Abstract

Context.—Myelodysplastic syndromes (MDSs) are clonal stem cell diseases characterized by ineffective hematopoiesis, multilineage dysplasia, and peripheral cytopenias with normocellular or hypercellular marrow. They represent a heterogeneous group of disorders with a varied spectrum of clinical, morphologic, biologic, and genetic characteristics. This heterogeneity in disease characterization has led to evolving classification systems, developing prognostic models, and continuing research efforts to elucidate its pathobiology and pathogenesis.

Objective.—To summarize updated information and provide a general overview of the clinicopathologic features, pathobiology, and cytogenetic and molecular pathogenesis of MDSs.

Data Sources.—Relevant articles indexed in PubMed (National Library of Medicine) between 1982 and 2005 and reference medical texts.

Conclusions.—Although MDSs remain a relatively poorly defined disease entity, recent advancements in cytogenetic and molecular studies have significantly contributed to our present knowledge of MDSs. Novel strategies for studying the pathogenesis and evolution of MDSs continue to shape our understanding of this disease and guide our approaches to diagnosis and treatment.

Myelodysplastic syndromes (MDSs) are a heterogeneous group of clonal disorders of hematopoietic stem cells that are characterized by ineffective hematopoiesis, multilineage dysplasia, peripheral cytopenias, and susceptibility to leukemic transformation. The heterogeneity of the clinical, morphologic, biologic, and genetic characteristics of MDSs has led to evolving classification systems and continuing research proposed to elucidate its pathobiology and disease mechanisms. Although it remains an inadequately characterized disorder, our understanding and treatment of MDSs continue to be enhanced by our growing knowledge of the processes that contribute to the disease pathogenesis.

This review is divided into 3 major sections: (1) summary of the clinicopathologic features of MDSs, including classification (French-American-British [FAB], World Health Organization [WHO]) and prognostic stratification (International Prognostic Scoring System [IPSS]); (2) overview of the pathobiology of MDSs, including clonality, multistep disease development, derangements in cell proliferation and differentiation, and apoptosis; and (3) consideration of the cytogenetics and molecular pathogenesis of MDSs, including data from recent complementary DNA (cDNA) microarray technology.

CLINICOPATHOLOGIC FEATURES

Demonstrating a varied spectrum of biologic, genetic, morphologic, and clinical characteristics, MDSs have a natural history that ranges from indolent disease that lasts for years to accelerated progression toward acute leukemia within months. Clinical features of MDSs often stem from manifestations of bone marrow failure and resultant cytopenias (anemia, neutropenia, thrombocytopenia). Although common presenting symptoms include fatigue, pallor, infection, bruising, and/or bleeding, patients may be asymptomatic at diagnosis. Currently, the diagnosis of MDSs is minimally based on a combination of peripheral blood cell counts and morphologic examination of peripheral blood and bone marrow. Additional studies useful in establishing diagnosis include cytogenetic analysis, immunophenotyping, in vitro colony growth assays, and molecular genetic tests.

Primary or de novo MDSs predominantly affect older populations, with a median age of onset of 60 to 70 years. Although actual epidemiologic statistics are unknown, MDSs have an estimated annual incidence of approximately 3.5 to 10 per 100 000 in the general population and 12 to 50 per 100 000 in the elderly population.1 The rising frequency and incidence of MDSs in the US population may be attributed to the growing aging population and increasing disease recognition and diagnosis.1,2 Although largely affecting older adults, MDSs have been documented in younger people at a lower incidence.3–5 Predisposing factors with variable relative risks for developing MDSs include occupational exposure to benzene, pesticides, organic solvents, and other cytotoxic agents or environmental carcinogens.

The wide variability in prognosis of MDSs is accompanied by heterogeneous diagnostic criteria and classification systems. Disease classification systems for MDSs have been developed and modified during the past several decades. Introduced in 1982, the FAB Classification provided the initial framework for morphologic classification and diagnostic evaluation of MDSs.6 This system defined 5 major subtypes of MDSs characterized by percentage of blasts, the presence of ringed sideroblasts, and the extent of monocytosis. Table 1 summarizes the criteria for peripheral blood and bone marrow findings for these FAB subtypes of refractory anemia (RA), refractory anemia with ringed sideroblasts (RARS), refractory anemia with excess blasts (RAEB), refractory anemia with excess blasts in transformation (RAEB-t), and chronic myelomonocytic leukemia. Since its introduction, the FAB Classification has realized widespread use and clinical utility despite its prognostic limitations.

Table 1. 

The French-American-British Classification of Myelodysplastic Syndromes (MDSs)

The French-American-British Classification of Myelodysplastic Syndromes (MDSs)
The French-American-British Classification of Myelodysplastic Syndromes (MDSs)

In 1999, the WHO established a modified scheme for the categorization of hematopoietic neoplasms that proposed to improve the prognostic significance of MDS classification.7 With incorporation of biologic and genetic features of disease to morphologic findings, the WHO guidelines offer refinements to subgroup designations. These changes include classifying chronic myelomonocytic leukemia into a distinct category of myelodysplastic/myeloproliferative diseases due to its potential for disease presentation that bridges the spectrum of MDSs and myeloproliferative disorders and eliminates the FAB definition of RAEB-t by reducing the defining threshold of blasts for acute myeloid leukemia (AML) to 20%. Also, cytogenetic data are incorporated with the addition of the subtype 5q- syndrome. Furthermore, the WHO proposals introduce an additional category designated as refractory cytopenia with multilineage dysplasia; this subtype comprises cases that demonstrate significant cytopenia and dysplasia but do not meet minimum blast criterion for the classification of RAEB. This group of patients has been shown to have slightly more favorable prognosis compared with patients with RAEB classification but worse prognosis than patients with unilineage dysplasia (RA, RARS).8 Although some revisions to the former organization of MDSs and AML remain controversial, the WHO recommendations for MDS classification generally are continuing to gain increasing acceptance. The WHO classification and criteria for MDSs along with corresponding FAB designations are presented in Table 2.

Table 2. 

The World Health Organization (WHO) Classification and Criteria for Myelodysplastic Syndromes (MDSs)*

The World Health Organization (WHO) Classification and Criteria for Myelodysplastic Syndromes (MDSs)*
The World Health Organization (WHO) Classification and Criteria for Myelodysplastic Syndromes (MDSs)*

As a complement to morphologic classification, the IPSS was devised as a risk-based classification system for prognostic stratification of newly diagnosed, untreated primary MDSs.9 Based on independent prognostic variables of percentage of bone marrow blasts, degree of cytopenia, and chromosomal pattern, the IPSS defines 4 distinctive risk groups with variable probability for survival and evolution to acute leukemia. In the prognostic model by Greenberg et al,9 median overall survival times for MDS patients based on IPSS risk categories are as follows: low risk, approximately 5.7 years; intermediate 1 risk, approximately 3.5 years; intermediate 2 risk, approximately 1.2 years; and high risk, approximately 0.4 years (Table 3). Similarly, by stratified risk groups, median intervals for 25% of patients to transform to AML are as follows: low risk, approximately 9.4 years; intermediate 1 risk, approximately 3.3 years; intermediate 2 risk, approximately 1.1 years; and high risk, approximately 0.2 year. Data on survival and AML evolution of MDS patients subgrouped according to the WHO classification system alone and in combination with IPSS risk stratification are summarized in Table 4. The IPSS model of MDSs proposes to be a valuable tool in the practical approach to evaluating disease prognosis.

Table 3. 

International Prognostic Scoring System (IPSS) for Predicting Survival and Acute Myeloid Leukemia (AML) Evolution in Myelodysplastic Syndromes*

International Prognostic Scoring System (IPSS) for Predicting Survival and Acute Myeloid Leukemia (AML) Evolution in Myelodysplastic Syndromes*
International Prognostic Scoring System (IPSS) for Predicting Survival and Acute Myeloid Leukemia (AML) Evolution in Myelodysplastic Syndromes*
Table 4. 

Data on Survival and Acute Myeloid Leukemia (AML) Evolution of Myelodysplastic Syndrome (MDS) Patients Subgrouped According to the World Health Organization (WHO) Classification System and Combined With International Prognostic Scoring System (IPSS) Risk Stratification*

Data on Survival and Acute Myeloid Leukemia (AML) Evolution of Myelodysplastic Syndrome (MDS) Patients Subgrouped According to the World Health Organization (WHO) Classification System and Combined With International Prognostic Scoring System (IPSS) Risk Stratification*
Data on Survival and Acute Myeloid Leukemia (AML) Evolution of Myelodysplastic Syndrome (MDS) Patients Subgrouped According to the World Health Organization (WHO) Classification System and Combined With International Prognostic Scoring System (IPSS) Risk Stratification*

Currently, the only curative treatment available to MDS patients is bone marrow or peripheral stem cell transplantation. With improving characterization of pathophysiologic pathways and potential molecular targets in MDSs, recent therapies have been developed, including DNA methyltransferase inhibitors, vascular endothelial growth factor (VEGF) inhibitors, farnesyl transferase inhibitors, thalidomide, arsenic trioxide, and anti-tumor necrosis factor α (anti–TNF-α).10–15 Greater insight into the underlying molecular mechanisms that lead to marrow failure and progression to acute leukemia may identify additional strategies and targets for diagnostic and therapeutic approaches.

