Acute myelofibrosis. Immunohistochemical study of four cases and comparison with acute megakaryocytic leukemia

Expression of the tyrosine kinase discoidin domain receptor 1 (DDR1) in human central nervous system myelin

During development of the mouse brain, the protein kinase discoidin domain receptor 1 (DDR1) is present prenatally in neurons of the proliferative areas, and postnatally, DDR1 expression is no longer detected in neurons, but a spatial-temporal expression pattern in oligodendrocytes that overlaps with the dynamics of the myelination process is detected. Notably, oligodendrocytic DDR1 expression is upregulated in mice during experimentally induced remyelination. Recently, we demonstrated that DDR1 expression is high in human brain and that there is an association between the gene and schizophrenia in a case-control study. However, data regarding expression of DDR1 in the human brain are scarce. Here, we describe the expression pattern of DDR1 in the human adult cerebral cortex. Using several immunohistological techniques and in situ hybridization, we identified DDR1 in the following: a) myelin, b) capillary endothelial cells in the gray as well as white matter, and c) in the soma of some oligodendrocytes and astrocytes in the white matter. The most important overall finding in this study was that DDR1 is present in myelin and is expressed by oligodendrocyte cells. We detected the presence of DDR1 mRNA and protein in myelin and observed that DDR1 co-localized with the classical myelin basic protein (MBP). Moreover, we found a strong positive correlation between expression levels of DDR1 and two myelin-associated genes, myelin-associated glycoprotein (MAG) and oligodendrocyte transcription factor 2 (OLIG2). These observations suggest that DDR1 could be an important constituent of myelin. Because defects in myelination are linked to several mental disorders such as schizophrenia, the function of DDR1 in the process of myelination warrants further investigation.

Acute Panmyelosis with Myelofibrosis: Clinical, Immunophenotypic and Cytogenetic Study of Twelve Cases

The clinical, cytogenetic, and immunophenotypic features in 12 adult patients with acute panmyelosis with myelofibrosis (APMF; ICD-0-3: 9931/3; C42.1) are reported (median age: 57 years; f/m = 1.4). The white cell count (WBC) was normal in 3 patients; 9 had leucopenia. The median hemoglobin value was 64.5 g/l, and median platelet count 12 x 10(9)/l. Bone marrow biopsy showed a hypercellular marrow in 10/12 patients with a significant infiltration of pathological blasts (range: 30 - 60%). All the cases had marked reticulin fibrosis. Immunophenotyping of bone marrow blast cells showed the expression of early (CD34) and lineage-unspecified antigens (HLA-DR) in 6/7, and 7/7 patients, respectively. "Early" myeloid antigens (CD13, CD33) were seen in 6/7 and 4/6 patients respectively. Monocyte antigen (CD14) was expressed in 3/7 patients. Megakaryocyte antigen (CD61) and erythroid cell antigen (GpA) were each expressed in only 1 patient. Two patients had expression of CD34, HLA-DR and "early" myeloid antigens by their bone marrow blast cells and 1 of these also had a co-expression of the antigens from a differentiated monocytic cell proliferation (lysozyme+, CD68+). Nonspecific chromosomal aberrations were recorded in 8/10 patients. The median survival was 2 months. These findings suggest an immature myeloid phenotype of blast cells in APMF. In 6/9 patients a leukemic cell differentiation into monocytic, megakaryocytic or erythroid lineage was also demonstrated.

