Tandem duplications of MLL and FLT3 are correlated with poor prognoses in pediatric acute myeloid leukemia: a study of the Japanese childhood AML Cooperative Study Group

NUP98::NSD1 and FLT3/ITD co-expression is an independent predictor of poor prognosis in pediatric AML patients

OBJECTIVE

Patients who carry NUP98::NSD1 or FLT3/ITD mutations are reported to have poor prognosis. Previous studies have confidently reported that the poor outcome in younger AML patients is owning to dual NUP98::NSD1 and FLT3/ITD positivity, with a high overlap for those two genetic lesions. In this study, we assessed the prognostic value of the presence of both NUP98::NSD1 and FLT3/ITD in pediatric AML patients.

METHODS

We screened a large cohort of 885 pediatric cases from the COG-National Cancer Institute (NCI) TARGET AML cohort and found 57 AML patients with NUP98 rearrangements.

RESULTS

The frequency of NUP98 gene fusion was 10.8% in 529 patients. NUP98::NSD1 fusion was the most common NUP98 rearrangement, with a frequency of 59.6%(34 of 57). NUP98::NSD1 -positive patients who carried FLT3/ITD mutations had a decreased CR1 or CR2 rate than those patients carried FLT3/ITD mutation alone (P = 0.0001). Moreover, patients harboring both NUP98::NSD1 fusion and FLT3/ITD mutation exhibited inferior event-free survival (EFS, P < 0.001) and overall survival (OS, P = 0.004) than patients who were dual negative for these two genetic lesions. The presence of only NUP98::NSD1 fusion had no significant impact on EFS or OS. We also found that cases with high FLT3/ITD AR levels ( > = 0.5) with or without NUP98::NSD1 had inferior prognosis. Multivariate analysis demonstrated that the presence of both NUP98::NSD1 and FLT3/ITD was an independent prognostic factors for EFS (hazard ratio: 3.2, P = 0.001) in patients with pediatric AML. However, there was no obvious correlation with OS (hazard ratio: 1.3, P = 0.618). Stem cell transplantation did not improve the survival rate of cases with NUP98 fusion or NUP98::NSD1 AML in terms of EFS or OS.

CONCLUSION

Presence of both NUP98::NSD1 and FLT3/ITD was found to be an independent factor for dismal prognosis in pediatric AML patients. Notably, lack of FLT3/ITD mutations in NUP98::NSD1 -positive patients did not retain its prognostic value.

A Review of Childhood Acute Myeloid Leukemia: Diagnosis and Novel Treatment

Acute myeloid leukemia (AML) is the second most common hematologic malignancy in children. The incidence of childhood AML is much lower than acute lymphoblastic leukemia (ALL), which makes childhood AML a rare disease in children. The role of genetic abnormalities in AML classification, management, and prognosis prediction is much more important than before. Disease classifications and risk group classifications, such as the WHO classification, the international consensus classification (ICC), and the European LeukemiaNet (ELN) classification, were revised in 2022. The application of the new information in childhood AML will be upcoming in the next few years. The frequency of each genetic abnormality in adult and childhood AML is different; therefore, in this review, we emphasize well-known genetic subtypes in childhood AML, including core-binding factor AML (CBF AML), KMT2Ar (KMT2A/11q23 rearrangement) AML, normal karyotype AML with somatic mutations, unbalanced cytogenetic abnormalities AML, NUP98 11p15/NUP09 rearrangement AML, and acute promyelocytic leukemia (APL). Current risk group classification, the management algorithm in childhood AML, and novel treatment modalities such as targeted therapy, immune therapy, and chimeric antigen receptor (CAR) T-cell therapy are reviewed. Finally, the indications of hematopoietic stem cell transplantation (HSCT) in AML are discussed.

UBTF-internal tandem duplication as a novel poor prognostic factor in pediatric acute myeloid leukemia

