Planimetric analysis of megakaryocytes in the four main groups of chronic myeloproliferative disorders

A critical reappraisal of the WHO classification of the chronic myeloproliferative disorders

Following the introduction of the WHO classification of chronic myeloproliferative disorders (MPDs), after approximately 5 years, a critical reappraisal appears to be warranted. Retrospective clinico-pathological evaluations conducted in the meantime, as well as the detection of new biomarkers, may aid in testing the validity of these new criteria. Based on a large series of patients with chronic myeloid leukemia (CML), an analysis of bone marrow (BM) features and risk classifications revealed that the fiber content exerted a most important and independent impact on prognosis. This finding was also supported in a prospective randomized study and therefore myelofibrosis should be included in any staging system in CML related to survival. Moreover, it is important to emphasize the dynamics of the disease process in MPDs, especially in polycythemia vera (PV) and chronic idiopathic myelofibrosis (CIMF). Latent-stage PV is difficult to recognize when adhering to the proposed limits for hemoglobin (or red cell mass) without regarding the erythropoietin (EPO) level, endogenous erythroid colonies (EECs) or BM histopathology. Initial PV may firstly present with complications and, when accompanied by a high platelet count, mimics essential thrombocythemia (ET). Consequently, BM morphology and EPO level should be entered as major diagnostic criteria for PV. To document more accurately the progress of disease, a simplified scoring system concerning myelofibrosis has to be included in the histological description of CIMF. The diagnostic guidelines of BM features in ET should be improved because, usually, there is neither a significant proliferation nor left-shifting of the granulo- and erythropoiesis detectable and no relevant increase in reticulin. A comparison of clinical data and BM morphology reveals that biomarkers (EPO, EECs, PRV-1, JAK2) show an overlapping pattern of positivity between the different subtypes of MPDs.

Megakaryocyte features and bcr/abl translocation in chronic myeloid leukemia following imatinib mesylate (STI571) therapy--a fluorescence in-situ hybridization study

Following therapy with imatinib (STI571) hematologic and cytogenetic response in chronic myeloid leukemia (CML) is associated with conspicuous alterations of bone marrow (BM) morphology. Besides reduction of cellularity and fibrosis, small megakaryocytes characteristic for this disorder were replaced by large, normally appearing cells of this lineage. However, it is not known whether and to which extent these changes are accompanied by a loss of the bcr/abl translocation. Therefore an immunohistochemical (CD61) and fluorescence in-situ hybridization (FISH) study was performed on sequential BM biopsies in 5 patients with CML receiving STI571 without any pretreatment. Morphometric analysis revealed that the prevalent population of 47% micromegakaryocytes (size < or = 150 microm2) was significantly reduced (15%) during therapy and that a conspicuous shift to medium-sized and large megakaryocytes occurred. According to FISH analysis in the initial BM biopsy sections 71% of all myeloid cells exhibited the bcr/abl gene and concerning megakaryopoiesis about 65% of the prominent micromegakaryocytes displayed positive signals. After treatment this peculiar cell population decreased significantly while the emerging large megakaryocytes (52%) totally lacked a bcr/abl labeling. Because cytogenetic response and reduction of micromegakaryocytes seem to be linked, this feature may be useful to monitor therapeutic efficacy by evaluating BM morphology.

Regression der Philadelphia-Chromosom (bcr/abl)-positiven Myelo- und Megakaryopoiese unter Imatinib(STI571)-Therapie bei chronischer myeloischer Leuk�mie (CML)

In chronic myeloid leukemia following therapy with Imatinib (STI571) hematologic and cytogenetic response is associated with conspicuous changes of bone marrow morphology. However, it is not known to which extent these alterations are accompanied by a loss of the bcr/abl translocation. To study regression of the leukemic cell population we recruited 14 patients lacking pretreatment. Therapy resulted in a reduction of CD61(+) megakaryopoiesis. Dwarf megakaryocytes characteristic for this disorder were replaced by large, normally appearing cells of this lineage. Morphometric analysis confirmed the significant decrease in the number of micromegakaryocytes and yielded planimetric parameters in keeping with normalization. Moreover, a fluorescence in-situ hybridization study in five patients of this cohort revealed that before therapy 70% of all myeloid cells exhibited the bcr/abl gene. Regarding megakaryopoiesis about 65% of the micromegakaryocytes displayed positive signals. Following treatment these bcr/abl(+) cell populations decreased significantly while the emerging large megakaryocytes lacked a proper labeling. Because cytogenetic response and reduction of atypical micromegakaryocytes are linked, this feature may be useful to monitor therapeutic efficacy.

