AML patients with CEBPalpha mutations mostly retain identical mutant patterns but frequently change in allelic distribution at relapse: a comparative analysis on paired diagnosis and relapse samples

CEBPA mutations in acute myeloid leukemia: implications in risk stratification and treatment

Mutations in CCAAT enhancer binding protein α (CEBPA) occur in approximately 10% of patients with de novo acute myeloid leukemia (AML). Emerging evidence supports that in-frame mutations in the basic leucine zipper domain of CEBPA (CEBPAbZIP-inf) confer a survival benefit, and CEBPAbZIP-inf replaced CEBPA double mutations (CEBPAdm) as a unique entity in the 2022 World Health Organization (WHO-2022) classification and International Consensus Classification (ICC). However, challenges remain in daily clinical practice since more than 30% patients with CEBPAbZIP-inf die of AML despite intensive treatment. This review aims to provide a comprehensive summary of the heterogeneities observed in AML with CEBPAdm and CEBPAbZIP-inf, and will discuss the prognostic implications of concurrent mutations and novel mechanistic targets that may inform future drug development. The ultimate goal is to optimize clinical management and to provide precision medicine for this category of patients.

Acute Myeloid Leukemia With CEBPA Mutations: Current Progress and Future Directions

Mutations in CCAAT enhancer binding protein A gene (CEBPA) are one of the common genetic alterations in acute myeloid leukemia (AML). Recently, the emergence of new evidence makes it necessary to reconsider the subsets and treatment of AML patients with CEBPA mutations. This review will summarize the history of research progress of CEBPA mutations in AML, the heterogeneities of AML with CEBPA double mutations (CEBPA ^dm), and two special subtypes of CEBPA mutated AML. We will discuss the treatment of AML with CEBPA mutations as well, and finally propose a new algorithm for the treatment of these patients, including both familial and sporadic CEBPA mutated AML patients. This review may be beneficial for further investigation and optimizing clinical management of AML patients with CEBPA mutations.

Novel insights of acute myeloid leukemia with CEBPA deregulation: Heterogeneity dissection and re-stratification

Acute myeloid leukemia with bi-allelic CEBPA mutation was categorized as an independent disease entity with favorable prognosis, however, recent researches have revealed huge heterogeneity within this disease group, and for some patients, relapse remained a major cause of treatment failure. Further risk stratification is essentially needed. Here by reviewing the latest literature, we summarized the characteristics of CEBPA mutation profiles and clinical features, with a special intention of dissecting the heterogeneity within the seemingly homogeneous AML with bi-allelic CEBPA mutations. Specifically, non-classical CEBPA mutation, miscellaneous companion genetic aberrations and the presence of germline CEBPA mutation are three major sources of heterogeneity. Identifying these factors can help us predict patients at a higher risk of relapse, for whom aggressive treatment may be recommended. Novel therapeutic approaches regarding manipulating potentially druggable targets as well as the debate over post remission consolidation regimens has also been discussed.

Genetic aberrations involved in relapse of pediatric acute myeloid leukemia: A literature review

Globally, 15-20% of all children diagnosed with leukemia suffer from acute myeloid leukemia (AML), a rapidly progressive, clinically and biologically heterogeneous disease leading to the impaired differentiation of myeloid blast cells. Although 80% of patients achieve complete remission after induction chemotherapy, many relapse, negatively affecting overall out comes. The mechanisms underlying relapse have not been fully elucidated. This review aims to provide an overview of genetic aberrations involved in relapse of disease. A literature review on molecular mechanisms implicated in pediatric AML relapse spanning from 2003 to 2017 was conducted. PubMed, Medline, and Google Scholar were interrogated using relevant search terms. Of note, we examined a total of final 10 research papers from four large study groups that have utilized whole genome sequencing and molecular targeting of trio or paired samples of initial diagnosis, remission, and relapse. Their findings reveal that the genomic landscape of pediatric AML varies from diagnosis to relapse in different populations. Pediatric AML relapse is a systemic evolutionary illness accompanied by synchronized mutational hits impairing differentiation function. The irregular proliferative function is a consequence of mutations in signal transduction genes such as FLT3, RAS, PTPN11, and c-KIT and genes that code for transcription factors such as CEBPα, WT1, SATB1, GFI1, KLF2, and TBP are associated with relapse of disease. Identification of molecular markers unique to different stages of the disease in distinct populations can provide valuable information about disease prognosis and management.

