Bone marrow stroma‐mediated resistance to FLT3 inhibitors in FLT3‐ITD AML is mediated by persistent activation of extracellular regulated kinase

A consistent pattern of response has been observed when FMS‐like tyrosine kinase 3 (FLT3) tyrosine kinase inhibitors (TKIs) have been used as monotherapy to treat patients with relapsed or refractory FLT3‐ internal tandem duplication (ITD) acute myeloid leukaemia (AML). Circulating blasts are cleared from the peripheral blood, while bone marrow blasts are either unaffected or are cleared from the marrow at a much slower rate. We used an in vitro model of FLT3‐ITD AML blasts co‐cultured with normal human bone marrow stromal cells to investigate the basis for this dichotomous response pattern to FLT3 inhibitors. We have found that in blasts on stroma, potent FLT3 inhibition predominantly results in cell cycle arrest rather than apoptosis. The anti‐apoptotic effect is mediated through a combination of direct cell‐cell contact and soluble factors. The addition of exogenous FLT3 ligand (FL) augments the protection, primarily by shifting the 50% inhibitory concentration for FLT3 inhibition upwards. Cytokine‐activated extracellular regulated kinase (ERK), rather than STAT5, appears to be the most important downstream signalling protein mediating the protective effect, and inhibition of MEK significantly abrogates stromal‐mediated resistance. These findings explain the phenomenon of peripheral blood versus bone marrow blast responses and suggest that the combination of potent FLT3 inhibition and MEK inhibition is a promising strategy for the treatment of FLT3‐ITD AML.     

FLT3/ITD expression increases expansion, survival and entry into cell cycle of human haematopoietic stem/progenitor cells

Activating mutation of FLT3 by internal tandem duplications (ITDs) in the juxtamembrane region is the most common molecular aberration found in acute myeloid leukaemia (AML). In this study, a lentiviral vector containing two promoters achieved consistent and efficient co-expression of FLT3/ITD and GFP in transduced human CD34(+) haematopoietic stem/progenitor cells (HSPCs). When cultured in medium containing stem cell factor, thrombopoietin and FLT3 ligand (FL), FLT3/ITD-transduced cells demonstrated enhanced self-renewal and survival potential, unaffected by the withdrawal of FL. These cells retained a CD34(+)CD38(-/dim) immunophenotype, typical of HSPCs. Compared to cells transduced with a vector expressing GFP alone, FLT3/ITD-transduced HSPCs had a higher fraction of cells in active cell cycle. FLT3/ITD-transduced HSPCs were more sensitive to the induction of cytotoxicity by CEP-701, a selective FLT3 inhibitor, indicating a rapid 'addiction' to signalling through this oncogenic pathway. The FLT3/ITD-transduced HSPCs showed increased expression of Pim-1, c-Myc and Cyclin D3 (CCND3), each of which may contribute to the altered genetic programme instituted by FLT3/ITD signalling. Taken together, these results indicate that FLT3/ITD mutations may contribute to leukaemic transformation of normal HSPCs by prolonging survival, promoting proliferation and partially blocking differentiation. CEP-701 may act as a potent therapeutic agent for AML stem cells harbouring FLT3/ITD mutations.     

The genotype nucleophosmin mutated and FLT3‐ITD negative is characterized by high bax/bcl‐2 ratio and favourable outcome in acute myeloid leukaemia

Nucleophosmin gene (NPM1) mutations characterize acute myeloid leukaemia (AML) with normal karyotype and frequently co‐exist with FLT3 internal tandem duplications (ITD). We evaluated bcl‐2, bax, NPM1 and FLT3‐ITD in 222 AML patients. Bax/bcl‐2 ratio >0·35 and NPM1 without FLT3‐ITD were significantly associated (P = 0·0001). NPM1‐mutated (mt)/FLT3‐ITD negative patients showed a higher complete remission (CR) rate (90%, P = 0·0002) and a longer overall survival (OS, P = 0·00007). NPM1‐mt/FLT3‐ITD negative plus bax/bcl‐2 > 0·35 subset showed a very high CR rate (96%), very long OS (P = 0·00005) and disease‐free survival (P = 0·004). The favourable prognosis of NPM1‐mt/FLT3‐ITD negative patients might be explained by a higher bax/bcl‐2 ratio.     

