Idiopathic myelofibrosis: pathogenesis, natural history and management

Gelatinous bone marrow transformation in a case of idiopathic myelofibrosis: a morphological paradox

A 74-year-old woman with severe, but asymptomatic weight loss was found to have splenomegaly, thrombocytosis, and neutrocytosis. A trephine biopsy showed a hypercellular bone marrow with a proliferation of abnormal megakaryocytes, mild reticulin fibrosis, and osteosclerosis, i.e., features of an early stage of idiopathic myelofibrosis. In contrast to this predominant pattern, the marrow also contained a distinct hypocellular focus of gelatinous transformation (GMT) in which hematopoietic and fat cells were replaced by gelatinous substances that were characterized as hyaluronic acid mucopolysaccharides histochemically. GMT is a rare disorder of unknown pathogenesis, and is an unspecific indicator of severe illness which most often occurs in patients with a background of weight loss. This is the first reported case of gelatinous changes in an otherwise fibrotic bone marrow, a constellation which a priori seemed to be incompatible.

Prognostic factors and current practice in treatment of myelofibrosis with myeloid metaplasia: an update anno 2000

Median survival of patients with myelofibrosis with myeloid metaplasia (MMM) ranges from 3.5 to 5 years, but there is a wide variability. The degree of anemia (Hb < 10 g/dL) is the most important prognostic factor, followed by constitutional symptoms and abnormal karyotype. In recent years, different prognostic scoring systems for MMM have been proposed. In some of them three prognostic groups (low, intermediate, and high risk) are recognized, while others recognize a high and a low-risk group only. Median survival of the low-risk group ranges from seven to nine years, while the minority of high-risk patients survive for a median of less than two years. Younger patients with MMM survive longer (median survival above ten years). Among the latter patients, based on Hb value, constitutional symptoms, and blood blast-cell percentage, two prognostic groups can also be identified, with median survival of less than three years and almost 15 years, respectively. Conventional treatment of MMM is mostly palliative and based on cytolytic treatment (usually hydroxyurea), androgen therapy and splenectomy in selected patients. Allogeneic hemopoietic transplant is a therapeutic possibility with the potential for cure in younger patients with bad prognostic features. The role in MMM of newer treatment strategies such as autologous transplantation or the administration of anti-angiogenic drugs such as thalidomide is currently being evaluated.

Evaluation and clinical correlations of bone marrow angiogenesis in myelofibrosis with myeloid metaplasia

Recent observations have underscored the biologic relevance of intratumoral angiogenesis and its potential impact on prognosis. Increased bone marrow angiogenesis has been demonstrated in a variety of hematologic disorders, including multiple myeloma. The extent and prognostic significance of bone marrow angiogenesis in 114 patients with myelofibrosis with myeloid metaplasia (MMM) was investigated. A control group of 44 patients without bone marrow disease, 15 patients with polycythemia vera, and 17 patients with essential thrombocythemia was also studied. Bone marrow microvessel density was assessed by a semiquantitative method, visual microvessel grading, and 2 separate quantitative methods, visual count and computerized image analysis. Angiogenesis estimation by all 3 methods was highly comparable. On visual microvessel grading, a grade 3 or 4 increase in bone marrow angiogenesis was demonstrated in 70% of patients with MMM, 33% of patients with polycythemia vera, 12% of patients with essential thrombocythemia, and 0% of normal controls. In a multivariate analysis, increased angiogenesis in MMM correlated significantly with increased spleen size and was found to be a significant and independent risk factor for overall survival. Increases in marrow angiogenesis correlated with hypercellularity and megakaryocyte clumping. In contrast, these 2 features were inversely proportional to reticulin fibrosis, whereas increases in marrow angiogenesis were independent of reticulin fibrosis. These preliminary findings suggest that neo-angiogenesis is an integral component of the bone marrow stromal reaction in MMM and may provide useful prognostic information and a rationale for the therapeutic investigation of anti-angiogenic agents.