Myelodysplastic syndrome with myelofibrosis: myelodysplastic syndrome as a major primary disorder for acute myelofibrosis

Seven cases of myelodysplastic syndrome with myelofibrosis, which is defined using the following criteria: (1) pancytopenia with less than 5% blasts in the peripheral blood; (2) minimal or no splenomegaly; (3) myelofibrosis with cellular marrow; (4) absence of diffuse proliferation of blasts in the bone marrow; and (5) presence of myelodysplastic features of bone marrow or peripheral blood cells, are presented. They were in the range of 52-82 years old and consisted of 3 males and 4 females. Six out of 7 cases developed into acute leukaemia after 5 to 8 months from the onset and died from between 2 weeks to 8 months from the evolution to leukaemia. The type of leukaemia was acute myeloblastic in 3 patients, and acute myelo-megakaryoblastic in 3 patients. Another patient died of severe hepatic injury after 5 months from the onset of the disease. These findings revealed that the complication of myelofibrosis in the patients with myelodysplastic syndrome was an indicative sign of rapid progression to overt leukaemia or otherwise poor prognosis for survival. In addition myelodysplastic syndrome is thought to be major primary disorder for acute myelofibrosis. Myelodysplastic syndrome with myelofibrosis is closely associated with the neoplastic proliferation of megakaryoblasts in a considerable number of patients.

Acute panmyelosis with myelofibrosis: an entity distinct from acute megakaryoblastic leukemia

The WHO criteria for diagnosing acute panmyelosis with myelofibrosis are somewhat distinct from those for acute megakaryoblastic leukemia. However, clinical and hematopathologic findings partially overlap. This has raised questions as to whether these are indeed separate, definable entities. To determine the potential importance of bone marrow biopsy supplemented by immunohistochemistry in distinguishing between these two conditions, we studied 17 bone marrow biopsies of well-characterized cases of acute panmyelosis with myelofibrosis (six cases) and acute megakaryoblastic leukemia (11 cases). We compared blast frequency, reticulin content, CD34 expression, and the degree of megakaryocytic differentiation of the blast cells in these two conditions. Our results demonstrate important differences. Acute panmyelosis with myelofibrosis is characterized by a multilineage myeloid proliferation with a less numerous population of blasts than acute megakaryoblastic leukemia (P<0.01). In the former condition, blasts are always positive with CD34, while in acute megakaryoblastic leukemia they express CD34 in 60% of the cases. The blasts in acute panmyelosis with myelofibrosis only rarely express megakaryocytic antigens. By contrast, acute megakaryoblastic leukemia has a significantly higher proportion of blasts expressing megakaryocytic antigens (P<0.01 with CD42b). Our results confirm that histology supplemented by immunohistochemistry permits the distinction of these conditions in routinely processed bone marrow biopsies.

Bone marrow biopsy: interpretive guidelines for the surgical pathologist

Ideally, the bone marrow core biopsy should be reviewed with knowledge of the clinical history, complete blood count, and findings in the peripheral blood and bone marrow aspirate smears. However, for a variety of reasons, the pathologist may receive the core biopsy and aspirate clot section without all of this information. Although this approach is not optimal, a great deal of valuable information can be generated from these specimens. Over the past 20 years, there has been considerable progress in the fields of flow cytometric analysis, immunohistochemistry, and molecular diagnostic studies that can be performed on smears or extracted DNA from paraffin embedded tissue. These modalities have augmented and refined diagnostic criteria formerly ascertained by light microscopy, cytochemistry, and cytogenetics. This is particularly true of some myeloid and lymphoreticular neoplasms where a collaborative and multidisciplinary approach to the diagnosis has become necessary. Despite this growing complexity and dependence on newer methodologies, the traditional role of histopathology in evaluating the bone marrow biopsy remains as important as it has been in the past. In this review, we focus on contemporary practices and expectations for interpreting bone marrow biopsies and clot sections.

The World Health Organization (WHO) classification of the myeloid neoplasms

A World Health Organization (WHO) classification of hematopoietic and lymphoid neoplasms has recently been published. This classification was developed through the collaborative efforts of the Society for Hematopathology, the European Association of Hematopathologists, and more than 100 clinical hematologists and scientists who are internationally recognized for their expertise in hematopoietic neoplasms. For the lymphoid neoplasms, this classification provides a refinement of the entities described in the Revised European-American Lymphoma (REAL) Classification-a system that is now used worldwide. To date, however, there has been no published explanation or rationale given for the WHO classification of the myeloid neoplasms. The purpose of this communication is to outline briefly the WHO classification of malignant myeloid diseases, to draw attention to major differences between it and antecedent classification schemes, and to provide the rationale for those differences.

