Incidence of FLT3 and nucleophosmin gene mutations in childhood acute myeloid leukemia: Serbian experience and the review of the literature

Mutations in the fms-like tyrosine kinase 3 (FLT3) gene (internal tandem duplication (ITD) and point mutation in the tyrosine kinase domain, FLT3/D835) as well as the nucleophosmin (NPM1) gene are the most common abnormalities in adult acute myeloid leukemia (AML). Their significance in pediatric AML is still unclear. In this study we evaluated the frequency of FLT3 and NPM1 mutations in childhood AML. We also examined clinical features and outcome of these patients. FLT3 and NPM1 mutations were analysed in 42 and 37 childhood AML patients, respectively, using polymerase chain reaction (PCR) and direct sequencing. FLT3 mutations were detected in 4/42 patients (9.5%). The frequencies of FLT3/ITD and FLT3/D835 were the same, 2/42 (4.7%). NMP1 mutations were found in 1/37 patients (2.7%). FLT3 gene mutations were correlated with induction failure. Here we report the results of the study of FLT3 and NPM1 gene mutations in childhood AML patients in Serbia. Low frequencies of these molecular markers point out that these abnormalities are rare in this cohort of patients. Comparative study of data on NPM1 mutations in childhood AML revealed that various NPM1 gene mutation types are associated with childhood AML. Our findings as well as previously reported data, contributes to a hypothesis of different biology and etiology of adult and childhood AML. More extensive studies of NPM1 and FLT3 mutations in childhood AML are needed to determine their biological and clinical importance.     

Stability and prognostic influence of FLT3 mutations in paired initial and relapsed AML samples.

In acute myeloid leukemia (AML), activating mutations in the fms-like tyrosine kinase 3 (FLT3) gene predict poor prognosis. We determined FLT3 internal tandem duplications (FLT3/ITD) and D835 point mutations in paired initial and relapse samples from 80 pediatric and adult AML patients. One D835 point mutation was found in an initial pediatric AML sample. Fms-like tyrosine kinase 3/ITDs were present in 21 initial and 22 relapse samples (26.3 and 27.5%, respectively). Interestingly, FLT3/ITD positivity was related to a significantly shorter time to relapse, most pronounced when the ITD-positive status was found at relapse (P<0.001). However, FLT3/ITD status changed between diagnosis and relapse in 14 cases. In four patients, the FLT3/ITD became undetectable at relapse in five patients FLT3/ITDs were only detected at relapse, and in five patients the length or number of FLT3/ITDs changed. Gain of FLT3/ITDs may suggest oligoclonality with selective outgrowth of the FLT3/ITD-positive clone, whereas losses may reflect ITDs in the more mature leukemic cells rather than in the leukemic stem cell, or, alternatively, that other genetic aberrations provided a greater selective advantage. Studying FLT3/ITD kinetics in minimal residual disease setting may provide some answers for the changes we observed. Fms-like tyrosine kinase 3/ITD is a relevant marker for prognosis, and remains an important target for therapeutic inhibition.     

Molecular Characterization of FLT3 Mutations in Acute Leukemia Patients

Fms-like tyrosine kinase 3 (FLT3) performs a vital role in the pathogenesis of hematopoietic malignancies.Therefore in recent times, the focus of several studies was on use of FLT3 as a prognostic marker. The presentstudy investigated the molecular characterization and incidence of FLT3 mutations in acute leukemia patients inPakistan. A total of 55 patients were studied, of which 25 were suffering from acute lymphoblastic leukemia (ALL)and 30 were suffering from acute myeloid leukemia (AML). The polymerase chain reaction demonstrated FLT3/ITD mutations in 1 (4%) of 25 ALL patients, a male with the L2 subtype. In AML cases the rate was 4 (13.3%) of30, three males and one female. The AML-M4 subtype was found in three and the AML M2 subtype in the other.In the AML cases, a statistically significant (p=0.009) relationship was found between WBC (109/L) and FLT3/ITD positivity. However, no significant relationship was found with other clinical parameters (p>0.05). In acutemyeloid leukemia (AML) FLT3/ITD+ mutation was more prevalent in elderly patients 31-40 age groups, 21-30and 51-60 age groups respectively. In acute lymphoblastic leukemia (ALL) statistically no significant relationshipwas found between clinical features and FLT3/ITD positivity (p>0.05). However, in acute lymphoblastic leukemia(ALL) FLT3/ITD+ mutation was more commonly found in age groups of 21-30.     

