"Atypical" leukemias: preleukemia, smoldering leukemia and hypoplastic leukemia

Clinical use of hematopoietic growth factors in the myelodysplastic syndromes

Recent advances in the molecular genetics of myelodysplastic syndromes (MDS) have shed new light on the pathogenesis of MDS allowing a better understanding of the defects of differentiation of the transformed clone and suppression of normal hematopoiesis. The clinical hematologist, however, continues to be challenged with the treatment of patients with MDS. Pancytopenia and defective function of neutrophils and platelets lead to a high risk of infectious and hemorrhagic complications. The progression to acute myeloid leukemia adds to morbidity and mortality. Supportive care including red blood cell and platelet transfusions are still the cornerstone of therapeutic management. While prophylactic administration of G-CSF or GM-CSF cannot be recommended, treatment of febrile neutropenia might benefit from administration of G-CSF in addition to antibiotics. Administration of high-dose erythropoietin will improve erythropoiesis in around 20% of the patients, mainly in those with rather preserved erythroid function and no or low transfusion need. Coadministration of erythropoietin with either G-CSF or GM-CSF could increase the response rate. Allogeneic stem cell transplantation still is the only curative treatment and prolongs survival. Intensive chemotherapy for advanced MDS is possible with an acceptably low rate of early death and a complete remission rate between 45% to 60%, while initial results of autologous transplantation are promising.

In vitro culture studies of childhood myelodysplastic syndrome: establishment of the cell line MUTZ-1

Myelodysplastic syndrome (MDS) in childhood is considered to be very rare and detailed pathobiological data are scarce. More biological information regarding MDS in children is clearly needed and in vitro culture studies provide one possibility for gaining further pathophysiological insights into this malignancy. Here, we incubated bone marrow samples from 30 children with MDS in liquid suspension culture in order to grow the transformed cells in vitro. In most cultures, the hematopoietic cells died quickly and only fibroblastic (stromal) background layers proliferated temporarily; several normal Epstein-Barr virus (EBV)-transformed B-lymphoblastoid cell lines (B-LCL) were established. Only in one instance, albeit from the peripheral blood and not from the bone marrow, could we establish a cell line, termed MUTZ-1, from the malignant cells of a 5-year-old girl with MDS (FAB subtype refractory anemia with excess of blasts). The MDS arose from a pre-existing Fanconi anemia and progressed quickly to an acute myeloid leukemia (FAB M2). Despite positivity for EBV, MUTZ-1 is not an EBV + B-LCL and further characterization of MUTZ-1 confirmed the derivation from the transformed clonal cells. Immunophenotyping showed a pre B-cell surface marker profile (CD10+ CD19+ cytoplasmic IgM+); receptor gene rearrangement analyses underlined the clonal B-cell nature of MUTZ-1 cells. MUTZ-1 cells exhibit a highly rearranged, unstable karyotype with a high frequency of spontaneous chromatid breaks and exchanges; del(5q) and additional rearrangements involving chromosome 5 [der(15)t(5;15)] were detected. The present data and results from a few other MDS-derived cell lines suggest that the transforming event in MDS seems to occur in an immature pluripotent progenitor cell. The new MDS-derived continuous cell line MUTZ-1 provides a useful in vitro model system for studies on the pathogenetic events leading to MDS.

Effect of GM-CSF, 1, 25-Dihydroxycholecalciferol (Vit.D) and All-Trans-Retinoic Acid (ATRA) on the Proliferation and Differentiation of MDS-Bone Marrow (BM)-Cells In Vitro

Myelodysplastic syndromes (MDS) are a heterogenous group of stem cell disorders characterized by an impaired differentiation of the pluripotent stem cell resulting in dysplastic changes of all three hemopoietic lineages. We studied the effect of vitamin D (Vit.D) or all-trans retinoic acid (ATRA; 10(-6) and 10(-8)M) in combination with GM-CSF on the proliferation and differentiation of mononuclear bone marrow-cells (MNC) of 48 MDS-patients as compared to 9 normal bone marrow (BM)-controls in a special colony assay: 30,000 MNC were cultured in agar plugs for 7 days (d) and the resulting colonies immunophenotyped in situ by a panel of monoclonal antibodies. In 14 of 48 cultured MDS-BM-samples hemopoietic clones could be grown which expressed myelomonocytic antigens (CD14 (21%*), CD15 (35%*)) as well as blast antigens (CD20 (9%*), CD34 (10%*), Glycophorin A (Glyco A, 18%*)) whereas all normal BM-colonies were negative for blast markers. Vit.D or ATRA in combination with GM-CSF could not induce an (immunologically measurable) increased differentiation (5 higher percentage of differentiated clones) as compared to GM-CSF alone. We conclude that Vit.D and ATRA have no sufficient differentiation effect on MDS-cells. Our colony assay in combination with immunophenotyping enables an in vitro measurement of differentiation and proliferation in MDS. We suggest the use of this technique to measure effects of therapy in the course of the disease.