CCAAT enhancer binding protein alpha (CEBPA) biallelic acute myeloid leukaemia: cooperating lesions, molecular mechanisms and clinical relevance

Recent advances in sequencing technologies have allowed for the identification of recurrent mutations in acute myeloid leukaemia (AML). The transcription factor CCAAT enhancer binding protein alpha (CEBPA) is frequently mutated in AML, and biallelic CEBPA-mutant AML was recognised as a separate disease entity in the recent World Health Organization classification. However, CEBPA mutations are co-occurring with other aberrations in AML, and together these lesions form the clonal hierarchy that comprises the leukaemia in the patient. Here, we aim to review the current understanding of co-occurring mutations in CEBPA-mutated AML and their implications for disease biology and clinical outcome. We will put emphasis on patterns of cooperation, how these lesions cooperate with CEBPA mutations and the underlying potential molecular mechanisms. Finally, we will relate this to patient outcome and future options for personalised medicine.

Molecular mechanisms for stemness maintenance of acute myeloid leukemia stem cells

Human acute myeloid leukemia (AML) is a fatal hematologic malignancy characterized with accumulation of myeloid blasts and differentiation arrest. The development of AML is associated with a serial of genetic and epigenetic alterations mainly occurred in hematopoietic stem and progenitor cells (HSPCs), which change HSPC state at the molecular and cellular levels and transform them into leukemia stem cells (LSCs). LSCs play critical roles in leukemia initiation, progression, and relapse, and need to be eradicated to achieve a cure in clinic. Key to successfully targeting LSCs is to fully understand the unique cellular and molecular mechanisms for maintaining their stemness. Here, we discuss LSCs in AML with a focus on identification of unique biological features of these stem cells to decipher the molecular mechanisms of LSC maintenance.

Mechanisms of drug resistance in acute myeloid leukemia

Acute myeloid leukemia (AML) is a kind of malignant hematopoietic system disease characterized by abnormal proliferation, poor cell differentiation, and infiltration of bone marrow, peripheral blood, or other tissues. To date, the first-line treatment of AML is still based on daunorubicin and cytosine arabinoside or idarubicin and cytosine arabinoside regimen. However, the complete remission rate of AML is still not optimistic, especially in elderly patients, and the recurrence rate after complete remission is still high. The resistance of leukemia cells to chemotherapy drugs becomes the main obstacle in the treatment of AML. At present, the research on the mechanisms of drug resistance in AML is very active. This article will elaborate on the main mechanisms of drug resistance currently being studied, including drug resistance-related proteins and enzymes, gene alterations, micro RNAs, and signal pathways.

Myeloid Neoplasm With Germline Predisposition: A 2016 Update for Pathologists

CONTEXT.—

Myeloid neoplasms with familial occurrence have been rarely reported in the past. With the advance of molecular technology and better understanding of the molecular pathogenesis of myeloid neoplasms, investigating the genetic causes of familial acute myeloid leukemia or myelodysplastic syndrome has become feasible in the clinical setting. Recent studies have identified a rapidly expanding list of germline mutations associated with increased risks of developing myeloid neoplasm in the affected families. It is important to recognize these entities, as such a diagnosis may dictate a unique approach in clinical management and surveillance for the patients and carriers.

OBJECTIVE.—

To raise the awareness of myeloid neoplasms arising in the setting of familial inheritance among practicing pathologists.

DATA SOURCES.—

Based on recent literature and the 2016 revision of the World Health Organization classification of hematopoietic neoplasms, we provide an up-to-date review of myeloid neoplasm with germline predisposition.

CONCLUSIONS.—

This short review focuses on the clinical, pathologic, and molecular characterization of myeloid neoplasm with germline predisposition. We emphasize the important features that will help practicing pathologists to recognize these newly described entities.

Variable outcome and methylation status according to CEBPA mutant type in double-mutated acute myeloid leukemia patients and the possible implications for treatment

Although CEBPA double-mutated (CEBPADM) acute myeloid leukemia is considered to be a favorable-risk disease, relapse remains a major cause of treatment failure. Most CEBPADM patients have a classic biallelic mutant combination with an N-terminal mutation leading to production of p30 protein plus a C-terminal loss-of-function in-frame indel mutation (CEBPAClassic-DM), but approximately one-third of cases have one or more non-classic mutations, with diverse combinations reported, and there is little information on the consequences of such mutants. We evaluated outcome in a cohort of 104 CEBPADM patients, 79 CEBPAClassic-DM and 25 with non-classic mutants, and found that the latter may have poorer survival (5-year overall survival 64% vs. 46%; P=0.05), particularly post relapse (41% vs. 0%; P=0.02). However, for this analysis, all non-classic cases were grouped together, irrespective of mutant combination. As CEBPADM cases have been reported to be hypermethylated, we used methylation profiling to assess whether this could segregate the different mutants. We developed a CEBPAClassic-DM methylation signature from a preliminary cohort of 10 CEBPADM (including 8 CEBPAClassic-DM) and 30 CEBPA wild-type (CEBPAWT) samples, and independently validated the signature in 17 CEBPAClassic-DM cases. Assessment of the signature in 16 CEBPADM cases with different non-classic mutant combinations showed that only 31% had a methylation profile equivalent to CEBPAClassic-DM whereas for 69% the profile was either intermediate between CEBPAClassic-DM and CEBPAWT or equivalent to CEBPAWT These results suggest that CEBPADM cases with non-classic mutants may be functionally different from those with CEBPAClassic-DM mutants, and should not automatically be included in the same prognostic group. (AML12 is registered under ISRCTN17833622 and AML15 under ISRCTN17161961).