Prognostic significance of FLT3 mutations in pediatric non-promyelocytic acute myeloid leukemia

FLT3 is a receptor tyrosine kinase involved in the survival of hematopoietic stem cells, and mutations of FLT3 have been reported to be of prognostic significance. This is the first study of FLT3 mutations in pediatric non-promyelocytic AML patients that received the same treatment scheme in single institute. FLT3 internal tandem duplication of the juxtamembrane domain (FLT3/ITD) and a point mutation in the tyrosine kinase domain (FLT3/TKD) were analyzed in 61 patients by PCR of genomic DNA. The incidence of FLT/ITD and FLT/TKD were 6.6% (4/61) and 3.3% (2/61), respectively. Patients with FLT3/TKD remain alive after autologous stem cell transplantation. The disease-free survival (DFS) of patients with FLT3/ITD (0%) was significantly lower than that of the others (52%). FLT3/ITD was the sole adverse prognostic factor for DFS by multivariate analysis (RR=5.6). Patients with FLT3/ITD relapsed early after complete remission even after receiving bone marrow transplantation from a matched related donor with little BuCy conditioning. New therapeutic scheme such as stem cell transplantation with more intensive conditioning just after complete remission could be applied in pediatric non-promyelocytic AML patients with the FLT3/ITD mutation.     

FLT3/ITD基因突变在不同血液肿瘤患者的表达及其临床意义

Objective:To analyze Fms-like tyrosine kinase 3(FLT3)/intemal-tandem duplications(ITD)murations in various kinds of hematologic malignancy patients.Methods:FLT3/ITD gene mutations were detected by polymerase chain reaction (PCR)in 103 acute myeloid leukemia(AML)cases,63 acute lymphocytic leukemia(ALL)cases,53 chronic myelogenous leukemia(CML)cases in chronic phase(CML-CP),34 CML cases in biast crisis(CML-BC),11 chronic lymphatic leukemia(CLL)cases,36 myelodysplastic syndrome (MDS)cases,9 multiple myeloma(MM)cases and 13 non-hodgkin's lymphoma (NHL)cases with marrow infiltration.Results:The expressions of FLT3/ITD gene mutations were detected in 22.3% AML cases.in 6.5%CML-BC cases.in 5.6%MDS cases and in 2.6%ALL cases.The two ALL cases with FLT3/ITD mutation were diagnosed as ALL-L2 with morphology and both with myeloid antigen expression,but finally were diagnosed as acute mixed-lineage leukemia after immunology examination.FLT3/ITD gene muIations were not detected in CML-CP,MM.NHL and CLL cases.In the 23 AML patients with FLT3/ITD gene mutation,including 2 of 8 M1(2.5%),8 of 33 M2(24-2%),7 of 24 M3(29.3%),2 of 11 M4(18.2%).3 of 21 M5(14.3%),1 of 5 M6(20%),and 0 of 1 M7 cases,and there were no significant differences in the positive rates of FLT3/ITD mutations between the FAB subtypes(P＞0.05).Statistical analyses showed that in AML patients,FLT3/ITD was associated with a higher pefipheral blood white cell(WBC)counts[(41.23±32.56)x 100/L vs (11.36±9.89)x109/L(P＜0.01)],higher percentage of bone marrow blast cells[(72.78±21.79)%vs(51.26±20.78)%(P＜0.05)],and higher cumulative relapse rates(63.6%vs 27.7%,P＜0.025)than those negative.Conclusion:FLT3/ITD gene mutation mainly pccurred in AML patients.and might be a strong prognostic factor which was associated with high peripheral WBC counts.bone marrow blast cell proportion and a increased relapse risk in AML.Detection of FLT3/ITD gene mutation might provide insights to explore a more accurate genotyping of leukemia,differential diagnosis between AML and ALL.subdivide risk level in AML and estimate prognosis of leukemia.     