Evaluation and clinical correlations of bone marrow angiogenesis in myelofibrosis with myeloid metaplasia

Recent observations have underscored the biologic relevance of intratumoral angiogenesis and its potential impact on prognosis. Increased bone marrow angiogenesis has been demonstrated in a variety of hematologic disorders, including multiple myeloma. The extent and prognostic significance of bone marrow angiogenesis in 114 patients with myelofibrosis with myeloid metaplasia (MMM) was investigated. A control group of 44 patients without bone marrow disease, 15 patients with polycythemia vera, and 17 patients with essential thrombocythemia was also studied. Bone marrow microvessel density was assessed by a semiquantitative method, visual microvessel grading, and 2 separate quantitative methods, visual count and computerized image analysis. Angiogenesis estimation by all 3 methods was highly comparable. On visual microvessel grading, a grade 3 or 4 increase in bone marrow angiogenesis was demonstrated in 70% of patients with MMM, 33% of patients with polycythemia vera, 12% of patients with essential thrombocythemia, and 0% of normal controls. In a multivariate analysis, increased angiogenesis in MMM correlated significantly with increased spleen size and was found to be a significant and independent risk factor for overall survival. Increases in marrow angiogenesis correlated with hypercellularity and megakaryocyte clumping. In contrast, these 2 features were inversely proportional to reticulin fibrosis, whereas increases in marrow angiogenesis were independent of reticulin fibrosis. These preliminary findings suggest that neo-angiogenesis is an integral component of the bone marrow stromal reaction in MMM and may provide useful prognostic information and a rationale for the therapeutic investigation of anti-angiogenic agents.

Interferon-alpha and the pathogenesis of myeloproliferative disorders

Interferon-alpha (IFN-alpha), a molecule with multiple biological actions, is widely used in the treatment of chronic myelogenous leukemia (CML) and the other myeloproliferative disorders. This glycoprotein belonging to the type I subfamily of interferons has been recombinantly manufactured and has been approved for the biotherapy of CML, now becoming the first line of treatment for CML patients in chronic phase who are not candidates for allogeneic hematopoietic stem cell or bone marrowtransplantation. Interferon-alpha action involves binding to its cell membrane receptor and initiation of an intracellular signal transduction cascade. Two major pathways mediate the biologic actions of IFN-alpha. The JAK-STAT pathway leads to phosphorylation and activation of STAT 1 and STAT 2 molecules and transcription of genes like p21 and caspase-1 resulting in cycle arrest and apoptosis. The PKR (protein kinase dsRNA-induced) kinase phosphorylates and inhibits the eukaryotic initiator of translation eIF-2alpha leading again to apoptosis. The PKR kinase cascade also leads to activation of the transcription factor NF-kappaB. The relevance of this activation is unclearand it is possiblethat NF-kappaB has not had the opportunity to transcribe its target genes as it is a substrate of effector caspases and is maybe cleaved by them before exerting any transcription activity. Through the JAK-STAT and the PKR kinase pathways IFN-alpha is able to modify the proliferative and antiapoptotic actions of the constitutively activated kinase bcr-abl, the product of the t(9;22) translocation present in CML, and has therapeutic effects in this disease.

Splenectomy in chronic myeloid leukemia and myelofibrosis with myeloid metaplasia

Myelofibrosis with myeloid metaplasia (MMM) is a collective term that describes the related disorders AMM, PPMM, and PTMM. The chronic myeloid disorders include chronic myeloid leukemia, polycythemia vera, essential thrombocythemia, and agnogenic myeloid metaplasia (myelofibrosis). These disorders display varying propensities for pathologic enlargement of the spleen which can lead to mechanical discomfort, hypercatabolic symptoms, anemia, thrombocytopenia, and portal hypertension. Splenectomy has been found to be of little benefit in the early stages of chronic myeloid leukemia. Similarly, the benefit of splenectomy in advanced cases is limited to symptomatic palliation and treatment of delayed engraftment after allogeneic bone marrow transplantation. Although polycythemia vera and essential thrombocythemia are also characterized by splenomegaly, splenectomy is not considered a therapeutic option in the absence of transformation of the disease into myelofibrosis with myeloid metaplasia. Splenectomy has been studied most in myelofibrosis with myeloid metaplasia. Although there is no clear survival advantage to splenectomy in this disorder, the surgical procedure can result in substantial palliation of mechanical discomfort, hypercatabolic symptoms, portal hypertension, and anemia. However, the procedure is associated with an approximately 9% mortality rate, and the postsplenectomy occurrence of extreme thrombocytosis, hepatomegaly, and leukemic transformation is of major concern.