PATHOBIOLOGY

The etiology and pathogenesis of MDSs remain poorly characterized. Underlying the marrow failure and peripheral cytopenias common in MDSs is deranged clonal proliferation of hematopoietic progenitor cells with inherited or acquired genetic mutation. Although its characterization continues to be controversial, clonality in MDSs has been supported by cytogenetics, fluorescence in situ hybridization analysis, and X-chromosome inactivation studies.2,16–22 These various studies strongly suggest clonal involvement of the myeloid lineages; however, the clonal character of the lymphoid lineage remains unclear. Importantly, the effect of this primary clonal mutation that involves pluripotent or multipotent hematopoietic cells may establish the MDS phenotype and its natural disease course.

Development of MDSs presumably occurs through multiple evolutionary stages. Likely representing an early-stage event in the multistep pathogenesis of MDSs, the initial genetic insult to hematopoietic stem cells leads to emergence of an aberrant clone that exhibits morphologic dysplasia, cellular dysfunction, and disparate proliferative advantage. Although the mechanisms that promote the initiation of MDSs are not well defined, events implicated in this process include somatic DNA injury, defective DNA repair, impaired immunologic surveillance, and dysregulated cell signal transduction.2,23–25 Furthermore, the initiating clonal defect is believed to promote genomic instability and heightened susceptibility to acquisition of additional genetic lesions. Subsequent evolution of this mutant clone is associated with progressive cellular dysfunction and ineffective hematopoiesis characterized by excessive apoptosis. Impaired cellular differentiation and maturation accompanying the dysregulated apoptosis contributes to the peripheral cytopenias characteristic of the MDS phenotype. Ultimately, as a potential final stage in its multistep pathogenesis, continued expansion of this abnormal clone with accumulated genetic damage and alteration of critical targets may result in neoplastic transformation to acute leukemia.

Derangements in hematopoietic cell proliferation and differentiation that characterize MDSs are associated with complex changes in biology. The early proliferative advantage of MDS clones may be represented by increased cellular proliferation particularly in the myeloid lineage and potentially all hematopoietic lineages.26 Accumulating multiple alterations that may affect cycle regulation, transcription factors, growth factor receptors, and tumor suppressors, these clonal cells further expand with abnormal maturation and increased rates of apoptosis. Opposing forces of increased cell proliferation and excessive cell death in concert with impaired differentiation of hematopoietic progenitor cells result in the ineffective marrow hematopoiesis and peripheral cytopenias observed in MDSs, often in the setting of normal to hypercellular bone marrow.

Particularly, the mechanism of programmed cell death (apoptosis) has been hypothesized as a possible explanation for the apparent paradoxical MDS phenotype of peripheral cytopenia alongside marrow cellularity. Excessive apoptosis of hematopoietic progenitor cells may contribute to the defining features of MDSs, including dysplastic morphologic features, ineffective hematopoiesis, and marrow failure.27–32 Studies have demonstrated morphologic evidence of increased apoptotic cell death in MDSs, particularly in less advanced disease.33–36 Alongside this observation, some studies suggest that disease progression may be accompanied by decreased rates of apoptosis, because susceptibility to intramedullary cell death changes with changing cellular phenotype.33,34,36–38 These studies offer evidence for increasing levels of antiapoptotic Bcl-2 marrow blasts with advancing MDS subtype.33,37,38 These observations are consistent with other reports of shifting ratios of proapoptotic and antiapoptotic proteins with the progression of MDS disease.39,40 Although increased programmed cell death in MDSs may occur as an early rescue or compensatory response to dysregulated clonal proliferation, it may also represent a pathophysiologic consequence of the epigenetic changes associated with the disease biology of MDSs. Possible mechanisms that contribute to excessive apoptosis in MDSs include essential genetic damage and a perturbed marrow microenvironment.23,41 Whether by direct injury to critical gene targets or complex downstream effects of elaborated cytokines and altered cellular milieu, diverse apoptotic stimuli may activate various signal transduction pathways for apoptosis that culminate in a common cell death program. The interesting relationship of cell death with dysregulated cellular proliferation and differentiation suggests a unique role for apoptosis in MDSs. The significance of apoptosis and other key mechanisms in the molecular pathogenesis of MDSs continues to be investigated as the complex biologic features of such hematologic diseases are further recognized.

CYTOGENETICS AND MOLECULAR PATHOGENESIS

The heterogeneity of the clinical and morphologic pictures of MDSs reflects the fundamentally complex genetic and biologic abnormalities manifested in its pathogenesis. Important aspects of this disease that can be investigated at the molecular level include the cytogenetic abnormalities and dysregulated gene pathways common to MDSs. Elucidating the pathogenetic processes and molecular mechanisms underlying MDSs is central to our understanding of disease biology and prognosis.

Clonal cytogenetic abnormalities are important in the characterization of MDSs. The presence of chromosomal abnormalities can be identified in approximately 30% to 50% of primary MDSs and in more than 80% of secondary or therapy-related MDSs.42 Karyotyping is particularly valuable in the clinical evaluation of MDSs and is integrated into the IPSS model for risk stratification for survival and AML evolution. Representing stages of the multistep pathogenesis of MDSs, single or complex cytogenetic abnormalities may manifest in early MDSs and persist or evolve with disease progression. More complex cytogenetics tend to be associated with disease progression and therapy-related MDSs. Structural and/or numerical chromosomal aberrations may be present. Unlike the chromosomal translocations frequently observed in AML, unbalanced chromosomal changes that consist of partial or complete losses are common in MDSs. Characteristic chromosomal deletions involve chromosome 5 [del(5q),−5], chromosome 11 [del(11q)], chromosome 12 [del(12q)], chromosome 20 [del(20q)], chromosome 7 [del(7q),−7], chromosome 17 [del(17p)], and chromosome 13 [del(13q)]. Other frequent chromosomal abnormalities include trisomy 8, trisomy 21, and inversion 3(q21q26). Rare reciprocal translocations include t(1;7)(q10;p10), t(1; 3)(p36;q21), t(3;3)(q21;q26), t(6;9)(p23;q34), and t(5; 12)(q33;p13); t(5;7)(q33;11.2).

The incidence of these cytogenetic aberrations may reflect the genomic instability of affected MDS clones and their susceptibility for acquisition of additional genetic lesions. In particular, chromosomal deletions in MDSs suggest aberrations of genes involved in tumor suppression or DNA repair. As the most common chromosomal aberrations in MDSs, abnormalities in chromosomes 5 and 7 have been investigated extensively. Partial or complete deletion of chromosome 5 is estimated to occur in 10% to 15% of MDSs that arise de novo and 50% of therapy-related disease.43,44 The critical region of interstitial deletion within chromosome 5[5q31–5q33] has been associated with genes that encode hematopoietic cytokines (colony-stimulating factor [CSF] 2, interleukin [IL] 3, IL-4, IL-5, IL-9), hormone and growth factor receptors (CSF1R, α1-adrenergic receptor [ADRA1], β2-adrenergic receptor [ADRB2], glucocorticoid receptor 1 [GRL1]), and proteins active in transcription and signal transduction (epidermal growth factor [EGF] 1, interferon regulatory factor 1 [IRF1]).45,46 Chromosomal 7 abnormalities associated with complete or partial deletions may occur in 10% of cases of primary MDS and AML and 50% to 75% in therapy-related MDSs and AML.47,48 Presumably involving tumor suppressor genes, critical deletions of the long arm have been localized to 7q22 and 7q32–34.47,49 Characterization of the genes associated with these and other recurrent chromosomal aberrations will contribute to our understanding of their normal physiology and role in the pathogenesis of MDSs.

Molecular abnormalities derived from genetic mutations likely mediate the development and progression of MDSs. Active research efforts in this area have led to the identification and characterization of important genes and molecular pathways.

To date, numerous genes have been implicated in the molecular pathogenesis of MDSs (Figure). These targets of interest include oncogenes, cell cycle regulatory genes, apoptotic genes, growth factor or angiogenesis genes, genes that regulate DNA methylation and histone deacetylation (epigenetic gene silencing), and immunomodulatory cytokine genes.