Realistic pathologic classification of acute myeloid leukemias

Most classification systems of acute myeloid leukemia (AML) rely largely on the criteria proposed by the French-American-British (FAB) Cooperative Group. The recently proposed World Health Organization (WHO) classification of neoplastic diseases of the hematopoietic and lymphoid tissues includes a classification of AMLs. The proposed WHO classification of AMLs includes traditional FAB-type categories of disease, as well as additional disease types that correlate with specific cytogenetic findings and AML associated with myelodysplasia. This system includes a large number of disease categories, many of which are of unknown clinical significance, and there seems to be substantial overlap between disease groups in the WHO proposal. Some disease types in the WHO proposal cannot be diagnosed without detailed clinical information, or they are diagnosed only by the cytogenetic findings. In this report, a realistic pathologic classification for AML is proposed that includes disease types that correlate with specific cytogenetic translocations and can be recognized reliably by morphologic evaluation and immunophenotyping and that incorporates the importance of associated myelodysplastic changes. This system would be supported by cytogenetic or molecular genetic studies and could be expanded as new recognizable clinicopathologic entities are described.

Distribution of laminin and fibronectin isoforms in oral mucosa and oral squamous cell carcinoma

The expression of laminin and fibronectin isoforms varies with cellular maturation and differentiation and these differences may well influence cellular processes such as adhesion and motility. The basement membrane (BM) of fetal oral squamous epithelium contains the laminin chains, alpha2, alpha3, alpha5, beta1, beta2, beta3, gamma1 and gamma2. The BM of adult normal oral squamous epithelium comprises the laminin chains, alpha3, alpha5, beta1, beta3, gamma1 and gamma2. A re-expression of the laminin alpha2 and beta2 chains could be shown in adult hyperproliferative, dysplastic and carcinomatous lesions. In dysplasia and oral squamous cell carcinoma (OSCC), multifocal breaks of the BM are present as indicated by laminin chain antibodies. These breaks correlate to malignancy grade in their extent. Moreover, in the invasion front the alpha3 and gamma2 chain of laminin-5 can immunohistochemically be found outside the BM within the cytoplasm of budding carcinoma cells and in the adjacent stroma. The correlation between the morphological pattern of invasive tumour clusters and a laminin-5 immunostaining in the adjacent stroma may suggest, first, that a laminin-5 deposition outside the BM is an immunohistochemical marker for invasion and second, that OSCC invasion is guided by the laminin-5 matrix. Expression of oncofetal fibronectins (IIICS de novo glycosylated fibronectin and ED-B fibronectin) could be demonstrated throughout the stromal compartment. However, the ED-B fibronectin synthesizing cells (RNA/RNA in situ hybridization) are confined to small stroma areas and to single stroma and inflammatory cells in the invasion front. A correlation of the number of ED-B fibronectin synthesizing cells to malignancy grade could not be seen. ED-B fibronectin mRNA-positive cells seem to be concentrated in areas of fibrous stroma recruitment with a linear alignment of stromal fibro-/myofibroblasts (desmoplasia). Double staining experiments (ED-B fibronectin in situ hybridization and alpha-smooth muscle actin immunohistochemistry) indicated that the stroma myofibroblasts are a preferential source of ED-B fibronectin. In conclusion, in OSCC, a fetal extracellular matrix conversion is demonstrable. Tumour cells (laminin alpha2 and beta2 chain) and recruited stromal myofibroblasts (oncofetal ED-B fibronectin) contribute to the fetal extracellular matrix milieu.