Identification of emerging FLT3 ITD‐positive clones during clinical remission and kinetics of disease relapse in acute myeloid leukaemia with mutated nucleophosmin

FLT3 internal tandem duplication (ITD) mutations are frequently detected at diagnosis in cytogenetically normal acute myeloid leukaemia (CN‐AML) and predict unfavourable outcome. FLT3 ITD is an unstable aberration and may be lost or acquired at relapse. Recent whole genome sequencing studies have suggested that FLT3 ITD⁺ve AML relapse may evolve from small subclones undetectable at diagnosis by routine polymerase chain reaction (PCR). We developed a patient‐specific real‐time quantitative‐PCR (RQ‐PCR) to implement FLT3 ITD detection in six AML patients whose blasts carried wild‐type FLT3 at diagnosis and who relapsed with FLT3 ITD by routine PCR. Patient‐specific forward primers were designed after cloning and sequencing the FLT3 ITD in each case. The assay allowed retrospective detection of FLT3 ITD in diagnostic samples of 4/6 cases and to establish the kinetics of clonal evolution preceding relapse. After conventional chemotherapy, all patients had early relapse despite having been classified as NPM1⁺ve/FLT3 ITD^?ve at presentation, with shorter remissions being observed in four patients re‐classified as FLT3 ITD⁺ve by the new assay. Notably, FLT3 ITD clone became detectable by conventional PCR in three patients tested during remission after initial treatment. Our data underscore the need of identifying low FLT3 ITD levels, which are probably associated with relapse in otherwise good prognosis CN‐AML.     

Acute myeloid leukaemia blast cells with a tyrosine kinase domain mutation of FLT3 are less sensitive to lestaurtinib than those with a FLT3 internal tandem duplication

FLT3 tyrosine kinase domain mutations (FLT3/TKDs) are associated with a favourable prognosis in acute myeloid leukaemia (AML), unlike FLT3 internal tandem duplications (FLT3/ITDs) that have a poor prognosis. Whilst FLT3/ITD+ cells are more susceptible to the cytotoxic effects of FLT3 inhibitors than wild type (WT) cells, the sensitivity of FLT3/TKD+ cells to therapeutic agents is unclear, as is the importance of the mutant level. We therefore studied the effect of cytarabine and the FLT3 inhibitor lestaurtinib, either alone or in combination, on in vitro survival of blast cells from 36 cases of AML (14 FLT3/WT, 11 FLT3/ITD+ and 11 FLT3/TKD+). All three groups showed similar sensitivity to the cytotoxic effects of cytarabine but FLT3/ITD mutant level was inversely correlated with cytarabine cytotoxicity (P = 0.04) whereas FLT3/TKD mutant level had no impact. FLT3/TKD+ cells showed a similar response to lestaurtinib as FLT3/WT cells, whereas FLT3/ITD+ cells were more sensitive (P = 0.004). There was no correlation between mutant level and lestaurtinib sensitivity for either FLT3/ITD+ or FLT3/TKD+ cells. Synergistic cytotoxicity of lestaurtinib plus cytarabine was demonstrated in all three groups. These results suggest that FLT3/TKD+ and FLT3/WT cases should not be differentiated when considering patients for treatment with FLT3 inhibitors.     