Polycythemia rubra vera versus secondary polycythemias. A clinicopathological evaluation of distinctive features in 199 patients

To determine parameters of distinctive value in polycythemia rubra vera (PV) versus secondary polycythemias (SP), a clinicopathological study was performed on 199 patients. These presented with a borderline to marked elevation of the hemoglobin level (> 18 g/dl in men and > 16 g/dl in women). Evaluations of clinical features and bone marrow histopathology were carried out independently. According to the results derived from laboratory data and representative pretreatment trephine biopsies, three groups of patients emerged: group I presenting with the concordant clinical and morphological findings of early to manifest PV (136 patients), group II consisting of 55 patients with the congruent signs and symptoms of SP mostly caused by various chronic bronchopulmonal disorders, and finally eight patients (group III) with divergent findings. Between group I and II patients (PV versus SP), a number of clinical parameters proved to be significantly different. With the exception, of the red cell mass, platelet count, leukocyte alkaline phosphatase, LDH, spleen size, and the erythropoietin level had a significantly discriminating impact. Morphological features of distinctive value consisted of a set of specific lesions. Contrasting SP with an only borderline to slight increase in cellularity associated with a moderate enlargement of the erythroblastic islets, PV was always characterized by a significant increase in hematopoiesis, revealing a trilinear proliferation (panmyelosis). Megakaryopoiesis was strikingly different in PV as compared to SP by displaying clustering and a pleomorphous appearance. i.e., very small and giant megakaryocytes with staghorn-like nuclei were neighboring each other. Moreover, conspicuous alterations of the interstitial compartment were recognizable in SP. These consisted of deposits of cell debris in histiocytic reticular cells, iron-laden macrophages, and a plasmacytosis, implying an inflammatory reaction. These changes were only very rarely observed in PV, as opposed to a minimal to slight increase in reticulin fibers in about 12% of patients. In conclusion, a more elaborate evaluation of bone marrow features resulted in a set of diagnostic criteria with discriminating capacity that should be considered in prospective clinical trials.

Bone marrow features and clinical findings in chronic myeloid leukemia--a comparative, multicenter, immunohistological and morphometric study on 614 patients

A multicenter, immunohistochemical and morphometric study was performed on diagnostic pretreatment bone marrow biopsies in 614 adult patients with Ph1+ chronic myeloid leukemia (CML) to compare histological features with clinical findings. For identification of megakaryopoiesis we used the monoclonal antibody CD61 and additionally the PAS reaction to determine the subfraction of atypical micromegakaryocytes and precursors. Labelling of erythroid precursors was carried out by a monoclonal antibody directed against glycophorin C. In order to selectively stain macrophages and their activated subset we applied CD68 and the GSA-I lectin. Density of argyrophilic fibers (reticulin plus collagen) was measured following Gomori's silver impregnation method. In accordance with laboratory data morphological variables revealed a comparable amount of congruence in the various groups of CML patients derived from different sources. In about 26% of patients early (reticulin) to advanced (collagen) fibrosis was detectable. Significant correlations were calculated between the extent of myelofibrosis with splenomegaly, anemia and increasing numbers of erythroblasts and myeloblasts in the peripheral blood count. These features were assumed to indicate more advanced stages of the disease process with ensuing transition into myeloid metaplasia and consequently were associated with an unfavorable prognosis. Significant relationships were revealed between the number of CD61+ megakaryocytes and more important, also their precursor fraction with the degree of fibrosis. This result extends previous experimental findings regarding the impact of immature elements of this cell lineage for the generation of myelofibrosis. The significant association of erythroid precursors with the number of mature (resident) macrophages including their activated GSA-I subset may shed some light on their functional involvement in iron turnover and hemoglobin synthesis. A modified histological classification of predominant bone marrow features is introduced. This simplified synthesis staging system (Cologne Classification) is not only associated with certain sets of laboratory data, but also with different survival patterns.