Analysis of FLT3 internal tandem duplication and D835 mutations in Chinese acute leukemia patients

Genomic aberrations of Fms-like tyrosine kinase 3 (FLT3), including internal tandem duplication (ITD) and point mutations, have been demonstrated in 25–30% of adults acute myeloid leukemia (AML) and are markers of poor prognosis. FLT3/ITD and D835 mutations were analyzed in 194 Chinese patients with acute leukemia and myelodysplastic syndromes (MDS) by polymerase chain reaction (PCR). FLT3/ITDs and D835 mutations were found in 25.9 and 6.3% of 143 AML patients, respectively. Two patients showed both ITD and point mutations. Among the FAB subtypes of AML, the rate of FLT3 aberration was significantly higher in M3 and M5. However, neither aberrations was found in 25 patients with acute lymphoblastic leukemia (ALL), 2 acute hybrid leukemia, 17 MDS and 7 chronic myeloid leukemia in blast crisis (CML-BC). FLT3/ITD was associated to leukocytosis and lower complete remission (CR) rate, and was more prevalent in patients with normal karyotype. In contrast, D835 mutation was not associated with leukocytosis or low CR rate. Our results confirm that FLT3 activating mutations also occur in a significant percentage in Chinese AML patients. FLT3/ITD⁺ patients treated with standard induction regimen could achieve lower complete remission rates compared with patients not harboring this defect. Early detection of FLT3 mutations and an intensification of induction therapy might thus be useful for this group of patients to overcome the poor prognosis.     

Acquisition of FLT3 or N-ras mutations is frequently associated with progression of myelodysplastic syndrome to acute myeloid leukemia.

The role of internal tandem duplication of fms-like tyrosine kinase 3 (FLT3/ITD), mutations at tyrosine kinase domain (FLT3/TKD) and N-ras mutations in the transformation of myelodysplastic syndrome (MDS) to AML was investigated in 82 MDS patients who later progressed to AML; 70 of them had paired marrow samples at diagnosis of MDS and AML available for comparative analysis. Five of the 82 patients had FLT3/ITD at presentation. Of the 70 paired samples, seven patients acquired FLT3/ITD during AML evolution. The incidence of FLT3/ITD at diagnosis of MDS was significantly lower than that at AML transformation (3/70 vs 10/70, P<0.001). FLT3/ITD(+) patients progressed to AML more rapidly than FLT3/ITD(-) patients (2.5+/-0.5 vs 11.9+/-1.5 months, P=0.114). FLT3/ITD(+) patients had a significantly shorter survival than FLT3/ITD(-) patients (5.6+/-1.3 vs 18.0+/-1.7 months, P=0.0008). After AML transformation, FLT3/ITD was also associated with an adverse prognosis. One patient had FLT3/TKD mutation (D835Y) at both MDS and AML stages. Additional three acquired FLT3/TKD (one each with D835 H, D835F and I836S) at AML transformation. Five of the 70 matched samples had N-ras mutation at diagnosis of MDS compared to 15 at AML transformation (P<0.001), one lost and 11 gained N-ras mutations at AML progression. Coexistence of FLT3/TKD and N-ras mutations was found in two AML samples. N-ras mutations had no prognostic impact either at the MDS or AML stage. Our results show that one-third of MDS patients acquire activating mutations of FLT3 or N-ras gene during AML evolution and FLT3/ITD predicts a poor outcome in MDS.     