Dysregulated genes in myelodysplastic syndromes

Dysregulated genes in myelodysplastic syndromes

Oncogenes

The RAS gene family and its signaling transduction pathway are among the most widely investigated molecular targets in oncogenesis. Activated by ligand binding to cell surface receptors such as tyrosine kinases, RAS proteins function in intracellular signaling pathways to promote cellular proliferation and differentiation. The mutated RAS gene product features constitutive activity in its persistent guanosine triphosphate–bound form to promote continuous kinase activity and signal transduction. Point mutations of the n-ras oncogene that demonstrate this dysregulated signal transduction have been reported in 10% to 40% of MDSs.50–53 Furthermore, n-ras mutations have been associated with decreased survival and higher incidence of leukemic progression.51,54 Many studies suggest that mutations of the ras oncogene in initial or advanced stages of disease may contribute to the pathogenesis of MDSs by stimulating early progressive clonal expansion or late leukemic transformation.51,55,56 

The FMS gene encodes the cell surface receptor of CSF-1 or macrophage CSF. Expressing ligand-dependent tyrosine kinase activity, this gene product bound to CSF-1 promotes the proliferation and differentiation of hematopoietic cells of the monocyte-macrophage series.57,58 Mutation in the c-fms gene results in an altered gene product, with conformational change supporting constitutive receptor transduction. Mapped to chromosome 5q33, the FMS gene region has been implicated in the pathogenesis of hematopoietic diseases, including MDSs.47,52,59,60 Point mutation at codon 969 has been reported with increased incidence in association with more advanced MDS subtypes.52,61 

Cell Cycle Regulatory Genes

Dysregulation of normal cell growth through the cell cycle may contribute to leukemogenesis and the pathogenesis of MDSs. Epigenetic alteration of the cyclin-dependent kinase inhibitor gene p15INK4B has been observed in hematopoietic progenitor cells in MDSs. Recent studies suggest that hypermethylation of CpG islands in the promoter region of cell cycle inhibitor p15INK4B may be associated with disease progression and leukemic transformation in MDSs.62–64 This mechanism for inactivation of regulatory genes such as p15INK4B suggests a process by which leukemic cells may evade the inhibitory signals imposed by the milieu.

EVI-1 is another gene that encodes for a complex transcription factor involved in myeloid maturation through interaction with multiple cell cycle regulators.65 Overexpression of the proto-oncogene EVI-1 has been documented in chronic myeloid leukemia and AML transformed from MDSs.66–68 Furthermore, data suggest that a fused AML1/EVI-1 chimeric gene product produced by the reciprocal t(3;21)(q26;q22) translocation may inhibit terminal hematopoietic progenitor cell differentiation in erythroid and granulocytic lineages.69–72 

Additional mutations that involve other genes, including CHK2, p53, and MLL, have been implicated in altered checkpoint controls or other cell cycle abnormalities that may contribute to the pathogenetic processes in MDSs.73–76 

Apoptotic Genes

Dysregulated genes responsible for the transcription of cytokines and growth factors that regulate apoptosis likely contribute to the ineffective hematopoiesis characteristic of MDSs. In addition to the direct effect of abnormal elaboration of apoptotic factors, the resulting disordered cellular-stromal microenvironment associated with altered levels of these gene products further potentiate cellular susceptibility to apoptosis and disrupt hematopoietic cell capacity for proliferation and survival in MDSs.23,77 Elevated levels of various cytokines have been associated with increased apoptotic cell death in MDSs, including TNF-α receptor, transforming growth factor β (TGF-β), IL-1β, IL-6, interferon-γ (IFN-γ), VEGF, and Fas/Fas ligand.26,28,78–80 Particularly, gene products for bcl-2 proto-oncogene, c-myc, and p53 have been implicated as key regulators in the apoptotic pathway. Bcl-2 represents the prototypical negative regulator of apoptosis from the Bcl-2 family of proapoptotic and antiapoptotic proteins. It primarily functions through dimerizations with family members and through interactions with other regulators, such as p53 and RAS. With subcellular localization to mitochondrial membrane, endoplasmic reticulum, and nuclear envelope, Bcl-2 has been reported to participate in ion channel formation and the alteration of membrane permeability necessary for the initiation of apoptosis.81,82 Increased bcl-2 expression has been correlated with MDS progression, with the highest bcl-2 overexpression observed in more advanced subtypes (RAEB and RAEB-t by FAB classification).37,38,83 c-myc and p53 are proapoptotic regulators that have also been shown to be abnormally expressed in hematopoietic cells of MDSs. c-Myc presumably accelerates apoptosis in hematopoietic cells through its association with designated growth factors and apoptotic regulators such as Bcl-2.84,85 Increased levels of c-myc relative to bcl-2 expression have been reported in MDS subtypes RA and RARS.39 p53 promotes apoptosis in various cell lineages, including the myeloid line, and functions through its interactions with numerous regulators of the apoptotic pathway. Enhanced p53 expression has been associated with MDS evolution to leukemia.38,86 

Growth Factor and Angiogenesis Genes

Dysregulation of genes that encode angiogenic factors involved in the growth of endothelial or hematopoietic cells87,88 may play an important role in the pathophysiology of hematologic malignancies such as MDSs. Reported mediators of angiogenesis include VEGF, basic fibroblast growth factor, angiogenin, angiotropin, angiopoietin-1, platelet-derived growth factor, hepatocyte growth factor, EGF, TNF-α, TGF-α, TNF-β, IL-1, IL-6, IL-8, and granulocyte-macrophage CSF.89–93 Increased angiogenesis has been observed in MDSs88,94,95 in association with elevated levels of VEGF, basic fibroblast growth factor, and hepatocyte growth factor.96 Furthermore, the extent of angiogenesis has been correlated with disease progression with increasing bone marrow vascularity associated with more advanced disease (progressive subtypes per FAB classification).88,94 Overexpression of specific angiogenic mediators in hematopoietic cells supports the influence of tumor microenvironment and suggests an autocrine role for these cytokine factors in promoting neoplastic growth and proliferation in MDSs.95,97 

Receptor Tyrosine Kinase Genes

FLT3, a frequently mutated gene in AML, encodes for a class III receptor tyrosine kinase preferentially expressed on hematopoietic progenitor cells. When engaged by its ligand, phosphorylated FLT3 activates signal transduction pathways involved in the proliferation of pluripotent and progenitor cells, including RAS/MAPK, STAT5, PLCγ, and SHIP.98–100 An internal tandem duplication of this gene (FLT-ITD) has been reported in approximately 20% of AML patients and 3% of MDS patients, and this mutation has been associated with poor prognosis or increased incidence of leukemic transformation in MDSs.101,102 Another mutation in the second tyrosine kinase domain (TDK) within the activation loop of FLT3 has also been identified in hematologic malignancies. One recent study reported this D835 mutation of the FLT3 gene in 30 (7%) of 429 AML cases, 1 (3.4%) of 29 MDS cases, and 1 (2.8%) of 36 acute lymphocytic leukemia cases.103 These mutations disrupt normal tyrosine kinase activity and likely contribute to the dysregulated cellular signaling associated with leukemic progression. The frequency of FLT3 mutations among hematologic malignancies suggests their significance in the pathophysiology of hematopoietic progenitor cells.

Genes Regulating DNA Methylation and Histone Deacetylation

Important mechanisms for epigenetic alteration of gene expression include DNA methylation and histone acetylation. Dysregulation of these genes that encode enzyme and protein products responsible for modifying chromatin structure and DNA methylation patterns contributes to carcinogenesis by transcriptional inactivation of critical genes; these genes may include tumor suppressor genes, DNA repair genes, or other genes involved in cellular proliferation and differentiation. Aberration of DNA methylation has been linked to various solid neoplasms and hematologic malignancies.104,105 Although genomic hypomethylation with chromosomal instability was initially observed in tumorigenesis,106–110 recent studies suggest that hypermethylation of CpG islands on promoter regions may represent a common mechanism for inactivation of tumor suppressor genes in many human cancers, including hematopoietic neoplasms.62–64,111–115 Hypermethylation of various genes, including E-cadherin,15,116,117 calcitonin,15,118–120 estrogen receptor,15,121 HIC1,122–125 and cyclin-dependent kinase inhibitor genes p15, p16, p21, and p57,62–64,111–115 have been implicated in hematologic malignancies.

Gene expression inactivation associated with DNA methylation may occur through multiple synergistic mechanisms. CpG methylation of gene promoter regions imposing steric obstruction to transcription factors may be accompanied by subsequent recruitment of methyl CpG binding domain proteins, histone deacetylase, and other transcriptional corepressors126–130; these interrelated mechanisms act in concert to repress transcription collaboratively. Chromatin modification through histone deacetylation is a related mechanism coupled to DNA methylation that stabilizes reduced chromatin conformations protected from transcriptional activity. When assembled to methylated promoters, histone deacetylases and other recruited binding proteins function as corepressors of transcription.

In MDSs, aberrant DNA methylation of calcitonin and p15INK4B has been reported with increased frequency.62–64,119,120 Particularly, hypermethylation of p15INK4B tumor suppressor gene has been described in association with MDS progression and leukemic transformation.62–64,131–133 ,p15 encodes an inhibitor of cyclin-dependent kinases 4 and 6, which mediate G1/S progression within the cell cycle with TGF-β induction.134–137 Correlating with absent p15 expression, hypermethylation of CpG promoter regions of p15INK4B has been observed in advanced MDS subtypes (FAB), including RAEB and RAEB-t.62,64,138 Furthermore, p15 gene methylation is reported at higher incidence in acute leukemia transformed from MDSs.64,131,132,138 These observations suggest that aberrant p15 methylation may represent a potential marker for detection of MDS progression and leukemic evolution.

Immunomodulatory Cytokine Genes

Immune dysregulation that involves the elaboration of proinflammatory or immunoregulatory molecules has been suggested as a pathophysiologic phenomenon underlying the marrow failure and hematopoietic insufficiency characteristic of MDSs. Dysregulation of genes that encode immunomodulatory cytokines in bone marrow stromal cells is believed to play an important role in the pathogenesis of MDS.

