Haemopoietic stem cell transplantation for advanced polycythaemia vera or essential thrombocythaemia

Therapeutic options for leukemic transformation in patients with myeloproliferative neoplasms

Approximately 5-10% of patients with Philadelphia chromosome negative myeloproliferative neoplasms (MPN) comprising of essential thrombocythemia, polycythemia vera and primary myelofibrosis) experience transformation to acute myeloid leukemia (AML, ≥20% blasts). Treatment options for post-MPN AML patients are limited, as conventional approaches like standard chemotherapy, fail to offer long-term benefit. Median survival for secondary AML is ∼2.4 months. Post-MPN AML therefore represents an area of urgent clinical need. At present, allogeneic stem cell transplant (ASCT) following induction therapy is the best therapeutic option. Patients ineligible for ASCT are treated with hypomethylating agents. New agents under investigation include histone deacetylase inhibitors, JAKinhibitors and agents targeting the BRD4 protein. Combined treatment strategies involving these novel agents are being tested. In this review we present the current evidence regarding treatment options for post-MPN AML patients.

Allogeneic hematopoietic stem cell transplantation for myelofibrosis and chronic myelomonocytic leukemia

The efficacy of hematopoietic stem cell transplantation (HSCT) is not well established in Philadelphia chromosome negative myeloproliferative neoplasms (Ph- MPNs). Without randomized prospective trials comparing HSCT to non-HSCT options or comparing HSCT regimens, physicians must rely on prognostic scoring systems and clinical experience when making decisions about who and when to transplant patients with Ph- MPNs. These patients are vulnerable to hepatic toxicity and graft failure after HSCT because of their increased likelihood of portal hypertension, massive splenomegaly, and extensive bone marrow fibrosis related to their disease. In this review, we aim to outline the indications and modalities of HSCT as they pertain to the Ph- MPNs and CMML based on the currently available evidence. We will further highlight the challenges of HSCT in these diseases, including but not limited to the incorporation of JAK inhibitors into HSCT for myelofibrosis.

An update on allogeneic hematopoietic progenitor cell transplantation for myeloproliferative neoplasms in the era of tyrosine kinase inhibitors

Myeloproliferative neoplasms are a category of diseases that have been traditionally amenable to allogeneic hematopoietic progenitor cell transplantation. Current developments in drug therapy have delayed transplantation for more advanced phases of the disease, especially for patients with CML, whereas transplantation remains a mainstream treatment modality for patients with advanced myelofibrosis and chronic myelomonocytic leukemia. Reduced-intensity conditioning has decreased the treatment-related mortality, and advances in the use of alternative donors for transplantation could extend the use of this procedure to an increasing number of patients with improved safety and efficacy. Here we review the current knowledge about allogeneic transplantation for myeloproliferative neoplasms and discuss the most important aspects to be considered when contemplating transplantation for patients with these diseases. Janus kinase 2 inhibitors offer the promise to improve spleen size and performance of patients with myelofibrosis and extend transplantation for patients with more advanced disease.

Treatment outcomes following leukemic transformation in Philadelphia-negative myeloproliferative neoplasms

Leukemic transformation (LT) is a rare but fatal complication of Philadelphia-negative myeloproliferative neoplasms (MPNs) for which optimal treatment strategies are not known. At our center, we have adopted a treatment approach for LT where patients within the transplant age group who have a reasonable fitness level are treated with curative intent and offered induction chemotherapy. Subsequently, those who respond and have a suitable donor are considered for allogeneic hematopoietic cell transplantation (HCT). In this study, we evaluated the clinical outcomes of this treatment approach in 75 patients with LT. The 2-year overall survival (OS) from the time of LT was 15%. A total of 39 patients (52%) were treated with curative intent (induction ± HCT) and had a 2-y OS of 26% compared with 3% in those noncuratively treated (P < .0001). In the curative intent group, 18 individuals (46%) achieved complete remission (CR) or CR with incomplete recovery and 12 (31%) reverted to a chronic MPN phase, with 17 patients undergoing HCT. Survival of patients posttransplant was significantly improved compared with those who responded to induction but were not transplanted (2-y OS of 47% vs 15%; P = .03). Thus, induction chemotherapy followed by HCT has the potential for long-term disease control in select patients with LT preceded by a MPN.