The prognosis of pediatric acute myeloid leukemia (AML) has improved via stratification therapy. However, relapse or death occurs in 30%-40% of cases. Novel genetic factors for pediatric AML need to be elucidated to improve prognosis. We detected recurrent internal tandem duplication in upstream binding transcription factor (UBTF-ITD) in 1.2% (6/503) of Japanese pediatric patients with de novo AML. No UBTF-ITD was detected in 175 adult patients with AML or in 65 cell lines that included 15 AML, 39 acute lymphoblastic leukemia, five chronic myeloid leukemia, and six neuroblastoma cell lines. All UBTF-ITDs were found in exon 13 and shared a duplicated region. UBTF-ITD was more frequently detected in patients with trisomy 8, FLT3-ITD, WT1 mutation, and/or high PRDM16 expression (trisomy 8, 3/6; FLT3-ITD, 5/6; WT1 mutation, 2/6; and high PRDM16 expression, 6/6). Gene expression patterns of patients with UBTF-ITD were similar to those of patients with NUP98::NSD1 or FUS::ERG. Survival analysis of the AML-05 cohort revealed that patients with UBTF-ITD had worse outcomes than those without UBTF-ITD (3-year event-free survival, 20% vs. 55%; 3-year overall survival, 40% vs. 74%). Moreover, among the 27 patients with trisomy 8, all three patients with UBTF -ITD had a poor prognosis resulting in early events (relapse or non-complete remission) within 1 year. Our findings suggest that UBTF-ITD may be a novel and significant prognostic factor for pediatric patients with AML.

FLT3-TKD in the prognosis of patients with acute myeloid leukemia: A meta-analysis

Background

Fms-like tyrosine kinase 3 (FLT3) gene mutations occur in approximately 30% of all patients with acute myeloid leukemia (AML). Internal tandem duplication (ITD) in the juxtamembrane domain and point mutations within the tyrosine kinase domain (TKD) are two distinct types of FLT3 mutations. FLT3-ITD has been determined as an independent poor prognostic factor, but the prognostic impact of potentially metabolically related FLT3-TKD remains controversial. Hence, we performed a meta-analysis to investigate the prognostic significance of FLT3-TKD in patients with AML.

Methods

A systematic retrieval of studies on FLT3-TKD in patients with AML was performed in PubMed, Embase, and Chinese National Knowledge Infrastructure databases on 30 September 2020. Hazard ratio (HR) and its 95% confidence intervals (95% CIs) were used to determine the effect size. Meta-regression model and subgroup analysis were used for heterogeneity analysis. Begg's and Egger's tests were performed to detect potential publication bias. The sensitivity analysis was performed to evaluate the stability of findings in meta-analysis.

Results

Twenty prospective cohort studies (n = 10,970) on the prognostic effect of FLT3-TKD in AML were included: 9,744 subjects with FLT3-WT and 1,226 subjects with FLT3-TKD. We found that FLT3-TKD revealed no significant effect on disease-free survival (DFS) (HR = 1.12, 95% CI: 0.90-1.41) and overall survival (OS) (HR = 0.98, 95% CI: 0.76-1.27) in general. However, meta-regressions demonstrated that patient source contributed to the high heterogeneity observed in the prognosis of FLT3-TKD in AML. To be specific, FLT3-TKD represented a beneficial prognosis of DFS (HR = 0.56, 95% CI: 0.37-0.85) and OS (HR = 0.63, 95% CI: 0.42-0.95) for Asians, whereas it represented an adverse prognosis of DFS for Caucasians with AML (HR = 1.34, 95% CI: 1.07-1.67).

Conclusion

FLT3-TKD revealed no significant effects on DFS and OS of patients with AML, which is consistent with the controversial status nowadays. Patient source (Asians or Caucasians) can be partially explained the different effects of FLT3-TKD in the prognosis of patients with AML.

Poor outcome of pediatric patients with acute myeloid leukemia harboring high FLT3/ITD allelic ratios

Activating FLT3 mutations are the most common mutations in acute myeloid leukemia (AML), but the optimal threshold of FLT3/ITD allelic ratio (AR) among pediatric AML patients remains controversial. Here, we present the outcome and prognostic significance of FLT3/ITD AR analysis among pediatric patients with AML from the TARGET dataset. Applying fitting curve models and threshold effect analysis using the restrictive cubic spline function following Cox proportional hazards models identifies the cut-off value of 0.5 on FLT3/ITD AR. Moreover, we observe that high FLT3/ITD AR patients have an inferior outcome when compared to low AR patients. Our study also demonstrates that stem cell transplantation may improve the outcome in pediatric AML patients with high FLT3/ITD AR and may be further improved when combined with additional therapies such as Gemtuzumab Ozogamicin. These findings underline the importance of individualized treatment of pediatric AML.

Activating FLT3 mutations are the most common mutations in AML. Here, the authors explore the relationship between the FLT3/ITD allelic ratio and prognosis in pediatric AML patients and identify an optimal threshold to stratify patients.