Localization of lymph capillaries and blood capillaries in human temporomandibular joint discs

The localization of lymph capillaries and blood capillaries in the human temporomandibular joint (TMJ) discs was examined immunohistologically with anti-human collagen IV antibody and anti-human von Willebrand factor in 26 human TMJ samples. The 16 internal derangement cases were then compared with the 10 normal control cases. The findings suggested that blood capillaries scarcely existed in all the fields of normal control TMJ discs (5/270, 1.9%) nor did lymph capillaries exist in the normal TMJ discs (0/270, 0%). New growth of blood capillaries had localized in all fields of the internal derangement discs specimens (113/378, 29.9%) and was concentrated in the lower area of the posterior part of the discs. The authors also observed a small distribution of lymph capillaries in all fields of this material (17/378, 4.5%). The new growth of lymph capillaries were always related to the blood capillary distribution and therefore their presence might be directly related to the capillary proliferation.

Immunohistochemical distribution of lymph capillaries and blood capillaries in the synovial membrane in cases of internal derangement of the temporomandibular joint

The distribution of lymph capillaries and blood capillaries in the synovial membrane was examined immunohistologically with anti-human collagen IV antibody and anti-human von Willebrand factor in 26 human temporomandibular joint (TMJ) samples comprising discs with adjoining synovial membrane from 10 control TMJs and from 16 TMJs with internal derangement. Three different distribution types were observed in the synovial membrane. In the control samples, the occurrence of blood capillaries and lymph capillaries was rare. In mildly hyperplastic synovitis, lymph capillaries were observed just beneath the surface of the synovial membrane, whereas blood capillaries occurred in a little deeper layer of the synovial membrane. In a severely hyperplastic synovitis, both lymph and blood capillaries were observed frequently. The present results suggest that the different distribution patterns of lymph capillaries and blood capillaries reflect the degree of synovitis but can not be attributed to specific clinical symptoms.

Clinicopathological impact of the interaction between megakaryocytes and myeloid stroma in chronic myeloproliferative disorders: a concise update

In this report an attempt has been made to discuss some of the issues pertinent to myelofibrosis complicating chronic myeloproliferative disorders (CMPDs) that are significantly associated with megakaryocyte function. In this context, biochemical, clinical and particularly morphological features were reviewed. Morphological findings based on elaborate techniques were in keeping with the assumption that in chronic myeloid leukemia (1) the number of CD61-positive megakaryocytes, and in particular their precursors were the parameters most closely associated with myelofibrosis (2) an increased content of reticulin fibers in follow-up biopsies significantly correlated with laboratory data indicative of a high tumor burden (anemia, peripheral blasts, hepatosplenomegaly) and thus a more advanced stage of the disease process (3) even a slight increase in reticulin, i.e. doubling of the normal fiber density was associated with a worse prognosis independent of therapeutic regimens given (4) Dynamics of myelofibrosis was significantly influenced by treatment. In this context, calculation of the myelofibrosis progression index (MPI) revealed a higher score following interferon therapy compared with busulfan. In addition, in idiopathic myelofibrosis (5) the evolution of myelofibrosis was unpredictable and according to the MPI, progression occurred at a relatively low rate (6) proliferation and dilatation of sinusoids accompanying intravascular hematopoiesis and collagen type IV deposits were predominant features in later (fibro-osteosclerotic) stages in the course of disease (7) transmural migration of megakaryocytes demonstrated by three dimensional reconstruction revealed a mole-like tunneling through the thickened sinusoidal wall. A very careful assessment of the numerous correlations between bone marrow features and laboratory data will allow clinicians and pathologists to gain a better insight into the mutual relationships between hematological and morphological findings in CMPDs.