Pathologic interaction between megakaryocytes and polymorphonuclear leukocytes in myelofibrosis

Idiopathic myelofibrosis (MF) is a myeloproliferative syndrome characterized by an increase in bone marrow collagen. Megakaryocytes (Mks), which store growth factors in their α granules, are known to be involved in the pathogenesis of MF. Previously, mice given bone marrow grafts infected with a retrovirus carrying murine thrombopoietin (TPO) complementary DNA developed a disease resembling human idiopathic MF. In this study, we used this murine model (TPO mice) to determine whether release of α granules is responsible for fibroblast activation and development of fibrosis. The intracellular trafficking of several α-granule proteins (von Willebrand factor, fibrinogen, and transforming growth factor β (TGFβ), which are stored in the granule matrix; and αIIbβ3 integrin and P-selectin (CD62p), which are located in the α-granule membrane) was studied with immune electron microscopy in bone marrow Mks from TPO mice. P-selectin immunolabeling increased consistently and was occasionally found lining the demarcation membrane system. Evidence of extensive emperipolesis was also found in TPO mouse Mks, involving almost exclusively neutrophil and eosinophil polymorphonuclear (PMN) cells with altered morphologic features. In parallel, the host Mks had myeloperoxidase-positive granules scattered in their cytoplasm, associated with marked ultrastructural cytoplasmic alterations and ruptured α-granule membranes. Similar observations were made in bone marrow biopsy specimens from 12 patients with idiopathic MF; indeed, there was an increased rate of emperipolesis involving mostly PMN cells, abnormal P-selectin expression, and mutual subcellular PMN and Mk alterations. This study indicates that in idiopathic MF, abnormal P-selectin distribution in Mks induces selective sequestration of PMN cells. This results in a release of α-granular proteins and growth factors, which in turn induces fibroblast activation and fibrosis deposition.

Pathologic interaction between megakaryocytes and polymorphonuclear leukocytes in myelofibrosis

Idiopathic myelofibrosis (MF) is a myeloproliferative syndrome characterized by an increase in bone marrow collagen. Megakaryocytes (Mks), which store growth factors in their α granules, are known to be involved in the pathogenesis of MF. Previously, mice given bone marrow grafts infected with a retrovirus carrying murine thrombopoietin (TPO) complementary DNA developed a disease resembling human idiopathic MF. In this study, we used this murine model (TPO mice) to determine whether release of α granules is responsible for fibroblast activation and development of fibrosis. The intracellular trafficking of several α-granule proteins (von Willebrand factor, fibrinogen, and transforming growth factor β (TGFβ), which are stored in the granule matrix; and αIIbβ3 integrin and P-selectin (CD62p), which are located in the α-granule membrane) was studied with immune electron microscopy in bone marrow Mks from TPO mice. P-selectin immunolabeling increased consistently and was occasionally found lining the demarcation membrane system. Evidence of extensive emperipolesis was also found in TPO mouse Mks, involving almost exclusively neutrophil and eosinophil polymorphonuclear (PMN) cells with altered morphologic features. In parallel, the host Mks had myeloperoxidase-positive granules scattered in their cytoplasm, associated with marked ultrastructural cytoplasmic alterations and ruptured α-granule membranes. Similar observations were made in bone marrow biopsy specimens from 12 patients with idiopathic MF; indeed, there was an increased rate of emperipolesis involving mostly PMN cells, abnormal P-selectin expression, and mutual subcellular PMN and Mk alterations. This study indicates that in idiopathic MF, abnormal P-selectin distribution in Mks induces selective sequestration of PMN cells. This results in a release of α-granular proteins and growth factors, which in turn induces fibroblast activation and fibrosis deposition.