Allogenic Stem Cell Transplantation Abrogates Negative Impact on Outcome of AML Patients with KMT2A Partial Tandem Duplication

Recently, a new subset of acute myeloid leukemia (AML) presenting a direct partial tandem duplication (PTD) of the KMT2A gene was described. The consequences of this alteration in terms of outcome and response to treatment remain unclear. We analyzed retrospectively a cohort of KMT2A-PTD-mutated patients with newly diagnosed AML. With a median follow-up of 3.6 years, the median overall survival was 12.1 months. KMT2A-PTD-mutated patients were highly enriched in mutations affecting epigenetic actors and the RTK/RAS signaling pathway. Integrating KMT2A-PTD in ELN classification abrogates its predictive value on survival suggesting that this mutation may overcome other genomic marker effects. In patients receiving intensive chemotherapy, hematopoietic stem cell transplantation (HSCT) significantly improved the outcome compared to non-transplanted patients. In the multivariate analysis, only HSCT at any time in complete remission (HR = 2.35; p = 0.034) and FLT3-ITD status (HR = 0.29; p = 0.014) were independent variables associated with overall survival, whereas age was not. In conclusion, our results emphasize that KMT2A-PTD should be considered as a potential adverse prognostic factor. However, as KMT2A-PTD-mutated patients are usually considered an intermediate risk group, upfront HSCT should be considered in first CR due to the high relapse rate observed in this subset of patients.

Panel-based next-generation sequencing facilitates the characterization of childhood acute myeloid leukemia in clinical settings

Acute myeloid leukemia (AML) accounts for ~20% of pediatric leukemia cases. The prognosis of pediatric AML has been improved in recent decades, but it trails that of most other types of pediatric cancer, with mortality rates of 30-40%. Consequently, newer more targeted drugs are required for incorporation into treatment plans. These newer drugs selectively target AML cells with specific gene alterations. However, there are significant differences in genetic alterations between adult and pediatric patients with AML. In the present study, inexpensive and rapid next-generation sequencing (NGS) of >150 cancer-related genes was performed for matched diagnostic, remission and relapse (if any) samples from 27 pediatric patients with AML. In this analysis, seven genes were recurrently mutated. KRAS was mutated in seven patients, NRAS was mutated in three patients, and KIT, GATA1, WT1, PTPN11, JAK3 and FLT3 were each mutated in two patients. Among patients with relapsed AML, six harbored KRAS mutations at diagnosis; however, four of these patients lost these mutations at relapse. Additionally, two genetic alterations (FLT3-ITD and TP53 alterations) were detected among patients who eventually relapsed, and these mutations are reported to be adverse prognostic factors for adult patients with AML. This panel-based, targeted sequencing approach may be useful in determining the genetic background of pediatric AML and improving the prediction of treatment response and detection of potentially targetable gene alterations. RAS pathway mutations were highly unstable at relapse; therefore, these mutations should be chosen as a target with caution. Incorporating this panel-based NGS approach into the clinical setting may allow for a patient-oriented strategy of precision treatment for childhood AML.

Transcriptome analysis offers a comprehensive illustration of the genetic background of pediatric acute myeloid leukemia

Recent advances in the genetic understanding of acute myeloid leukemia (AML) have improved clinical outcomes in pediatric patients. However, ∼40% of patients with pediatric AML relapse, resulting in a relatively low overall survival rate of ∼70%. The objective of this study was to reveal the comprehensive genetic background of pediatric AML. We performed transcriptome analysis (RNA sequencing [RNA-seq]) in 139 of the 369 patients with de novo pediatric AML who were enrolled in the Japanese Pediatric Leukemia/Lymphoma Study Group AML-05 trial and investigated correlations between genetic aberrations and clinical information. Using RNA-seq, we identified 54 in-frame gene fusions and 1 RUNX1 out-of-frame fusion in 53 of 139 patients. Moreover, we found at least 258 gene fusions in 369 patients (70%) through reverse transcription polymerase chain reaction and RNA-seq. Five gene rearrangements were newly identified, namely, NPM1-CCDC28A, TRIP12-NPM1, MLLT10-DNAJC1, TBL1XR1-RARB, and RUNX1-FNBP1. In addition, we found rare gene rearrangements, namely, MYB-GATA1, NPM1-MLF1, ETV6-NCOA2, ETV6-MECOM, ETV6-CTNNB1, RUNX1-PRDM16, RUNX1-CBFA2T2, and RUNX1-CBFA2T3. Among the remaining 111 patients, KMT2A-PTD, biallelic CEBPA, and NPM1 gene mutations were found in 11, 23, and 17 patients, respectively. These mutations were completely mutually exclusive with any gene fusions. RNA-seq unmasked the complexity of gene rearrangements and mutations in pediatric AML. We identified potentially disease-causing alterations in nearly all patients with AML, including novel gene fusions. Our results indicated that a subset of patients with pediatric AML represent a distinct entity that may be discriminated from their adult counterparts. Based on these results, risk stratification should be reconsidered.