急性髓系白血病患者外周血细胞中FLT3基因表达与FLT3／ITD突变的关系及其意义

背景与目的：研究表明FLT3／ITD突变的急性髓性白血病（acutemyeloid leukemia,AML）患者预后差,但关于AML患者FLT3基因的表达水平在预后中的作用及其与FLT3／ITD突变关系的研究尚不充分。本研究探讨初治AML患者FLT3基因的表达水平与FLT3／ITD突变的关系及其临床意义。方法：建立实时荧光定量PCR检测FLT3基因表达水平及PCR检测FLT3／ITD突变的方法。分析79例初治AML患者FLT3基因水平、FLT3／ITD突变及与预后的关系。结果：22．7％（18／79）的AML患者存在FLT3／ITD突变。92．4％（73／79）的患者标本中可检测到FLT3基因表达,FLT3基因表达水平为0-7320,中位数为312,正常对照组未检测到FLT3基因的表达。FLT3基因高表达及FLT3／ITD突变AML组的白细胞计数及骨髓白血病细胞均显著高于低表达和无突变AML组（P〈0．05）。FLT3基因高表达的AML组FLT3／ITD突变率（25．6％）同低表达的AML组（20．0％）相比,差异无统计学意义（P〉0．05）,FLT3／ITD突变AML患者FLT3基因表达中位数与无突变组比较差异也无统计学意义。FLT3／ITD突变组的完全缓解率（58．8％）显著低于无FLT3／ITD突变组（82．1％）（P〈0．05）;FLT3基因高表达AML组FLT3／ITD的完全缓解率（68．6％）同低表达AML组（84．2％）相比差异无统计学意义（P〉0．05）,但无FLT3／ITD突变组中,FLT3基因高表达组完全缓解率（69．2％）显著低于低表达组（93-3％）（P〈0．05）。结论：FLT3高表达与FLT3／ITD突变之间无明显相关性,FLT3高表达对于无FLT3／ITD突变AML患者可能是一个预后不良的指标。     

Mutant FLT3 signaling contributes to a block in myeloid differentiation

FLT3 is a member of the class III receptor tyrosine kinase family and is primarily expressed on hematopoietic stem/progenitor cells. Somatic mutations of FLT3 involving internal tandem duplication (ITD) of the juxtamembrane domain or point mutations in the activation loop have been identified in ∼17 - 34% and 7 - 9% of acute myeloid leukemia (AML) patients, respectively. The ITD mutations appear to activate the tyrosine kinase domain through receptor dimerization in a FLT3 ligand-independent manner. Constitutively activated FLT3 provides cells with proliferative and anti-apoptotic advantages and portends an especially poor prognosis for patients with this mutation. FLT3/ITD mutations also contribute to a block of myeloid differentiation. FLT3 tyrosine kinase inhibitors suppress the growth and induce apoptosis and differentiation of leukemia cells expressing FLT3/ITD mutants. Therefore, FLT3 is a therapeutic target and inhibition of FLT3 tyrosine kinase activity may provide a new approach in the treatment of leukemia carrying these mutations.     

Fms-Like Tyrosine Kinase 3 Mutations in Childhood Acute Leukemias and their Association with Prognosis

Introduction: In recent years, Fms-like tyrosin kinase (FLT) 3 has been the subject of several studies as a prognostic marker. Objective: In this study, the presence of FLT3 mutations in childhood acute leukemias patients and their association with prognosis were investigated. Materials and Methods: A total of 120 patients, 80 with acute lymphoblastic leukemia (ALL) and 40 with acute myeloblastic leukemia (AML), were included. Real time polymerase chain reaction methods on a high resolution melting analysis device were used to determine FLT3 mutations. Results: FLT3/ITD (internal tandem duplication) mutations were found in 6 (7.5%) of the patients with ALL and in 9 (22.5%) of those with AML, whereas no FLT3/TKD (trans kinase domain) mutation was evident in any case. There was no difference between the ALL patients positive and negative for FLT3/ITD with regard to overall survival (OS), event free survival (EFS) and disease free survival (DFS) (p=0.37, p=0.23, p=0.023, respectively). However, in FLT3/ITD positive and negative AML patients, there was a statistically significant difference in OS (p=0.0041), but not EFS and DFS (p=0.09, p=0.095, respectively). A significant difference was found between age and FLT3/ITD positivity (p=0.036). Conclusion: We found that FLT3/ITD positivity increased with age and that it was associated with decrease in OS in AML patients, providing further evidence that it is an independent factor negatively influencing prognosis.     