C/EBPα deregulation as a paradigm for leukemogenesis

Myeloid master regulator CCAAT enhancer-binding protein alpha (C/EBPα) is deregulated by multiple mechanisms in leukemia. Inhibition of C/EBPα function plays pivotal roles in leukemogenesis. While much is known about how C/EBPα orchestrates granulopoiesis, our understanding of molecular transformation events, the role(s) of cooperating mutations and clonal evolution during C/EBPα deregulation in leukemia remains elusive. In this review, we will summarize the latest research addressing these topics with special emphasis on CEBPA mutations. We conclude by describing emerging therapeutic strategies to restore C/EBPα function.

Molecular and genetic alterations associated with therapy resistance and relapse of acute myeloid leukemia

Background

The majority of individuals with acute myeloid leukemia (AML) respond to initial chemotherapy and achieve a complete remission, yet only a minority experience long-term survival because a large proportion of patients eventually relapse with therapy-resistant disease. Relapse therefore represents a central problem in the treatment of AML. Despite this, and in contrast to the extensive knowledge about the molecular events underlying the process of leukemogenesis, information about the mechanisms leading to therapy resistance and relapse is still limited.

Purpose and content of review

Recently, a number of studies have aimed to fill this gap and provided valuable information about the clonal composition and evolution of leukemic cell populations during the course of disease, and about genetic, epigenetic, and gene expression changes associated with relapse. In this review, these studies are summarized and discussed, and the data reported in them are compiled in order to provide a resource for the identification of molecular aberrations recurrently acquired at, and thus potentially contributing to, disease recurrence and the associated therapy resistance. This survey indeed uncovered genetic aberrations with known associations with therapy resistance that were newly gained at relapse in a subset of patients. Furthermore, the expression of a number of protein coding and microRNA genes was reported to change between diagnosis and relapse in a statistically significant manner.

Conclusions

Together, these findings foster the expectation that future studies on larger and more homogeneous patient cohorts will uncover pathways that are robustly associated with relapse, thus representing potential targets for rationally designed therapies that may improve the treatment of patients with relapsed AML, or even facilitate the prevention of relapse in the first place.

Electronic supplementary material

The online version of this article (doi:10.1186/s13045-017-0416-0) contains supplementary material, which is available to authorized users.

Disease evolution and outcomes in familial AML with germline CEBPA mutations

In-depth molecular investigation of familial leukemia has been limited by the rarity of recognized cases. This study examines the genetic events initiating leukemia and details the clinical progression of disease across multiple families harboring germ-line CEBPA mutations. Clinical data were collected from 10 CEBPA-mutated families, representing 24 members with acute myeloid leukemia (AML). Whole-exome (WES) and deep sequencing were performed to genetically profile tumors and define patterns of clonal evolution. Germline CEBPA mutations clustered within the N-terminal and were highly penetrant, with AML presenting at a median age of 24.5 years (range, 1.75-46 years). In all diagnostic tumors tested (n = 18), double CEBPA mutations (CEBPAdm) were detected, with acquired (somatic) mutations preferentially targeting the C-terminal. Somatic CEBPA mutations were unstable throughout the disease course, with different mutations identified at recurrence. Deep sequencing of diagnostic and relapse paired samples confirmed that relapse-associated CEBPA mutations were absent at diagnosis, suggesting recurrence was triggered by novel, independent clones. Integrated WES and deep sequencing subsequently revealed an entirely new complement of mutations at relapse, verifying the presentation of a de novo leukemic episode. The cumulative incidence of relapse in familial AML was 56% at 10 years (n = 11), and 3 patients experienced ≥3 disease episodes over a period of 17 to 20 years. Durable responses to secondary therapies were observed, with prolonged median survival after relapse (8 years) and long-term overall survival (10-year overall survival, 67%). Our data reveal that familial CEBPA-mutated AML exhibits a unique model of disease progression, associated with favorable long-term outcomes.