One of the most well-characterized immunomodulatory cytokines, TNF-α has been shown to express strong inhibitory activity in hematopoiesis.139–141 It has also been implicated in effecting the function or expression of related negative regulatory cytokines such as IFN-γ, IFN-γ receptor, and Fas in hematopoietic cells.142 Both TNF-α and IFN-γ have been shown to promote up-regulation of Fas and Fas-ligand in hematopoietic precursors.142,143 Furthermore, data suggest that TNF-α is involved in the signaling pathways of apoptosis,26,78,144–146 and elevated levels of TNF-α have been correlated with excessive apoptotic death in MDSs.26,142,147–149 Several studies report up-regulation of TNF-α in bone marrow cells (macrophages and fibroblasts) and stroma of MDS patients.78,145,147,150–152 Highest TNF-α positivity has been associated with RA subtype145 and advanced MDS subtypes RAEB and RAEB-t.153 Despite the unclear relationship between TNF-α expression and MDS disease stage, growing evidence supports the central role of TNF-α in cytokine-mediated hematopoietic suppression and apoptotic cell death in MDS pathogenesis.

Other cytokines reportedly involved in the processes leading to ineffective hematopoiesis in MDSs include TGF-β, IL-1β, and TNF-related signaling molecules TRADD/ FADD, RIP, and TRAIL (TNF-related apoptosis inducing ligand).144,152,154–157 

Other Novel Genes Recently Identified by cDNA Microarray Technology

The completion of the human genome project has enabled us to exploit high-throughput genomic approaches in studying the pathogenesis of MDSs and the molecular pathways important in disease initiation and evolution. Within the past 4 years, application of cDNA microarray technology to evaluate RNA expression profiles has facilitated the identification of numerous previously unidentified genes associated with MDSs (Table 5).158–162 However, the results from various studies have been inconsistent and occasionally conflicting. In the work of Miyazato et al,160 comparing 5 MDS patients with 5 patients with de novo AML, only a few genes were identified as putatively “MDS specific”; these genes included those encoding for Dlk (also known as fetal antigen 1 and stromal cell protein 1), Tec, and inositol 1,4,5-triphosphate receptor type 1. In contrast, Hofmann et al158 described numerous genes identified as differentially regulated in MDS patient populations at the time of diagnosis; these genes further discriminated low-risk from high-risk MDS patients. Ueda et al162 identified 11 poor prognosis genes and 6 good prognosis genes from the blast cells of 30 MDS patients that correlated with MDS progression. However, none of the prognostic genes in studies by Hofmann et al or Ueda et al was cited in common.158,162 Among the several genes implicated in MDS progression by Ueda et al, only one gene (IL1-R) was up-regulated in the group of high-risk MDS patients evaluated by Chen et al.159 Although these studies yield interesting data, they are limited by the small number of cases evaluated, the retrospective nature of their study design, and the lack of longitudinal comparison of the studied populations. Nonetheless, these studies demonstrate the potential for the application of genome-wide approaches in investigating the molecular pathogenesis of MDSs. Continuing refinement of this technology with accompanying improvements in research design and application may potentially enable us to (1) define the precise mechanisms involved in the initiation and progression of MDSs, (2) identify biomarkers for accurately diagnosing and predicting progression of MDSs, and (3) develop novel targeted therapies for preventing the onset or progression of MDSs.

Table 5. 

Summary of Complementary DNA Microarray Data in Myelodysplastic Syndromes Cited in the Literature158–162

Summary of Complementary DNA Microarray Data in Myelodysplastic Syndromes Cited in the Literature158–162
Summary of Complementary DNA Microarray Data in Myelodysplastic Syndromes Cited in the Literature158–162

CONCLUSION

The MDSs remain inadequately characterized disorders; however, novel strategies for studying disease pathogenesis and progression continue to shape our understanding of and approach to diagnosing and treating MDSs. The heterogeneity of the clinical, morphologic, biologic, and genetic characteristics of MDSs has led to evolving classification systems and active research proposed to elucidate its pathobiology and disease processes. Mechanisms of this complex disease include pluripotent stem cell injury with multistep pathogenesis and deranged hematopoietic proliferation, differentiation, and apoptosis. Furthermore, development and progression of MDSs are likely mediated by genetic abnormalities at the molecular level. Underlying the marrow failure and evolutionary potential in MDSs is dysregulation of multiple genes, including those involving oncogenesis, cell cycle regulation, apoptosis, angiogenesis, immunomodulation, and epigenetic modulation.

Improvements in our approaches to cytogenetic and molecular studies of MDSs have started to clarify the molecular pathogenesis of this disease. Evolving characterization of MDSs will continue to enhance our understanding of the pathogenetic mechanisms and improve current strategies for managing these diseases.

