts of these mutations on clinical outcomes, and assess the efficacy of different therapeutic regimens (allo-HSCT, sorafenib, or conventional chemotherapy) for AML patients with FLT3 mutations after the standard induction therapy.We analyzed DNA samples from 158 consecutive de novo AML patients (18-60 years, excluding APL) with FLT3 mutations between July 2010 and October 2015.We found that AML patients with FLT3-TKD mutations have more favorable clinical outcomes than those with FLT3-ITD mutations. We also found that allo-HSCT therapy subgroup achieved longer OS and RFS than non-allo-HSCT therapy subgroup for FLT3-ITD positive patients (p 0.001, p = 0.071). However, compared with the clinical outcomes in non-primary refractory patients, sorafenib did not show an obvious beneficial effect for the primary refractory patients. Further study on a large scale is still recommended.FLT3-TKD-mutated AML patients have more favorable clinical outcomes than those with FLT3-ITD mutations. Allo-HSCT therapy subgroup achieved longer OS and RFS than non-allo-HSCT therapy subgroup for FLT3-ITD positive patients. Compared with the clinical outcomes in non-primary refractory patients, sorafenib did not show an obvious beneficial effect for the primary refractory patients.

FLT3 mutations, generally associated with a poor prognosis, are found in approximately one-third of patients with acute myeloid leukemia (AML) and represent an attractive therapeutic target. FLT3 inhibitors undergoing clinical evaluation include first-generation relatively non-specific small molecules and second-generation compounds with higher potency and selectivity against mutant FLT3. Recently presented results from a prospective randomized clinical trial will likely lead to a change in the standard of care for younger patients with FLT3-mutated AML: addition of the multi-targeted FLT3 inhibitor midostaurin to standard induction and consolidation chemotherapy. Thus, personalized therapies for this subset of AML will soon be possible.

FLT3-internal tandem duplication occurs in 20–30% of acute myeloid leukemia and confers an adverse prognosis with its allelic ratio being a key risk stratifier. The US Food and Drug Administration recently approved FLT3 inhibitors midostaurin and gilteritinib in FLT3 mutation-positive acute myeloid leukemia. Historically, FLT3 was tested by fragment analysis, which has become the standard method endorsed by international guidelines. However, next generation sequencing is increasingly used at acute myeloid leukemia diagnosis given its ability to simultaneously evaluate multiple clinically informative markers. As FLT3-internal tandem duplication detection was known to be challenging by next generation sequencing and the results carry profound prognostic and therapeutic implications, it is important to thoroughly examine its performance in FLT3-internal tandem duplication detection and allelic ratio classification. In a comparative study with fragment analysis, we retrospectively reviewed our experience using a custom-designed, hybridization capture-based, targeted next generation sequencing panel. Among 7902 cases, FLT3-internal tandem duplication was detected in 335 with variable sizes (3–231 bp) and insertion sites. Fragment analysis was also performed in 402 cases, demonstrating 100% concordance in FLT3-internal tandem duplication detection. In 136 dual-tested, positive cases, 128/136 (94%) exhibited concordant high/low allelic ratio classifications. The remaining 6% showed borderline low allelic ratio by next generation sequencing. The two methods were concordant in FLT3-tyrosine kinase domain mutation detection at the hotspot D835/I836 targeted by fragment analysis. Furthermore, seven mutations which may benefit from FLT3 inhibitor therapy were detected by next generation sequencing, in regions not covered by fragment analysis. Our study demonstrates that using a hybridization capture-based chemistry and optimized bioinformatics pipeline, next generation sequencing can reliably detect FLT3-internal tandem duplication and classify its allelic ratio for acute myeloid leukemia risk stratification. Next generation sequencing also exhibits superior comprehensiveness in FLT3 mutation detection and may further improve personalized, targeted therapy in acute myeloid leukemia.

FLT3 is one of the most frequently mutated genes in acute myeloid leukemia. Previous studies have reported FLT3 mutation in as many as 9.2% of myeloproliferative neoplasms (MPNs) and myelodysplastic/myeloproliferative neoplasms (MDS/MPNs), as well as in chronic myelogenous leukemia, that are negative for the JAK2 V617F gene mutation; no FLT3 mutation has been found in JAK2-positive MPNs, suggesting that the mutations are mutually exclusive. The goal of our study is to evaluate the mutational status of the FLT3 gene in patients with an MPN or MDS/MPN, in correlation with the JAK2 mutational status. Patient specimens were retrospectively identified on the basis of MPN or MDS/MPN diagnosis and JAK2 analysis from February 2006 to December 2011. FLT3 mutation analysis was performed on DNA extracted from 152 patients using polymerase chain reaction amplification and analysis of amplicons by gel electrophoresis for internal tandem duplication mutations and by restriction endonuclease digestion fragment analysis for the D835 point mutation. FLT3 mutation analysis was performed on 90 cases of JAK2-negative MPN or MDS/MPN and 62 cases of JAK2-positive MPN. One FLT3 internal tandem duplication mutation was identified in the JAK2-negative group (1.1%), and none were identified in the JAK2-positive group, confirming the absence of FLT3 mutations in JAK2-positive specimens. The FLT3-positive MPN patient was diagnosed with MPN, unclassifiable, and was later found to have myeloid sarcoma; thus, FLT3 mutation was not seen in the usual types of MPN in our series. Our result of 1.1% FLT3 mutations in JAK2-negative MPN and MDS/MPN cases is lower than the 9.2% previously reported.

FMS-like tyrosine kinase 3 (FLT3) internal tandem duplication (ITD) mutations resulting in constitutive kinase activity are common in acute myeloid leukemia (AML) and carry a poor prognosis. Several agents targeting FLT3 have been developed, but their limited clinical activity suggests that the inhibition of other factors contributing to the malignant phenotype is required. We examined gene expression data sets as well as primary specimens and found that the expression of GLI2, a major effector of the Hedgehog (Hh) signaling pathway, was increased in FLT3-ITD compared to wild-type FLT3 AML. To examine the functional role of the Hh pathway, we studied mice in which Flt3-ITD expression results in an indolent myeloproliferative state and found that constitutive Hh signaling accelerated the development of AML by enhancing signal transducer and activator of transcription 5 (STAT5) signaling and the proliferation of bone marrow myeloid progenitors. Furthermore, combined FLT3 and Hh pathway inhibition limited leukemic growth in vitro and in vivo, and this approach may serve as a therapeutic strategy for FLT3-ITD AML.

Asian Pacific Journal of Cancer Prevention, 17, 9