Mutation position within evolutionary subclonal architecture in AML

Cytogenetic data suggest that acute myeloid leukemia (AML) develops through a process of branching evolution, especially during relapse and progression. Recent genomic data from AML cases using digital sequencing, temporal comparisons, xenograft cloning, and single-cell analysis indicate that most, if not all, AML cases emerge through branching evolution. According to a review of the current literature, the balanced translocations (t[15;17], t[8;21], and inv[16]) and nucleotide variants in DNMT3A and TET2 most commonly occur in the founding clone at diagnosis. These mutations are rarely gained or lost at relapse, and the latter 2 mutations are observed in elderly subjects with mosaic hematopoiesis antedating overt leukemia. In contrast, +8, +13, +22, -X, -Y, and nucleotide variants in FLT3, NRAS/KRAS, WT1, and KIT frequently occur in subclones and are observed either to emerge or to be lost at relapse. Because drugs that target mutations within a subclone are unlikely to eliminate all leukemic cells, it will be essential to understand not only which mutations a patient has but also how they organize within the leukemic subclonal architecture.

Concise review: preleukemic stem cells: molecular biology and clinical implications of the precursors to leukemia stem cells

Recent experimental evidence has shown that acute myeloid leukemia (AML) and myelodysplastic syndromes (MDS) arise from transformed immature hematopoietic cells following the accumulation of multiple stepwise genetic and epigenetic changes in hematopoietic stem cells and committed progenitors. The series of transforming events initially gives rise to preleukemic stem cells (pre-LSC), preceding the formation of fully transformed leukemia stem cells (LSC). Despite the established use of poly-chemotherapy, relapse continues to be the most common cause of death in AML and MDS. The therapeutic elimination of all LSC, as well as pre-LSC, which provide a silent reservoir for the re-formation of LSC, will be essential for achieving lasting cures. Conventional sequencing and next-generation genome sequencing have allowed us to describe many of the recurrent mutations in the bulk cell populations in AML and MDS, and recent work has also focused on identifying the initial molecular changes contributing to leukemogenesis. Here we review recent and ongoing advances in understanding the roles of pre-LSC, and the aberrations that lead to pre-LSC formation and subsequent LSC transformation.

DNA methylation and cancer

Cancer has been considered a genetic disease with a wide array of well-characterized gene mutations and chromosomal abnormalities. Of late, aberrant epigenetic modifications have been elucidated in cancer, and together with genetic alterations, they have been helpful in understanding the complex traits observed in neoplasia. "Cancer Epigenetics" therefore has contributed substantially towards understanding the complexity and diversity of various cancers. However, the positioning of epigenetic events during cancer progression is still not clear, though there are some reports implicating aberrant epigenetic modifications in very early stages of cancer. Amongst the most studied aberrant epigenetic modifications are the DNA methylation differences at the promoter regions of genes affecting their expression. Hypomethylation mediated increased expression of oncogenes and hypermethylation mediated silencing of tumor suppressor genes are well known examples. This chapter also explores the correlation of DNA methylation and demethylation enzymes with cancer.

Molecular evaluation of CEBPA gene mutation in normal karyotype acute myeloid leukemia: a comparison of two methods and report of novel CEBPA mutations from Indian acute myeloid leukemia patients

BACKGROUND AND AIM

Mutation in the CAAT/enhancer binding protein-α (CEBPA) gene has been reported as being one of the common genetic abnormalities in acute myeloid leukemia (AML) and is associated with a good clinical outcome. We intend to explore the prevalence of CEBPA mutations and evaluate the efficacy of fragment and sequencing analysis methods for CEBPA mutation detection in Indian AML patients.

MATERIALS AND METHODS

The coding region of the CEBPA gene was screened in 36 normal karyotype AML patients by fragment analysis and direct sequencing.

RESULTS

We identified five CEBPA sequence variations in three patient samples (8.3%) by direct sequencing analysis, of which three were novel mutations. These mutations were clustered mostly in the TAD1 and basic region leucine zipper region of the CEBPA protein. Six cases demonstrated a previously reported polymorphism. Two of the three positive cases showed double mutations, and one case had a single mutation. All five mutations were also detected by fragment analysis, indicating a sensitivity of 100% (5/5). No correlation with clinical parameters including age, sex, white blood cell count, hemoglobin, and platelet count between patients with and without mutation was observed. Interestingly, CEBPA mutations were significantly higher in patients with WT1 mutation, while no correlation with FLT3 and NPM1 was observed.

CONCLUSION

We report for the first time the frequency of CEBPA mutation from an Indian patients (8.3%). The identification of novel CEBPA mutations added new insights into the genetic heterogeneity of AML. Our result suggests that the optimal approach for detecting CEBPA mutations in AML can be a combination of fragment analysis and direct sequencing.