Classification and staging of Ph-negative myeloproliferative disorders by histopathology from bone marrow biopsies

The present study illustrates characteristic features of histopathology in the 3 non-leukemic, Ph-negative groups of chronic myeloproliferative diseases (CMPD). Attention is paid to the final outcome of CMPD, especially its transformation into acute leukemias and the occurrence of myelofibrosis from bone marrow biopsies (BMB) in a total of 1,716 CMPD patients. Essential thrombocythemia (ET), polycythemia vera (P. vera), and chronic megakaryocytic granulocytic myelosis (CMGM) can readily be distinguished by histopathology from BMB in the great majority of patients without regarding laboratory data, leaving a compartment of about 12% unclassifiable cases. Histologic patterns of staging are the increase in number and pleomorphism of megakaryocytes (MK), increase in number and density of reticulin fibers and collagen fibrosis, and excess of blasts. These 3 criteria are each graded from 0 to 3 in every biopsy. From these, a staging results by means of the histology of BMB in each of the Ph-negative CMPD. This staging provides a classification by defined criteria which permits comparative studies, the possibility of monitoring the individual patients by follow-up histology, and offers a baseline for reliable evaluation of results from therapy protocols.

Acute myelofibrosis terminating in acute lymphoblastic leukemia: case report and review of the literature

Acute myelofibrosis (AMF), as defined by an acute panmyelopathy associated with marked megakaryocytic hyperplasia and marrow fibrosis, appears to be a stem cell disorder. Even though it is most difficult to distinguish from various myeloproliferative and myelodysplastic disorders as well as acute myelogenous leukemia, it has rarely been reported to terminate as acute lymphoblastic leukemia (ALL). Only five cases have been reported in the literature; two from the pediatric literature and only three from the adult literature. Of the three adult cases, two were defined by light microscopy alone. Among the cases with follow-up (3/5), all died within 2 weeks to 2 months of diagnosis. We report an additional case in an adult; the ALL was defined by morphology, flow cytometric immunophenotyping, and cytogenetic analysis. The interval from diagnosis of AMF to ALL was 3 months. Our patient was treated with standard therapy for ALL, was in complete remission at last follow-up (3 months off maintenance therapy), and represents the only reported case who attained a complete remission. There are too few cases to determine the prognostic significance of termination of AMF in an acute leukemia of lymphoid origin vs. myeloid origin.

Trisomy 14, deletion 20q and t(3;3) (q21;q26) in a case of myelodysplastic syndrome with myelofibrosis

We describe a patient with trilineage myelodysplasia and hyperplastic megakaryopoiesis associated with significant myelofibrosis at diagnosis, who developed acute myeloid leukaemia two months afterwards. The clinical and pathological features were consistent with a myelodysplasia/myelofibrosis syndrome with leukemic transformation. Cytogenetic investigation showed trisomy 14, del(20q) and t(3;3) (q21;q26). These findings are of possible significance in the understanding of the association between myelodysplasia and myelofibrosis.

Hematopoietic precursor cells within the yolk sac tumor component are the source of secondary hematopoietic malignancies in patients with mediastinal germ cell tumors

BACKGROUND

Patients with mediastinal germ cell tumors (MGCT) have a high incidence of hematologic malignancies unrelated to cytotoxic chemotherapy. It has been suggested that these leukemic conditions originate from a MGCT progenitor cell capable of undergoing non-germ cell (hematopoietic) differentiation.

METHODS

To assess this hypothesis, histologic material from six patients with MGCTs associated with leukemia was examined using monoclonal and polyclonal antibodies capable of labeling cells of the different marrow cell lineages.

RESULTS

Morphologically identifiable hematologic cells were found within the yolk sac tumor component of the MGCT in four of these patients. In three of the four cases, the cells consisted of poorly differentiated blast cells, whereas in the fourth, clusters of erythroblasts were identified. The leukemic cells within the MGCT and in the bone marrow had similar morphology, constant expression of the early progenitor cell marker CD34, and variable expression of more mature myeloid, monocytic, erythroid, and megakaryocytic markers. Three cases expressed p53, a nuclear protein associated with neoplastic transformation in a wide range of malignancies, including testicular cancers, but which rarely is reported in leukemias. Karyotype of the leukemia was assessed in five cases: two showed an i(12p), a cytogenetic marker of GCT not identified in the usual cases of leukemia.