Molecular detection of c-mpl thrombopoietin receptor gene expression in chronic myeloproliferative disorders

BACKGROUND

Chronic myeloproliferative disorders (CMPD) originate from a pluripotent haematopoietic progenitor cell but show a marked degree of heterogeneity, especially between Philadelphia chromosome positive and negative disease entities. Abnormal megakaryopoiesis is a frequent finding in CMPD, often associated with thrombocythaemic cell counts. Recent experimental data have suggested that the c-Mpl thrombopoietin receptor, together with its ligand thrombopoietin, are not only the major physiological regulators of megakaryopoiesis and platelet production, but also play a crucial role in chronic myeloproliferation.

METHODS

A total of 18 peripheral blood mononuclear cell samples obtained from patients with CMPD (chronic myelocytic leukaemia (CML), n = 10; polycythaemia vera (PV), n = 6; and primary thrombocythaemia (PTH), n = 2) were analysed for c-mpl mRNA using the reverse transcriptase polymerase chain reaction (RTPCR). In another 20 patients (CML, n = 10; chronic megakaryocytic granulocytic myelosis (CMGM), n = 3; PV, n = 3; PTH, n = 4), we compared the number of haematopoietic progenitors expressing c-Mpl, as characterised by coexpression with the CD34 antigen, in the bone marrow using double immunofluorescence staining.

RESULTS

c-mpl mRNA was detected in all samples from patients with CML analysed, whereas only two of six PV and one of two PTH samples were positive (p < or = 0.008; chi 2 test). Expression of the c-mpl receptor gene was absent in healthy subjects used as controls. Similarly, an increase of c-Mpl expressing CD34 positive haematopoietic cells was detected in seven of 10 bone marrow aspirates obtained from patients with CML. Increased numbers of c-Mpl positive CD34 positive cells were found in only one of four patients with PTH, whereas in PV and CMGM the numbers of c-Mpl positive CD34 positive cells did not exceed normal values, despite thrombocythaemic cell counts.

CONCLUSIONS

These data confirm recent findings showing an impaired expression of the c-mpl thrombopoietin receptor gene in Philadelphia chromosome negative CMPD when compared with patients with Philadelphia chromosome positive CML. The relevance of this observation to the functional and morphological characteristics of abnormal megakaryopoiesis remains unclear. Thrombocythaemic cell counts and a mature phenotype in megakaryocytes occur frequently in Philadelphia chromosome negative CMPD but require an intact c-Mpl receptor under physiological conditions. Therefore, further studies are warranted to elucidate the mechanisms contributing to megakaryopoiesis in CMPD disease entities with decreased c-mpl gene expression.

Clinicopathological diagnosis and differential criteria of thrombocythemias in various myeloproliferative disorders by histopathology, histochemistry and immunostaining from bone marrow biopsies

Differentiation of essential thrombocythemia (ET) from thrombocythemias occurring in various subtypes of chronic myeloproliferative disorders (MPDs) is controversial, because of the lack of uniform clinical and morphological criteria. A retrospective clinicopathologic study was performed on 375 patients presenting with a MPD and a platelet count exceeding 500 x 10(9/)l. For comparison 35 patients with reactive thrombocytosis (RT) and five patients with a myelodysplastic syndrome (MDS-5q(-) syndrome) were enrolled into this study. In addition to a complete clinicopathological work-up, procedures included histochemical and immunological staining techniques and morphometry of bone marrow biopsies for proper evaluation of megakaryocytes (CD61) and erythroid precursors (Ret40f). Because of the high patient's age on admission, relative survival rates with corresponding disease-specific loss of life expectancy were calculated. Analysis of clinical and morphological characteristics, in particular megakaryopoiesis revealed features which enabled a clear-cut distinction between thrombocythemias in MPDs and thrombocythemic states in MDS. This rationale proved to be most important for the diagnostic discrimination of the 33 patients with initial (prefibrotic) stages of idiopathic myelofibrosis (IMF) from ET (40 patients). A new set of relevant criteria for the diagnosis of IMF with special regard to early stages and its distinction from ET has been proposed. Hemorrhagic episodes were more frequently observed in ET than in thrombocythemias associated with polycythemia vera (PV). Computation of specific loss of life expectancy revealed two extremes: thrombocythemia in CML (81%) and ET (3%), whereas thrombocythemias in PV and IMF did not show a significantly different life loss (19-22%). The revised criteria for ET, PV and IMF are reliable by taking histopathological features from bone marrow biopsies into consideration, particularly for the diagnosis of ET and its differentiation from thrombocythemias as a presenting symptom accompanying the various subtypes of MPDs.

