Myeloproliferative Neoplasms

Question 1

What are myeloproliferative disorders and what are some underlying pathogenetic factors?

Answer 1

• The hallmark diseases that are now referred to as Myeloproliferative Neoplasms (MPN), include:
  
  • chronic myeloid leukemia (CML)
  • BCR-ABL negative MPN
  • essential thrombocytosis (ET)
  • polycythemia vera (PV)
  • fprimary myelofibrosis (PMF)
• The myeloproliferative neoplasms (MPN) are characterized by:
  
  • clonal proliferation of hematopoietic stem cells
  • indolence, with disease durations sometimes measured in decades
  • tendencies toward thrombosis
  • extramedullary hematopoiesis (usually splenomegaly)
  • myelofibrosis
  • transition to acute leukemia
• The discovery of the Philadelphia chromosome, due to a translocation of chromosomes 9 and 22, and its product, BCR-ABL, has led to targeted therapy with tyrosine kinase inhibitors (Imatinib, Nilotinib, Dasatinib, Bosutinib, Ponatinib), which have dramatically altered the natural history of CML
  
  • The molecular underpinnings of the BCR-ABL negative MPN have been better understood since the discovery of JAK2 V617F in 2005, and now, the calreticulin gene mutations in 2013
  • Though these mutations are prevalent, they may not be the causative lesions or sole abnormalities, and as a result, targeted therapy (JAK-inhibitors) has had less of an effect than hoped in patients with BCR-ABL negative MPN

Question 2

What are some features of MDS that differentiate it from MPN?

Answer 2

• The MPN are sometimes confused with myelodysplastic disorders (MDS)
• MDS is typically characterized by:
  
  • decreased (rather than increased) counts of one or more of the myeloid lineages in the peripheral blood
  • increase in myeloid cell numbers in the bone marrow
  • abnormal myeloid cell morphology termed “dysplasia”—in the case of MDS, hematopoiesis is ineffective
• In some patients, features of MPN and MDS are seen concurrently
  
  • The most recent WHO classification recognizes this category of patients with an overlap syndrome, coined “MDS/MPN”
  • The most common overlap is chronic myelomonocytic leukemia (CMML)

Question 3

Describe how the Philadelphia Chromosome (BCR-ABL) contributes to MPN.

Answer 3

• The recognition of the Philadelphia (Ph) chromosome in 1960 represented a landmark discovery as it was the first leukemia associated with a consistent and specific chromosomal abnormality, ushering in era of cytogenetic analysis in hematology
  
  • The Ph chromosome (t9;22) is comprised from a translocation of the Abelson (ABL) proto-oncogene from chromosome 22 to the long arm of chromosome 9 (BCR), resulting in a BCR-ABL fusion gene
    
    • This is a tumor specific abnormality
• The most common protein expression of this fusion gene, p210, displays tyrosine kinase activity, activating signaling pathways (RAS, PI3-K and c-MYC) that both enhance bone marrow progenitor proliferation and decrease apoptosis (programmed cell death)
  
  • What results is an increase in number of normal appearing granulocytes
  • Differentially is initially preserved, until, there is failure, and immature white blood cells, including blasts can appear in the blood
• Almost all patients with typical CML have the BCR-ABL fusion gene
• The targeting of BCR-ABL has been one of the greatest success stories in hematology-oncology

Question 4

Desccribe how the JAK2 V617F mutation contributes to MPN.

Answer 4

• The discovery of the JAK2 V617F mutation in 2005 has provided significant insight into the pathogenesis of the BCR-ABL negative MPN, and provides some rationale for the shared clinical features seen in these diseases
• The Janus Kinase receptors (JAK2-wild type) are integral for normal hematopoiesis
  
  • When the appropriate ligand (Epo, GCSF, GM-CSF, thrombopoietin) binds its receptor, JAK2 becomes activated via phosphorylation, and then transmits its signal through phosphorylation of downstream intracellular pathways (STAT), which regulate gene transcription
  • What results is the proliferation and differentiation of erythroid, granulocytic, and megakaryocytic precursors
• The JAK2 V617F mutation is characterized by a switch from valine to phenylalanine at position 617 in exon 14 of the JAK2 gene
  
  • What results is a loss of negative regulation—in other words, when mutant, JAK2 is constitutively active
  • Therefore, downstream signaling is constitutively active; the drive for proliferation and differentiation through this normal pathway becomes more robust
• JAK-inhibitors are available, but the effects do not compare to those of CML targeted therapy, in part because this is a normal pathway, and the drug effects both normal and mutant signaling
• JAK2 V617F mutations are found in: 95% of PV; 50-60% of ET; and 50-60% of MF

Question 5

How do calreticulin gene mutations contribute to the pathogenesis of PMN?