CONCLUSIONS

The results support the hypothesis that these leukemic conditions originate in the MGCT through a mechanism of differentiation from a yolk sac tumor-derived progenitor cell, with subsequent homing to the marrow.

Review of the cytogenetic changes in acute megakaryoblastic leukemia: one disease or several?

The karyotypes of 116 cases of acute megakaryoblastic leukemia (AMKL) were reviewed, including 43 pediatric patients with Down syndrome (DS) and 73 non-DS patients. DS patients with AMKL often had a history of transient leukemia or myelodysplasia with an early age of onset of AMKL (median 23 months). In these patients, the frequency of additional cytogenetic change (numerical or structural) was low, with 10 of the 43 DS patients showing no additional cytogenetic change. A second group of patients had t(1;22)(p13;q13) or other cytogenetic abnormality involving 22q13. These patients had no history of transient leukemia but showed very early onset of AMKL. In this group of patients, marked organomegaly was noted; these patients also showed few specific additional cytogenetic changes. The remaining AMKL patients had a median age of 30 years with much more frequent cytogenetic changes, including rearrangement of 3q21 and 3q26-27, trisomy 21, and other specific changes. Based on the karyotype and clinical data, we hypothesize that AMKL may represent at least three separate disease entities with different genetic alterations giving rise to similar, but not identical, disorders. Subclassification of AMKL on the basis of the cytogenetic changes in the leukemic cells appears to be justified.

Bone marrow histology. 3: Value of bone marrow core biopsy in acute leukaemia, myelodysplastic syndromes, and chronic myeloid leukaemia

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Idiopathic myelofibrosis: a clinical study of 80 patients

A series of 122 consecutive patients with bone marrow fibrosis initially referred or categorized as idiopathic myelofibrosis is described. After a clinical and pathological review 14 patients were classified as postpolycythaemic myelofibrosis and 7 patients as a transitional myeloproliferative disorder. In 13 patients a diagnosis of hairy cell leukaemia was made, 3 patients had malignant lymphoma, 2 had malignant histiocytosis, and 1 patient had systemic lupus erythematosus with myelofibrosis. Two patients were excluded for further analysis owing to insufficient data. In the remaining 80 patients a diagnosis of idiopathic myelofibrosis was made. The clinical and laboratory findings in this series of patients are presented and compared to those in previous series. Infectious, cardiovascular, thromboembolic, and haemorrhagic complications were frequent, being recorded in 63%, 50%, 40%, and 33% of the patients, respectively. Various autoimmune phenomena were found in a proportion of the patients, but none had clinical evidence of connective tissue disease. Fifteen patients (19%) had a syndrome of acute myelofibrosis. The diagnostic criteria for this disease entity and its place within the spectrum of myeloproliferative disorders are discussed. In the present series acute myelofibrosis was found to encompass various transitional stages toward the evolution of acute leukaemia. It is proposed that acute or malignant myelofibrosis is considered as an acute variant of idiopathic myelofibrosis. Within this syndrome the acute variant seems to be far more common than previously recognized, which may also explain the marked clinical heterogeneity of the myelofibrosis/osteomyelosclerosis syndrome in this and most previous series.

Aggressive polychemotherapy for acute myelofibrosis

Acute myelofibrosis is a rare and still ill-defined disease. Based on morphological observation, immunophenotyping and ultrastructural analysis, we support the assumption that acute myelofibrosis is a malignant disorder mainly of the megakaryocytic lineage and is closely related to acute megakaryocytic/blastic leukaemia. Consequently, the 11 patients reported here were treated with aggressive polychemotherapy with combinations including daunorubicin and cytosine arabinoside and 6-thioguanin or VP16-213. 4 complete remissions, 2 partial remissions and 1 minor response were observed. Duration of aplasia was not significantly prolonged. These findings indicate that the use of aggressive polychemotherapy is feasible in acute myelofibrosis and results in a significant number of remissions.