[Clinical characteristics and prognosis of 34 cases of acute myeloid leukemia with FLT3 internal tandem duplication and MLL gene rearrangement]

Objective: To analyze the clinical characteristics and prognosis of 34 cases of acute myeloid leukemia (AML) with FLT3 internal tandem duplication (FLT3-ITD) and MLL gene rearrangement. Methods: The clinical data of 34 AML patients with FLT3-ITD and MLL gene rearrangement was compared and analyzed for the therapeutic efficacy, prognostic factors when treated with chemotherapy, chemotherapy combined with targeted therapy or allogenic hematopoietic stem cell transplantation (allo-HSCT). Results: Of the thirty-four cases with median age 41 (4-71) years old, 63.6% presented with white blood cells (WBC) greater than 30×10(9)/L, 39.4% greater than 50 × 10(9)/L respectively on admission. M(5) (35.3%) made up the highest proportion. The cytogenetic abnormality reached 61.8%, of which the complex cytogenetic abnormality accounted for 11.8%. Eleven patients (32.35%) had both FLT3-ITD and MLL gene abnormalities. In addition to FLT3 and MLL abnormalities, 23 patients (67.6%) had one or more other gene abnormalities (multiple gene abnormalities). Of the 34 cases, 29.4% patients went into complete remission (CR) after two courses of chemotherapy. 20.6% (7 patients) went into CR after 3 or more courses of chemotherapy. The rate of early relapse in the CR group was 52.9%. Patients with WBC>50×10(9)/L or multiple gene abnormalities had a lower remission rate (7.7%, 5.4%) after two courses of chemotherapy. CR rate for the patients with more than three gene abnormalities was 0. The total 2-year overall survival (OS) in the 34 patients was 28.8% (95% CI 13.5%-46.0%) and the disease-free survival (DFS) was 27.1% (95% CI 12.5%-44.0%). Of the 18 patients treated with chemotherapy alone or chemotherapy combined with targeted therapy, 17 cases died within 2 years and 1 lost follow-up after giving up treatment. For the 16 patients received allo-HSCT, the 3-year OS was 43.4% (95% CI 13.7%-70.4%) and DFS 42.7% (95% CI 13.4%-69.7%). Conclusion: AML patients with FLT3-ITD and MLL gene rearrangement often presented with M(5), accompanied by hyperleukocytosis, cytogenetic or multiple gene abnormalities. Those patients were observed to have low response rate and high early relapse when treated with chemotherapy without allo-HSCT. Patients had multiple gene abnormalities may be an important poor prognostic factor. Allo-HSCT is an effective treatment which could significantly improve the prognosis and survival of AML patients with FLT3-ITD and MLL gene abnormalities.

Whole-exome sequencing reveals the spectrum of gene mutations and the clonal evolution patterns in paediatric acute myeloid leukaemia

Acute myeloid leukaemia (AML) is a molecularly and clinically heterogeneous disease. Targeted sequencing efforts have identified several mutations with diagnostic and prognostic values in KIT, NPM1, CEBPA and FLT3 in both adult and paediatric AML. In addition, massively parallel sequencing enabled the discovery of recurrent mutations (i.e. IDH1/2 and DNMT3A) in adult AML. In this study, whole-exome sequencing (WES) of 22 paediatric AML patients revealed mutations in components of the cohesin complex (RAD21 and SMC3), BCORL1 and ASXL2 in addition to previously known gene mutations. We also revealed intratumoural heterogeneities in many patients, implicating multiple clonal evolution events in the development of AML. Furthermore, targeted deep sequencing in 182 paediatric AML patients identified three major categories of recurrently mutated genes: cohesion complex genes [STAG2, RAD21 and SMC3 in 17 patients (8·3%)], epigenetic regulators [ASXL1/ASXL2 in 17 patients (8·3%), BCOR/BCORL1 in 7 patients (3·4%)] and signalling molecules. We also performed WES in four patients with relapsed AML. Relapsed AML evolved from one of the subclones at the initial phase and was accompanied by many additional mutations, including common driver mutations that were absent or existed only with lower allele frequency in the diagnostic samples, indicating a multistep process causing leukaemia recurrence.