Frequency of FLT3 Internal Tandem Duplications in Adult Syrian Patients with Acute Myeloid Leukemia and Normal Karyotype

Objective: Activating mutations of the fms-like tyrosine kinase 3 gene (FLT3) by internal tandem duplications (ITDs) in the juxtamembrane domain (JMD) have been reported in ~30% of adult acute myeloid leukemia (AML) patients with cytogenetically normal karyotype (CN). However, FLT3/ITD mutations are frequently accompanied with leukocytosis, high percentage of blasts in bone marrow (BM), and increased the risk of treatment failure in AML patients. FLT3-ITD mutated AML patients mainly with normal karyotype have higher relapse probability and shorter duration of complete remission (CR) after chemotherapy, so FLT3-ITD mutation is considered as an independent poor prognostic factor in AML. Methods: FLT3-ITD and FLT3-KTD were studied by polymerase chain reaction (PCR) and restriction fragment length polymorphism- PCR (RFLP-PCR) in 44 adults AML patients with cytogenetically normal karyotype (AML-CN) at diagnosis to characterize FLT3 status. The results were correlated with the prognostic factors. Results: In this study, FLT3-ITD mutations were identified in 7 (15.9%) of the 44 AML-CN patients. Among the 7 patients with FLT3/ITD mutations, 6 patients revealed a typical ITDs mutation (fragment size was 329 bp) and one patient showed untypical ITD mutation (fragment size was ~400 bp). Whereas 37 patients (61.7%) were FLT3-ITD. None of all AML-CN patients examined showed FLT3-KTD mutations. Conclusions: Our results support that FLT3-ITD are independent adverse prognostic factors for elderly AML-CN patients and are associated with low overall survival (OS), low rate of CR, high relapse rate (RR), and high percentage of BM blast at diagnosis. We concluded, FLT3 mutation analysis should be performed as a routine test in AML-CN patients.     

Internal tandem duplication of fms-like tyrosine kinase 3 is associated with poor outcome in patients with myelodysplastic syndrome

BACKGROUND: The prognostic significance of internal tandem duplication (ITD) of the fms-like tyrosine kinase 3 gene (FLT3) for patients with myelodysplastic syndrome (MDS) is not clearly defined. In the current study, the authors sought to assess the value of FLT3/ITD mutation status as a prognostic genetic marker for patients with MDS. METHODS: FLT3/ITD mutation status was evaluated by performing DNA polymerase chain reaction assays on 198 bone marrow samples obtained from patients with MDS at initial diagnosis. All aberrant products were sequenced, and GeneScan analysis was performed to measure FLT3/ITD mutant levels. RESULTS: Five patients (2.5%)--2 of the 99 patients who had refractory anemia with excess blasts and 3 of the 51 patients who had chronic myelomonocytic leukemia--had FLT3/ITD mutations. FLT3/ITD was not observed in any of the 48 patients who had refractory anemia (with or without ringed sideroblasts). There was no significant difference in clinicohematologic characteristics, cytogenetic characteristics, or International Prognostic Scoring System score between the FLT3/ITD-positive group and the FLT3/ITD-negative group. Four of the 5 patients carrying the FLT3/ITD mutation experienced progression of disease to acute myeloid leukemia (AML), compared with 70 of the 193 patients who did not have FLT3/ITD (P = 0.066). In addition, progression to AML was more rapid in patients with FLT3/ITD-positive disease than in patients with FLT3/ITD-negative disease (mean +/- standard error, 3.0 +/- 0.5 months vs. 62.8 +/- 5.6 months; P < 0.0001). Patients with FLT3/ITD-positive disease also had significantly shorter survival compared with patients who had FLT3/ITD-negative disease (mean +/- standard error, 5.2 +/- 1.4 months vs. 33.7 +/- 3.1 months; P < 0.0001). On multivariate analysis, FLT3/ITD was identified as an independent predictor of reduced time to development of AML (P = 0.0001) and reduced overall survival (P = 0.002). CONCLUSIONS: The results of the current study demonstrate that FLT3/ITD is associated with a high risk of transformation to AML, rapid progression of AML, and poor survival in patients with MDS.     