Overexpression of wild-type or mutants forms of CEBPA alter normal human hematopoiesis

C/EBPα (CEBPA) is mutated in approximately 8 % of AML in both familial and sporadic AML and, with FLT3 and NPM1, has received most attention as a predictive marker of outcome in patients with normal karyotype disease. Mutations clustering to either the N- or C-terminal (N-and C-ter) portions of the protein have different consequences on the protein function. In familial cases the N-ter form is inherited with patients exhibiting long latency period before the onset of overt disease, typically with the acquisition of a C-ter mutation. Despite the essential insights murine models provide the functional consequences of wild-type C/EBPα in human hematopoiesis and how different mutations are involved in AML development have received less attention. Our data underline the critical role of C/EBPα in human hematopoiesis and demonstrate that C/EBPα mutations (alone or in combination) are insufficient to convert normal human hematopoietic stem/progenitors (HSC/HPCs) into leukemic initiating cells, although individually each altered normal hematopoiesis. It provides the first insight into the effects of N- and C-terminal mutations acting alone and to the combined effects of N/C double mutants. Our results mimicked closely what happens in CEBPA mutated patients.

Acute myeloid leukemia stem cells and CD33-targeted immunotherapy

Although the identification of cancer stem cells as therapeutic targets is now actively being pursued in many human malignancies, the leukemic stem cells in acute myeloid leukemia (AML) are a paradigm of such a strategy. Heterogeneity of these cells was suggested by clonal analyses indicating the existence of both leukemias resulting from transformed multipotent CD33(-) stem cells as well others arising from, or predominantly involving, committed CD33(+) myeloid precursors. The latter leukemias, which may be associated with an intrinsically better prognosis, offer a particularly attractive target for stem cell-directed therapies. Targeting the CD33 differentiation antigen with gemtuzumab ozogamicin was the first attempt of such an approach. Emerging clinical data indicate that gemtuzumab ozogamicin is efficacious not only for acute promyelocytic leukemia but, in combination with conventional chemotherapy, also for other favorable- and intermediate-risk AMLs, providing the first proof-of-principle evidence for the validity of this strategy. Herein, we review studies on the nature of stem cells in AML, discuss clinical data on the effectiveness of CD33-directed therapy, and consider the mechanistic basis for success and failure in various AML subsets.

FLT3-internal tandem duplication and age are the major prognostic factors in patients with relapsed acute myeloid leukemia with normal karyotype

BACKGROUND

Several genetic aberrations with prognostic impact in first-line therapy have been described in patients with acute myeloid leukemia and normal karyotype. However, little is known about the influence of these aberrations on outcome after relapse. This study aimed to identify clinical and molecular risk factors for patients with relapsed acute myeloid leukemia with normal karyotype.

DESIGN AND METHODS

We analyzed 94 patients with acute myeloid leukemia and normal karyotype after first relapse for clinical and molecular risk factors for survival. All patients had received first-line treatment and follow-up within two prospective, multicenter trials. Leukemic blasts were analyzed at diagnosis for genetic aberrations in the FLT3, NPM1, CEBPA, WT1, IDH1 and IDH2 genes by polymerase chain reaction and/or direct sequencing.

RESULTS

A second complete remission was achieved in 52% of patients who received re-induction therapy. The presence of an FLT3-internal tandem duplication, duration of first complete remission less than 6 months and age above the median of 47 years were associated with a significantly lower rate of second complete remission. The median survival after relapse was 11 months and the 6-year survival rate was 28%. In multivariate analysis, FLT3-internal tandem duplication and age above the median were the only independent negative prognostic factors for survival. The 6-year survival rate of patients with none of these factors was 56%, whereas it was significantly inferior in patients with one or both of these factors (15% and 6%, respectively). This was also true for patients who underwent allogeneic stem cell transplantation after relapse.

CONCLUSIONS

FLT3-internal tandem duplication and age are the major prognostic factors in patients with relapsed acute myeloid leukemia with a normal karyotype. Patients with at least one of these risk factors have a dismal outcome and might be considered for investigational treatment approaches after relapse. (ClinicalTrials.gov Identifier: NCT00209833).

Two types of C/EBPα mutations play distinct but collaborative roles in leukemogenesis: lessons from clinical data and BMT models

Two types of mutations of a transcription factor CCAAT-enhancer binding protein α (C/EBPα) are found in leukemic cells of 5%-14% of acute myeloid leukemia (AML) patients: N-terminal mutations expressing dominant negative p30 and C-terminal mutations in the basic leucine zipper domain. Our results showed that a mutation of C/EBPα in one allele was observed in AML after myelodysplastic syndrome, while the 2 alleles are mutated in de novo AML. Unlike an N-terminal frame-shift mutant (C/EBPα-Nm)–transduced cells, a C-terminal mutant (C/EBPα-Cm)–transduced cells alone induced AML with leukopenia in mice 4-12 months after bone marrow transplantation. Coexpression of both mutants induced AML with marked leukocytosis with shorter latencies. Interestingly, C/EBPα-Cm collaborated with an Flt3-activating mutant Flt3-ITD in inducing AML. Moreover, C/EBPα-Cm strongly blocked myeloid differentiation of 32Dcl3 cells, suggesting its class II mutation-like role in leukemogenesis. Although C/EBPα-Cm failed to inhibit transcriptional activity of wild-type C/EBPα, it suppressed the synergistic effect between C/EBPα and PU.1. On the other hand, C/EBPα-Nm inhibited C/EBPα activation in the absence of PU.1, despite low expression levels of p30 protein generated by C/EBPα-Nm. Thus, 2 types of C/EBPα mutations are implicated in leukemo-genesis, involving different and cooperating molecular mechanisms.