References

References
Kasper
,
D. L. M.
,
A. S. M.
Fauci
,
D. L. M.
Longo
,
E. M.
Braunwald
,
S. L. M.
Hauser
, and
J. L. M.
Jameson
.
eds
.
Harrison's Principles of Internal Medicine. 16th ed.
Columbus, Ohio: McGraw-Hill Companies Inc; 2005
.
Aul
,
C.
,
D. T.
Bowen
, and
Y.
Yoshida
.
Pathogenesis, etiology and epidemiology of myelodysplastic syndromes.
Haematologica
1998
.
83
:
71
86
.
Haas
,
O. A.
and
H.
Gadner
.
Pathogenesis, biology, and management of myelodysplastic syndromes in children.
Semin Hematol
1996
.
33
:
225
235
.
Locatelli
,
F.
,
M.
Zecca
,
A.
Pession
,
E.
Maserati
,
P.
De Stefano
, and
F.
Severi
.
Myelodysplastic syndromes: the pediatric point of view.
Haematologica
1995
.
80
:
268
279
.
McMullin
,
M. F.
,
M.
Chisholm
, and
J. M.
Hows
.
Congenital myelodysplasia: a newly described disease entity?
Br J Haematol
1991
.
79
:
340
342
.
Bennett
,
J. M.
,
D.
Catovsky
, and
M. T.
Daniel
.
et al
.
Proposals for the classification of the myelodysplastic syndromes.
Br J Haematol
1982
.
51
:
189
199
.
Harris
,
N. L.
,
E. S.
Jaffe
, and
J.
Diebold
.
et al
.
The World Health Organization classification of neoplasms of the hematopoietic and lymphoid tissues: report of the Clinical Advisory Committee meeting–Airlie House, Virginia, November, 1997.
Hematol J
2000
.
1
:
53
66
.
Vardiman
,
J. W.
,
N. L.
Harris
, and
R. D.
Brunning
.
The World Health Organization (WHO) classification of the myeloid neoplasms [see comment].
Blood
2002
.
100
:
2292
2302
.
Greenberg
,
P.
,
C.
Cox
, and
M. M.
LeBeau
.
et al
.
International scoring system for evaluating prognosis in myelodysplastic syndromes.
Blood
1997
.
89
:
2079
2088
.
Faderl
,
S.
and
H. M.
Kantarjian
.
Novel therapies for myelodysplastic syndromes.
Cancer
2004
.
101
:
226
241
.
Cilloni
,
D.
,
F.
Messa
, and
S.
Carturan
.
et al
.
Myelodysplastic syndromes.
Ann N Y Acad Sci
2004
.
1028
:
400
408
.
Erba
,
H. P.
Recent progress in the treatment of myelodysplastic syndrome in adult patients.
Curr Opin Oncol
2003
.
15
:
1
9
.
Greenberg
,
P. L.
,
N. S.
Young
, and
N.
Gattermann
.
Myelodysplastic syndromes.
Hematology (Am Soc Hematol Educ Program). 2002:136–161
.
Silverman
,
L. R.
DNA methyltransferase inhibitors in myelodysplastic syndrome.
Best Pract Res Clin Haematol
2004
.
17
:
585
594
.
Leone
,
G.
,
L.
Teofili
,
M. T.
Voso
, and
M.
Lubbert
.
DNA methylation and demethylating drugs in myelodysplastic syndromes and secondary leukemias.
Haematologica
2002
.
87
:
1324
1341
.
Hirai
,
H.
Molecular mechanisms of myelodysplastic syndrome.
Jpn J Clin Oncol
2003
.
33
:
153
160
.
Boultwood
,
J.
and
J. S.
Wainscoat
.
Clonality in the myelodysplastic syndromes.
Int J Hematol
2001
.
73
:
411
415
.
Busque
,
L.
and
D. G.
Gilliland
.
X-inactivation analysis in the 1990s: promise and potential problems.
Leukemia
1998
.
12
:
128
135
.
Raskind
,
W. H.
,
L.
Steinmann
, and
V.
Najfeld
.
Clonal development of myeloproliferative disorders: clues to hematopoietic differentiation and multistep pathogenesis of cancer.
Leukemia
1998
.
12
:
108
116
.
Delforge
,
M.
,
H.
Demuynck
, and
G.
Verhoef
.
et al
.
Patients with high-risk myelodysplastic syndrome can have polyclonal or clonal haemopoiesis in complete haematological remission.
Br J Haematol
1998
.
102
:
486
494
.
Weimar
,
I. S.
,
J. H.
Bourhis
,
G. C.
De Gast
, and
W. R.
Gerritsen
.
Clonality in myelodysplastic syndromes.
Leuk Lymphoma
1994
.
13
:
215
221
.
Yoshida
,
Y.
,
J.
Stephenson
, and
G. J.
Mufti
.
Myelodysplastic syndromes: from morphology to molecular biology, part I: classification, natural history and cell biology of myelodysplasia.
Int J Hematol
1993
.
57
:
87
97
.
Hellstrom-Lindberg
,
E.
,
C.
Willman
,
A. J.
Barrett
, and
Y.
Saunthararajah
.
Achievements in understanding and treatment of myelodysplastic syndromes.
Hematology (Am Soc Hematol Educ Program). 2000:110–132
.
Barrett
,
J.
Myelodysplastic syndrome and aplastic anemia: diagnostic and conceptual uncertainties.
Leuk Res
2000
.
24
:
595
596
.
Molldrem
,
J. J.
,
E.
Leifer
, and
E.
Bahceci
.
et al
.
Antithymocyte globulin for treatment of the bone marrow failure associated with myelodysplastic syndromes.
Ann Intern Med
2002
.
137
:
156
163
.
Raza
,
A.
,
S.
Mundle
, and
V.
Shetty
.
et al
.
Novel insights into the biology of myelodysplastic syndromes: excessive apoptosis and the role of cytokines.
Int J Hematol
1996
.
63
:
265
278
.
Heaney
,
M. L.
and
D. W.
Golde
.
Myelodysplasia.
N Engl JMed
1999
.
340
:
1649
1660
.
Rosenfeld
,
C.
and
A.
List
.
A hypothesis for the pathogenesis of myelodysplastic syndromes: implications for new therapies.
Leukemia
2000
.
14
:
2
8
.
Hoagland
,
H. C.
Myelodysplastic(preleukemia) syndromes: the bone marrow factory failure problem.
Mayo Clin Proc
1995
.
70
:
673
676
.
quiz 677
.
Huh
,
Y. O.
,
I.
Jilani
, and
E.
Estey
.
et al
.
More cell death in refractory anemia with excess blasts in transformation than in acute myeloid leukemia.
Leukemia
2002
.
16
:
2249
2252
.
Kouides
,
P. A.
and
J. M.
Bennett
.
Understanding the myelodysplastic syndromes.
Oncologist
1997
.
2
:
389
401
.
Mufti
,
G. J.
and
D. A.
Galton
.
Myelodysplastic syndromes: natural history and features of prognostic importance.
Clin Haematol
1986
.
15
:
953
971
.
Parker
,
J. E.
and
G. J.
Mufti
.
Excessive apoptosis in low risk myelodysplastic syndromes (MDS).
Leuk Lymphoma
2000
.
40
:
1
24
.
Parker
,
J. E.
,
G. J.
Mufti
,
F.
Rasool
,
A.
Mijovic
,
S.
Devereux
, and
A.
Pagliuca
.
The role of apoptosis, proliferation, and the Bcl-2-related proteins in the myelodysplastic syndromes and acute myeloid leukemia secondary to MDS.
Blood
2000
.
96
:
3932
3938
.
Tsoplou
,
P.
,
A.
Kouraklis-Symeonidis
,
E.
Thanopoulou
,
P.
Zikos
,
V.
Orphanos
, and
N. C.
Zoumbos
.
Apoptosis in patients with myelodysplastic syndromes: differential involvement of marrow cells in ‘good’ versus ‘poor’ prognosis patients and correlation with apoptosis-related genes.
Leukemia
1999
.
13
:
1554
1563
.
Parker
,
J. E.
,
K. L.
Fishlock
,
A.
Mijovic
,
B.
Czepulkowski
,
A.
Pagliuca
, and
G. J.
Mufti
.
‘Low-risk’ myelodysplastic syndrome is associated with excessive apoptosis and an increased ratio of pro- versus anti-apoptotic bcl-2-related proteins.
Br J Haematol
1998
.
103
:
1075
1082
.
Davis
,
R. E.
and
P. L.
Greenberg
.
Bcl-2 expression by myeloid precursors in myelodysplastic syndromes: relation to disease progression.
Leuk Res
1998
.
22
:
767
777
.
Kurotaki
,
H.
,
Y.
Tsushima
,
K.
Nagai
, and
S.
Yagihashi
.
Apoptosis, bcl-2 expression and p53 accumulation in myelodysplastic syndrome, myelodysplastic-syndrome-derived acute myelogenous leukemia and de novo acute myelogenous leukemia.
Acta Haematol
2000
.
102
:
115
123
.
Rajapaksa
,
R.
,
N.
Ginzton
,
L. S.
Rott
, and
P. L.
Greenberg
.
Altered oncoprotein expression and apoptosis in myelodysplastic syndrome marrow cells.
Blood
1996
.
88
:
4275
4287
.
Boudard
,
D.
,
C.
Vasselon
, and
M. F.
Bertheas
.
et al
.
Expression and prognostic significance of Bcl-2 family proteins in myelodysplastic syndromes.
Am J Hematol
2002
.
70
:
115
125
.
Mufti
,
G. J.
Pathobiology, classification, and diagnosis of myelodysplastic syndrome.
Best Practice Clin Haematol
2004
.
17
:
543
557
.
Hofmann
,
W. K.
and
H. P.
Koeffler
.
Myelodysplastic syndrome.
Annu Rev Med
2005
.
56
:
1
16
.
Van den Berghe
,
H.
and
L.
Michaux
.
5q-, twenty-five years later: a synopsis.
Cancer Genet Cytogenet
1997
.
94
:
1
7
.
Nimer
,
S. D.
and
D. W.
Golde
.
The 5q- abnormality.
Blood
1987
.
70
:
1705
1712
.
Le Beau
,
M. M.
,
R. I. I. I.
Espinosa
, and
W. L.
Neuman
.
et al
.