Analysis of bone marrow and peripheral blood immunoregulatory lymphocytes in patients with myelodysplastic syndrome

The cell surface phenotype of immunoregulatory lymphocytes in bone marrow (BM) and peripheral blood (PB) in myelodysplastic syndrome (MDS), a stem cell disorder, was analyzed. Mononuclear cells from 25 patients with refractory anemia (RA) and nine with RA with an excess of blasts (RAEB) were characterized by two-color flow cytometry using various monoclonal antibodies. No significant change of CD3+, CD4+, and CD8+ cells in PB, but a decrease of the percent of positive cells for CD8++ among the total lymphocyte (%CD8++) was noticed in RA patients. On the other hand, in BM of RA patients, a decrease in the number of CD4+ cells, but not CD8++ cells, was noted. In RAEB patients, the absolute numbers of CD3+, CD4+, CD8+, and CD8++ cells in BM were decreased; however, the ratio of these lymphocytes was not changed. No change was observed among the CD4+ subsets in PB of RA or RAEB patients. In BM, a decrease in percentage of CD4+CD45RA+ (%CD4+CD45RA+; naive cell) and increases in CD4+CD45RO+ (%CD4+CD45RO+; memory cell) and CD4+CD29+ (%CD4+CD29+; helper/inducer) among CD4+ cells were found in both RA and RAEB patients. Analysis of the CD8++ subset showed an increased number of CD8++CD11a+ cells (activated CTL) in both BM and PB of RA patients, but not of RAEB patients. Furthermore, increments in CD56+ and CD16+ cells among CD3- cells (natural killer; NK cells) were seen in RA patients but not in RAEB patients. It remains unclear whether lymphocytes in MDS patients were involved in the abnormal (MDS) clones, but our results regarding the increments of CD8++CD11a+ and NK cells in RA patients suggest that the mechanism of immune surveillance against the abnormal MDS clones was activated in these RA patients, but not in RAEB patients. Further investigation is required to clarify the functions of these immunoregulatory lymphocytes in MDS patients.

Myelodysplastic syndromes--a population-based study on transformation and survival

A retrospective analysis was done on 113 patients (median age 73 years) with myelodysplastic syndromes (MDS), consecutively diagnosed at our center during a 10-year period. Patients with refractory anemia (RA) and refractory anemia with ringed sideroblasts (RARS) had significantly longer survival than patients with refractory anemia with excess blasts (RAEB), chronic myelomonocytic leukemia (CMML) or refractory anemia with excess blasts in transformation (RAEB-T). Thirty-seven patients (33%) subsequently developed acute myelogenous leukemia (AML). The percentages of AML transformation for the subgroups were: RA: 26%, RARS: 14%, RAEB: 38%, CMML: 25% and RAEB-T: 69%. A total of 9 patients received high-dose chemotherapy, 7 of them already at the time of MDS diagnosis. Six of the RAEB-T patients entered complete and two partial remission. The median age in the group of RAEB-T patients was significantly lower (62 years) than in the other MDS subgroups. It seems that high-dose chemotherapy, at least in RAEB-T, may induce complete remission and improve survival time.

Recombinant human erythropoietin (rHuEPO) for treatment of myelodysplastic syndrome

Sixteen patients (ages 53 to 85) with myelodysplastic syndrome (MDS) were treated with recombinant human erythropoietin (rHuEPO) to observe its effects on hematopoiesis. All were transfusion dependent and had Hb levels less than 9.0 g/dl and less than 10% marrow blasts. Eight patients had refractory anemia (RA), one had refractory anemia with excess blasts (RAEB), and seven had refractory anemia with ringed sideroblasts (RARS). A response was defined as an increase in Hb by greater than 2 g/dl and/or a decrease in transfusion requirement by greater than 50%. Patients were considered to be evaluable if on study greater than two months. Three of thirteen evaluable patients had a response. One patient with RA had a sustained trilineage hematologic response with no evidence of disease progression. None of the patients had trouble with hypertension or with thrombotic events. This suggests than an occasional patient with MDS will respond to rHuEPO. In some patients, this may be beneficial clinically.