High PRDM16 expression identifies a prognostic subgroup of pediatric acute myeloid leukaemia correlated to FLT3-ITD, KMT2A-PTD, and NUP98-NSD1: the results of the Japanese Paediatric Leukaemia/Lymphoma Study Group AML-05 trial

Recent reports described the NUP98-NSD1 fusion as an adverse prognostic marker for acute myeloid leukaemia (AML) and PRDM16 (also known as MEL1) as the representative overexpressed gene in patients harbouring NUP98-NSD1 fusion. PRDM16 gene expression levels were measured via real-time polymerase chain reaction in 369 paediatric patients with de novo AML, of whom 84 (23%) exhibited PRDM16 overexpression (PRDM16/ABL1 ratio ≥0·010). The frequencies of patients with high or low PRDM16 expression differed widely with respect to each genetic alteration, as follows: t(8;21), 4% vs. 96%, P < 0·001; inv(16), 0% vs. 100%, P < 0·001; KMT2A (also termed MLL)- partial tandem duplication, 100% vs. 0%, P < 0·001; NUP98-NSD1, 100% vs. 0%, P < 0·001. The overall survival (OS) and event-free survival (EFS) among PRDM16-overexpressing patients were significantly worse than in patients with low PRDM16 expression (3-year OS: 51% vs. 81%, P < 0·001, 3-year EFS: 32% vs. 64%, P < 0·001) irrespective of other cytogenetic alterations except for NPM1. PRDM16 gene expression was particularly useful for stratifying FLT3-internal tandem duplication-positive AML patients (3-year OS: high = 30% vs. low = 70%, P < 0·001). PRDM16 overexpression was highly recurrent in de novo paediatric AML patients with high/intermediate-risk cytogenetic profiles and was independently associated with an adverse outcome.

CSF3R and CALR mutations in paediatric myeloid disorders and the association of CSF3R mutations with translocations, including t(8; 21)

Mutations in the colony-stimulating factor 3 receptor (CSF3R) and calreticulin (CALR) genes have been reported in a proportion of adults with myeloproliferative disease. However, little is known about CSF3R or CALR mutations in paediatric myeloid disorders. We analysed CSF3R exons 14 and 17, and CALR exon 9, using direct sequencing in samples of paediatric acute myeloid leukaemia (AML; n = 521), juvenile myelomonocytic leukaemia (JMML; n = 40), myelodysplastic syndrome (MDS; n = 20) and essential thrombocythaemia (ET; n = 21). CSF3R mutations were found in 10 (1.2%) of 521 patients with AML; two in exon 14 (both missense mutations resulting in p.T618I) and eight in exon 17 (three frameshift mutations: p.S715X, p.Q774R, and p.S783Q; and five novel missense mutations: p.Q754K, p.R769H, p.L777F, p.T781I, and S795R). All of the patients with mutations in CSF3R exon 17 had chromosomal translocations, including four with t(8;21). At the time of reporting, seven of these ten patients are alive; three have died, due to side effects of chemotherapy. No CSF3R mutations were found in cases of MDS, JMML or ET. The only mutation found in the CALR gene was a frameshift (p.L367 fs) in one ET patient. We discuss the potential impact of these findings for the leukaemogenesis and clinical features of paediatric myeloid disorders.

Outcome of children with relapsed acute myeloid leukemia following initial therapy under the AML99 protocol

The outcomes of children with relapsed acute myeloid leukemia (AML) are known to be poor, but remain obscure. We retrospectively analyzed 71 patients who had relapsed following first-line treatment under the AML99 protocol. We investigated the time and site of recurrence, response to re-induction therapy, and performance of hematopoietic stem cell transplantation (HSCT) in relapsed cases, and performed a multivariate analysis to identify prognostic factors. The 5-year overall-survival (OS) rate after relapse was 37 %. Of 71 patients, three died without any anti-leukemic therapy and two underwent allogeneic HSCT. The remaining 66 patients received re-induction chemotherapy, and 33 (50 %) achieved second CR (CR2). Twenty-two of 25 (88 %) late relapse patients and 11 of 41 (27 %) early relapse patients achieved CR2 (P < 0.001). Twenty-nine CR2 cases and 35 non-CR2 cases underwent allogeneic HSCT. The 5-year OS rate was significantly higher in patients who underwent HSCT in CR2 than those in non-CR2 (66 vs. 17 %, P < 0.000001). Multivariate analysis indicated that early relapse (P < 0.05) and the positivity of the FMS-like tyrosine kinase 3--internal tandem duplication (P < 0.05) were adverse prognostic factors for survival. In conclusion, the etiology of relapsed pediatric AML needs to be elucidated and effective chemotherapy should be administered to obtain CR2.