Lack of interferon-alpha-induced tyrosine phosphorylation of Vav proto-oncogene in patients with myelofibrosis with myeloid metaplasia

Myelofibrosis with myeloid metaplasia (MMM) is an uncommon chronic myeloproliferative disorder characterized by clonal stem cell proliferation and reactive non-clonal proliferation of bone marrow fibroblasts with fibrosis. In the absence of curative therapy, the current management for the majority of patients is directed towards alleviation of symptoms and improvement in quality of life. A number of experimental therapies have been investigated, among which is the use of type I interferon (IFN)-alpha, whose overall results are disappointing. We recently showed that the Vav proto-oncogene product, p95Vav, which is phosphorylated under IFN-alpha treatment, associates with both chains that constitute the functional type I IFN receptor and contributes to the antiproliferative effects of IFN-alpha. The involvement of p95Vav in IFN-alpha signalling and the frequent non-responsiveness of patients to IFN-alpha led us to investigate for any functional defect(s) of Vav in response to IFN in MMM patients. Our results showed that in the majority of patients Vav is constitutively hyperphosphorylated and that IFN-alpha failed to increase substantially such a tyrosine phosphorylation of p95Vav.

Matrix metalloproteinase and tissue inhibitor of metalloproteinase in human bone marrow tissues-an immunohistochemical study

Unlike other tissues, bone marrow (BM) seldom displays fibrosis after injury, suggesting a possible suppressive mechanism against secondary myelofibrosis in BM tissues. We investigated if fibrosis-related factors, such as matrix metalloproteinase (MMP) and tissue inhibitor of metalloproteinase (TIMP), were expressed in BM tissues in vivo. We attempted immunohistochemical studies on specimens of 16 BM aspiration materials with normal hematological findings and 21 BM tissues from autopsy cases who had succumbed to acute heart failure or cerebrovascular diseases without any BM injuries. Identification of immunohistochemically reactive MMP-2, MMP-9 and TIMP-2 in BM tissue samples revealed for the first time that MMP-2 was localized in the myeloid cells, erythroblasts and megakaryocytes, MMP-9 in the myeloid cells and megakaryocytes. In addition, expression of TIMP-2 in the megakaryocytes as well as in the histiocytes within the stroma was verified. In the non-pathological condition, MMP/TIMP expressions were not encountered in BM stromal cells, such as fibroblasts, vascular endothelial cells, reticulum cells on adipocytes, except for TIMP-2 identification in stromal histiocytes. It is highly possible that these MMP and TIMP expressions in the BM hematopoietic cells and stromal histiocytes are significantly associated with suppression or induction of myelofibrosis.

Bone marrow fibrosis (pseudo-myelofibrosis) in human kala-azar

Thirty cases of human kala-azar were diagnosed by iliac crest biopsy and myeloculture. Histological analysis of 12 patients showed diffuse thickening of reticulin fibers. To the best of our knowledge, this is the third report describing secondary bone marrow fibrosis (myelofibrosis-like) associated with kala-azar. Patients with positive bone marrow fibrosis (pbmf = 12) were compared to patients without detectable bone marrow fibrosis (wbmf = 18). There were no significant differences in clinical and blood parameters following treatment. All patients showed regression of hepatosplenomegaly. Our findings suggest that associated bone marrow fibrosis is transient and did not interfere in the evolution of treated patients.

Safety and efficacy of splenic irradiation in the treatment of patients with idiopathic myelofibrosis: a report on 15 patients

Splenic irradiation in idiopathic myelofibrosis (IMF) has often been use d in selected situations when other therapies were unefficient or contraindicated. This could improve quality of life of patients, but literature remains rare in this field. We have assessed the impact of splenic irradiation in 15 patients with IMF. All of them were no longer responsive to usual treatments, and they presented at least one of the following features: constitutional symptoms, splenic pain, large splenic size, and anemia requiring >2 units of red blood cell transfusion per month. The planned schedule of radiotherapy consisted in daily fractions of 0.4-1 Gy. The median dose of radiotherapy per treatment was 9.8 Gy (range, 0.6-30.5). The overall response rate was 59% with a median duration of 10 months (range, 1-19). Splenic irradiation was more effective on constitutional symptoms, splenic pain, and spleen size. The best responses were noted when full doses of radiotherapy could be delivered, and when patients were previously fewly transfused. Splenic irradiation effectively palliates IMF-related symptoms, and constitute an alternative therapy for patients refractory to usual treatments.

