Therapy-related myelodysplastic syndromes deserve specific diagnostic sub-classification and risk-stratification-an approach to classification of patients with t-MDS.

In the current World Health Organization (WHO)-classification, therapy-related myelodysplastic syndromes (t-MDS) are categorized together with therapy-related acute myeloid leukemia (AML) and t-myelodysplastic/myeloproliferative neoplasms into one subgroup independent of morphologic or prognostic features. Analyzing data of 2087 t-MDS patients from different international MDS groups to evaluate classification and prognostication tools we found that applying the WHO classification for p-MDS successfully predicts time to transformation and survival (both p < 0.001). The results regarding carefully reviewed cytogenetic data, classifications, and prognostic scores confirmed that t-MDS are similarly heterogeneous as p-MDS and therefore deserve the same careful differentiation regarding risk. As reference, these results were compared with 4593 primary MDS (p-MDS) patients represented in the International Working Group for Prognosis in MDS database (IWG-PM). Although a less favorable clinical outcome occurred in each t-MDS subset compared with p-MDS subgroups, FAB and WHO-classification, IPSS-R, and WPSS-R separated t-MDS patients into differing risk groups effectively, indicating that all established risk factors for p-MDS maintained relevance in t-MDS, with cytogenetic features having enhanced predictive power. These data strongly argue to classify t-MDS as a separate entity distinct from other WHO-classified t-myeloid neoplasms, which would enhance treatment decisions and facilitate the inclusion of t-MDS patients into clinical studies.

The effects of recombinant interleukin 2-activated natural killer cells on autologous peripheral blood hematopoietic progenitors.

In the present study, we demonstrate that resting and rIL-2-activated NK cells had no inhibitory effects on peripheral blood-derived hematopoietic progenitor (HP) cells. Peripheral blood HP cells were similar to bone marrow progenitors in phenotype and clonogenic colony formation capabilities. Peripheral blood HP cells could be cocultured in vitro with rIL-2-activated autologous NK cells for 3 d without adverse effects on the HP cells. Acute myelogenous leukemia patients in stable remission were shown to have normal percentages of NK cells and elevated percentages of peripheral blood HP cells. NK cells from most of these patients could be activated with rIL-2 to lyse fresh uncultured tumor cells as well as autologous leukemia cells without effecting the peripheral blood HP cells. These results suggest that rIL-2-activated NK cells may be used to purge peripheral blood HP cell preparations of residual tumor cells before hematopoietic reconstitution.

The use of colony stimulating factors in clinical bone marrow transplantation.

The use of colony stimulating factors in clinical bone marrow transplantation is rapidly evolving. Both granulocyte colony stimulating factor and granulocyte macrophage colony stimulating factor have shown efficacy in bone marrow transplant patients in accelerating the rate of myeloid recovery. The use of colony stimulating factor primed peripheral blood progenitor cells appears to accelerate platelet recovery as well as myeloid recovery.

Cytotoxic effects of interferon in vitro on granulocytic progenitor cells.

We have utilized in vitro marrow culture techniques to evaluate the cytotoxicity for granulocytic progenitor cells of two highly purified human leukocyte interferon preparations. Concentration- and time-related decrements in granulocytic colony-forming capacity in agar occurred with human and mouse marrow. Although mouse marrow cells were less sensitive than were human cells, these data indicate lack of strict species specificity for the cell growth-inhibitory effects of interferon. Similar cytotoxicity was noted for normal and leukemic human clonogenic cells exposed to interferon for prolonged periods. The decrease in the proportion of granulocytic progenitor cells in DNA synthesis, which occurred at high concentrations, and the diminution by interferon of the cytotoxicity caused by cytosine arabinoside demonstrate that interferon decreases DNA synthesis of granulocytic progenitor cells. The lack of enhanced cytotoxicity for rapidly proliferating mouse post-endotoxin marrow cells indicates that interferon is not a cell cycle-stage-specific drug. These data seem useful for evaluating the suppressive effects of interferon on granulopoiesis and for devising clinical trials with this agent.

Functional interactions between colony-stimulating factors and the insulin family hormones for human myeloid leukemic cells.