FLT3-ITD mutation in relation to FLT3 expression in pediatric AML: a prospective study from India

There is lack of data with regard to FLT3 expression in FLT3-ITD positive pediatric AML patients. Further, FLT3-ITD has not been systematically analyzed for outcome from Indian subcontinent. Amongst 64 consecutive pediatric AML patients, FLT3-ITD was present in 12 (19%) patients. All patients with FLT3-ITD achieved CR; those with FLT3-ITD mutation had inferior DFS (P = .029). FLT3 expression by flow-cytometry was observed in all FLT3-ITD positive patients, whereas 40/52 (77%) FLT3-ITD negative patients expressed FLT3 (P = .06). FLT3 expression in 12 FLT3-ITD positive patients was unable to show an association between FLT3 expression and outcome. In FLT3-ITD negative patients, higher surface expression of FLT3 significantly predicted poor EFS (P = .001) and OS (P = .007).

High-resolution melting curve analysis, a rapid and affordable method for mutation analysis in childhood acute myeloid leukemia

BACKGROUND

Molecular genetic alterations with prognostic significance have been described in childhood acute myeloid leukemia (AML). The aim of this study was to establish cost-effective techniques to detect mutations of FMS-like tyrosine kinase 3 (FLT3), nucleophosmin 1 (NPM1), and a partial tandem duplication within the mixed-lineage leukemia (MLL-PTD) genes in childhood AML.

PROCEDURE

Ninety-nine children with newly diagnosed AML were included in this study. We developed a fluorescent dye SYTO-82 based high-resolution melting (HRM) curve analysis to detect FLT3 internal tandem duplication (FLT3-ITD), FLT3 tyrosine kinase domain (FLT3-TKD), and NPM1 mutations. MLL-PTD was screened by real-time quantitative PCR.

RESULTS

The HRM methodology correlated well with gold standard Sanger sequencing with less cost. Among the 99 patients studied, the FLT3-ITD mutation was associated with significantly worse event-free survival (EFS). Patients with the NPM1 mutation had significantly better EFS and overall survival. However, HRM was not sensitive enough for minimal residual disease monitoring.

CONCLUSION

High-resolution melting was a rapid and efficient method for screening of FLT3 and NPM1 gene mutations. It was both affordable and accurate, especially in resource underprivileged regions. Our results indicated that HRM could be a useful clinical tool for rapid and cost-effective screening of the FLT3 and NPM1 mutations in AML patients.

WT1 mutation in pediatric patients with acute myeloid leukemia: a report from the Japanese Childhood AML Cooperative Study Group

Mutations in Wilms tumor 1 (WT1) have been reported in 10-22 % of patients with cytogenetically normal acute myeloid leukemia (CN-AML), but the prognostic implications of these abnormalities have not been clarified in either adults or children. One hundred and fifty-seven pediatric AML patients were analyzed for WT1 mutations around hotspots at exons 7 and 9; however, amplification of the WT1 gene by the reverse transcriptase-polymerase chain reaction was not completed in four cases (2.5 %). Of the 153 evaluable patients, 10 patients (6.5 %) had a mutation in WT1. The incidence of WT1 mutations was significantly higher in CN-AML than in others (15.2 vs. 4.5 %, respectively, P = 0.03). Of the 10 WT1-mutated cases, eight (80 %) had mutations in other genes, including FLT3-ITD in two cases, FLT3-D835 mutation in two, KIT mutation in three, MLL-PTD in three, NRAS mutation in one, and KRAS mutation in two (in some cases, more than one additional gene was mutated). The incidences of KIT and FLT3-D835 mutations were significantly higher in patients with than in those without WT1 mutation. No significant differences were observed in the 3-year overall survival and disease-free survival; however, the presence of WT1 mutation was related to a poor prognosis in patients with CN-AML, excluding those with FLT3-ITD and those younger than 3 years.

NUP98-NSD1 gene fusion and its related gene expression signature are strongly associated with a poor prognosis in pediatric acute myeloid leukemia

The cryptic t(5;11)(q35;p15.5) creates a fusion gene between the NUP98 and NSD1 genes. To ascertain the significance of this gene fusion, we explored its frequency, clinical impact, and gene expression pattern using DNA microarray in pediatric acute myeloid leukemia (AML) patients. NUP98-NSD1 fusion transcripts were detected in 6 (4.8%) of 124 pediatric AML patients. Supervised hierarchical clustering analyses using probe sets that were differentially expressed in these patients detected a characteristic gene expression pattern, including 18 NUP98-NSD1-negative patients (NUP98-NSD1-like patients). In total, a NUP98-NSD1-related gene expression signature (NUP98-NSD1 signature) was found in 19% (24/124) and in 58% (15/26) of cytogenetically normal cases. Their 4-year overall survival (OS) and event-free survival (EFS) were poor (33.3% in NUP98-NSD1-positive and 38.9% in NUP98-NSD1-like patients) compared with 100 NUP98-NSD1 signature-negative patients (4-year OS: 86.0%, 4-year EFS: 72.0%). Interestingly, t(7;11)(p15;p15)/NUP98-HOXA13, t(6;11)(q27;q23)/MLL-MLLT4 and t(6;9)(p22;q34)/DEK-NUP214, which are known as poor prognostic markers, were found in NUP98-NSD1-like patients. Furthermore, another type of NUP98-NSD1 fusion transcript was identified by additional RT-PCR analyses using other primers in a NUP98-NSD1-like patient, revealing the significance of this signature to detect NUP98-NSD1 gene fusions and to identify a new poor prognostic subgroup in AML.