Myelodysplastic syndromes. Pathogenesis, diagnosis and treatment

Our understanding of the biology of leukemia and myelodysplasia is still only partial. The diagnosis of myelodysplasia is often based on quantitative and qualitative findings in the peripheral blood and bone marrow. These findings are often shared by other disorders. There is a need for sensitive and inexpensive laboratory tests to determine clonality and karyotypic abnormalities in this disorder. Future classifications of these syndromes will need to be based on morphologic and biologic markers that are closely linked to disease progression, response to treatment, and survival. Our limited understanding of the pathogenesis of MDS decreases the specificity and effectiveness of our therapeutic interventions. Agents that are minimally toxic such as CRA, danazol, 1,25-dihydroxyvitamin D3, androgens, and pyridoxine are seldom useful. Antileukemic therapy and allogeneic bone marrow transplantation have a major role to play in patients younger than 45 years of age; in older patients these treatment modalities remain controversial because of their toxicity. Hematopoietic growth factors, used alone or in combination, may improve the quality of life and improve survival of patients with MDS. Growth factors may also decrease treatment-related mortality associated with chemotherapy and bone marrow transplantation and render these treatment modalities available for a higher percentage of patients. The development of more specific differentiating agents may permit hematopoietic differentiation while minimizing side effects.

Interleukin-3 in the treatment of myelodysplastic syndromes

Patients with myelodysplastic syndromes frequently present with anemia, leukopenia and thrombocytopenia due to defective maturation of bone marrow cells. Clinical studies with hematopoietic growth factors, including interleukin-3 (IL-3), have been undertaken to evaluate the possibility to reverse cytopenia. In initial phase I/II trials, treatment with IL-3 has resulted in an increase of neutrophil counts in 59%, of platelet counts in 34%, and in reticulocyte counts in 25% of the patients. Adverse effects were rather mild but in individual patients a reversible decrease in platelet counts and in the number of blast cells in blood and bone marrow were observed. Further clinical trials should concentrate on the combination of an early acting cytokine like IL-3 and later acting hemopoietic growth factors like erythropoietin and granulocyte colony-stimulating factor.

Circulating CD34+ cells: an adverse prognostic factor in the myelodysplastic syndromes

As part of an epidemiological survey of myelodysplastic syndromes (MDS) in southern Tasmania, 62 MDS patients identified over a 2 year period were tested for the presence of CD34, the human progenitor cell antigen (HPCA), in their peripheral blood. The results were correlated with transformation to acute myeloid leukemia (AML) and patient survival, and CD34+ status was compared as a prognostic indicator with Bournemouth score, cytogenetics, and CFU-GM colony growth which were also assessed. Circulating CD34+ cells were found in 23 of the 62 MDS patients; 9 of the 23 patients with circulating CD34+ cells transformed to AML, as compared with none of the 39 CD34 negative patients (P less than 0.0001); and 11 of the 23 patients with circulating CD34+ cells were dead at the end of the 2 year period, as opposed to 6 of the 39 with no CD34+ cells (P less than 0.03). The Bournemouth score was also significantly associated with transformation to AML (P less than 0.0001) and poor survival (P less than 0.04). These were the only significant associations of the possible prognostic factors studied with either transformation or survival. In summary, the presence of circulating CD34+ cells was significantly associated with both progression to AML and poor survival and was found to be a better prognostic indicator than cytogenetics or CFU-GM colony growth.

Prognostic factors in the myelodysplastic syndromes

The myelodysplastic syndromes are acquired clonal hematologic malignancies characterized by progressive cytopenia and an increased risk of evolution to acute myeloid leukemia. It mainly affects elderly people, but may also be found in younger patients and children. MDS represents a heterogeneous group of disorders. Some patients will experience prolonged survival, whereas a substantial number of patients will die within the first year after diagnosis. Treatment of patients should be based on life expectancy. Patients with pancytopenia, excess of bone marrow blasts, complex chromosome abnormalities, abnormal chromosome 7, older age and secondary MDS have a poor prognosis. Several simple scoring systems are available, based on peripheral counts, percent of bone marrow blasts and age, that provide significant prognostic information about life expectancy in patients with MDS. The most widely used is the Bournemouth scoring system. The prognostic factors and the scoring systems are reviewed.