Allogeneic stem cell transplantation for myelofibrosis with leukemic transformation

Leukemic transformation (LT) from myelofibrosis has a very poor prognosis with the current treatment strategies. We hypothesized that allogeneic stem cell transplantation (ASCT) can improve outcomes for patients with LT, and reviewed 55 consecutive patients that were treated for myelofibrosis with ASCT at our institution. Fourteen patients (25%) were identified to have LT. Thirteen of these patients received induction chemotherapy and 6 achieved remission at the time of transplant. Conditioning regimen was melphalan (Mel)-based in 9 patients. All patients engrafted and achieved remission after transplant, whereas 4 subsequently relapsed. After a median follow-up of 31 months, 6 patients (49%) survived long term. Although limited by a small number of patients, this study suggests that patients with myelofibrosis and LT may achieve long-term remission after induction chemotherapy and ASCT.

Stem cell transplantation for polycythemia vera

Polycythemia vera (PV) is a rare disease in children. A 9-year-old male was diagnosed following laboratory results acquired because of an acute appendicitis. Regular phlebotomy was performed for over 2 years followed by alpha-interferon treatment. At the age of 12 years, HLA-matched unrelated stem cell transplantation including T-cell depletion was done. The conditioning regimen consisted of busulfan, cyclophosphamide, and ATG. Chimerism was monitored during the whole post-transplant period. A single dose of donor T-lymphocytes was given at month 3. One year after transplantation, chimerism was complete. The patient is in complete remission and shows no signs of transplant-related morbidity at month 78.

Molecular basis of the diagnosis and treatment of polycythemia vera and essential thrombocythemia

Recent insights into the molecular mechanisms of polycythemia vera (PV) and essential thrombocythemia (ET) are challenging the traditional diagnostic classification of these myeloproliferative disorders (MPDs). Clonality analysis using X-chromosome inactivation patterns has revealed apparent heterogeneity among the MPDs. The recently discovered single somatic activating point mutation in the JAK2 gene (JAK2-V617F) is found in the great majority of patients with PV, but also in many patients with phenotypically classified ET and other MPDs. In contrast to the acquired MPDs, mutations of the erythropoietin receptor and thrombopoietin receptor have been identified in familial forms of nonclonal erythrocytosis and thrombocytosis, respectively. The mechanisms of major clinical complications of PV and ET remain poorly understood. Quantitative or qualitative abnormalities of red cells and platelets do not provide clear explanations for the thrombotic and bleeding tendency in these MPDs, suggesting the need for entirely new lines of research in this area. Recently reported randomized clinical trials have demonstrated the efficacy and safety of low-dose aspirin in PV, and an excess rate of arterial thrombosis, major bleeding, and myelofibrotic transformation, but decreased venous thrombosis, in patients with ET treated with anagrelide plus aspirin compared to hydroxyurea plus aspirin.

Leukemic transformation of polycythemia vera: a single center study of 23 patients

BACKGROUND

Acute leukemia (AL) may occur as rare and late event of polycythemia vera (PV).

METHODS

The current study included 23 patients who developed acute leukemia in a cohort of 414 consecutive PV patients with long-term observation (3208 person years of follow-up). Kaplan-Meier Product-Limit method was used to estimate the cumulative probability of survival; Gehan-Wilcoxon test was applied to compare survival in different groups of patients.

RESULTS

Median age was 68 years, and 18 patients (78%) were > 60 years of age. At diagnosis of AL, most patients had a white blood count > 10 x 10(9)/L (n = 17; 74%), Hgb < 10 g/dL (n = 13; 57%), and platelet count > 50 x 10(9)/L (n = 17; 74%). Of 14 patients in whom cytogenetic analysis was available at leukemic transformation, 12 showed high-risk abnormalities including complex karyotype (n = 10), del (7)(q22) sole (n = 1) and del (X)(q26) sole (n = 1), whereas 2 had a normal karyotype. In patients whose karyotype was available at diagnosis of PV, cytogenetic evolution was documented at progression to AL. Treatment consisted of supportive care and/or low-dose chemotherapy (n = 15), or induction chemotherapy (n = 8). This included idarubicin plus cytarabine (n = 3), high-dose cytarabine (n = 4), and fludarabine-based regimen (n = 1). Allogenic stem cell transplantation was offered to a single patient, who is alive at Day + 70. The outcome of patients was poor, with a median survival of 2.9 months (range, 0.6-20.1 mos), with no significant differences between palliation and intensive treatments.