C/EBPα regulated microRNA-34a targets E2F3 during granulopoiesis and is down-regulated in AML with CEBPA mutations

The transcription factor, CCAAT enhancer binding protein alpha (C/EBPα), is crucial for granulopoiesis and is deregulated by various mechanisms in acute myeloid leukemia (AML). Mutations in the CEBPA gene are reported in 10% of human patients with AML. Even though the C/EBPα mutants are known to display distinct biologic function during leukemogenesis, the molecular basis for this subtype of AML remains elusive. We have recently showed the significance of deregulation of C/EBPα-regulated microRNA (miR) in AML. In this study, we report that miR-34a is a novel target of C/EBPα in granulopoiesis. During granulopoiesis, miR-34a targets E2F3 and blocks myeloid cell proliferation. Analysis of AML samples with CEBPA mutations revealed a lower expression of miR-34a and elevated levels of E2F3 as well as E2F1, a transcriptional target of E2F3. Manipulation of miR-34a reprograms granulocytic differentiation of AML blast cells with CEBPA mutations. These results define miR-34a as a novel therapeutic target in AML with CEBPA mutations.

Molecular mechanisms underlying deregulation of C/EBPalpha in acute myeloid leukemia

The CEBPA gene encodes a transcription factor protein that is crucial for granulocytic differentiation, regulation of myeloid gene expression and growth arrest. Mutations in one or both alleles of CEBPA are observed in about 10% of patients with acute myeloid leukemia (AML). Moreover, other genetic events associated with AML have been identified to deregulate C/EBPalpha expression and function at various levels. Recently developed mouse models that accurately mimic the genetic C/EBPalpha alterations in human AML demonstrate C/EBPalpha's gatekeeper function in the control of self-renewal and lineage commitment of hematopoietic stem cells (HSCs). Moreover, these studies indicate that CEBPA mutations affect HSCs in early leukemia development by inducing proliferation and limiting their lineage potential. However, the exact relationship between 'pre-leukemic' HCSs and those cells that finally initiate leukemia (leukemia-initiating cells) with disturbed differentiation and aberrant proliferation remains elusive. More research is needed to identify and characterize these functionally distinct populations and the exact role of the different genetic alterations in the process of leukemia initiation and maintenance.

A family harboring a germ-line N-terminal C/EBPalpha mutation and development of acute myeloid leukemia with an additional somatic C-terminal C/EBPalpha mutation

C/EBPalpha plays an essential role as a transcription factor in myeloid cell differentiation. Here, we describe a Japanese family in which two individuals with acute myeloid leukemia (AML) and one healthy individual had an identical 4-base pair insertion in the N-terminal region of CEBPA (350_351insCTAC), resulting in the termination at codon 107 (I68fsX107). The father and a son at diagnosis of AML had different in-frame insertion mutations in the C-terminal region of C/EBPalpha. These C-terminal mutations disappeared upon remission in both patients. Interestingly, the father showed different in-frame insertion mutations in the C-terminal CEBPA at the time of diagnosis and relapse. These data strongly suggest that the N-terminal C/EBPalpha mutation predisposes to the occurrence of a C-terminal C/EBPalpha mutation as a secondary genetic hit, causing AML.

Acute myeloid leukemia with biallelic CEBPA gene mutations and normal karyotype represents a distinct genetic entity associated with a favorable clinical outcome

PURPOSE

CEBPA mutations are found as either biallelic (biCEBPA) or monoallelic (moCEBPA). We set out to explore whether the kind of CEBPA mutation is of prognostic relevance in cytogenetically normal (CN) acute myeloid leukemia (AML).

PATIENTS AND METHODS

Four hundred sixty-seven homogeneously treated patients with CN-AML were subdivided into moCEBPA, biCEBPA, and wild-type (wt) CEBPA patients. The subgroups were analyzed for clinical parameters and for additional mutations in the NPM1, FLT3, and MLL genes. Furthermore, we obtained gene expression profiles using oligonucleotide microarrays.