Mild chronic graft‐versus‐host disease may alleviate poor prognosis associated with FLT3 internal tandem duplication for adult acute myeloid leukemia following allogeneic stem cell transplantation with myeloablative conditioning in first complete remission: a retrospective study

Internal tandem duplication (ITD) of the FLT3 gene (Fms‐like tyrosine kinase 3) is the most commonly found mutation in acute myeloid leukemia (AML). The significance of FLT3‐ITD at diagnosis was retrospectively estimated for allo‐HSCT (allogeneic hematopoietic stem cell transplantation) outcomes in 140 patients, median age of 38, undergoing allo‐HSCT after myeloablative conditioning in first complete remission of AML. FLT3‐ITD was detected at AML diagnosis in 42/140 (30%) of included into this study patients. At 3 years, relapse incidence (RI) following allo‐HSCT in AML patients with intermediate or normal karyotype was significantly higher in those FLT3‐ITD positive than FLT3‐ITD negative [52.9 vs. 20.4%, P = 0.002]. Additionally, patients with mild chronic graft‐versus‐host disease (cGvHD) had significantly lower RI compared to patients with moderate or severe grade cGvHD or those not experiencing cGvHD, respectively, 4.8 vs. 36.0 vs. 27.8%, P = 0.032. FLT3‐ITD was harboring a poor prognosis in AML with intermediate or normal karyotype and significantly increased risk of relapse following allo‐HSCT. It appears that allo‐HSCT does not cure patients with FLT3‐ITD, unless they develop symptoms of mild cGvHD and graft versus leukemia, which may decrease RI.     

Salvage therapy using FLT3 inhibitors may improve long‐term outcome of relapsed or refractory AML in patients with FLT3‐ITD

To determine the long‐term efficacy of FLT3 inhibitors (FLT3i) in the salvage setting for relapsed and refractory (rel/ref) acute myeloid leukemia (AML) with FLT3 internal tandem duplication (AML FLT3‐ITD), we conducted a retrospective study of 120 patients with rel/ref AML FLT3‐ITD who received salvage therapy with either FLT3i‐containing regimen (FLT3i group, N = 45) or conventional cytotoxic regimen (conventional group, N = 75). The median overall survival (OS) after the first salvage in the FLT3i group was 6·9 vs. 4·6 months in the conventional group (P = 0·17). The OS was better in the FLT3i group among patients with initial complete remission (CR) duration ≤12 months or with primary refractory disease (6·9 vs. 3·7 months; P < 0·01). The OS was better when FLT3i was combined with cytotoxic agents versus monotherapy (17 vs. 4·8 months; P = 0·017). Multivariate analysis revealed that the use of FLT3i was an independent predictor of OS (hazard ratio 0·58; 95% confidence interval, 0·38–0·88). Incorporating FLT3i into salvage strategies may improve long‐term outcome of patients with AML FLT3‐ITD. Prospective studies to validate this conclusion are warranted.     

Pediatric AML primary samples with FLT3/ITD mutations are preferentially killed by FLT3 inhibition

Pediatric acute myelogenous leukemia (AML) has a poor prognosis, and novel therapies are needed. The FLT3 tyrosine kinase represents a promising target in pediatric AML. FLT3 is constitutively activated either by an internal tandem duplication (ITD) or by a point mutation (PM) in 17% to 24% of pediatric AML cases. Autocrine stimulation of wild-type (WT) FLT3 by coexpressed FLT3 ligand (FL) occurs in many other cases. FLT3/ITD mutations confer a particularly poor prognosis in pediatric AML patients. Inhibitors of FLT3 are being tested in adult AML patients, with promising preliminary results. In this study, cytotoxicity and apoptosis assays were performed on 44 diagnostic pediatric AML blast samples (14 FLT3/WT, 15 FLT3/ITD, 15 FLT3/PM) using CEP-701, a potent and selective FLT3 inhibitor. Pronounced cytotoxicity and induction of apoptosis were observed in a higher percentage of FLT3/ITD samples (93%) than FLT3/PM (27%) or FLT3/WT (29%). The cytotoxicity was greatest in samples with a high FLT3/ITD mutant-to-wild-type allelic ratio. The addition of FL enhanced the survival and augmented the sensitivity to FLT3 inhibition for the CEP-701-responsive subset of FLT3/WT and FLT3/PM samples. Clinical testing of FLT3 inhibitors as molecularly targeted agents for the improvement of outcome of pediatric AML patients is warranted.     