Outcome in 146 patients with paediatric acute myeloid leukaemia treated according to the AML99 protocol in the period 2003-06 from the Japan Association of Childhood Leukaemia Study

The acute myeloid leukaemia (AML) 99 trial conducted previously in Japan for the treatment of de novo paediatric AML showed excellent results, with a 5-year overall survival (OS) and event-free survival (EFS) of 75·6% and 61·6%, respectively. To examine reproducibility of these results in another cohort, the outcome of 146 newly diagnosed AML paediatric patients prospectively registered in the Japan Association of Childhood Leukaemia Study (JACLS) from 2003 to 2006 was compared to that of 240 patients in the original AML 99 clinical trial. The 5-year EFS and OS achieved in the new cohort was 66·7 ± 4·0% and 77·7 ± 8·0% respectively, which were comparable to those obtained in the original AML 99 clinical trial, although less frequent core-binding factor (CBF) AML (29·5% vs. 37%) and an almost equal frequency of allogeneic haematopoietic stem cell transplantation (allo-HSCT) during first complete remission (16·5% vs. 19%) were observed. The 5-year EFS in patients with a normal karyotype (NK) (n = 35, 54·9 ± 15·1%) was inferior in the present cohort when compared to the original AML99 trial. This study confirmed the excellent outcome of the original AML99 protocol.

High WT1 mRNA expression after induction chemotherapy and FLT3-ITD have prognostic impact in pediatric acute myeloid leukemia: a study of the Japanese Childhood AML Cooperative Study Group

The prognostic value of WT1 mRNA expression in pediatric acute myeloid leukemia (AML) remains controversial. A sample of newly diagnosed (n = 158) AML patients from the Japanese Childhood AML Cooperative Treatment Protocol, AML 99, were simultaneously analyzed for WT1 expression, cytogenetic abnormalities and gene alterations (FLT3, KIT, MLL, and RAS). WT1 expression (including more than 2,500 copies/μgRNA) was detected in 122 of the 158 (77.8 %) initial diagnostic AML bone marrow samples (median 45,500 copies/μgRNA). Higher WT1 expression was detected in French American British (FAB)-M0, M3, M7 and lower expression in M4 and M5. Higher WT1 expression was detected in AML with inv(16), t(15;17) and Down syndrome and lower in AML with 11q23 abnormalities. Multivariate analyses demonstrated that FLT3-internal tandem duplication (ITD), KIT mutation, MLL-partial tandem duplication were correlated with poor prognosis; however, higher WT1 expression was not. FLT3-ITD was correlated with WT1 expression and prognosis. Furthermore, 74 WT1 expression after induction chemotherapy was analyzed. Higher WT1 expression after induction chemotherapy was significantly correlated with M1 or M2/M3 marrow, FLT3-ITD and poor prognosis. Multivariate analyses in 74 AML patients revealed that FLT3-ITD, MLL-PTD, and KIT mutations were associated with poor prognosis; however, NRAS Mutation, KRAS mutation and high WT1 expression (>10,000 copies/μgRNA) did not show poor prognosis. Our findings suggest that higher WT1 expression at diagnosis does not correlate with poor prognosis, but that WT1 expression after induction chemotherapy is considered to be a useful predictor of clinical outcome in pediatric AML.