Exposure histories in acute nonlymphocytic leukemia patients with a prior preleukemic condition

A subset of patients with acute nonlymphocytic leukemia (ANLL) have evidence of a myelodysplastic syndrome (MDS), low infiltrate leukemia, or other preleukemic condition that may be present for several months before onset of disease. The hypothesis that these conditions act as markers for environmentally induced cancer was examined in 270 ANLL patients, 46 with a preleukemic phase and 224 with an acute onset. Although the effects of previously identified risk factors (male sex, age older than 50 years, prior cytotoxic therapy) were demonstrated, no associations with common environmental conditions (cigarette smoking, alcohol use, occupations with exposure to chemicals or radiation) were present with the exception of hobbies involving potential chemical exposure, odds ratio (OR) and 95% confidence intervals = 4.2 (1.4 to 12.3) and self-reported exposure to pesticides, OR = 10.2 (1.8 to 63.1). These may be chance associations although a previous case-control study of MDS reported similar findings.

A study of serum free medium culture on the cloning efficiency of human bone marrow myeloid and erythroid progenitors

Thirteen different combinations of serum-free media were tested to assess their suitability to replace serum containing medium for in vitro culture of human hemopoietic progenitors (CFU-GM and BFU-E). Bone marrow samples from patients with and without hematological diseases were tested. All tested media supported the growth of CFU-GM and BFU-E colonies, however our results have shown that the cloning efficiency of all commercially available serum-free media tested was lower (mean 18% and 12% of controls for CFU-GM and BFU-E respectively) and the colony size was smaller than those in serum-containing medium. In the serum-free cultures, there was no linear relationship between the colony numbers and cell concentration plated. Depletion of T-lymphocytes and monocytes did not improve the cloning efficiency of the serum-free medium culture. Furthermore, the addition of high concentration of insulin, transferrin and other supplements to the serum-free media did not improve the cloning efficiency. These results have indicated that the currently available commercial serum-free media do not provide optimal requirements for hemopoietic progenitor cell cultures and that other factors contained in serum are essential for their optimal growth.

Myelodysplastic syndromes: a study of surface markers and in vitro growth patterns

A study of surface markers and in vitro growth in semi-solid and liquid medium was performed in 35 patients with newly diagnosed myelodysplastic syndrome (MDS). Surface markers were studied by CD34, CD13, CD14, CD15, and CD33 monoclonal antibodies. There was no strict correlation with the FAB typing, but CD34 was expressed only in refractory anemia with excess of blasts (RAEB) or RAEB in transformation (RAEB-t). CD14 was markedly positive in the 4 cases of chronic myelomonocytic leukemia. Colony-forming cells were assessed by culture in semi-solid medium in the presence of HTB9 as growth factor. Four growth patterns were identified: a) normal growth (6 cases); b) no growth or low plating efficiency (10 cases); c) low colony and high cluster number (15 cases); and d) normal or high colony number with high number of clusters (4 cases). Expression of CD34 was associated with low colony and high cluster number. Finally we studied the proliferation and differentiation capacities in liquid culture without stimulating factor. Fifteen patients had a spontaneous proliferation. This was not correlated with any surface marker. Differentiation assessed by the loss of CD34 and/or the increase of CD15 by more than 20% at day 7 was observed in 21 cases. None of the surface markers or growth patterns was associated with a specific chromosomal abnormality, except the lack of growth in liquid culture observed in all 5q deletion cases. In univariate analysis, RAEB and RAEB-t FAB subtypes, percentage of blasts higher than 5%, staining by CD33 and CD34, and lack of differentiation in liquid culture were significantly associated with progression to leukemia and shorter survival. In multivariate analysis, only CD34 expression (P = .002) and percentage of blasts (P = .05) remained independent significant variables. CD34 was the only significant variable for prediction of survival (P = .05). It is concluded that surface marker analysis at diagnosis and after liquid culture may be a useful tool for the initial evaluation of MDS.

Bone marrow cultures and prognosis in primary myelodysplastic syndromes

Bone marrow cultures and survival time were studied in 39 patients with primary myelodysplastic syndromes. We divided the patients into two groups according to the CFU-GM numbers on day 10: type I with low colony (CFU-GM less than 30) and type II with normal to high colony formation (CFU-GM greater than or equal to 30). The median survival time was shorter for patients with an in vitro growth type II (5 months) than it was for patients with an in vitro growth type I (greater than 36 months). No relations was found between growth types and FAB-type, Bournemouth score or initial karyotype. The initial bone marrow blast percentage correlated well with the in vitro growth number.