Acute myeloid leukaemia (AML) with t(6;9)(p23;q34) is associated with poor outcome in childhood AML regardless of FLT3‐ITD status: a report from the Children's Oncology Group

Acute myeloid leukaemia (AML) with t(6;9)(p23;q34) is a rare subtype associated with FLT3‐internal tandem duplication (ITD) and poor outcomes. The clinical outcomes of paediatric patients with t(6;9) with and without FLT3‐ITD treated on six consecutive cooperative trails were evaluated. In contrast to patients without t(6;9), those with t(6;9) had a significantly lower complete remission rate, higher relapse rate (RR), and poor overall survival (OS). Within t(6;9) patients, those with and without FLT3‐ITD had an OS of 40% and 27% respectively (P > 0·9), demonstrating that t(6;9) is a high‐risk cytogenetic feature in paediatric AML and its clinical impact is independent of the presence of FLT3‐ITD.     

FLT3/ ITD regulates leukaemia cell adhesion through α4β1 integrin and Pyk2 signalling

Internal tandem duplication of FMS-like receptor tyrosine kinase 3 (FLT3/ITD) within its juxtamembrane domain is a frequent mutation in adult acute myeloid leukaemia (AML). This mutation causes constitutive activation of FLT3 and is associated with poor prognosis. The high relapse rate of FLT3/ITD-positive AML might be partly because of insufficient eradication of slow-cycling leukaemic stem cells in the bone marrow microenvironment. β1 integrin mediates haematopoietic stem and progenitor cell homing along with their retention in the bone marrow and also inhibits haematopoietic proliferation and differentiation. Here, we demonstrate that inhibition of FLT3/ITD kinase activity by a FLT3 selective inhibitor named FI-700 decreases affinity of α4β1 integrin to soluble VCAM-1. α4β1 integrin deactivation by FI-700 is independent of Rap1, which is the critical regulator of integrin inside-out signalling. In addition, selective inhibition of FLT3/ITD induces Pyk2 dephosphorylation together with the inhibition of phosphatidylinositol-3-kinase (PI3K)/Akt pathway. Both wild-type and ITD-FLT3 proteins co-immunoprecipitated with β1 integrin and Pyk2 indicating the signal crosstalk between FLT3, β1 integrin and Pyk2. These results collectively indicated that the inhibition of FLT3 kinase might contribute not only to the induction of apoptosis, but also to the leukaemia cell detachment from the bone marrow microenvironment in the treatment of AML.     

C/EBPA gene mutation and C/EBPA promoter hypermethylation in acute myeloid leukemia with normal cytogenetics

In the current study, we investigated C/EBPA gene mutations and promoter hypermethylation in a series of 53 patients with CN‐AML. In addition, we also analyzed two other frequent mutations (FLT3/ITD and NPM1) in these patients and correlated them with C/EBPA gene alterations. 13/53 patients were FLT3/ITD+/NPM1‐, 11/53 patients were FLT3/ITD+/NPM1+, 9/53 patients were FLT3/ITD‐/NPM1+, and 20/53 patients were FLT3/ITD‐/NPM1‐. Four of 53 cases displayed C/EBPA mutations, whereas 49 cases had only C/EBPA wild‐type alleles. Of the four positive cases, three patients had N‐terminal mutations only, whereas one patient had mutations in both the N‐ and C‐terminal region. Two of the four positive cases also harbored both FLT3/ITD and NPM1 mutation simultaneously, whereas the other two patients had neither FLT3/ITD nor NPM1 mutations. Furthermore, 7/53 cases displayed C/EBPA promoter hypermethylation. Interestingly, they were all in CN‐AML cases without FLT3/ITD or NPM1 mutations. None of the seven patients with C/EBPA promoter hypermethylation showed C/EBPA mutation. In conclusion, C/EBPA mutation and promoter hypermethylation can be detected at a relatively low frequency in de novo CN‐AML patients, suggesting they may contribute to leukemogenesis. C/EBPA mutation appears to be seen in “high‐risk” AML (FLT3/ITD+/NPM1+; FLT3/ITD+/NPM1‐ or FLT3/ITD‐/NPM1‐), while C/EBPA hypermethylation appears to be more common in AML with FLT3/ITD‐ /NPM1‐ and is not associated with C/EBPA mutation. Am. J. Hematol. 2010. © 2010 Wiley‐Liss, Inc.     