Acute myelofibrosis: response to recombinant human interferon alpha-2a

Acute myelofibrosis is a rare myeloproliferative syndrome characterized by bone marrow proliferation of atypical megakaryocytes, poor response to conventional leukemic therapy, and a fulminant clinical course. Because alpha interferon exhibits potent antiproliferative effects against megakaryocyte progenitors and human fibroblast cell lines, we treated two patients with acute myelofibrosis or the related syndrome of acute myelodysplasia with myelofibrosis with recombinant human interferon alpha-2a. Patient 1 received a 12-week course of interferon alpha (1-6 x 10(6) IU/d) after failure of two cytarabine-based chemotherapy regimens. Interferon administration resulted in prompt improvement in symptoms, stabilization of leukocyte count, and a reduction in circulating blast forms. Primary treatment with interferon (1-3 x 10(6) IU/d x 4 weeks) in patient 2 produced complete hematologic recovery with restoration of marrow cellularity and reduced marrow fibrosis. Our findings suggest that interferon alpha may have significant activity in the treatment of patients with acute myelofibrosis.

Acute megakaryoblastic leukemia: a case report

We present a case of acute megakaryoblastic leukemia identified by electron microscopy and platelet-specific antibodies. The histological examination of bone marrow showed distinct myelofibrosis. In accordance with recent communications, low-dose cytosine arabinoside treatment (20 mg twice daily s.c. over 21 days) was initiated. The subsequent bone marrow examination showed a severe hypoplasia with persistent blasts. Amsacrine and VP-16 were given without success. Finally the patient died of septicemia without proof of pathogen uninfluenced by antibiotic and antiseptic therapy 6 weeks after diagnosis. Our case report confirms the poor prognosis of acute megakaryoblastic leukemia.

Translocation t(6;9) occurring in acute myelofibrosis, myelodysplastic syndrome, and acute nonlymphocytic leukemia suggests multipotent stem cell involvement

The cytological and cytogenetic features of six patients with myeloid neoplasia and t(6;9)(p23;q34) including a case of acute myelofibrosis (AMF), a refractory anemia with excess of blasts (RAEB), and four cases of acute nonlymphocytic leukemia (ANLL) are described. Two patients in this series, both affected by ANLL type M2, presented an increase of bone marrow basophils, suggesting that this cytological-cytogenetic association is not absolute and that it may be more frequently observed in ANLL with maturation. All patients with de novo ANLL showed associated myelodysplastic features, and one patient presented a dysmyelopoietic syndrome, later evolving into ANLL. The presence of the t(6;9) in a range of myeloid neoplasias, with either concurrent myelodysplastic features or a preleukemic phase in cases of ANLL, provide evidence that this chromosome aberration may always involve a multipotent myeloid stem cell. Data on toxic exposure of the patients suggests that myeloproliferative disorders with the t(6;9) may frequently represent environmentally induced neoplasias.

Use of monoclonal anti-actin as a megakaryocyte marker in paraffin wax embedded bone marrow biopsy specimens

Monoclonal anti-actin was used as a marker of megakaryocytes in Zenker's fixed, paraffin wax embedded bone marrow tissue, using an immunoperoxidase staining method. Twenty bone marrow samples were studied, including controls, and different myeloproliferative and myelodysplastic syndromes. The results were compared with those obtained using factor VIII related antigen (F VIII RAg) immunolabelling. Anti-actin is as good a marker for megakaryocytes as anti-FVIIIRAg and is potentially clinically useful when morphological identification is difficult, when bone marrow aspiration is unsuccessful, or when quantitative evaluation of tissue sections is required.