Differentiation induction therapy of myelodysplastic syndromes

Myelodysplastic syndromes are a heterogenous group of haemopoietic stem cell disorders characterized by dysplastic haematopoiesis and a defective maturation of a slowly expanding or sometimes of a stable population of haemopoietic progenitors. Defective maturation, which may involve one or more of the marrow cell lineages is regarded as the central pathophysiological feature of myelodysplastic syndromes. Patients with myelodysplastic syndromes respond poorly to conventional cytotoxic chemotherapy, frequently developing a prolonged marrow aplasia. The alternative and more appropriate form of therapy is differentiation induction therapy. The results of few preliminary clinical studies in myelodysplastic patients showed that a combination of differentiating agents is superior to single agent differentiation therapy. An extensive pre-clinical screening of the response of fresh cells from myelodysplastic patients in primary culture is needed to establish the optimal doses and conditions for significant synergies between various differentiating agents followed by large controlled randomized clinical trials based on differentiation induction therapy for patients with myelodysplastic syndromes.

Deficiency of pluripotent hemopoietic progenitor cells in myelodysplastic syndromes

Pluripotent (CFU-MIX), erythroid (BFU-E) and granulocyte/macrophage (CFU-GM) progenitor cells were examined in bone marrow (BM) from 23 patients with myelodysplastic syndromes (MDS). Patients were grouped according to the FAB classification: Refractory anemia (RA), n = 3; RA with ring sideroblasts (RARS), n = 3; RA with excess of blasts (RAEB), n = 8; RA with excess of blasts in transformation (RAEBt), n = 7; chronic myelomonocytic leukemia (CMML), n = 2. In FAB groups RA, RARS, RAEB and RAEBt CFU-GM concentrations were normal or decreased but both CMML-patients had increased CFU-GM values. Abnormal cluster growth was observed in 9 of 23 MDS-patients. BFU-E colony formation was subnormal in all cases. Mixed-colony assay values were at the lower limit of controls in one patient and decreased in the remaining 22 MDS-patients. A similar growth pattern of hemopoietic progenitor cells was observed in 19 patients with acute nonlymphocytic leukemia (ANLL), who were studied for comparison. These data suggest a quantitative or qualitative/functional defect of the pluripotent progenitor cell compartment as the major cause for the cytopenia in MDS-patients.

Myelodysplastic syndromes: evolution of overt leukaemia by one or several steps of transformation

The evolution of leukaemia was studied prospectively in 29 patients with myelodysplastic syndrome (MDS) followed for 2-6 years by sequential blast counts, cell kinetics derived from quantitative 14C-autoradiography and karyotype analysis. Overt leukaemia developed in seven patients. Two distinct patterns of leukaemic evolution were identified. The first was characterized by a gradual increase in blast cell count and in the frequency of labelled blasts, and a corresponding reduction in myeloid maturation index indicating increased intracompartmental myeloblast divisions and premature myeloid cell death. A second pattern of leukaemic evolution was marked by a sudden rise in the blast cell population in a previously stable MDS. This rise was attributed both to an increased rate of blast proliferation, and the accumulation of non-proliferating blasts. In an additional patient with smouldering ANLL and multiple karyotype abnormalities, transient clinical remission took place following prednisone and oxymetholone therapy, characterized by a sideroblastic morphology, normal karyotype, and persistence of a highly abnormal myeloid maturation index. The sudden emergence of overt leukaemia in previously stable MDS in some of our patients and the temporary reversal of overt leukaemia into sideroblastic anaemia in one case, lend support to the notion of leukaemic evolution by several steps of transformation. On the other hand, the gradual transition of MDS into overt leukaemia in other patients is compatible with a single step leukaemia transformation, although the possibility of clonal disease prior to the development of MDS cannot be excluded with certainty.

Biology of myelodysplastic syndromes

Myelodysplastic syndromes (MDS) represent a diverse spectrum of disorders ranging from refractory anemia to a preleukemic state. Peripheral cytopenias, cellular marrow, dysplasias and dysfunctions of myeloid and lymphoid cells constitute hematological hallmarks, and are caused by ineffective hemopoiesis. Investigations of cell cultures and cellular functions indicate that the disease originates in a stem cell pluripotent to all myeloid cells and possibly lymphoid cells as well. The disease commonly runs a chronic indolent course, often terminating in acute leukemia or nonleukemic death, notably infections and/or hemorrhage due to cytopenias and cellular dysfunctions. Clonal expansion or clonal evolution appears to be related to the disease progression with a greater degree of malignancy. However, the initial sequence of events causing damage to stem cells is still undefined.