Splenectomy in myelofibrosis with myeloid metaplasia: a single-institution experience with 223 patients

In a 20-year period, 223 patients (median age, 64.8 years) with myelofibrosis with myeloid metaplasia (MMM) had therapeutic splenectomy at our institution. Primary indications for surgery were transfusion-dependent anemia (45.3%), symptomatic splenomegaly (39.0%), portal hypertension (10.8%), and severe thrombocytopenia (4.9%). Operative mortality and morbidity rates were 9% and 31%, respectively. The 203 survivors of surgery had a median postsplenectomy survival time (PSS) of 27 months (range, 0-155). Among preoperative variables, thrombocytopenia (platelet count less than 100 × 109/L) and nonhypercellular bone marrow were identified as independent risk factors for decreased PSS. Durable remissions in constitutional symptoms, transfusion-dependent anemia, portal hypertension, and severe thrombocytopenia were achieved in 67%, 23%, 50%, and 0% of the patients, respectively. Histologic or cytogenetic features of bone marrow obtained before splenectomy did not predict a response in cytopenias. After splenectomy, substantial enlargement of the liver and marked thrombocytosis occurred in 16.1% and 22.0% of the patients, respectively. The thrombocytosis was associated with an increased risk of perioperative thrombosis and decreased PSS. The rate of blast transformation (BT) was 16.3%, and the risk of BT was higher in the presence of increased spleen mass and preoperative thrombocytopenia. However, the PSS of patients with BT was not significantly different from that of patients without BT. We conclude that presplenectomy thrombocytopenia in MMM may be a surrogate for advanced disease and is associated with an increased risk of BT and inferior PSS. However, the development of BT after splenectomy may not affect overall survival and does not undermine the palliative role of the procedure for the other indications.

Splenectomy in myelofibrosis with myeloid metaplasia: a single-institution experience with 223 patients

In a 20-year period, 223 patients (median age, 64.8 years) with myelofibrosis with myeloid metaplasia (MMM) had therapeutic splenectomy at our institution. Primary indications for surgery were transfusion-dependent anemia (45.3%), symptomatic splenomegaly (39.0%), portal hypertension (10.8%), and severe thrombocytopenia (4.9%). Operative mortality and morbidity rates were 9% and 31%, respectively. The 203 survivors of surgery had a median postsplenectomy survival time (PSS) of 27 months (range, 0-155). Among preoperative variables, thrombocytopenia (platelet count less than 100 × 109/L) and nonhypercellular bone marrow were identified as independent risk factors for decreased PSS. Durable remissions in constitutional symptoms, transfusion-dependent anemia, portal hypertension, and severe thrombocytopenia were achieved in 67%, 23%, 50%, and 0% of the patients, respectively. Histologic or cytogenetic features of bone marrow obtained before splenectomy did not predict a response in cytopenias. After splenectomy, substantial enlargement of the liver and marked thrombocytosis occurred in 16.1% and 22.0% of the patients, respectively. The thrombocytosis was associated with an increased risk of perioperative thrombosis and decreased PSS. The rate of blast transformation (BT) was 16.3%, and the risk of BT was higher in the presence of increased spleen mass and preoperative thrombocytopenia. However, the PSS of patients with BT was not significantly different from that of patients without BT. We conclude that presplenectomy thrombocytopenia in MMM may be a surrogate for advanced disease and is associated with an increased risk of BT and inferior PSS. However, the development of BT after splenectomy may not affect overall survival and does not undermine the palliative role of the procedure for the other indications.