We investigated functional interactions between granulocyte-monocyte-colony-stimulating factor (GM-CSF) and the insulin family hormones using the GM-CSF- and insulin-dependent human acute myeloid leukemia cell line AML-193. Recombinant human GM-CSF and insulin enhanced AML-193 cell proliferation 3- and 5-fold, respectively, and showed a synergistic 10-fold increase when added in combination. Insulin-like growth factors I and II (IGFI and IGFII) increased AML-193 cell proliferation 4-fold and 2-fold, respectively, and also demonstrated synergy when combined with GM-CSF. Blocking experiments with monoclonal antibodies against the insulin and IGFI receptors indicated that the proliferative effects of insulin and IGFI were mediated through both their homologous and heterologous receptors. Pertussis toxin and cholera toxin, which ADP ribosylate GTP-binding proteins (G proteins), and the cyclic AMP analogue, dibutyryl cyclic AMP, decreased the proliferation induced by GM-CSF or insulin. Specific receptor binding of 125I-insulin, -IGFI, and -GM-CSF to AML-193 cells was demonstrated and not affected by preincubation with pertussis toxin or cholera toxin. Radiolabeled GM-CSF, insulin, and IGFI did not cross-compete with the heterologous ligands for receptor binding. These studies demonstrate (a) association between receptor binding and proliferative effects of GM-CSF and the insulin family hormones, (b) involvement of the G proteins in signal transduction provoked by these hormones which occurs at a postreceptor-binding level, and (c) synergistic mitogenic interactions between GM-CSF and the insulin family hormones, suggesting that their receptors are linked to divergent signaling mechanisms in addition to sharing G protein-coupled pathways.

Cytotoxic effects of 1-beta-D-arabinofuranosylcytosine and 6-thioguanine in vitro on granulocytic progenitor cells.

We have utilized an in vitro clonogenic assay of mouse and human marrow granulocytic progenitor cells to determine the cytotoxic effects on granulopoiesis of the chemotherapeutic agents 1-beta-D-arabinofuranosylcytosine (ara-C) and 6-thioguanine. Concentration- and time-dependent decrements to plateau levels of granulocytic colony-forming capacity occurred. The sequence of drug administration was important and synergistic cytotoxicity was noted when certain schedules of ara-C and 6-thioguanine combinations were used. Endotoxin-stimulated colony-forming cells had increased sensitivity to the in vitro ara-C exposure. High or intermittent doses of ara-C demonstrated enhanced cytotoxicity when short exposure times (1 to 8 hr) were utilized, whereas low doses were markedly cytotoxic with prolonged exposure (10 days). Normal and leukemic human colony-forming cells had similar susceptibility to the cytotoxic effects of ara-C. Exposure of granulocytic precursors to these drugs in vitro produced effects similar to those previously reported with in vivo drug administration. These techniques appear applicable for providing improved screening models to evaluate chemotherapeutic regimens for clinical use.

13-cis retinoic acid treatment for myelodysplastic syndromes.

To test the biologic activity of 13-cis retinoic acid (13-CRA) in patients with myelodysplastic states (MDS), we administered 13-CRA orally (2.5 mg/kg/d initially, escalated to 4 mg/kg/d) for 8 weeks to 15 consecutive patients. Eight of 15 patients (53%) experienced an increase in peripheral granulocyte counts of greater than 20% (range, 22% to 700%). In five patients, the absolute increase in peripheral granulocyte count was greater than 500 cells/microL. Two of 15 patients experienced a decrease in the circulating granulocyte count of greater than or equal to 20%. Comparable values for peripheral platelet counts were 27% (4/15 patients) greater than 20% increase and 33% (5/15 patients) greater than 20% decrease. No patient experienced a major change in erythrocyte transfusion requirement while receiving 13-CRA in comparison with pretreatment status. Thirteen patients had morphologic and cytogenetic evaluation of marrow cells before 13-CRA treatment, and with one exception, marrow morphologic and cytogenetic abnormalities persisted following 13-CRA administration. The exception occurred in the patient with the most dramatic response, whose granulocyte count increased from 400 to 2,800 cells/microL along with a normalization of the leukocyte alkaline phosphatase score, a morphologic improvement in granulocyte maturation, and a disappearance of the initial chromosome abnormality. These changes did not persist after cessation of 13-CRA administration, but were reproduced following drug readministration. No patients experienced serious decrements in peripheral blood counts or leukemic transformation while receiving 13-CRA. All patients had mild to marked dermatologic toxicity (cheilosis, skin dryness). No other major toxicity was encountered. We conclude that 13-CRA may be safely administered and may increase peripheral granulocyte counts in a proportion of patients with MDS.