The histopathology of chronic myeloproliferative diseases

This chapter discusses the histopathology of five groups of chronic myeloproliferative diseases: chronic myeloid leukaemia, polycythaemia vera, essential thrombocythaemia, chronic idiopathic myelofibrosis and unclassifiable myeloproliferation. Histological staging of the four haematologically defined diseases is performed by grading the three most prominent variables: megakaryocytes, fibres and blasts. Histological outcome is correlated to the staging of diagnostic bone marrow biopsies; megakaryocytic involvement is correlated with the risk of myelofibrosis. An excess of blasts is related to the risk of leukaemic transformation. The progression of myelofibrosis depends on the grade of fibre increase at diagnosis. These three statements are highly significant and valid for all types of chronic myeloproliferative disorders. The results of cytogenetics are discussed in relation to the histological classification for these patient groups. Changes in bone marrow histology following myelosuppressive therapy is presented. Prospective studies under standardized protocol therapy are recommended, so that the long-term effects of therapy can be assessed.

Inverse immunostaining pattern for synthesized versus endocytosed alpha-granule proteins in human bone marrow megakaryocytes

The time of appearance and pattern of expression of several alpha-granule proteins, von Willebrand factor (VWF), fibrinogen and immunoglobulins (Ig) were examined and compared in human bone marrow megakaryocytes (MK) using an immunocytochemical approach. VWF is synthesized by immature MK, whereas it has been shown that fibrinogen is incorporated from the plasma into alpha-granules. The present study was undertaken in order to determine whether there are chronological and morphological differences in the expression of VWF and fibrinogen in vivo in human MK. Seven paraffin-embedded biopsies of normal human bone marrow were labelled with specific antibodies for VWF and for fibrinogen, detected by the alkaline phosphatase anti-alkaline phosphatase (APAAP) method. and analysed by immunomorphometry. We found a clear, statistically significant. difference in the labelling pattern of VWF and fibrinogen. The expression of other endocytosed alpha-granule proteins, immunoglobulins G and A, was therefore studied in bone marrow MK from two patients with multiple myeloma, one with monoclonal IgG and one with monoclonal IgA. The immunostaining pattern was similar to that of fibrinogen and different from VWF, and characteristic of endocytosed alpha-granule proteins. This study demonstrates that: (i) immunohistochemical staining of MK alpha-granules proteins distinguishes the peripheral cockade distribution pattern of endocytosed protein from the perinuclear pattern of endogenously synthesized proteins; (ii) VWF is present in human bone marrow MK when fibrinogen is not yet detectable: (iii) VWF synthesis ceases while fibrinogen is still being incorporated: (iv) immunoglobulins can be detected in MK cytoplasm, with a staining pattern resembling that of fibrinogen.

A histomorphometric study of haematological disorders with respect to marrow fibrosis and osteosclerosis

A retrospective investigation of 75 EDTA-decalcified Jamshidi biopsies collected over a 2-year period at Aarhus University Hospital was performed. The biopsies originated from 75 patients suffering from idiopathic myelofibrosis, other chronic myeloproliferative disorders, or other conditions with known associations with bone marrow fibrosis. The relative volumes of trabecular and woven bone, as well as haematopoietic and non-haematopoietic tissue, were estimated histomorphometrically. The degree of fibrosis was estimated semiquantitatively. Finally, the thickness of trabecular osteons was estimated from the number of lamellae by counting. Patients with idiopathic myelofibrosis had statistically significantly more bone tissue than the other groups of patients. The osteosclerosis was primarily due to woven bone. Larger cancellous osteons also suggested a positive balance in bone remodelling. The amount of bone tissue showed furthermore a statistically significant increase through the groups of polycythaemia vera, essential thrombocythaemia, chronic myelogenous leukaemia and idiopathic myelofibrosis. Parallel to the increase in the amount of bone, an increase in the degree of marrow fibrosis was detected. The positive correlation between the amount of bone and the degree of marrow fibrosis was statistically highly significant (p=0.0008).