Cytogenetic and molecular delineation of the smallest commonly deleted region of chromosome 5 in malignant myeloid diseases.
Proc Natl Acad Sci U S A
1993
.
90
:
5484
5488
.
Willman
,
C. L.
,
C. E.
Sever
, and
M. G.
Pallavicini
.
et al
.
Deletion of IRF-1, mapping to chromosome 5q31.1, in human leukemia and preleukemic myelodysplasia.
Science
1993
.
259
:
968
971
.
Le Beau
,
M. M.
,
R. I. I. I.
Espinosa
,
E. M.
Davis
,
J. D.
Eisenbart
,
R. A.
Larson
, and
E. D.
Green
.
Cytogenetic and molecular delineation of a region of chromosome 7 commonly deleted in malignant myeloid diseases.
Blood
1996
.
88
:
1930
1935
.
Pedersen-Bjergaard
,
J.
,
P.
Philip
,
S. O.
Larsen
,
G.
Jensen
, and
K.
Byrsting
.
Chromosome aberrations and prognostic factors in therapy-related myelodysplasia and acute nonlymphocytic leukemia.
Blood
1990
.
76
:
1083
1091
.
Neuman
,
W. L.
,
C. M.
Rubin
, and
R. B.
Rios
.
et al
.
Chromosomal loss and deletion are the most common mechanisms for loss of heterozygosity from chromosomes 5 and 7 in malignant myeloid disorders.
Blood
1992
.
79
:
1501
1510
.
Neubauer
,
A.
,
P.
Greenberg
,
R.
Negrin
,
N.
Ginzton
, and
E.
Liu
.
Mutations in the ras proto-oncogenes in patients with myelodysplastic syndromes.
Leukemia
1994
.
8
:
638
641
.
Yunis
,
J. J.
,
A. J.
Boot
,
M. G.
Mayer
, and
J. L.
Bos
.
Mechanisms of ras mutation in myelodysplastic syndrome.
Oncogene
1989
.
4
:
609
614
.
Padua
,
R. A.
,
B. A.
Guinn
, and
A. I.
Al-Sabah
.
et al
.
RAS, FMS and p53 mutations and poor clinical outcome in myelodysplasias: a 10-year follow-up.
Leukemia
1998
.
12
:
887
892
.
Lyons
,
J.
,
J. W.
Janssen
,
C.
Bartram
,
M.
Layton
, and
G. J.
Mufti
.
Mutation of Ki-ras and N-ras oncogenes in myelodysplastic syndromes.
Blood
1988
.
71
:
1707
1712
.
Paquette
,
R. L.
,
E. M.
Landaw
, and
R. V.
Pierre
.
et al
.
N-ras mutations are associated with poor prognosis and increased risk of leukemia in myelodysplastic syndrome.
Blood
1993
.
82
:
590
599
.
Bos
,
J. L.
ras oncogenes in human cancer: a review.
Cancer Res
1989
.
49
:
4682
4689
.
Hirai
,
H.
and
F.
Ishikawa
.
The N-ras oncogene in myelodysplastic syndrome and leukemia.
Nippon Ketsueki Gakkai Zasshi
1988
.
51
:
1463
1470
.
Pixley
,
F. J.
and
E. R.
Stanley
.
CSF-1 regulation of the wandering macrophage: complexity in action.
Trends Cell Biol
2004
.
14
:
628
638
.
Rettenmier
,
C. W.
and
M. F.
Roussel
.
Differential processing of colony-stimulating factor 1 precursors encoded by two human cDNAs.
Mol Cell Biol
1988
.
8
:
5026
5034
.
Tobal
,
K.
,
A.
Pagliuca
,
B.
Bhatt
,
N.
Bailey
,
D. M.
Layton
, and
G. J.
Mufti
.
Mutation of the human FMS gene (M-CSF receptor) in myelodysplastic syndromes and acute myeloid leukemia.
Leukemia
1990
.
4
:
486
489
.
Nienhuis
,
A. W.
,
H. F.
Bunn
, and
P. H.
Turner
.
et al
.
Expression of the human c-fms proto-oncogene in hematopoietic cells and its deletion in the 5q- syndrome.
Cell
1985
.
42
:
421
428
.
Ridge
,
S. A.
,
M.
Worwood
,
D.
Oscier
,
A.
Jacobs
, and
R. A.
Padua
.
FMS mutations in myelodysplastic, leukemic, and normal subjects.
Proc Natl Acad Sci U S A
1990
.
87
:
1377
1380
.
Uchida
,
T.
,
T.
Kinoshita
, and
H.
Nagai
.
et al
.
Hypermethylation of the p15INK4B gene in myelodysplastic syndromes.
Blood
1997
.
90
:
1403
1409
.
Aoki
,
E.
,
T.
Uchida
, and
H.
Ohashi
.
et al
.
Methylation status of the p15INK4B gene in hematopoietic progenitors and peripheral blood cells in myelodysplastic syndromes.
Leukemia
2000
.
14
:
586
593
.
Tien
,
H. F.
,
J. H.
Tang
, and
W.
Tsay
.
et al
.
Methylation of the p15(INK4B) gene in myelodysplastic syndrome: it can be detected early at diagnosis or during disease progression and is highly associated with leukaemic transformation.
Br J Haematol
2001
.
112
:
148
154
.
Chakraborty
,
S.
,
V.
Senyuk
,
S.
Sitailo
,
Y.
Chi
, and
G.
Nucifora
.
Interaction of EVI1 with cAMP-responsive element-binding protein-binding protein (CBP) and p300/ CBP-associated factor (P/CAF) results in reversible acetylation of EVI1 and in co-localization in nuclear speckles.
J Biol Chem
2001
.
276
:
44936
44943
.
Mitani
,
K.
Chromosomal abnormalities and oncogenes.
Int J Hematol
1996
.
63
:
81
93
.
Brooks
,
D. J.
,
S.
Woodward
, and
F. H.
Thompson
.
et al
.
Expression of the zinc finger gene EVI-1 in ovarian and other cancers.
Br J Cancer
1996
.
74
:
1518
1525
.
Ogawa
,
S.
,
K.
Mitani
, and
M.
Kurokawa
.
et al
.
Abnormal expression of Evi-1 gene in human leukemias.
Human Cell
1996
.
9
:
323
332
.
Sitailo
,
S.
,
R.
Sood
,
K.
Barton
, and
G.
Nucifora
.
Forced expression of the leukemia-associated gene EVI1 in ES cells: a model for myeloid leukemia with 3q26 rearrangements.
Leukemia
1999
.
13
:
1639
1645
.
Morishita
,
K.
,
E.
Parganas
,
T.
Matsugi
, and
J. N.
Ihle
.
Expression of the Evi-1 zinc finger gene in 32Dc13 myeloid cells blocks granulocytic differentiation in response to granulocyte colony-stimulating factor.
Mol Cell Biol
1992
.
12
:
183
189
.
Kreider
,
B. L.
,
S. H.
Orkin
, and
J. N.
Ihle
.
Loss of erythropoietin responsiveness in erythroid progenitors due to expression of the Evi-1 myeloid-transforming gene.
Proc Natl Acad Sci U S A
1993
.
90
:
6454
6258
.
Tanaka
,
T.
,
K.
Mitani
, and
M.
Kurokawa
.
et al
.
Dual functions of the AML1/Evi-1 chimeric protein in the mechanism of leukemogenesis in t(3;21) leukemias.
Mol Cell Biol
1995
.
15
:
2383
2392
.
Aktas
,
D.
,
M. J.
Arno
,
F.
Rassool
, and
G. J.
Mufti
.
Analysis of CHK2 in patients with myelodysplastic syndromes.
Leuk Res
2002
.
26
:
985
987
.
Hofmann
,
W. K.
,
C. W.
Miller
, and
K.
Tsukasaki
.
et al
.
Mutation analysis of the DNA-damage checkpoint gene CHK2 in myelodysplastic syndromes and acute myeloid leukemias.
Leuk Res
2001
.
25
:
333
338
.
Kikukawa
,
M.
,
N.
Aoki
,
Y.
Sakamoto
, and
M.
Mori
.
Study of p53 in elderly patients with myelodysplastic syndromes by immunohistochemistry and DNA analysis.
Am J Pathol
1999
.
155
:
717
721
.
Poppe
,
B.
,
J.
Vandesompele
, and
C.
Schoch
.
et al
.
Expression analyses identify MLL as a prominent target of 11q23 amplification and support an etiologic role for MLL gain of function in myeloid malignancies.
Blood
2004
.
103
:
229
235
.
Voura
,
E. B.
,
F.
Billia
,
N. N.
Iscove
, and
R. G.
Hawley
.
Expression mapping of adhesion receptor genes during differentiation of individual hematopoietic precursors.
Exp Hematol
1997
.
25
:
1172
1179
.
Flores-Figueroa
,
E.
,
G.
Gutierrez-Espindola
,
J. J.
Montesinos
,
R. M.
Arana-Trejo
, and
H.
Mayani
.
In vitro characterization of hematopoietic microenvironment cells from patients with myelodysplastic syndrome [see comment].
Leuk Res
2002
.
26
:
677
686
.
Allampallam
,
K.
,
V. T.
Shetty
, and
A.
Raza
.
Cytokines and MDS.
Cancer Treat Res
2001
.
108
:
93
100
.
Mundle
,
S. D.
,
P.
Venugopal
, and
J. D.
Cartlidge
.
et al
.
Indication of an involvement of interleukin-1 beta converting enzyme-like protease in intramedullary apoptotic cell death in the bone marrow of patients with myelodysplastic syndromes.
Blood
1996
.
88
:
2640
2647
.
Krajewski
,
S.
,
S.
Tanaka
,
S.
Takayama
,
M. J.
Schibler
,
W.
Fenton
, and
J. C.
Reed
.
Investigation of the subcellular distribution of the bcl-2 oncoprotein: residence in the nuclear envelope, endoplasmic reticulum, and outer mitochondrial membranes.
Cancer Res
1993
.
53
:
4701
4714
.
Petit
,
P. X.
,
S. A.
Susin
,
N.
Zamzami
,
B.
Mignotte
, and
G.
Kroemer
.
Mitochondria and programmed cell death: back to the future.
FEBS Lett
1996
.
396
:
7
13
.
Delia
,
D.
,
A.
Aiello
, and
D.
Soligo
.
et al
.
bcl-2 proto-oncogene expression in normal and neoplastic human myeloid cells.
Blood
1992
.
79
:
1291
1298
.
Lotem
,
J.
and
L.
Sachs
.