Effects of granulocyte colony-stimulating factor therapy on in vitro hemopoiesis in myelodysplastic syndromes.

We evaluated the effects of 2 months of G-CSF treatment on in vitro hematopoiesis in 17 patients with myelodysplastic syndromes (MDS). Although in vitro marrow myeloid progenitor cell (CFU-GM) growth stimulated by G-CSF generally remained subnormal, in the majority of neutrophil responders significantly augmented incremental change (termed AIC) of CFU-GM numbers occurred after treatment, as did neutrophilic differentiation. The neutrophil non-responders had less prominent in vitro myeloid responses and lower basal neutrophil levels (p < 0.05). Following G-CSF treatment, the initially subnormal erythroid burst-forming unit (BFU-E) values underwent AIC in five of 11 patients along with increased reticulocyte responses in vivo, whereas four of the five patients who lacked AIC of BFU-E did not. Three patients with persisting cytogenetic abnormalities and increased neutrophilic differentiation in vitro also responded in vivo, suggesting that G-CSF induced in vivo cellular differentiation from the abnormal clone. Two of the three patients who developed blastic responses in vivo had increased CFU-GM growth pre- and post-therapy. These results indicate in vivo-in vitro correlations for myeloid and erythroid responses of MDS marrow cells which related to treatment with G-CSF.

Murine granulopoiesis after fractionated total lymphoid irradiation and allogeneic bone marrow transplantation.

We investigated the effects of fractionated total lymphoid irradiation (TLI) and allogeneic bone marrow transplantation on murine granulopoiesis in order to evaluate the hemopoietic microenvironment of radiation chimeras (RC). BALB/c mice received 3400 rad TLI (17 daily 200 rad fractions) with or without 3 X 10(7) C57Bl/Ka marrow cells injected intravenously. Radiation resulted in prolonged depression of granulocyte-macrophage progenitor cells (CFU-GM) and endosteal colony-stimulating-activity (CSA) production in irradiated humeri. Allogeneic marrow transplantation partially restored endosteal CSA production and led to complete, although delayed, restoration of CFU-GM. Major compensatory granulopoiesis occurred in the spleen. Marrow fat-laden adherent cells (FLAC) were cultured in vitro from RC 30 weeks post TLI and transplantation. As determined by indirect immunofluorescence utilizing anti-H-2 antibodies, 23-25% of these cells reacted with antibodies possessing donor specificity. These findings suggest that the hemopoietic microenvironment, represented functionally by endosteal CSA production and morphologically by cultured FLAC, is transplantable by the intravenous route.

Modulation of apoptosis in human myeloid leukemic cells by GM-CSF.

Apoptosis (programmed cell death) regulates cell population size. To determine the mechanisms whereby hematopoietic growth factors (HGFs) modulate apoptosis in human myeloid leukemic cells, we evaluated the roles of protein and mRNA synthesis for altering apoptosis in growth factor-stimulated vs. quiescent leukemic TF1 cells. Lysates of cells from the granulocyte-macrophage colony-stimulating factor (GM-CSF)-dependent myeloid leukemic cell line TF1 were separated into high molecular weight (HMW) pellets of intact DNA and supernatants of fragmented low MW (LMW) DNA, and the DNA purified from these fractions was quantified. In the absence of both GM-CSF and fetal bovine serum (FBS), 70% of the DNA was fragmented after 3 days in culture, with a characteristic apoptotic ladder-like pattern on agarose gel electrophoresis, whereas this proportion had initially been < 5%. In contrast, less than 5% of the DNA was fragmented in cells incubated with GM-CSF plus FBS or GM-CSF alone. Delayed addition of GM-CSF, but not FBS, permitted partial rescue of the cells, inhibiting increasing rates of accumulation of fragmented DNA. When the macro-molecular synthesis inhibitor cycloheximide (CHX) or actinomycin D (Act D) was present for 26 hours in the absence of GM-CSF and FBS, apoptosis was inhibited. In contrast, in the presence of GM-CSF or FBS, apoptosis was enhanced upon addition of CHX or Act D. The latter effect persisted even with the late addition of CHX. These findings indicate that disparate mechanisms of enhancing or inhibiting apoptosis exist in myeloid leukemic cells related to environmental conditions, including HGF-regulated cellular synthesis of distinct proteins and mRNA.