Erythromegakaryocytic cells synthesize laminin-8 (alpha4beta1gamma1)

Blood platelets contain laminin-8 (alpha4beta1gamma1), a recently described laminin isoform, but the origin of platelet laminin is at present unknown. Laminin of platelets could be synthesized by megakaryocytes or, alternatively, endocytosed from plasma or other sources. In the present study, the synthesis and presence of laminin-8 in erythromegakaryocytic HEL and DAMI cells were explored. In HEL cells, transcripts for alpha4, beta1, and gamma1 laminin chains were readily detected by RT-PCR. Immunofluorescence flow cytometry demonstrated reactivity of mAbs to laminin beta1 and gamma1 chains with permeabilized cells. Metabolic labeling of HEL cells using [(35)S]methionine and [(35)S]cysteine followed by immunoprecipitation with monoclonal antibodies to beta1 and gamma1 chains revealed bands of approximately 220 and 200 kDa. In the HEL cell lysate, polypeptides of 220 and 200 kDa were recognized by monoclonal antibodies to laminin beta1 and gamma1 chains, respectively, whereas immunoaffinity-purified rabbit antibodies to laminin alpha4 chain gave inconclusive results. However, following immunoaffinity purification on a laminin beta1 antibody-Sepharose column, a 200-kDa band was readily detected by the antibodies to laminin alpha4 chain. Similar results were obtained with DAMI cells. The size of laminin chains of HEL/DAMI cells was similar, though not identical, to the one of platelets, and the alpha4 chain was noncovalently associated to disulfide-bonded beta1gamma1 heterodimer, as in platelets. We conclude that erythromegakaryocytic cells synthesize laminin-8.

A pilot study of recombinant human interleukin-4 therapy of myelofibrosis

Twelve patients with myelofibrosis were treated with recombinant human interleukin-4 (IL-4) administered subcutaneously thrice weekly. Dosage ranged from 1 microg/kg to 4 microg/kg. Median patient age was 65 years (range 36-74). Five patients had transient minor responses, and 5 patients had progressive disease. One patient had a transient minor response, rapidly followed by progressive disease. One patient suffered angioneurotic edema with first injection. Other significant toxicities included fever, flu-like symptoms, peripheral edema, and ascites. IL-4 at this schedule was toxic and had no significant activity in myelofibrosis.

Bone marrow effects of anagrelide therapy in patients with myelofibrosis with myeloid metaplasia

In a prospective study investigating the therapeutic role of anagrelide in myelofibrosis with myeloid metaplasia, 20 patients received anagrelide in daily oral doses of 0.5-3 mg. 17 patients were evaluable and received anagrelide for a median of 2 years (range 0.5-4 years). No patient had a clinically appreciable benefit. Bone marrow (BM) examinations at baseline and after 6 and 12 months of treatment were available for 17, 17 and 12 patients, respectively. In all evaluable cases, BM megakaryocyte number increased after 6 months of anagrelide treatment. Also, Ulex europaeus agglutinin-1 staining of megakaryocytes revealed a left-shifted maturation pattern in most patients with a platelet response to anagrelide. However, megakaryocyte staining intensity for transforming (TGF-beta) and platelet-derived (PDGF) growth factors was not affected consistently by treatment. No patient had a >/=2 grade change in either BM fibrosis or osteosclerosis. These in-vivo data support our previous in-vitro observations that anagrelide interferes with megakaryocyte maturation rather than proliferation. Lack of a positive treatment effect is consistent with the finding that anagrelide did not significantly alter megakaryocyte expression of TGF-beta and PDGF.

Splenic irradiation in myelofibrosis with myeloid metaplasia: a review

Morbidity from myeloid metaplasia and myelofibrosis arises from progressive anemia and abdominal discomfort related to massive splenomegaly, which may be associated with hypercatabolic symptoms. To date, no therapy, other than allogeneic bone marrow transplantation, has been shown to cure or to prolong the survival of these patients. Thus, current management strategies are palliative and include red cell transfusional support and androgen therapy for anemia; chemotherapeutic agents for control of thrombocytosis, leukocytosis, and hypermetabolic symptoms; and splenectomy or splenic irradiation for symptomatic splenomegaly. The major indication for splenic irradiation is left upper quadrant discomfort related to massive splenomegaly, usually in patients for whom splenectomy is contraindicated or has been declined. In most patients, it provides relief from abdominal pain and a moderate reduction in splenic size. Although responses are transient, some patients may experience prolonged relief. Splenic irradiation can result in prolonged myelosuppression in certain patients. This calls for cautious dosing, because individual sensitivity is variable and cannot be predicted. The use of splenic irradiation does not preclude subsequent splenectomy; however, the increased risk of postoperative hemorrhage should discourage consideration of splenic irradiation as an alternative or a temporizing measure before splenectomy when indicated.