FLT3 K663Q is a novel AML-associated oncogenic kinase: Determination of biochemical properties and sensitivity to Sunitinib (SU11248).

Somatic mutations of FLT3 resulting in constitutive kinase activation are the most common acquired genomic abnormality found in acute myeloid leukemia (AML). The majority of these mutations are internal tandem duplications (ITD) of the juxtamembrane region (JM). In addition, a minority of cases of AML are associated with mutation of the FLT3 activation loop (AL), typically involving codons D835 and/or I836. We hypothesized that other novel mutations of FLT3 could also contribute to leukemogenesis. We genotyped 109 cases of AML and identified two novel gain-of-function mutations. The first mutation, N841 H, is similar to previously described mutations involving amino-acid substitutions of codon 841. The other novel mutation, FLT3 K663Q, is the first AML-associated gain-of-function mutation located outside the JM and AL domains. Of note, this mutation was potently inhibited by Sunitinib (SU11248), a previously described FLT3 kinase inhibitor. Sunitinib reduced the proliferation and induced apoptosis of transformed Ba/F3 cells expressing FLT3 K663Q. The potency of Sunitinib against FLT3 K663Q was similar to its potency against FLT3 ITD mutations. We conclude that FLT3 mutations in AML can involve novel regions of the TK1. Future studies are needed to define the incidence and prognostic significance of FLT3 mutations outside the well-established JM and AL regions.     

Better detection of FLT3 internal tandem duplication using peripheral blood plasma DNA.

Somatic mutation of the FLT3 gene as an internal tandem duplication (ITD) of the juxtamembrane domain-coding sequence causes constitutive tyrosine phosphorylation and activation. Tumor-specific DNA has been documented in the sera of patients with solid tumors even when it is in an early stage. We compared the detection of FLT3 ITD in DNA extracted from cells of bone marrow (BM) aspirations with DNA extracted from peripheral blood (PB) plasma in patients newly diagnosed with acute myeloid leukemia (AML; 85 patients), myelodysplastic syndrome (MDS; 16 patients), and acute lymphocytic leukemia (ALL; 16 patients). FLT3 ITD was detected in 18 (21%) AML samples and in one (6%) MDS sample in both cellular and plasma DNA but in none of the ALL samples. Hemizygous/homozygous FLT3 ITD was detected in five (28%) of the FLT3 ITD-positive AML using plasma DNA, whereas only four of these cases showed hemizygous/homozygous FLT3 ITD using cellular DNA. The presence of FLT3 ITD was associated with significantly shorter survival (P = 0.02) when only patients younger than 50 years of age (48 AML+MDS patients) were considered. This finding was independent of cytogenetics in this age group. However, patients with the FLT3 ITD hemizygous/homozygous phenotype had even shorter survival (P = <0.001). As expected, the presence of FLT3 ITD correlated with higher white blood cell (WBC) counts. These data demonstrate that plasma DNA is a reliable alternative resource for detecting FLT3ITD, especially the hemizygous/homozygous genotype. Furthermore, the data derived from this study support the notion that the presence of FLT3 ITD in conjunction with the absence of the wild-type FLT3 allele predicts an especially poor prognosis for patients with AML.     

FLT3-TKD mutation in childhood acute myeloid leukemia.

Mutations of receptor tyrosine kinases are implicated in the constitutive activation and development of human hematologic malignancies. An internal tandem duplication (ITD) of the juxtamembrane domain-coding sequence of the FLT3 gene (FLT3-ITD) is found in 20-25% of adult acute myeloid leukemia (AML) and at a lower frequency in childhood AML. FLT3-ITD is associated with leukocytosis and a poor prognosis, especially in patients with normal karyotype. Recently, there have been three reports on point mutations at codon 835 of the FLT3 gene (D835 mutations) in adult AML. These mutations are located in the activation loop of the second tyrosine kinase domain (TKD) of FLT3 (FLT3-TKD). The clinical and prognostic relevance of the TKD mutations is less clear. To the best of our knowledge, there has been no report to describe FLT3-TKD mutations in childhood AML. In this pediatric series, FLT3-TKD mutations occurred in three of 91 patients (3.3%), an incidence significantly lower than that of FLT3-ITD (14 of 91 patients, 15.4%) in the same cohort of patients. None of them had both FLT3-TKD and FLT3-ITD mutations. Sequence analysis showed one each of D835 Y, D835 V, and D835 H. Of the three patients carrying FLT3-TKD, two had AML-M3 with one each of L- and V-type PML-RARalpha, and another one had AML-M2 with AML1-ETO. None of our patients with FLT3-TKD had leukocytosis at diagnosis. At bone marrow relapse, one of the four patients examined acquired FLT3-ITD mutation and none gained FLT3-TKD mutation.     