Validation of WHO classification-based Prognostic Scoring System (WPSS) for myelodysplastic syndromes and comparison with the revised International Prognostic Scoring System (IPSS-R). A study of the International Working Group for Prognosis in Myelodysplasia (IWG-PM).

A risk-adapted treatment strategy is mandatory for myelodysplastic syndromes (MDS). We refined the World Health Organization (WHO)-classification-based Prognostic Scoring System (WPSS) by determining the impact of the newer clinical and cytogenetic features, and we compared its prognostic power to that of the revised International Prognostic Scoring System (IPSS-R). A population of 5326 untreated MDS was considered. We analyzed single WPSS parameters and confirmed that the WHO classification and severe anemia provide important prognostic information in MDS. A strong correlation was found between the WPSS including the new cytogenetic risk stratification and WPSS adopting original criteria. We then compared WPSS with the IPSS-R prognostic system. A highly significant correlation was found between the WPSS and IPSS-R risk classifications. Discrepancies did occur among lower-risk patients in whom the number of dysplastic hematopoietic lineages as assessed by morphology did not reflect the severity of peripheral blood cytopenias and/or increased marrow blast count. Moreover, severe anemia has higher prognostic weight in the WPSS versus IPSS-R model. Overall, both systems well represent the prognostic risk of MDS patients defined by WHO morphologic criteria. This study provides relevant in formation for the implementation of risk-adapted strategies in MDS.

Treatment of myelodysplastic syndromes.

Therapeutic options have been rapidly evolving for management of patients with the indolent myeloid clonal hemopathies termed myelodysplastic syndromes (MDS). Heterogeneity of MDS has been demonstrated on the basis of marrow morphology and biologic features and has been useful for prognostication into high and low risk groups for transformation to acute leukemia. Such stratification has been important for evaluating responses to various treatments. These therapeutic options include the differentiation-inducing vitamins retinoic acid and vitamin D, and cytokines such as alpha and gamma interferon, to which there has been a generally low response. The use of intensive or low dose chemotherapy has been associated with relatively low response rates, few durable responses and a high degree of hemopoietic toxicity. Allogeneic bone marrow transplantation (BMT) has shown durable responses for a subset of MDS patients, particularly those who are young and who are in the low risk subgroups. however, due to the elderly nature of the majority of MDS patients, and the toxicity associated with BMT, this option has limited utility for most of these patients. Major focus has been on the recent therapeutic use of recombinant human hemopoietic growth factors, particularly G-CSF, GM-CSF and IL3. These agents have been well-tolerated and generally produce a high incidence of sustained improvements in neutrophil counts and marrow morphology, although hemoglobin and platelet counts have generally not been altered. More extensive clinical trials evaluating the impact of these hemopoietic growth factors on the natural history of MDS are ongoing.

Subacute myeloid leukemia: a clinical review.

The data on 31 patients who fit into the clinical spectrum of subacute myeloid leukemia have been reviewed. The majority of patients were male with a median age of 61 years. The interval from onset of symptoms to actual diagnosis was extremely variable, with a mean of 16 months and a median of six months. Most patients presented with anemia and thrombocytopenia, although the white blood cell count varied from striking leukopenia to marked leukocytosis. Examination of the bone marrow invariably revealed abnormalities of all cell lines with megaloblastoid erythrogenesis and dysplastic megakaryocytopoiesis. Although the white cell line showed prominence of immature forms, there was more maturation than is seen in acute myeloid leukemia. Survival from diagnosis was variable, from less than one month to greater than 68 months, with a median of only six months. Anemia and hepatosplenomegaly were prognosticators of a poor outlook; patients with hepatosplenomegaly in association with either leukocytosis or thrombocytopenia had a particularly poor outlook, with a median survival of only one and a half months. Approximately half the patients received chemotherapy with no demonstrated effect on survival.

Apoptosis and its role in the myelodysplastic syndromes: implications for disease natural history and treatment.