CONCLUSIONS

AL following PV has distinct clinical and biologic features. Outcome of patients is poor irrespective of the treatment employed.

Partial splenectomy before a hematopoietic stem cell transplantation in children

Hematopoietic stem cell (HSC) engraftment is delayed in children with hypersplenism, and splenectomy may improve HSC engraftment. However, the use of total splenectomy in children is limited because of concerns for postsplenectomy sepsis. In this study, the authors sought to assess the role of partial splenectomy for children with hypersplenism undergoing HSC transplantation.

METHODS

Five children with a variety of conditions and associated hypersplenism underwent partial splenectomy before an HSC transplantation at the authors' institution between 2000 and 2003. Primary outcome measures were rates of neutrophil and platelet engraftment. Secondary outcome measures included perioperative complications, splenic regrowth, graft-versus-host disease, and infection rate. All outcomes were compared with recipients of an HSC transplant from both age-matched nonsplenectomized children (n = 497) and hypersplenic children who underwent total splenectomy (n = 10). Outcomes were compared using Wilcoxon's rank sum test.

RESULTS

The rate of both neutrophil and platelet engraftment was faster in children who underwent either partial or total splenectomy as compared with nonsplenectomized children (mean rates of neutrophil engraftment were 26, 19, and 19 days for the nonsplenectomy, total splenectomy, and partial splenectomy groups, respectively; mean rates of platelet engraftment were 97, 37, and 45 days for the nonsplenectomy, total splenectomy, and partial splenectomy groups, respectively). Graft-versus-host disease rates were similar between the 3 groups. The mean percentage of splenic regrowth after partial splenectomy was 39%. There were no perioperative complications.

CONCLUSIONS

Partial splenectomy may be safely performed before HSC transplantation and, similar to total splenectomy, may improve the rate of HSC engraftment. Although this series has a limited number of patients, the use of partial splenectomy appears to be safe and may allow for splenic salvage to minimize the risk of postsplenectomy sepsis.

Interferon α therapy for patients with essential thrombocythemia

BACKGROUND

In 1986, a Phase II trial of recombinant interferon-alpha (IFN-alpha) was initiated as therapy for patients with essential thrombocythemia (ET).

METHODS

Patients were treated with subcutaneous IFN-alpha at a dose of 5 x 10(6) units/m(2) daily. In responding patients, the therapy lasted at least 3 years.

RESULTS

Twenty-three patients (14 females and 9 males; median age, 41 years; age range, 20-63 years) with a median platelet count of 1350 x 10(9)/L were treated. After a median follow-up of 174 months (14.5 years), 15 of 20 evaluable patients (75%) responded, including 14 patients who achieved a complete hematologic response (CHR) (6 of them with bone marrow remission) and 1 patient who demonstrated a partial response. The median time to response was 6 months (range, 0.5-36 months), and the median response duration was 48 months (range, 5-114 months). Seven patients who achieved a CHR and were taken off therapy after they completed 3 years of maintenance therapy sustained their response for a median of 28 months. No symptoms or signs of thrombosis or hemorrhage were observed in responding patients. Eleven of 14 patients (78%) who achieved a CHR developed a recurrence, and 2 of 5 patients with recurrences who were rechallenged with IFN-alpha achieved a second response. The treatment was tolerated relatively well.

CONCLUSIONS

IFN-alpha was safe and effective therapy for patients with ET, and the ability of IFN-alpha to reverse disease pathology and possibly modify the clinical course of patients with ET warrants its investigation in larger, prospective trials.