Answer 5

• Approximately 40 to 50% of patients with ET and MF lack JAK2 V617F mutations, but often the clinical phenotype is generally similar
• In late 2013, two groups simultaneously reported the frequent mutation of the calreticulin gene
  
  • This mutation was identified in a substantial proportion of patients who have JAK2 V617F negative ET or MF, filling a diagnostic gap
  • This mutation is mutually exclusive from the JAK2 V617F mutation
  • Just how the mutation leads to the clinical phenotype of ET or MF is not yet clear, though one group was able to show activation of similar downstream pathways (STAT)
  • This mutation can be tested for in the clinic
• Additional mutations (we can test patients for these as well):
  
  • JAK2 exon 12 (2-3% of PV patients); MPL mutations (5-10% of ET and PMF patients)

Question 6

What are some less common mutations in PMN?

Answer 6

• C-KIT (KIT D816V) in Systemic Mastocytosis
• PDGFRA, PDGRFB, and FGFR1 clonal rearrangements in MPNs associated with eosinophilia.

Question 7

What are some common disease features in PMN?

Answer 7

• Indolence, initially
• Bone marrow hypercellularity, associated with increased numbers of granulocytes, red blood cells, and/or platelets
• Organomegaly (particularly splenomegaly)
• Thrombotic or hemorrhagic complications
• Initial presence of bone marrow fibrosis, or evolution to fibrotic phase, with eventual marrow failure (ET and PV)
• Transformation to an acute, blast phase

Question 8

What are the uniqe features and epidemiology of Chronic Myeloid Leukemia (CML)?

Answer 8

• Unique features:
  
  • Often marked leukocytosis, with mature and immature granulocytes, along with basophilia
  • Hallmark is the Philadelphia chromosome
• Epidemiology:
  
  • ~1 new cases per 100,000 persons per year (slight male predominance)
  • Typically a disease of middle-age (6th decade)
  • Possible associations with radiation exposure (increased incidence in survivors of Hiroshima)

Question 9

What is the differential diagnosis, diagnosis, clinical concerns, and natural history of CML?

Answer 9

• Differential diagnosis:
  
  • Exclude other MPN, such as ET and MF which can mimic
  • Severe infection causing leukocytosis can mimic as well (leukemoid reaction)
• Diagnosis:
  
  • Patients present with a pronounced leukocytosis, often with WBC of 50 to 200 x 109/L
  • left shifted granulopoiesis (all stages often present in peripheral blood), with metamyelocytes, myelocytes, promyelocytes and even blasts
  • Frequent basophilia
  • Thrombocytosis can be present
  • BCR-ABL can be identified by testing of the peripheral blood (FISH or qPCR) or bone marrow (FISH, conventional cytogenetics, qPCR).
• Clinical concerns
  
  • Many patients may be asymptomatic, and identified based on a routine blood count
  • Others may have fevers, sweats, fatigue, or pain from an enlarged spleen (can be noted on physical)
  • Aside from leukocytosis, patients may or may not have anemia, thrombocytopenia, or thrombocytosis
• Natural history:
  
  • CML exists in 3 phases:
    
    • a chronic phase
    • an accelerated phase marked by progressive symptoms, splenomegaly, basophilia, thrombocytosis or thrombocytopenia, and increasing blasts/immaturity of the white cell lineage
    • a blast phase, akin to acute leukemia (myeloid or lymphoid)

Question 10

What is the treatment for CML?