Apoptosis (programmed cell death) is an active cellular process which regulates cell population size by decreasing cell survival. In this review the underlying cellular and molecular mechanisms of apoptosis in hemopoietic and non-hemopoietic cells are described, with specific focus on these issues in the myelodysplastic syndrome (MDS), a myeloid clonal hemopathy. Apoptosis-regulating genes exist as families whose protein products are either anti-apoptotic or pro-apoptotic. Numerous stimuli can serve as initiators of the cell death pathway, including essentially all chemotherapeutic drugs, irradiation, certain inhibitory cytokines and deprivation of relevant growth factors. Morphological evidence of increased apoptosis in marrow hemopoietic cells has been demonstrated in patients with MDS. The reviewed data provide support for the hypothesis that early in MDS, increased apoptosis is associated with ineffective progenitor and maturing hemopoietic cell survival, and occurs concomitant with cytopenias/ineffective hemopoiesis; conversely, the progression of MDS toward AML occurs in concert with decreased apoptosis and an increased degree of neoplastic cell survival, leading to subsequent expansion of the abnormal precursor cells. These processes are associated with alterations in the balance between pro- and anti-apoptotic oncoprotein expression within the hemopoietic precursors, which may be modified by cytokine treatment. Investigations evaluating apoptotic events in MDS have improved our understanding of the biology of hemopoietic cell survival as related to pathogenetic features of this disease. By modifying levels of apoptosis, such studies provide a framework for future potentially beneficial therapeutic approaches to treat patients with MDS.

Risk factors and their relationship to prognosis in myelodysplastic syndromes.

Recent efforts have been directed at improving the methodology for predicting clinical outcomes in patients with myelodysplastic syndromes (MDS). This review focuses on the development of a consensual, prognostic, risk-based analysis system generated by the International MDS Risk Analysis Workshop. In the workshop, cytogenetic, morphological, and clinical data were combined and collated from a relatively large group of patients with primary MDS. Critical prognostic variables were evaluated using the data set. Based on these findings, the International Prognostic Scoring System (IPSS) was developed, compared with other systems, and shown to provide more accurate prognoses regarding survival and evolution to acute myeloid leukemia in MDS patients. The improvement was due to several features of the workshop model: more refined cytogenetic categorization, inclusion of cytopenias, improved subdivision of marrow blast percentages, four subgroups defining outcome, and separate stratification for age. The IPSS should result in better-defined clinical outcomes in MDS and provide a framework for future studies determining the possible role of molecular determinants (e.g. oncogenes, tumor suppressor genes, cytokine expression and responsiveness) for evaluating prognoses. The IPSS will likely prove useful in the design and analysis of therapeutic trials in MDS as well as in patient management.

Bcl-2 expression by myeloid precursors in myelodysplastic syndromes: relation to disease progression.

RATIONALE AND METHODS: the bcl-2 oncogene blocks apoptosis in various cell types and is expressed by normal myeloid precursors, declining with maturation. To investigate whether bcl-2 plays a role in the increase of myeloblasts in myelodysplastic syndromes (MDS) and their progression to acute myeloid leukemia (AML), we studied bcl-2 expression in initial (pre-therapy) bone marrow biopsies from MDS at early (refractory anemia, RA, with or without ring sideroblasts) and advanced stages (RA with excess blasts, and in transformation). Sequential biopsies were also studied to evaluate the effect of time or disease progression, including evolution to AML, or therapy with granulocyte colony stimulating factor (G-CSF). Early myeloid precursors (EMPs), predominantly myeloblasts, were identified in paraffin sections after immunostaining; bcl-2-positive EMPs were enumerated as a percentage of all EMPs (Bcl-2%), and by their absolute frequency per x 900 microscopic field (Bcl-2 index). FINDINGS: in initial biopsies, the Bcl-2% and Bcl-2 index in early MDS (9.9+/-2.6 and 1.4+/-0.6, respectively; mean+/-S.E.) were significantly lower than in advanced MDS (26.4+/-3.6, 4.6+/-1.4), but similar to controls (8.1+/-0.3 and 0.8+/-0.1). The Bcl-2% and Bcl-2 index in three patients with AML evolved from MDS (57.4+/-17.9 and 85.1+/-62.4) were similar to values for seven patients with de novo AML (63.0+/-10.0, 98.4+/-29.8) and significantly higher than values for other groups. Bcl-2% showed relative increments with time or disease progression (range, 21-273%; 11 of 18 sequential biopsies from six of ten MDS patients), which was not clearly altered by G-CSF therapy (four of six patients with, two of four patients without treatment). CONCLUSIONS: bcl-2 expression by EMPs (in both proportion and absolute number) correlated with initial MDS stage, progressed over time independent of G-CSF therapy, and was associated with evolution to AML. These data provide support for the hypothesis that MDS progression is related to accumulation of immature myeloid cells with increased bcl-2 expression and decreased apoptosis.