Allogeneic hematopoietic stem cell transplantation for myelofibrosis

Fifty-six patients, 10 to 66 years of age, with idiopathic myelofibrosis (IMF) or end-stage polycythemia vera or essential thrombocythemia received allogeneic hematopoietic cell transplants from related (n = 36) or unrelated (n = 20) donors. Forty-four patients were prepared with busulfan plus cyclophosphamide and 12 with total body irradiation plus chemotherapy. The source of stem cells was marrow in 33 and peripheral blood in 23 patients. All but 3 patients achieved engraftment. While 50 patients showed complete donor chimerism, 3 patients were found to be mixed chimeras at 26, 48, and 86 months after transplantation, respectively. Two patients died from relapse/progressive disease, and 18 died from other causes. There are 36 patients surviving at 0.5 to 11.6 (median, 2.8) years, for a 3-year Kaplan-Meier estimate of 58% (CI, 43%-73%). Dupriez score, cytogenetic abnormalities, and degree of marrow fibrosis were the most significant risk factors for posttransplantation mortality. Patients conditioned with a regimen of busulfan targeted to plasma levels of 800 to 900 ng/mL plus cyclophosphamide had a higher probability of survival (76% [CI, 62%-91%]) than other patients. Results with unrelated donors were comparable with those with HLA-identical sibling transplants. Thus, allogeneic hematopoietic cell transplantation offers long-term relapse-free survival for patients with myelofibrosis.

Collection of autologous PBSC in patients with polycythemia vera

BACKGROUND

Allogeneic stem-cell transplantation (SCT) can eradicate myelofibrosis (MF), but is limited by donor availability and toxicity. We previously reported normalization of counts and resolution of MF after ablative, syngeneic SCT in spent phase polycythemia vera (PV). Hence, GvL is not required to eradicate MF. Autologous SCT may advance treatment for spent phase PV by restoring effective hematopoiesis. The influence of organomegaly, myelosuppression and MF on PBSC collection has not been studied in the setting of PV.

METHODS

Sixteen patients with PV underwent PBSC collection. Mobilization was with filgrastim alone, with a target cell content of 2.5 x 10(6) CD34(+)/kg. All myelosuppression was discontinued 2 weeks prior to collection.

RESULTS

Median ages at diagnosis and collection were 47 and 57 years, respectively. Organomegaly, MF and use of myelosuppressive therapies were present in 10 (63%), 4 (25%) and 7 (44%) patients. Median total nucleated cells (TNC) and CD34(+) counts were 8.3 x 10(8)/kg and 4.98 x 10(8)/kg. MF had an adverse effect on TNC (p=0.05) but not on the CD34(+) content. Time from diagnosis and the use of myelosuppresion had no influence on TNC and CD34(+) contents. Four patients had CD34(+) contents <2.5 x 10(6)/kg. Complete blood count (CBC) parameters were not predictive of CD34(+) content.

DISCUSSION

Autologous PBSC collection is feasible in PV several years after diagnosis. Organomegaly and MF are not absolute contraindications for collection. Discontinuing myelosuppresion for 2 weeks before mobilization appears sufficient to collect adequate numbers of CD34(+) progenitors.

Allogeneic hematopoietic stem cell transplantation for myeloproliferative disorders and myelodysplastic syndromes

Allogeneic SCT is the most effective method to achieve cure in patients with MPD and MDS. This approach is associated with significant risk of morbidity (eg, GVHD) and TRM, although the incidence and severity vary based on donor and recipient characteristics. For young patients with HLA-matched donors, SCT is the preferred therapy. Efforts to improve outcome for older patients and for patients with alternative donors have led to decreased treatment-associated complications with associated better long-term DFS.

Hematopoietic cell transplantation for adult patients with myelodysplastic syndromes and myeloproliferative disorders

Hematopoietic cell transplantation (HCT) is currently the only treatment with curative potential for myelodysplastic syndromes (MDS) and myeloproliferative disorders (MPD). Among patients with less advanced MDS, 3-year survival rates of 65% to 75% are achieved with HLA-identical related and unrelated donors. The probability of relapse is less than 5%. Among patients with advanced MDS (> or = 5% marrow blasts), about 35% to 45% who receive transplants from related donors and 25% to 30% who receive transplants from unrelated donors are in remission beyond 3 years. The incidence of posttransplantation relapse is 10% to 35%. Criteria of the International Prognostic Scoring System (originally developed for nontransplant patients) also predict relapse and survival after HCT. Transplantation is successful in 50% to 80% of patients with MPD if performed before leukemic transformation. Depending on the individual risk profile, a considerable number of patients with MDS or MPD are cured by allogeneic HCT. However, HCT should be performed before disease progression. Outcome of patients with treatment-related MDS or with relapse after transplantation remains poor. At present, no definite conclusions can be made with regard to reduced-intensity transplantation regimens.