RESULTS

Only patients with biCEBPA had an improved median overall survival when compared with patients with wtCEBPA (not reached v 20.4 months, respectively; P = .018), whereas patients with moCEBPA (20.9 months) and wtCEBPA had a similar outcome (P = .506). Multivariable analysis confirmed biCEBPA, but not moCEBPA, mutations as an independent favorable prognostic factor. Interestingly, biCEBPA mutations, compared with wtCEBPA, were never associated with mutated NPM1 (0% v 43%, respectively; P < .001) and rarely associated with FLT3 internal tandem duplication (ITD; 5% v 23%, respectively; P = .059), whereas patients with moCEBPA had a similar frequency of mutated NPM1 and a significantly higher association with FLT3-ITD compared with patients with wtCEBPA (44% v 23%, respectively; P = .037). Furthermore, patients with biCEBPA showed a homogeneous gene expression profile that was characterized by downregulation of HOX genes, whereas patients with moCEBPA showed greater heterogeneity in their gene expression profiles.

CONCLUSION

Biallelic disruption of the N and C terminus of CEBPA is required for the favorable clinical outcome of CEBPA-mutated patients and represents a distinct molecular subtype of CN-AML with a different frequency of associated gene mutations. These findings are of great significance for risk-adapted therapeutic strategies in AML.

Hematopoietic stem cell expansion precedes the generation of committed myeloid leukemia-initiating cells in C/EBPalpha mutant AML

We here use knockin mutagenesis in the mouse to model the spectrum of acquired CEBPA mutations in human acute myeloid leukemia. We find that C-terminal C/EBPalpha mutations increase the proliferation of long-term hematopoietic stem cells (LT-HSCs) in a cell-intrinsic manner and override normal HSC homeostasis, leading to expansion of premalignant HSCs. However, such mutations impair myeloid programming of HSCs and block myeloid lineage commitment when homozygous. In contrast, N-terminal C/EBPalpha mutations are silent with regards to HSC expansion, but allow the formation of committed myeloid progenitors, the templates for leukemia-initiating cells. The combination of N- and C-terminal C/EBPalpha mutations incorporates both features, accelerating disease development and explaining the clinical prevalence of this configuration of CEBPA mutations.

How and why minimal residual disease studies are necessary in leukemia: a review from WP10 and WP12 of the European LeukaemiaNet

Resistance to therapeutic agents is a major factor in the failure of cancer treatments. In leukemia, the resistant cells remaining in the bone marrow and/or peripheral blood constitute minimal residual disease and are detectable by highly sensitive assays when the patient appears to be in complete remission. Early detection of the expansion of residual cells permits clinical intervention with the aim of reversing the proliferation of resistant leukemic cells. Therefore, accurate and precise measurement of minimal residual disease can greatly enhance optimization of oncology patients' clinical management. This notion is supported by a large body of data among chronic myeloid leukemia patients, but minimal residual disease detection and monitoring is increasingly applied to other types of leukemia, and is starting to be a factor in decision-making for some therapeutic trials in childhood acute lymphoblastic leukemia. Here, from the solid ground of minimal residual disease detection in chronic myeloid leukemia, the current state of the art and development of molecular techniques in other leukemias and the growing field of multiparameter flow cytometry are reviewed in two separate parts reporting on the respective advances, advantages and pitfalls of these emerging methods.

Prevalence and prognostic implications of CEBPA mutations in pediatric acute myeloid leukemia (AML): a report from the Children's Oncology Group

CEBPA mutations have been associated with improved outcome in adult acute myeloid leukemia (AML). We evaluated the prevalence and prognostic significance of CEBPA mutations in 847 children with AML treated on 3 consecutive pediatric trials. Two types of CEBPA mutations-N-terminal truncating mutations and in-frame bZip-domain mutations-were detected in 38 (4.5%) of 847 patients tested; 31 (82%) of 38 patients with mutations harbored both mutation types. Mutation status was correlated with laboratory and clinical characteristics and clinical outcome. CEBPA mutations were significantly more common in older patients, patients with FAB M1 or M2, and patients with normal karyotype. Mutations did not occur in patients with either favorable or unfavorable cytogenetics. Actuarial event-free survival at 5 years was 70% versus 38% (P = .015) with a cumulative incidence of relapse from complete remission of 13% versus 44% (P = .007) for those with and without CEBPA mutations. The presence of CEBPA mutations was an independent prognostic factor for improved outcome (HR = 0.24, P = .047). As CEBPA mutations are associated with lower relapse rate and improved survival, CEBPA mutation analysis needs to be incorporated into initial screening for risk identification and therapy allocation at diagnosis.