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.

Diagnostic and differential criteria of essential thrombocythemia and reactive thrombocytosis

Among the chronic myeloproliferative disorders essential thrombocythemia (ET) is known to be a distinct clinical entity in which an excessive number of morphologically and functionally abnormal platelets are produced. The clonal nature of the disease is well established. Based on a review of the literature the present authors propose the following novel criteria for the diagnosis of ET: A1. Platelet count in excess of 600 x 10(9)/L. A2. No increase in red-cell mass (RCM) in the presence of stainable iron in the bone marrow or failure of iron trial (RCM < 36 mL/kg in males and < 32 mL/kg in females; or RCM < 25% above mean normal predicted value*). A3. No Philadelphia chromosome. A4. Megakaryocytic hyperplasia (= increased megakaryocyte number and size) in histological sections of bone marrow and/or increased megakaryocytic ploidy (two-color flow cytometry); no collagen fibrosis. B1. Splenomegaly on isotopic scan or echogram. B2. Unstimulated growth of BFU-E and/or CFU-Meg present. B3. Normal ESR/fibrinogen. The diagnosis of ET is considered to be established if A1 + A2 + A3 + A4 or A1 + A2 + A3 + two B-criteria are fulfilled. (* Br J Haematol 1995; 89:748-756.)

Evidence from molecular genetic and cytogenetic analyses that bone marrow histopathology is reliable in the diagnosis of chronic myeloproliferative disorders

The reliability of histopathological diagnosis in bone marrow specimens from patients with chronic myeloproliferative disorders (CMPD) was evaluated by correlating the histological findings with molecular genetic and cytogenetic analyses of the Ph1-translocation. A rearrangement of m-bcr was detected only in patients (28/30) diagnosed histologically as chronic myeloid leukemia (CML). This finding was supported by the presence of a Ph1-chromosome in 24/26 patients with CML examined. All the patients with other types of CMPD, including polycythemia vera (PV), primary thrombocythemia (PTH) and chronic megakaryocytic-granulocytic myelosis (CMGM), as well as those with unclassifiable CMPD (CMPD.UC) were Ph1-negative (n = 38). The histopathological discrimination of CML from Ph1-negative varieties of CMPD was also reliable for patients with myelofibrosis complicating CML, CMGM and CMPD.UC. The results demonstrate that bone marrow histopathology allows a reliable diagnosis of CML. This is in contrast with hematological data such as high platelet counts which show considerable overlapping in the various forms of CMPD.

The impact of megakaryocyte proliferation of the evolution of myelofibrosis. Histological follow-up study in 186 patients with chronic myeloid leukaemia

A histological study on sequential bone marrow biopsies in patients with chronic myeloid leukaemia (CML) was performed. We wished to answer the question as to whether a different content of megakaryopoiesis in the bone marrow of CML patients has a prognostic significance for the development of myelofibrosis during the course of disease. In addition, the significance of possible changes in the quantity of megakaryopoiesis in this process was assessed. In 186 patients who had no fibre increase at first diagnosis, the rate of subsequent myelofibrosis varied from 19% for the common or granulocytic subtype (CML.CT) to 40% for patients with features of megakaryocytic increase (CML.MI). No significant differences were found either in the rapidity of progression to fibrosis or in the final rate of osteomyelosclerosis. Whereas in CML.MI most patients (75%) showed an increase of fibres only, this was accompanied by an additional increase of megakaryocytes in CML.CT, changing the histological pattern from CML.CT to .MI or .MP, respectively. The data therefore revealed a correlation between fibre increase and subtyping of CML as suggested by the Hannover classification of chronic myeloproliferative diseases. Subtypes of CML with megakaryocytic increase could be shown to present a "pre-myelofibrotic" stage of disease and may therefore be conceived as a particular pathway of acceleration.