RAS mutations are frequent in FAB type M4 and M5 of acute myeloid leukemia, and related to late relapse: a study of the Japanese Childhood AML Cooperative Study Group

Mutations in RAS are frequent in acute myeloid leukemia (AML), and are thought to contribute to leukemogenesis in a subset of patients; however, their prognostic significance has not been firmly established. One hundred and fifty-seven pediatric patients with AML were analyzed for NRAS and KRAS mutations around hot spots at codons 12, 13, and 61. Twenty-nine patients (18.5%) had an activating mutation of RAS. We found KRAS mutations to be more frequent than NRAS mutations (18/29, 62.1% of patients with RAS mutation), in contrast to previous reports (18-40%). The frequency of RAS mutation was higher in French-American-British types M4 and M5 than other types (P = 0.02). There were no significant differences in other clinical manifestations or distribution in cytogenetic subgroups, or aberrations of other genes, including KIT mutation, FLT3-ITD, and MLL-PTD, between patients with and without RAS mutations. No significant differences were observed in the 3-year overall survival and disease-free survival; however, the presence of RAS mutation was related to late relapse. The occurrence of clinical events at relatively late period should be monitored for in AML patients with mutations in RAS.

FLT3 mutation and expression did not adversely affect clinical outcome of childhood acute leukaemia: a study of 531 Southeast Asian children by the Ma-Spore study group

FMS-like tyrosine kinase 3 (FLT3) is critical for normal haematopoiesis and have been reported to be expressed in the majority of acute myeloid and lymphoid malignancies. We correlated the impact of FLT3 mutations and its expression with age, WHO 2008 classification and treatment outcome in 531 childhood acute leukaemias. Of 150 acute myeloid leukaemia (AMLs), 18 (12%) harboured FLT3-ITD while nine (6%) had FLT3-TKD. FLT3-ITD and -TKD were rare in acute megakaryoblastic leukaemia (AMKL; FLT3-ITD 0/26, FLT3-TKD 1/26) and children below 3 years (n = 2/48). Acute promyelocytic leukaemia (APL) with t(15;17);PML-RARα (n = 7/18; 39%) harboured the highest frequency of FLT3 mutations, followed by myelomonocytic (n = 4/18; 22%) and AML with t(8;21);RUNX1-RUNX1T1 (n = 2/21; 9%). FLT3 expression levels were also lowest in AMKL, both in Down's and non-Down's (p = 0.002) followed by patients <3 years (p = 0.001). The rarity of FLT3 mutations and expression levels in AMKL were independent of age. Conversely, only 2% of childhood acute lymphoblastic leukaemia (ALL) harboured FLT3 mutations (ITD = 1/381; TKD = 6/381). FLT3 was highly expressed in hyperdiploid ALL (p < 0.001). Of the 121 AMLs with clinical history, there were no significant differences in 4-year event-free survival (EFS) (46% vs. 38%; p = 0.46) and overall-survival (OS) (55% vs. 43%; p = 0.30) between FLT3-wildtype and ITD+ patients. Similarly, FLT3 expression levels did not influence survival in AML in both the good risk and non-good risk subgroups. FLT3 does not appear to be involved in the pathogenesis of AMKL, both in Down's and non-Down's. Therapeutic targets using FLT3 inhibitors may not be useful in AMKL and in young children with AML.

FLT3 inhibitors in the treatment of acute myeloid leukemia: the start of an era?

Despite recent modest improvements in the chemotherapy regimens used to treat acute myeloid leukemia (AML), many patients diagnosed with AML ultimately die of the disease. Commonly occurring genetic alterations have been identified that strongly affect the prognosis for patients with AML. These alterations represent possible targets for investigational therapies that could act to specifically halt the aberrant growth of AML cells while limiting damage to normal cells. One such gene is the Fms-like tyrosine kinase 3 (FLT3) gene, which is mutated in approximately 30% of adult patients with AML and has a significant impact on prognosis. In particular, internal tandem duplications in FLT3 confer a poor prognosis to this large subgroup of patients with AML. Agents that target FLT3 are in development for the treatment of patients who have AML and offer a potential paradigm change in the current standard treatment of AML. For this report, the authors reviewed the prognostic significance of genetic alterations observed in AML with a focus on the therapeutic implications of targeting FLT3. The introduction of such agents may be the next major step toward the era of personalized therapy in AML.

Genetic aberrations in paediatric acute leukaemias and implications for management of patients

The process of malignant transformation in paediatric acute leukaemias is complex, requiring at least two deleterious events resulting in DNA damage. This damage ranges from point-mutations to double-strand DNA breaks leading to various types of chromosomal rearrangements. In this review we summarise the most common genetic aberrations for the three main subtypes of paediatric acute leukaemia: B-cell-precursor acute lymphoblastic leukaemia, T-cell acute lymphoblastic leukaemia and acute myeloid leukaemia. Several genetic aberrations are independent prognostic factors, and are now used in risk stratification for treatment. Molecular pathways activated by genetic aberrations could provide potential molecular targets for novel therapies. Some genetic aberrations represent sensitive targets for molecular detection of minimal residual disease. This provides hope for the development of targeted therapies, effective against leukaemic cells.