Transplant decision-making strategies in the myeloproliferative disorders

Myelofibrosis with myeloid metaplasia, also known as idiopathic myelofibrosis (IF) or agnogenic myeloid metaplasia, is one of the characteristic manifestations of polycythemia vera (PV) in the spent phase, and has a particularly adverse prognosis. IF may also present de novo. To date, treatment strategies for both spent-phase PV and IF have frustrated both clinicians and patients, with little clear progress made over the past 50 years. Treatment modalities with some benefit in chronic myeloid leukemia (CML), such as interferon (IFN), have been used to shrink the massive organomegaly seen in these patients and to improve their marrow function, but are not curative, and not all patients respond or can tolerate the agent. A curative approach is allogeneic peripheral hematopoietic stem cell transplantation. The preparative regimens used in fully ablative techniques rule out older patients for consideration, and many younger patients with good prognostic criteria may do sufficiently well on medical treatment or observation to avoid transplantation. Older patients may have the option to undergo a human leukocyte antigen (HLA)-identical sibling transplant using a reduced intensity preparative regimen in order to minimize peritransplant mortality. Thus a prerequisite to the broad use of transplantation is objective determination of candidacy. Several evaluation methods agree that anemia, age, and cytogenetic abnormalities all predict poor survival in IF, suggesting that patients with anemia and an abnormal karyotype are the prime candidates for allogeneic transplantation. Experimental peripheral blood models that may reflect the degree of marrow fibrosis, such as the serum procollagen 3 peptide assay, have been used to determine if they are more informative of patient status than a single, random bone marrow sampling. Marrow fibrosis may be patchy, and thus a marrow biopsy alone without other data about marrow function may be misleading. Considerable long-term success in eradicating fibrosis and restoring normal cytogenetics, normal bone marrow morphology, and normal complete blood cell counts through transplantation has been reported. Many questions remain to be answered, however, before the appropriate role of hematopoietic stem cell transplantation in the setting of both spent-phase PV and IF can be determined.