CCAAT/enhancer binding protein-alpha polymorphisms occur more frequently than mutations in acute myeloid leukemia and exist across all cytogenetic risk groups and leukemia subtypes

CCAAT/enhancer binding protein-alpha (CEBPA) belongs to a family of leucine zipper transcription factors necessary for late differentiation events of many cell types. CEBPA gene has recently been recognized as the target of genetic alterations in acute myeloid leukemia (AML). CEBPA mutations and polymorphisms were determined in a large series of Southeast Asian AML (n = 247) using polymerase chain reaction and direct sequencing. Chromosome and FLT3 mutation analyses were also undertaken. Thirty-two distinct types of nucleotide changes (7 known and 25 novel mutations) were identified in 34 cases (13.8%). Three types of polymorphisms were found in 60 cases (24.3%) including a novel nt1401C>T polymorphism. All polymorphisms were located at the C-terminal region whereas the majority of mutations (62.5%) occurred at the N-terminal region. The most common polymorphism was the nt1175_1180dup resulting in the predicted P194_H195 duplication protein in 50 cases. Although CEBPA mutations were predominantly associated with a normal karyotype (76%), 15.7% of patients with an unfavorable risk and 4.3% of patients with a favorable risk also had the mutations. Moreover, CEBPA polymorphisms were similarly found across all cytogenetic risk groups and occurred in all leukemia subtypes. FLT3 mutations were comparably discovered among patients with CEBPA mutations, polymorphisms and wild-type (26-30%). In conclusion, CEBPA polymorphisms occurred more frequently than CEBPA mutations and could be identified across all prognostic risk groups. The high occurrence of CEBPA polymorphisms should be recognized in order not to include this group of patients with CEBPA polymorphisms for prognostic evaluation of CEBPA mutations in any clinical trials.

Rapid and sensitive screening for CEBPA mutations in acute myeloid leukaemia

The presence of CCAAT/enhancer binding protein alpha (CEBPA) gene mutations in patients with cytogenetically normal acute myeloid leukaemia (CN-AML) confers a favourable prognosis. Routine screening of all CN-AML patients for CEBPA mutations is therefore important for individual risk-adapted post-remission therapy and requires a fast and easy screening method. CEBPA mutations are distributed over the entire CEBPA gene and the functional and clinical consequences of the different mutations are still largely unknown. Therefore, we developed a multiplex polymerase chain reaction-based fragment length analysis mutation screening method for the entire CEBPA coding region. We initially evaluated our method by analysing 120 CN-AML samples both by fragment analysis and nucleotide sequencing and reached a sensitivity of 100% and a specificity of 90%. 349 CN-AML samples were subsequently screened for CEBPA mutations by fragment length analysis. Among a total of 469 CN-AML patient samples, 58 CEBPA mutations were detected in 38 CN-AML patients (8.1%). In conclusion, we established a fast and sensitive CEBPA mutation screening method suitable for inclusion in routine AML diagnostics.

Modeling of C/EBPalpha mutant acute myeloid leukemia reveals a common expression signature of committed myeloid leukemia-initiating cells

Mutations in the CEBPA gene are present in 7%-10% of human patients with acute myeloid leukemia (AML). However, no genetic models exist that demonstrate their etiological relevance. To mimic the most common mutations affecting CEBPA-that is, those leading to loss of the 42 kDa C/EBPalpha isoform (p42) while retaining the 30kDa isoform (p30)-we modified the mouse Cebpa locus to express only p30. p30 supported the formation of granulocyte-macrophage progenitors. However, p42 was required for control of myeloid progenitor proliferation, and p42-deficient mice developed AML with complete penetrance. p42-deficient leukemia could be transferred by a Mac1+c-Kit+ population that gave rise only to myeloid cells in recipient mice. Expression profiling of this population against normal Mac1+c-Kit+ progenitors revealed a signature shared with MLL-AF9-transformed AML.

Transcriptional dysregulation during myeloid transformation in AML

The current paradigm on leukemogenesis indicates that leukemias are propagated by leukemic stem cells. The genomic events and pathways involved in the transformation of hematopoietic precursors into leukemic stem cells are increasingly understood. This concept is based on genomic mutations or functional dysregulation of transcription factors in malignant cells of patients with acute myeloid leukemia (AML). Loss of the CCAAT/enhancer binding protein-alpha (CEBPA) function in myeloid cells in vitro and in vivo leads to a differentiation block, similar to that observed in blasts from AML patients. CEBPA alterations in specific subgroups of AML comprise genomic mutations leading to dominant-negative mutant proteins, transcriptional suppression by leukemic fusion proteins, translational inhibition by activated RNA-binding proteins, and functional inhibition by phosphorylation or increased proteasomal-dependent degradation. The PU.1 gene can be mutated or its expression or function can be blocked by leukemogenic fusion proteins in AML. Point mutations in the RUNX1/AML1 gene are also observed in specific subtypes of AML, in addition to RUNX1 being the most frequent target for chromosomal translocation in AML. These data are persuasive evidence that impaired function of particular transcription factors contributes directly to the development of human AML, and restoring their function represents a promising target for novel therapeutic strategies in AML.