Prognostic significance of FLT3 internal tandem duplication and tyrosine kinase domain mutations for acute myeloid leukemia: a meta-analysis.

Two distinct forms of fms-like tyrosine kinase (FLT3) gene aberrations, internal tandem duplication (ITD) and tyrosine kinase domain (TKD) mutations, have been recognized in a substantial proportion of patients with acute myeloid leukemia (AML). To investigate their prognostic significance, we performed a meta-analysis of the four published studies that provided survival information according to the FLT3 status: ITD, TKD mutation, and wild type. The summary hazard ratios for disease-free survival (DFS) were 1.88 (95% confidence interval (CI) 1.58-2.23; P<0.001) for FLT3 mutations, 1.86 (95% CI: 1.52-2.29; P<0.001) for ITD, and 1.90 (95% CI: 1.40-2.60; P<0.001) for TKD mutation. The corresponding ratios for overall survival were 1.61 (95% CI: 1.37-1.89; P<0.001), 1.68 (95% CI: 1.39-2.03; P<0.001), and 1.37 (95% CI: 0.94-2.01; P=0.104). Neither white blood cell count at diagnosis nor cytogenetic risk category was a significant source of heterogeneity. These findings indicate that FLT3 mutations have an adverse effect on the outcome for AML, and that the negative impact of TKD mutation seems comparable to that of ITD with regard to DFS. Although it should be borne in mind that this meta-analysis was based on data abstracted from observational studies, these results may justify the risk-adapted therapeutic strategies for AML according to the FLT3 status.     

FLT3 and NPM1 gene mutations in childhood acute myeloblastic leukemia

Mutations of receptor tyrosine kinases are implicated in the constitutive activation and development of human hematologic malignancies. Mutations in fms-like tyrosine kinase 3 (FLT3) gene including internal tandem duplication (ITD) and point mutation in the tyrosine kinase domain (TKD) as well as in nucleoplasmin (NPM1) gene are associated with pathogenesis of acute myeloblastic leukemia (AML). Several reports have demonstrated high incidences of the FLT3 and NPM1 mutations in adult AML patients. Since the pathogenesis of pediatric AML is different from that of adult and the FLT3 and NPM1 mutations have not been well characterized in childhood AML. Therefore, the objective of this study was to determine the frequencies of FLT3 and NPM1 mutations in 64 newly diagnosed childhood AML patients. All blood and bone marrow samples were previously diagnosed with AML by using flow cytometry and/or cytochemistry. FLT3-ITD and FLT3-TKD were detected by PCR and PCR-RFLP methods, respectively. The NPM1 mutation was analyzed by PCR and direct DNA sequencing. The FLT3 mutations were detected in 7 of 64 (11.1%), including FLT3-ITD in 4 of 64 (6.3%) and FLT-TKD in 3 of 62 (4.8%). The NPM1 mutation was not detected in this cohort. By multivariate analysis, white blood cell counts, peripheral blood and bone marrow blast cell counts at diagnosis were significantly higher in children with FLT3-ITD (P<0.05). In addition, the median percentage of CD117 was significantly higher in leukemic blast cells with FLT3-ITD than those with wild type (P=0.01). We did not find any FLT3 mutations in children aged less than 5 years. The AML M3 cell type was most frequently associated with FLT3 gene mutations (50%). In conclusion, the FLT3 mutations was found in 11.1% but none of NPM1 mutation was detected in Thai children with AML. These data support the hypothesis of different biology and pathogenesis between adult and childhood AML.