Defective in vitro growth of the hemopoietic progenitor cells in the acquired immunodeficiency syndrome

In addition to immunologic derangement, hematological abnormalities have been reported in the majority of patients with acquired immunodeficiency syndrome (AIDS). In this study 15 patients with AIDS or AIDS-related complex (ARC) were evaluated for the in vitro growth of hemopoietic progenitor cells. In all patients a significant reduction of growth (mean +/- SEM) of colony-forming unit-granulocyte, erythrocyte, macrophage, (megakaryocyte) (CFU-GEM) (1.2 +/- 0.3), burst-forming unit-erythroid (BFU-E) (17 +/- 10), CFU-megakaryocyte (CFU-Mk) (1.7 +/- 0.6), and CFU-granulocyte-macrophage (CFU-GM) (35 +/- 10) was observed in comparison with normal controls. Depletion of T cells from the bone marrow before culture led to a significant increase in colony growth, which indicated an imbalance of the normally modulating T cell subsets. This increase was reversed by readdition of autologous T cells causing a decrease in colony growth to a degree, dependent on the T4 to T8 ratio. A decreased number of hemopoietic progenitor cells and/or a defective modulation of progenitor cell growth, normally carried out by T lymphocyte subsets, might be the cause of the hematological abnormalities in AIDS patients.

A randomized trial of 13-cis retinoic acid with or without cytosine arabinoside in patients with the myelodysplastic syndrome

Ninety-eight consecutive patients with myelodysplastic syndrome were randomized to a treated or a control group, both receiving conventional supportive therapy. The treated group were given 13-cis-retinoic acid 20 mg/d if marrow blasts were less than or equal to 5% or cytosine arabinoside 10 mg/d subcutaneously on 6 d/week if marrow blasts were 6-30%, to which retinoic acid was added after 12 weeks. Serum levels of the drugs in the treated group were similar to those that would produce inhibition of CFU-GM growth in vitro. In patients in the low blast group receiving retinoic acid, myeloid surface antigens reverted from an abnormal to a normal pattern. Log rank analysis carried out after 25 months showed no significant difference in survival between the treated and control group, either in the total patient population or in the high and low blast groups considered separately. However, analysis of 39 non-sideroblastic patients with less than or equal to 5% blasts showed an increase in survival in the treated group.

Management of myelodysplastic syndromes

The treatment of myelodysplastic syndromes is reviewed, with emphasis on recently published clinical trials. Pyridoxine is rarely effective, but a trial in patients with refractory anemia with ringed sideroblasts is justifiable. Corticosteroids do not appear indicated unless in vitro data suggest response. Androgens are generally not beneficial, although danazol merits further evaluation. Both 13-cis-retinoic acid and low-dose cytosine arabinoside have considerable toxicity and yield short-lived partial responses that may not have a significant impact on survival. Combination chemotherapy may be considered in selected patients with refractory anemia with excess of blasts, refractory anemia with excess of blasts in transformation, and chronic myelomonocytic leukemia; however, in general, its toxicity outweighs potential benefit. For unusual patients under 30 years old, bone marrow transplantation should be considered as first-line therapy. Until more effective and less toxic agents are available, supportive care may still be the most appropriate therapy for many of these generally elderly patients.

Myelodysplastic syndromes: pathogenesis, functional abnormalities, and clinical implications

The myelodysplastic syndromes represent a preleukaemic state in which a clonal abnormality of haemopoietic stem cell is characterised by a variety of phenotypic manifestations with varying degrees of ineffective haemopoiesis. This state probably develops as a sequence of events in which the earliest stages may be difficult to detect by conventional pathological techniques. The process is characterised by genetic changes leading to abnormal control of cell proliferation and differentiation. Expansion of an abnormal clone may be related to independence from normal growth factors, insensitivity to normal inhibitory factors, suppression of normal clonal growth, or changes in the immunological or nutritional condition of the host. The haematological picture is of peripheral blood cytopenias: a cellular bone marrow, and functional abnormalities of erythroid, myeloid, and megakaryocytic cells. In most cases marrow cells have an abnormal DNA content, often with disturbances of the cell cycle: an abnormal karyotype is common in premalignant clones. Growth abnormalities of erythroid or granulocyte-macrophage progenitors are common in marrow cultures, and lineage specific surface membrane markers indicate aberrations of differentiation. Progression of the disorder may occur through clonal expansion or through clonal evolution with a greater degree of malignancy. Current attempts to influence abnormal growth and differentiation have had only limited success. Clinical recognition of the syndrome depends on an acute awareness of the signs combined with the identification of clonal and functional abnormalities.