Pathogenesis and management of idiopathic myelofibrosis

Idiopathic myelofibrosis is the least common and carries the worst prognosis of the chronic myeloproliferative disorders. The primary disease process is a clonal haematopoietic stem cell disorder which results in a chronic myeloproliferation and an atypical megakaryocyte hyperplasia. In contrast, the characteristic stromal proliferation is a reactive phenomenon, resulting from the inappropriate release of megakaryocyte/platelet-derived growth factors, including PDGF, TGF-beta bFGF and calmodulin. The median survival is approximately 4 years, although individual survival varies greatly. A variety of prognostic schema have been developed which enable the identification of high-risk patients, for whom bone marrow transplantation should be considered. Management for the majority of patients, however, is directed towards the alleviation of symptoms and improvement in quality of life. This review summarizes the recent advances in our understanding of the disease's pathogenesis and discusses the limited therapeutic options available to clinicians.

Molecular genetics and cytogenetics of myeloproliferative disorders

The myeloproliferative disorders are believed to represent clonal malignancies resulting from transformation of a pluripotent stem cell. X-inactivation patterns of peripheral blood cells have been proposed as a useful diagnostic tool but this method is limited by the finding of a clonal X-inactivation pattern in a significant proportion of normal elderly women. There is no pathognomonic chromosomal abnormality associated with the myeloproliferative disorders. However, consistent acquired cytogenetic changes include del(20q), del(13q), trisomy 8 and 9 and duplication of segments of 1q, all of which have been observed at diagnosis or before cytoreductive therapy and therefore represent early lesions which contribute to the pathogenesis of these disorders. Although, the acquired molecular defects underlying most myeloproliferative disorders have not yet been elucidated, translocations associated with the rare 8p11 syndrome have permitted identification of a novel fusion protein. The role of a number of candidate genes in the other myeloproliferative disorders has also been studied, but no mutations have been identified so far. It is likely that a number of genes will be involved, given the varied phenotypes of the diseases. Identification of causal genes will be of considerable interest to both clinicians, who currently lack a specific and sensitive diagnostic test, and scientists interested in fundamental issues of stem cell behaviour.

Myelofibrosis with myeloid metaplasia in young individuals: disease characteristics, prognostic factors and identification of risk groups

Myelofibrosis with myeloid metaplasia (MMM) is an uncommon disorder in young individuals, for whom haemopoietic stem cell transplantation offers the only possibility of cure. However, although the latter procedure is associated with significant morbidity and mortality, the clinical course of MMM is variable, with some patients surviving for less than a year and others showing an indolent course. Selection of young MMM patients for transplantation or other newer therapies is currently difficult since no prognostic data exists for this subgroup. In the present collaborative study a number of initial clinical and laboratory parameters have been evaluated for prognosis in 121 MMM patients aged 55 years or less. Median survival of the series was 128 months (95% CI 90-172). In the Cox proportional hazard regression model three initial variables were independently associated with shorter survival: Hb <10 g/dl (P <0.0001), the presence of constitutional symptoms (fever, sweats, weight loss) (P=0.001), and circulating blasts >/=1% (P=0.003). Based on the above three criteria, of the 116 patients with complete data, two groups were identified: a 'low-risk' group, characterized by 88 patients with up to one adverse prognostic factor, in whom MMM had an indolent course (median survival 176 months, 95% CI 130-188), and a 'high-risk' group, including 28 patients with two or three factors, who had a more aggressive disease (median survival 33 months, 95% CI 20-42). The above prognostic scoring system showed a high positive predictive value, sensitivity and specificity to predict survival in the series, and could be of help in making treatment decisions in young patients with MMM.