Chronic myeloproliferative disorders

The Philadelphia chromosome-negative chronic myeloproliferative disorders (CMPD), polycythemia vera (PV), essential thrombocythemia (ET) and chronic idiopathic myelofibrosis (IMF), have overlapping clinical features but exhibit different natural histories and different therapeutic requirements. Phenotypic mimicry amongst these disorders and between them and nonclonal hematopoietic disorders, lack of clonal diagnostic markers, lack of understanding of their molecular basis and paucity of controlled, prospective therapeutic trials have made the diagnosis and management of PV, ET and IMF difficult. In Section I, Dr. Jerry Spivak introduces current clinical controversies involving the CMPD, in particular the diagnostic challenges. Two new molecular assays may prove useful in the diagnosis and classification of CMPD. In 2000, the overexpression in PV granulocytes of the mRNA for the neutrophil antigen NBI/CD177, a member of the uPAR/Ly6/CD59 family of plasma membrane proteins, was documented. Overexpression of PRV-1 mRNA appeared to be specific for PV since it was not observed in secondary erythrocytosis. At this time, it appears that overexpression of granulocyte PRV-1 in the presence of an elevated red cell mass supports a diagnosis of PV; absence of PRV-1 expression, however, should not be grounds for excluding PV as a diagnostic possibility. Impaired expression of Mpl, the receptor for thrombopoietin, in platelets and megakaryocytes has been first described in PV, but it has also been observed in some patients with ET and IMF. The biologic basis appears to be either alternative splicing of Mpl mRNA or a single nucleotide polymorphism, both of which involve Mpl exon 2 and both of which lead to impaired posttranslational glycosylation and a dominant negative effect on normal Mpl expression. To date, no Mpl DNA structural abnormality or mutation has been identified in PV, ET or IMF. In Section II, Dr. Tiziano Barbui reviews the best clinical evidence for treatment strategy design in PV and ET. Current recommendations for cytoreductive therapy in PV are still largely similar to those at the end of the PVSG era. Phlebotomy to reduce the red cell mass and keep it at a safe level (hematocrit < 45%) remains the cornerstone of treatment. Venesection is an effective and safe therapy and previous concerns about potential side effects, including severe iron deficiency and an increased tendency to thrombosis or myelofibrosis, were erroneous. Many patients require no other therapy for many years. For others, however, poor compliance to phlebotomy or progressive myeloproliferation, as indicated by increasing splenomegaly or very high leukocyte or platelet counts, may call for the introduction of cytoreductive drugs. In ET, the therapeutic trade-off between reducing thrombotic events and increasing the risk of leukemia with the use of cytoreductive drugs should be approached by patient risk stratification. Thrombotic deaths seem very rare in low-risk ET subjects and there are no data indicating that fatalities can be prevented by starting cytoreductive drugs early. Therefore, withholding chemotherapy might be justifiable in young, asymptomatic ET patients with a platelet count below 1500000/mm(3) and with no additional risk factors for thrombosis. If cardiovascular risk factors together with ET are identified (smoking, obesity, hypertension, hyperlipidemia) it is wise to consider platelet-lowering agents on an individual basis. In Section III, Dr. Gianni Tognoni discusses the role of aspirin therapy in PV based on the recently completed European Collaboration on Low-dose Aspirin in Polycythemia Vera (ECLAP) Study, a multi-country, multicenter project aimed at describing the natural history of PV as well as the efficacy of low-dose aspirin. Aspirin treatment lowered the risk of cardiovascular death, non-fatal myocardial infarction, and non-fatal stroke (relative risk 0.41 [95% CI 0.15-1.15], P =.0912). Total and cardiovascular mortality were also reduced by 46% and 59%, respectively. Major bleedings were slightly increased nonsignificnsignificantly by aspirin (relative risk 1.62, 95% CI 0.27-9.71). In Section IV, Dr. Giovanni Barosi reviews our current understanding of the pathophysiology of IMF and, in particular, the contributions of anomalous megakaryocyte proliferation, neoangiogenesis and abnormal CD34(+) stem cell trafficking to disease pathogenesis. The role of newer therapies, such as low-conditioning stem cell transplantation and thalidomide, is discussed in the context of a general treatment strategy for IMF. The results of a Phase II trial of low-dose thalidomide as a single agent in 63 patients with myelofibrosis with meloid metaplasia (MMM) using a dose-escalation design and an overall low dose of the drug (The European Collaboration on MMM) will be presented. Considering only patients who completed 4 weeks of treatment, 31% had a response: this was mostly due to a beneficial effect of thalidomide on patients with transfusion dependent anemia, 39% of whom abolished transfusions, patients with moderate to severe thrombocytopenia, 28% of whom increased their platelet count by more than 50 x 10(9)/L, and patients with the largest splenomegalies, 42% of whom reduced spleen size of more than 2 cm.

Essential thrombocythemia (ET): moving from palliation to cure

Essential thrombocythemia (ET) is a clonal hematopoietic stem cell myeloproliferative disorder characterized by megakaryocytic hyperplasia and persistent thrombocytosis. The clinical presentation and evolution of ET are heterogeneous. This review highlights the current treatment options in the management of ET, including hydroxyurea, anagrelide and both regular and pegylated interferons. Anagrelide, while very effective at controlling counts and symptoms in most patients, may not consistently reduce the bone marrow megakaryocyte mass. Interferon is very effective and not associated with leukemogenesis, but has not been proven to restore polyclonal hematopoiesis and has significant dose-related adverse events. Pegylated interferon represents a significant improvement over the unmodified interferon preparations. Novel therapeutic options directed towards eradication of the malignant ET clone are required.