Regulation by bcl-2, c-myc, and p53 of susceptibility to induction of apoptosis by heat shock and cancer chemotherapy compounds in differentiation-competent and -defective myeloid leukemic cells.
Cell Growth Differ
1993
.
4
:
41
47
.
Askew
,
D. S.
,
R. A.
Ashmun
,
B. C.
Simmons
, and
J. L.
Cleveland
.
Constitutive c-myc expression in an IL-3-dependent myeloid cell line suppresses cell cycle arrest and accelerates apoptosis.
Oncogene
1991
.
6
:
1915
1922
.
Kitagawa
,
M.
,
S.
Yoshida
,
T.
Kuwata
,
T.
Tanizawa
, and
R.
Kamiyama
.
p53 expression in myeloid cells of myelodysplastic syndrome: association with evolution of overt leukemia.
Am J Pathol
1994
.
145
:
338
344
.
Schott
,
R. J.
and
L. A.
Morrow
.
Growth factors and angiogenesis.
Cardiovasc Res
1993
.
27
:
1155
1161
.
Pruneri
,
G.
,
F.
Bertolini
, and
D.
Soligo
.
et al
.
Angiogenesis in myelodysplastic syndromes.
Br J Cancer
1999
.
81
:
1398
1401
.
Estey
,
E. H.
Modulation of angiogenesis in patients with myelodysplastic syndrome.
Best Pract Res Clin Haematol
2004
.
17
:
623
639
.
Bertolini
,
F.
,
P.
Mancuso
,
A.
Gobbi
, and
G.
Pruneri
.
The thin red line: angiogenesis in normal and malignant hematopoiesis.
Exp Hematol
2000
.
28
:
993
1000
.
Mangi
,
M. H.
and
A. C.
Newland
.
Angiogenesis and angiogenic mediators in haematological malignancies.
Br J Haematol
2000
.
111
:
43
51
.
Talks
,
K. L.
and
A. L.
Harris
.
Current status of antiangiogenic factors.
Br J Haematol
2000
.
109
:
477
489
.
Fox
,
S. B.
and
A. L.
Harris
.
Markers of tumor angiogenesis: clinical applications in prognosis and anti-angiogenic therapy.
Invest New Drugs
1997
.
15
:
15
28
.
Korkolopoulou
,
P.
,
E.
Apostolidou
, and
P. M.
Pavlopoulos
.
et al
.
Prognostic evaluation of the microvascular network in myelodysplastic syndromes.
Leukemia
2001
.
15
:
1369
1376
.
Albitar
,
M.
Angiogenesis in acute myeloid leukemia and myelodysplastic syndrome.
Acta Haematol
2001
.
106
:
170
176
.
Aguayo
,
A.
,
H.
Kantarjian
, and
T.
Manshouri
.
et al
.
Angiogenesis in acute and chronic leukemias and myelodysplastic syndromes.
Blood
2000
.
96
:
2240
2245
.
Zhou
,
J.
,
K.
Mauerer
,
L.
Farina
, and
J. G.
Gribben
.
The role of the tumor microenvironment in hematological malignancies and implication for therapy.
Front Biosci
2005
.
10
:
1581
1596
.
Marchetto
,
S.
,
E.
Fournier
, and
N.
Beslu
.
et al
.
SHC and SHIP phosphorylation and interaction in response to activation of the FLT3 receptor.
Leukemia
1999
.
13
:
1374
1382
.
Zhang
,
S.
,
C.
Mantel
, and
H. E.
Broxmeyer
.
Flt3 signaling involves tyrosyl-phosphorylation of SHP-2 and SHIP and their association with Grb2 and Shc in Baf3/ Flt3 cells.
J Leukoc Biol
1999
.
65
:
372
380
.
Lyman
,
S. D.
and
D. E.
Williams
.
Biology and potential clinical applications of flt3 ligand.
Curr Opin Hematol
1995
.
2
:
177
181
.
Horiike
,
S.
,
S.
Yokota
, and
M.
Nakao
.
et al
.
Tandem duplications of the FLT3 receptor gene are associated with leukemic transformation of myelodysplasia.
Leukemia
1997
.
11
:
1442
1446
.
Yokota
,
S.
,
H.
Kiyoi
, and
M.
Nakao
.
et al
.
Internal tandem duplication of the FLT3 gene is preferentially seen in acute myeloid leukemia and myelodysplastic syndrome among various hematological malignancies: a study on a large series of patients and cell lines.
Leukemia
1997
.
11
:
1605
1609
.
Yamamoto
,
Y.
,
H.
Kiyoi
, and
Y.
Nakano
.
et al
.
Activating mutation of D835 within the activation loop of FLT3 in human hematologic malignancies.
Blood
2001
.
97
:
2434
2439
.
Jones
,
P. A.
and
P. W.
Laird
.
Cancer epigenetics comes of age.
Nat Genet
1999
.
21
:
163
167
.
Laird
,
P. W.
and
R.
Jaenisch
.
DNA methylation and cancer.
Hum Mol Genet
1994
.
3
:(
review issue 1
).
1487
1495
.
Schulz
,
W. A.
,
J. P.
Elo
, and
A. R.
Florl
.
et al
.
Genomewide DNA hypomethylation is associated with alterations on chromosome 8 in prostate carcinoma.
Genes Chromosomes Cancer
2002
.
35
:
58
65
.
Feinberg
,
A. P.
,
C. W.
Gehrke
,
K. C.
Kuo
, and
M.
Ehrlich
.
Reduced genomic 5-methylcytosine content in human colonic neoplasia.
Cancer Res
1988
.
48
:
1159
1161
.
De Smet
,
C.
,
O.
De Backer
,
I.
Faraoni
,
C.
Lurquin
,
F.
Brasseur
, and
T.
Boon
.
The activation of human gene MAGE-1 in tumor cells is correlated with genome-wide demethylation.
Proc Natl Acad Sci U S A
1996
.
93
:
7149
7153
.
Ehrlich
,
M.
DNA methylation in cancer: too much, but also too little.
Oncogene
2002
.
21
:
5400
5413
.
Suter
,
C. M.
,
D. I.
Martin
, and
R. L.
Ward
.
Hypomethylation of L1 retrotransposons in colorectal cancer and adjacent normal tissue.
Int J Colorectal Dis
2004
.
19
:
95
101
.
Herman
,
J. G.
,
C. I.
Civin
,
J. P.
Issa
,
M. I.
Collector
,
S. J.
Sharkis
, and
S. B.
Baylin
.
Distinct patterns of inactivation of p15INK4B and p16INK4A characterize the major types of hematological malignancies.
Cancer Res
1997
.
57
:
837
841
.
Boldt
,
D. H.
p21(CIP1/WAF1/SDI1) hypermethylation: an exciting new lead in ALL biology.
Blood
2002
.
99
:
2283
.
Roman-Gomez
,
J.
,
J. A.
Castillejo
, and
A.
Jimenez
.
et al
.
5′ CpG island hypermethylation is associated with transcriptional silencing of the p21(CIP1/WAF1/ SDI1) gene and confers poor prognosis in acute lymphoblastic leukemia.
Blood
2002
.
99
:
2291
2296
.
Shen
,
L.
,
M.
Toyota
, and
Y.
Kondo
.
et al
.
Aberrant DNA methylation of p57KIP2 identifies a cell-cycle regulatory pathway with prognostic impact in adult acute lymphocytic leukemia.
Blood
2003
.
101
:
4131
4136
.
Li
,
Y.
,
H.
Nagai
, and
T.
Ohno
.
et al
.
Aberrant DNA methylation of p57(KIP2) gene in the promoter region in lymphoid malignancies of B-cell phenotype.
Blood
2002
.
100
:
2572
2577
.
Roman-Gomez
,
J.
,
J. A.
Castillejo
, and
A.
Jimenez
.
et al
.
Cadherin-13, a mediator of calcium-dependent cell-cell adhesion, is silenced by methylation in chronic myeloid leukemia and correlates with pretreatment risk profile and cytogenetic response to interferon alfa.
J Clin Oncol
2003
.
21
:
1472
1479
.
Melki
,
J. R.
,
P. C.
Vincent
,
R. D.
Brown
, and
S. J.
Clark
.
Hypermethylation of E-cadherin in leukemia.
Blood
2000
.
95
:
3208
3213
.
Marinitch
,
D. V.
,
I. A.
Vorobyev
, and
J. A.
Holmes
.
et al
.
Hypermethylation of 5′-region of the human calcitonin gene in leukemias: structural features and diagnostic significance.
Biochemistry (Mosc)
2004
.
69
:
340
349
.
Dhodapkar
,
M.
,
J.
Grill
, and
J. A.
Lust
.
Abnormal regional hypermethylation of the calcitonin gene in myelodysplastic syndromes.
Leuk Res
1995
.
19
:
719
726
.
Ihalainen
,
J.
,
S.
Pakkala
,
E. R.
Savolainen
,
S. E.
Jansson
, and
A.
Palotie
.
Hypermethylation of the calcitonin gene in the myelodysplastic syndromes.
Leukemia
1993
.
7
:
263
267
.
Ruter
,
B.
,
P. W.
Wijermans
, and
M.
Lubbert
.
DNA methylation as a therapeutic target in hematologic disorders: recent results in older patients with myelodysplasia and acute myeloid leukemia.
Int J Hematol
2004
.
80
:
128
135
.
Issa
,
J. P.
,
B. A.
Zehnbauer
,
S. H.
Kaufmann
,
M. A.
Biel
, and
S. B.
Baylin
.
HIC1 hypermethylation is a late event in hematopoietic neoplasms.
Cancer Res
1997
.
57
:
1678
1681
.
Melki
,
J. R.
,
P. C.
Vincent
, and
S. J.
Clark
.
Cancer-specific region of hypermethylation identified within the HIC1 putative tumour suppressor gene in acute myeloid leukaemia.
Leukemia
1999
.
13
:
877
883
.
Melki
,
J. R.
,
P. C.
Vincent
, and
S. J.
Clark
.
Concurrent DNA hypermethylation of multiple genes in acute myeloid leukemia.
Cancer Res
1999
.
59
:
3730
3740
.
Ekmekci
,
C. G.
,
M. I.
Gutierrez
,
A. K.
Siraj
,
U.
Ozbek
, and
K.
Bhatia
.
Aberrant methylation of multiple tumor suppressor genes in acute myeloid leukemia.