FLT3 mutations in myeloid sarcoma

Myeloid sarcoma is an extramedullary tumour that typically occurs in the setting of acute myeloid leukaemia (AML), or myeloproliferative disorders. In AML, two types of mutations in Fms-like tyrosine kinase 3 (FLT3) have been described; internal tandem duplications (ITD) and point mutations at aspartic acid residue 835 (D835). We analysed 24 myeloid sarcoma specimens from 20 patients for FLT3 ITD and D835 mutations. FLT3 ITD mutations were identified in three of 20 cases (15%); no D835 mutations were identified. The ITD inserts ranged in size from 33 to 198 base pairs (bp) and represented approximately 20-40% of the FLT3 alleles. Two cases showed discordance in FLT3 ITD mutational status. In one case, the leukaemia specimen was positive for a FLT3 ITD mutation and the myeloid sarcoma specimen was negative. In the second case, the myeloid sarcoma was positive for a FLT3 ITD mutation at diagnosis, but negative in subsequent relapse samples. Our findings suggest that small molecule inhibitors of FLT3 may be useful therapeutic agents for treatment of myeloid sarcomas-containing FLT3 mutations, however, the potential for discordance between the leukaemia and myeloid sarcoma, necessitates that the myeloid sarcoma tumour itself be analysed for FLT3 mutations.     

Haematopoietic cell transplantation with and without sorafenib maintenance for patients with FLT3‐ITD acute myeloid leukaemia in first complete remission

We performed a retrospective study analysing the effect of sorafenib, an oral fms‐Like Tyrosine Kinase 3 (FLT3)/multikinase inhibitor, as post‐transplant maintenance in adult patients with FLT3‐internal tandem duplication (ITD) acute myeloid leukaemia (AML). We identified consecutive patients with FLT3‐ITD AML diagnosed between 2008 and 2014 who received haematopoietic cell transplantation (HCT) in first complete remission (CR1). Post‐HCT initiation of sorafenib (yes/no) was evaluated as a time‐varying covariate in the overall survival/progression‐free survival (OS/PFS) analysis and we performed a landmark analysis of controls alive without relapse at the median date of sorafenib initiation. We identified 26 sorafenib patients and 55 controls. Median follow‐up was 27·2 months post‐HCT for sorafenib survivors, and 38·4 months for controls (P = 0·021). The median time to initiating sorafenib was 68 days post‐HCT; 43 controls were alive without relapse at this cut‐off. Sorafenib patients had improved 2‐year OS in the d+68 landmark analysis (81% vs. 62%, P = 0·029). Sorafenib was associated with improved 2‐year PFS (82% vs. 53%, P = 0·0081) and lower 2‐year cumulative incidence of relapse (8·2% vs. 37·7%, P = 0·0077). In multivariate analysis, sorafenib significantly improved OS [Hazard ratio (HR) 0·26, P = 0·021] and PFS (HR 0·25, P = 0·016). There was no difference in 2‐year non‐relapse mortality (9·8% vs. 9·3%, P = 0·82) or 1‐year chronic graft‐versus‐host disease (55·5% vs. 37·2%, P = 0·28). These findings suggest potential benefit of post‐HCT sorafenib in FLT3‐ITD AML, and support further evaluation of post‐HCT FLT3 inhibition.     