Clinical and scientific advances in the Philadelphia-chromosome negative chronic myeloproliferative disorders

The chronic myeloproliferative disorders are clonal hematopoietic stem cell disorders and include chronic myeloid leukemia (CML), polycythemia vera (PV), essential thrombocythemia (ET), and agnogenic myeloid metaplasia (AMM). These diseases are characterized by clonal expansion of the myeloid compartment, increased marrow angiogenesis, and varying risks for blastic transformation. A clear molecular abnormality exists (t(9;22) leading to the fusion of BCR-Abl) only for CML, which led to effective targeted therapy (STI-571). Since no similar pathogenetic mechanism has been discovered for the t(9;22) negative chronic myeloproliferative disorders, their respective diagnosis is currently based on a variety of rather cumbersome diagnostic criteria. Polycythemia vera is distinguished from reactive erythrocytosis through erythropoietin independent growth of erythroid progenitors in vitro, suppressed levels of endogenous erythropoietin, possible overexpression of PRV-1 (polycythemia rubra vera-1), decreased c-Mpl expression on megakaryocytes, as well as overexpression of bcl-xL, and potentially aberrant activity of the Jak-Stat pathway. ET is defined by thrombocytosis and is distinguished from reactive states by decreased megakaryocyte c-Mpl expression, and a propensity for thrombosis. AMM has been associated with a variety of observations including increased concentrations of pro-fibrotic cytokines, increased angiogenesis, and myeloid expansion. AMM is often indistinguishable clinically and prognostically from the advanced phases of other CMPD (specifically post-polycythemic and post-thrombocythemia myeloid metaplasia), all of which are subentities of a diagnosis of myelofibrosis with myeloid metaplasia (MMM). The management of CMPD patients is quite varied given the broad range of disease severity and survival observed. The role of stem cell transplantation is limited by the age and comorbidities encountered in CMPD patients. Since no broadly applicable therapy effects the mortality of the CMPD, management currently focuses on the prevention/palliation of disease morbidity (i.e. vascular complications, pruritus, organomegaly, constitutional symptoms). Palliative strategies which currently focus on non-specific myelosuppresion, will hopefully be soon replaced by targeted therapies as insight into pathogenetic mechanisms of these diseases evolves.

Curative therapy of advanced essential thrombocythemia or polycythemia vera by hemopoietic stem cell transplantation

Twenty-five patients with advanced essential thrombocythemia (ET; n = 13) or polycythemia vera (PV; n = 12) received hemopoietic stem cell transplants (HSCT) at the Fred Hutchinson Cancer Research Center. In most cases the indication to perform an HSCT was myelofibrosis with splenomegaly and peripheral blood cytopenias or the development of a myelodysplastic syndrome (MDS) or acute myeloid leukemia (AML). Patients were 18-60 (median 43) years old with intervals from diagnosis to HSCT of 8-348 (median 168) months. All but five patients had been treated with cytotoxic agents, and nine patients were splenectomized before transplant. Conditioning was performed with chemotherapy only or chemotherapy plus total body irradiation regimens followed by the infusion of either marrow (n = 19) or peripheral blood stem cells (n = 6) from related (n = 16) or unrelated (n = 9) donors. All evaluable patients showed sustained neutrophil engraftment. Nine patients (seven with AML/MDS, two with myelofibrosis) died of transplant-related complications, and 16 are surviving, 14 of them in continuous unmaintained remission. With a median follow-up of 41 (range 5-116) months after transplant, survival at 3 years is 64%. These data provide evidence that HSCT can be a curative treatment for patients with advanced PV and ET.

Thrombocytosis and thrombocythemia

Thrombocytosis is caused by three major pathophysiological mechanisms: (1) reactive or secondary thrombocytosis; (2) familial thrombocytosis; and (3) clonal thrombocytosis, including essential thrombocythemia and related myeloproliferative disorders. Recent work has begun to elucidate the abnormal megakaryocytopoiesis of essential thrombocythemia, which is associated with paradoxically elevated plasma levels of thrombopoietin. The clonal nature of all cases of essential thrombocythemia has been challenged. Thrombotic complications are the major causes of morbidity and mortality in this disease. Indications for platelet cytoreduction and antiplatelet therapy, as well as complications of treatment, are being clarified.