Effects of CSFs in preleukemia.

Based on pre-clinical and in vitro studies demonstrating enhanced granulocytic proliferation and differentiation induced by granulocyte-monocyte and granulocyte-colony stimulating factors (GM-CSF and G-CSF), these recombinant human hormones have been used to treat cytopenic patients with preleukemia [i.e., myelodysplastic syndromes (MDS)]. To date, five studies have been reported using GM-CSF short-term (generally 7-14 days, x 1-5 courses). Thirty-eight of 45 treated patients had improvements in neutrophil counts, 14 had increased reticulocyte counts with three of these individuals having decreased RBC transfusion requirements, and eight had transient increases in platelets. In 12 patients an increase in marrow and/or peripheral blood blasts was noted. Seven patients progressed to acute myeloid leukemia (AML), particularly patients with greater than 15% marrow blasts. In a longer term study, five patients received GM-CSF for 2 to 9 weeks, although only one individual maintained increased neutrophil counts, one developed antibodies to GM-CSF and one evolved into AML. Eighteen patients have been treated for 2 months with G-CSF, 16 of whom had normalization of neutrophil counts with improved marrow maturation, five had increased reticulocyte counts with three having decreased transfusion requirements, no substantial changes in platelet counts were noted. Eleven patients have received maintenance therapy with G-CSF for 6-16 months, ten had persistent increases in neutrophil counts with enhanced marrow myeloid maturation and five had increased reticulocytes. Decreased infectious episodes were notedat times of neutrophil improvements. Four of the 18 individuals have subsequently developed AML after 6-16 months.(ABSTRACT TRUNCATED AT 250 WORDS)

Granulocyte-monocyte and Granulocyte-Colony Stimulating Factors in Myelodysplastic Syndromes.

Myelodysplastic syndromes (MDS) are a heterogenous group of clonal disorders of hemopoiesis entailing hypoproliferative and ineffective hematopoiesis. The biology of MDS may relate to uncoupling of hemopoietic cellular differentiative and proliferative programs. The MDS provide a clinical setting for evaluating the evolution of relative benign hematologic disorders into frankly malignant diseases similar to acute myelogenous leukemia (AML). In vitro marrow hemopoietic cultures were utilized to evaluate the effect of granulocyte-monocyte colony-stimulating factor (GM-CSF) and granulocyte-colony stimulating factors (G-CSF) on proliferating differentiative and regenerative responsiveness of marrow cells from MDS patients. We determined possible differing effects of G-CSF and GM-CSF in morphological and cytogenetical subgroups of MDS patients. G-CSF was able to induce granulocytic differentiation of enriched hemopoietic precursors from MDS patients, generally without increased clonal self-generation. G-CSF has greater granulocytic differentiative and less proliferative activity for MDS marrow cells than GM-CSF in vitro, particularly for patients with refractory anemia with excess blasts (RAEB) and RAEB in transformation (RAEB-T) and those with normal cytogenetics. These findings provided a biologic rationale for in vivo clinical trials using G-CSF in MDS patients. Prospective investigations will be necessary to determine the possible utility of such in vitro studies for designing future in vivo clinical trials with these colony stimulating factors.

Molecular and genetic features of myelodysplastic syndromes.

Multifactorial pathogenetic features underlying myelodysplastic syndromes (MDS) relate to inherent abnormalities within the hematopoietic precursor cell population. The predominant final common pathogenetic pathway causing ineffective hematopoiesis in MDS has been the varying degrees of apoptosis of the hematopoietic precursors and their progeny. A variety of molecular abnormalities have been demonstrated in MDS. These lesions are attributable to nonrandom cytogenetic and oncogenic mutations, indicative of chromosomal and genetic instability, transcriptional RNA splicing abnormalities, and epigenetic changes. Evolutionary cytogenetic changes may occur during the course of the disorder, which are associated with disease progression. These genetic derangements reflect a multistep process believed to underlie the transformation of MDS to acute myeloid leukemia. Recent findings provide molecular insights into specific gene mutations playing major roles for the development and clinical outcome of MDS and their propensity to progress to a more aggressive stage. Use of more comprehensive and sensitive methods for molecular profiling using 'next-generation' sequencing techniques for MDS marrow cells will likely further define critical biologic lesions underlying this spectrum of diseases.