Lymphotoxin‐β receptor in microenvironmental cells promotes the development of T‐cell acute lymphoblastic leukaemia with cortical/mature immunophenotype

Lymphotoxin‐mediated activation of the lymphotoxin‐β receptor (LTβR; LTBR) has been implicated in cancer, but its role in T‐cell acute lymphoblastic leukaemia (T‐ALL) has remained elusive. Here we show that the genes encoding lymphotoxin (LT)‐α and LTβ (LTA, LTB) are expressed in T‐ALL patient samples, mostly of the TAL/LMO molecular subtype, and in the TEL‐JAK2 transgenic mouse model of cortical/mature T‐ALL (Lta, Ltb). In these mice, expression of Lta and Ltb is elevated in early stage T‐ALL. Surface LTα₁β₂ protein is expressed in primary mouse T‐ALL cells, but only in the absence of microenvironmental LTβR interaction. Indeed, surface LT expression is suppressed in leukaemic cells contacting Ltbr‐expressing but not Ltbr‐deficient stromal cells, both in vitro and in vivo, thus indicating that dynamic surface LT expression in leukaemic cells depends on interaction with its receptor. Supporting the notion that LT signalling plays a role in T‐ALL, inactivation of Ltbr results in a significant delay in TEL‐JAK2‐induced leukaemia onset. Moreover, young asymptomatic TEL‐JAK2;Ltbr^?/? mice present markedly less leukaemic thymocytes than age‐matched TEL‐JAK2;Ltbr^+/+ mice and interference with LTβR function at this early stage delayed T‐ALL development. We conclude that LT expression by T‐ALL cells activates LTβR signalling in thymic stromal cells, thus promoting leukaemogenesis.     

Immunophenotypic features of acute myeloid leukaemia patients exhibiting high FLT3 expression not associated with mutations

FMS-related tyrosine kinase 3 (FLT3) mutations are found in 30% of cases of acute myeloid leukaemia (AML). In addition, recent studies have lead to the identification of about 10-15% of AML patients displaying high expression of FLT3, not associated with mutations of the receptor (FLT3 Wild-type High, FLT3WTH). These AMLs, as well as those displaying internal tandem duplication (ITD) are associated with an unfavourable prognosis. However, the biological features of these AMLs are poorly characterized. The present study explored the immunophenotypic features of FLT3WTH AMLs in 94 de novo cases of AML. The levels of FLT3 expression, as assessed by flow cytometry and FLT3 mutational status, was used to identify four AML subgroups: FLT3WTH (14/94); FLT3 Wild-type low (FLT3WTL, 48/94); FLT3 internal tandem duplication (FLT3ITD 26/94); FLT3 aspartic acid 835 (FLT3D835, 6/94). FLT3WTH and FLT3ITD were characterized by: high white blast cell counts; predominance of M4 and M5 French-American-British classification subtypes and associated expression of myelo-monocytic markers; high expression of CD123 and TRAIL-Rs; high expression of receptors for angiogenic growth factors. Addition of FLT3 Ligand to human CD34(+) or monocytic cells stimulated CD123 and TRAIL-R expression. These findings are of potential value for the development of new therapeutic strategies.     

Comparison of effects of midostaurin,crenolanib, quizartinib,gilteritinib, sorafenib and BLU-285 on oncogenic mutants of KIT,CBL and FLT3 in haematological malignancies

