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Chronic Myeloproliferative Disorders Treatment (PDQ®): Treatment - Health Professional Information [NCI] - Primary Myelofibrosis

Disease Overview

Primary myelofibrosis (also known as agnogenic myeloid metaplasia, chronic idiopathic myelofibrosis, myelosclerosis with myeloid metaplasia, and idiopathic myelofibrosis) is characterized by splenomegaly, immature peripheral blood granulocytes and erythrocytes, and teardrop-shaped red blood cells.[1] In its early phase, the disease is characterized by elevated numbers of CD34-positive cells in the marrow, while the later phases involve marrow fibrosis with decreasing CD34 cells in the marrow and a corresponding increase in splenic and liver engorgement with CD34 cells.

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As distinguished from chronic myelogenous leukemia (CML), primary myelofibrosis usually presents as follows:[2]

  • A white blood cell count smaller than 30,000/mm3.
  • Prominent teardrops on peripheral smear.
  • Normocellular or hypocellular marrow with moderate to marked fibrosis.
  • An absence of the Philadelphia chromosome or the BCR/ABL translocation.
  • Frequent positivity for the JAK2 mutation.

In addition to the clonal proliferation of a multipotent hematopoietic progenitor cell, an event common to all chronic myeloproliferative disorders, myeloid metaplasia is characterized by colonization of extramedullary sites such as the spleen or liver.[3,4]

Most patients are older than 60 years at diagnosis, and 33% of patients are asymptomatic at presentation. Splenomegaly, sometimes massive, is a characteristic finding.

Symptoms include:

(Refer to the PDQ summaries on Pain; Fatigue; Fever, Sweats, and Hot Flashes; and Nutrition for information on many of the symptoms listed above.)

The proposed World Health Organization criteria for the diagnosis of primary myelofibrosis requires all three major criteria and two minor criteria.[5]

Major Criteria

  1. Presence of megakaryocyte proliferation and atypia, usually accompanied by either reticulin and/or collagen fibrosis; or, in the absence of significant reticulin fibrosis, the megakaryocyte changes must be accompanied by increased bone marrow cellularity characterized by granulocytic proliferation and often decreased erythropoiesis (so-called prefibrotic cellular-phase disease).
  2. Not meeting criteria for polycythemia vera, chronic myelogenous leukemia, myelodysplastic syndrome, or other myeloid neoplasm.
  3. Demonstration of JAK2 617V greater than F or other clonal marker; or, in the absence of a clonal marker, no evidence of bone marrow fibrosis caused by an underlying inflammatory disease or another neoplastic disease.

Minor Criteria

  1. Leukoerythroblastosis.
  2. Increased serum level of lactate dehydrogenase.
  3. Anemia.
  4. Palpable splenomegaly.

The median survival is 3.5 years to 5.5 years, but patients younger than 55 years have a median survival of 11 years.[3,4] The major causes of death include:[6]

  • Progressive marrow failure.
  • Transformation to acute nonlymphoblastic leukemia.
  • Infection.
  • Thrombohemorrhagic events.
  • Heart failure.
  • Portal hypertension.

Fatal and nonfatal thrombosis was associated with age more than 60 years and JAK2 617V positivity in a multivariable analysis of 707 patients followed from 1973 to 2008.[7] Bone marrow examination including cytogenetic testing may exclude other causes of myelophthisis, such as CML, myelodysplastic syndrome, metastatic cancer, lymphomas, and plasma cell disorders.[4] In acute myelofibrosis, patients present with pancytopenia but no splenomegaly or peripheral blood myelophthisis. Peripheral blood or marrow monocytosis is suggestive for myelodysplasia in this setting.

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