Am J Hematol
2004
.
77
:
233
240
.
Ng
,
H. H.
,
P.
Jeppesen
, and
A.
Bird
.
Active repression of methylated genes by the chromosomal protein MBD1.
Mol Cell Biol
2000
.
20
:
1394
1406
.
Ng
,
H. H.
,
Y.
Zhang
, and
B.
Hendrich
.
et al
.
MBD2 is a transcriptional repressor belonging to the MeCP1 histone deacetylase complex.
Nat Genet
1999
.
23
:
58
61
.
Jones
,
P. L.
,
G. J.
Veenstra
, and
P. A.
Wade
.
et al
.
Methylated DNA and MeCP2 recruit histone deacetylase to repress transcription.
Nat Genet
1998
.
19
:
187
191
.
Hendrich
,
B.
and
A.
Bird
.
Identification and characterization of a family of mammalian methyl-CpG binding proteins.
Mol Cell Biol
1998
.
18
:
6538
6547
.
Nan
,
X.
,
F. J.
Campoy
, and
A.
Bird
.
MeCP2 is a transcriptional repressor with abundant binding sites in genomic chromatin.
Cell
1997
.
88
:
471
481
.
Uchida
,
T.
,
T.
Kinoshita
,
T.
Hotta
, and
T.
Murate
.
High-risk myelodysplastic syndromes and hypermethylation of the p15Ink4B gene.
Leuk Lymphoma
1998
.
32
:
9
18
.
Quesnel
,
B.
,
G.
Guillerm
, and
R.
Vereecque
.
et al
.
Methylation of the p15(INK4b) gene in myelodysplastic syndromes is frequent and acquired during disease progression.
Blood
1998
.
91
:
2985
2990
.
Lubbert
,
M.
Gene silencing of the p15/INK4B cell-cycle inhibitor by hypermethylation: an early or later epigenetic alteration in myelodysplastic syndromes?
Leukemia
2003
.
17
:
1762
1764
.
Reynisdottir
,
I.
and
J.
Massague
.
The subcellular locations of p15(Ink4b) and p27(Kip1) coordinate their inhibitory interactions with cdk4 and cdk2.
Genes Dev
1997
.
11
:
492
503
.
Serrano
,
M.
,
G. J.
Hannon
, and
D.
Beach
.
A new regulatory motif in cell-cycle control causing specific inhibition of cyclin D/CDK4.
Nature
1993
.
366
:
704
707
.
Li
,
J. M.
,
M. A.
Nichols
,
S.
Chandrasekharan
,
Y.
Xiong
, and
X. F.
Wang
.
Transforming growth factor beta activates the promoter of cyclin-dependent kinase inhibitor p15INK4B through an Sp1 consensus site.
J Biol Chem
1995
.
270
:
26750
26753
.
Hannon
,
G. J.
and
D.
Beach
.
p15INK4B is a potential effector of TGF-beta-induced cell cycle arrest.
Nature
1994
.
371
:
257
261
.
Quesnel
,
B.
and
P.
Fenaux
.
P15INK4b gene methylation and myelodysplastic syndromes.
Leuk Lymphoma
1999
.
35
:
437
443
.
Broxmeyer
,
H. E.
,
D. E.
Williams
, and
L.
Lu
.
et al
.
The suppressive influences of human tumor necrosis factors on bone marrow hematopoietic progenitor cells from normal donors and patients with leukemia: synergism of tumor necrosis factor and interferon-gamma.
J Immunol
1986
.
136
:
4487
4495
.
Smith
,
C. A.
,
T.
Farrah
, and
R. G.
Goodwin
.
The TNF receptor superfamily of cellular and viral proteins: activation, costimulation, and death.
Cell
1994
.
76
:
959
962
.
Nagata
,
S.
and
P.
Golstein
.
The Fas death factor.
Science
1995
.
267
:
1449
1456
.
Maciejewski
,
J.
,
C.
Selleri
,
S.
Anderson
, and
N. S.
Young
.
Fas antigen expression on CD34+ human marrow cells is induced by interferon gamma and tumor necrosis factor alpha and potentiates cytokine-mediated hematopoietic suppression in vitro.
Blood
1995
.
85
:
3183
3190
.
Yamaguchi
,
M.
,
S.
Nadler
,
J. W.
Lee
, and
H. J.
Deeg
.
Induction of negative regulators of haematopoiesis in human bone marrow cells by HLA-DR cross-linking.
Transpl Immunol
1999
.
7
:
159
168
.
Sawanobori
,
M.
,
S.
Yamaguchi
, and
M.
Hasegawa
.
et al
.
Expression of TNF receptors and related signaling molecules in the bone marrow from patients with myelodysplastic syndromes.
Leuk Res
2003
.
27
:
583
591
.
Gersuk
,
G. M.
,
C.
Beckham
, and
M. R.
Loken
.
et al
.
A role for tumour necrosis factor-alpha, Fas and Fas-Ligand in marrow failure associated with myelodysplastic syndrome.
Br J Haematol
1998
.
103
:
176
188
.
Bogdanovic
,
A. D.
,
G. M.
Jankovic
,
M. D.
Colovic
,
D. P.
Trpinac
, and
V. Z.
Bumbasirevic
.
Apoptosis in bone marrow of myelodysplastic syndrome patients.
Blood
1996
.
87
:
3064
.
Shetty
,
V.
,
S.
Mundle
, and
S.
Alvi
.
et al
.
Measurement of apoptosis, proliferation and three cytokines in 46 patients with myelodysplastic syndromes.
Leuk Res
1996
.
20
:
891
900
.
Raza
,
A.
,
S.
Gezer
, and
S.
Mundle
.
et al
.
Apoptosis in bone marrow biopsy samples involving stromal and hematopoietic cells in 50 patients with myelodysplastic syndromes.
Blood
1995
.
86
:
268
276
.
Dar
,
S.
,
S.
Mundle
, and
T.
Andric
.
et al
.
Biological characteristics of myelodysplastic syndrome patients who demonstrated high versus no intramedullary apoptosis.
Eur J Haematol
1999
.
62
:
90
94
.
Kitagawa
,
M.
,
I.
Saito
, and
T.
Kuwata
.
et al
.
Overexpression of tumor necrosis factor (TNF)-alpha and interferon (IFN)-gamma by bone marrow cells from patients with myelodysplastic syndromes.
Leukemia
1997
.
11
:
2049
2054
.
Deeg
,
H. J.
,
C.
Beckham
, and
M. R.
Loken
.
et al
.
Negative regulators of hemopoiesis and stroma function in patients with myelodysplastic syndrome.
Leuk Lymphoma
2000
.
37
:
405
414
.
Allampallam
,
K.
,
V.
Shetty
, and
S.
Mundle
.
et al
.
Biological significance of proliferation, apoptosis, cytokines, and monocyte/macrophage cells in bone marrow biopsies of 145 patients with myelodysplastic syndrome.
Int J Hematol
2002
.
75
:
289
297
.
Reza
,
S.
,
S.
Dar
, and
T.
Andric
.
et al
.
Biologic characteristics of 164 patients with myelodysplastic syndromes.
Leuk Lymphoma
1999
.
33
:
281
287
.
Raza
,
A.
,
S.
Mundle
, and
V.
Shetty
.
et al
.
A paradigm shift in myelodysplastic syndromes.
Leukemia
1996
.
10
:
1648
1652
.
Kayagaki
,
N.
,
N.
Yamaguchi
, and
M.
Abe
.
et al
.
Suppression of antibody production by TNF-related apoptosis-inducing ligand (TRAIL).
Cell Immunol
2002
.
219
:
82
91
.
Zang
,
D. Y.
,
R. G.
Goodwin
,
M. R.
Loken
,
E.
Bryant
, and
H. J.
Deeg
.
Expression of tumor necrosis factor-related apoptosis-inducing ligand, Apo2L, and its receptors in myelodysplastic syndrome: effects on in vitro hemopoiesis.
Blood
2001
.
98
:
3058
3065
.
Plasilova
,
M.
,
J.
Zivny
, and
J.
Jelinek
.
et al
.
TRAIL (Apo2L) suppresses growth of primary human leukemia and myelodysplasia progenitors.
Leukemia
2002
.
16
:
67
73
.
Hofmann
,
W. K.
,
S.
de Vos
,
M.
Komor
,
D.
Hoelzer
,
W.
Wachsman
, and
H. P.
Koeffler
.
Characterization of gene expression of CD34+ cells from normal and myelodysplastic bone marrow.
Blood
2002
.
100
:
3553
3560
.
Chen
,
G.
,
W.
Zeng
, and
A.
Miyazato
.
et al
.
Distinctive gene expression profiles of CD34 cells from patients with myelodysplastic syndrome characterized by specific chromosomal abnormalities.
Blood
2004
.
104
:
4210
4218
.
Miyazato
,
A.
,
S.
Ueno
, and
K.
Ohmine
.
et al
.
Identification of myelodysplastic syndrome-specific genes by DNA microarray analysis with purified hematopoietic stem cell fraction.
Blood
2001
.
98
:
422
427
.
Pellagatti
,
A.
,
N.
Esoof
, and
F.
Watkins
.
et al
.
Gene expression profiling in the myelodysplastic syndromes using cDNA microarray technology.
Br J Haematol
2004
.
125
:
576
583
.
Ueda
,
M.
,
J.
Ota
, and
Y.
Yamashita
.
et al
.
DNA microarray analysis of stage progression mechanism in myelodysplastic syndrome.
Br J Haematol
2003
.
123
:
288
296
.
Germing
,
U.
,
N.
Gattermann
,
C.
Strupp
,
M.
Aivado
, and
C.
Aul
.
Validation of the WHO proposals for a new classification of primary myelodysplastic syndromes: a retrospective analysis of 1600 patients.
Leuk Res
2000
.
24
:
983
992
.

The authors have no relevant financial interest in the products or companies described in this article.

Author notes

Reprints: Chung-Che Chang, MD, PhD, Department of Pathology, The Methodist Hospital, 6565 Fannin, MS205, Houston, TX 77030 (jeffchang@tmh.tmc.edu)