Mutations in two type-3 receptor tyrosine kinases (RTKs), KIT and FLT3, are common in both acute myeloid leukaemia (AML) and systemic mastocytosis (SM) and lead to hyperactivation of key signalling pathways. A large number of tyrosine kinase inhibitors (TKIs) have been developed that target either FLT3 or KIT and significant clinical benefit has been demonstrated in multiple clinical trials. Given the structural similarity of FLT3 and KIT, it is not surprising that some of these TKIs inhibit both of these receptors. This is typified by midostaurin, which has been approved by the US Food and Drug Administration for mutant FLT3-positive AML and for KIT D816V-positive SM. Here, we compare the in vitro activities of the clinically available FLT3 and KIT inhibitors with those of midostaurin against a panel of cells expressing a variety of oncogenic FLT3 or KIT receptors, including wild-type (wt) FLT3, FLT3-internal tandem duplication (ITD), FLT3 D835Y, the resistance mutant FLT3-ITD+ F691L, KIT D816V, and KIT N822K. We also examined the effects of these inhibitors in vitro and in vivo on cells expressing mutations in c-CBL found in AML that result in hypersensitization of RTKs, such as FLT3 and KIT. The results show a wide spectrum of activity of these various mutations to these clinically available TKIs.     

The expression of P-glycoprotein in AML cells with FLT3 internal tandem duplications is associated with reduced apoptosis in response to FLT3 inhibitors

P-glycoprotein (pgp), a membrane efflux pump, is recognized to have an anti-apoptotic function. Internal tandem duplications (ITDs) of the Fms-like tyrosine kinase 3 (FLT3) receptor are the most common mutations in acute myeloid leukaemia (AML). Both ITDs and pgp positivity confer an adverse clinical prognosis. FLT3 inhibitors induce variable apoptosis in cell lines transfected with FLT3 ITDs. We studied the effect of herbimycin A, AG1296 and PKC412 on primary AML blasts. All compounds showed significantly higher cell kill after 48-h incubation in samples with an ITD compared with wild type (Herbimicin P < 0.001; AG1296 P = 0.001, PKC412, P = 0.002). Pgp-positive samples were significantly less sensitive to herbimycin and AG1296 than pgp-negative samples, although neither molecule inhibited the efflux function of pgp. The concurrent incubation with the pgp inhibitor PSC833 resulted in an enhanced cell kill in 4/5 ITD pgp-positive samples versus two of nine ITD pgp-negative samples. PKC412 inhibited pgp function and induced cell death in FLT3 ITD/pgp-positive samples. We conclude that AML samples with a FLT3 ITD are more susceptible to these inhibitors than wild-type samples. However, the expression of pgp in cells with FLT3 ITDs can reduce their sensitivity to FLT3 inhibitors and therefore pgp expression should be assessed in clinical trials of FLT3 inhibitors.     

急性淋巴细胞白血病患者FLT3基因及FLT3/ITD基因突变的检测及临床意义

目的:研究急性淋巴细胞白血病(ALL)患者FLT3基因及其内部串联重复(ITD)突变情况。方法:采用多聚酶链反应(PCR)联合单链构象多态性(SSCP)方法检测76例不同免疫分型ALL患者FLT3基因及FLT3/ITD基因突变。结果:76例ALL患者经PCR扩增发现46例(60.5%)FLT3基因检测阳性,其中前前B细胞ALL、前B细胞ALL、成熟B细胞ALL及T细胞系ALL患者FLT3基因检测阳性率分别为88.2%(15/17),73.9%(17/23),40.0%(6/15)和23.5%(4/17);前前B细胞ALL和前B细胞患者ALL FLT3基因检测阳性率80.0%,显著高于成熟B细胞ALL(40.0%)(P<0.01);B细胞系ALL患者FLT3基因检测阳性率为69.1%,显著高于T细胞系ALL患者(23.5%)(P<0.01)。76例ALL患者中仅有2例(2.6%)出现FLT3/ITD基因突变,此2例均为伴有2种髓系抗原表达,免疫学检查诊断为急性混合细胞白血病患者,均伴有外周血高白细胞数、骨髓中高白血病细胞比例及预后较差。结论:B细胞系ALL和T细胞系ALL患者均可检测出FLT3基因,但B细胞系ALL患者FLT3基因检测阳性率显著高于T细胞系ALL;B细胞系ALL中细胞分化越成熟则FLT3基因检测率阳性越低。ALL患者一般不出现FLT3/ITD基因突变,FLT3/ITD基因突变检测可能有助于急性白血病基因分型及预后判断。