Answer 10

• The treatment of CML has been revolutionized by the advent of BCR-ABL tyrosine kinase inhibitor therapy
• The first in this class was imatinib, which now has more the 10 years of follow-up
  
  • 8 year follow-up showed excellent survival (89-95%)
• Prior to the advent of this class, patients almost uniformly progressed to blast phase in 3-5 years without bone marrow transplant
• Currently, TKI’s have dramatically reduced the proportion of patients that accelerate
  
  • There are now second and third generation TKI’s that are quite effective, even if a patient has developed resistance to Imatinib (or intolerance)
• The prognosis is influenced by meeting certain milestones, including cytogenetic remission (disappearance of the Ph chromosome) and molecular remission (decreased minimal residual disease burden, measured by PCR)
• Some patients acquire mutations in the BCR-ABL kinase domain which leads to loss of response to therapy and disease progression
  
  • Previously, the T315I mutation conferred resistance to all TKI’s, but now, patients with this mutation can be treated with ponatinib

Question 11

List the classical BCR-ABL negative Myeloproliferative Neoplasms.

Answer 11

• Polycythemia vera
• Essential thrombocytosis
• Primary myelofibrosis

Question 12

What are the unique features and epidemiology of polycythemia vera?

Answer 12

• Unique features:
  
  • Absolute erythrocytosis (increase in red cell mass and plasma volume)
• Epidemiology:
  
  • 2 new cases per 100,000 persons per year
  • Slight male predominance, often in the 6th or 7th decade

Question 13

What is the differential diagnosis, diagnosis, clinical concerns, and prognosis of polycythemia vera?

Answer 13

• Differential diagnosis:
  
  • Exclude secondary causes of erythrocytosis (a high hemoglobin):
    
    • Hypoxia
    • High affinity Hemoglobin
    • Methemoglobinemia
    • Increased Epo production
    • Dehydration
    • “Stress” erythropoiesis
• Diagnosis (Proposed per the WHO revisions)
  
  • Major criteria:
    
    • Hb > 18.5 g/dl in men; > 16.5 g/dl in women
    • JAK2 V617F mutation or JAK2 exon 12 mutation
  • Minor criteria:
    
    • Leukocytosis/thrombocytosis or hypercellular marrow (& undetectable iron storage)
    • Low Epo level (autonomous rbc production in PV)
    • Endogenous Erythroid Colony formation (growth w/o epo)
• Clinical concerns:
  
  • Symptoms from hyperviscosity: Headaches, Malaise, Fatigue, Plethora/Ruddy complexion
  • Platelet hypersensitivity: erythromelalgia, pruritus (also due to mast cell and basophil proliferation)
  • Thrombotic complications (arterial and/or venous); bleeding problems
  • Disease transformation (to myelofibrosis and acute leukemia)
• Prognosis: ~20 years median survival

Question 14

What is the treatment of polycythemia vera?

Answer 14

• Aspirin: Lowers vascular risk
• Phlebotomy: Reduction of RBC mass and viscosity, until iron deficient (goal Hct 45% or less)
• Chemotherapy: (Hydroxyurea)-often in those over 60, or w/ prior thrombosis
• JAK-inhibition: Ruxolitinib, a JAK1/JAK2 inhibitor was approved in December 2014
• Pegylated Interferon: Potential disease-modifying effects

Question 15

What are the unique features and epidemiology of essential thrombocytosis?

Answer 15

• Unique features:
  
  • None! Thrombocytosis can be a feature of PV and MF, as well as CML, and other malignancies
• Epidemiology:
  
  • 0.5 new cases per 100,000 persons per year
  • female predominance, often in 6th or 7th decade, though another peak appears in younger women in 3rd to 5th decade

Question 16

What is the differential diagnosis, diagnosis, clinical concerns, and prognosis of essential thrombocytosis?

Answer 16

• Differential Diagnosis:
  
  • Exclude reactive thrombocytosis (high platelet counts):
    
    • Iron deficiency
    • Chronic inflammatory states
    • Infectious diseases
    • Post-splenectomy
    • Solid tumors
  • Other MPN: PV, PMF, CML
• Diagnosis (Proposed per the WHO revisions):
  
  • Sustained platelet count > 450 x 109/L
  • Megakaryocyte proliferation (enlarged/mature) in the bone marrow
  • Exclusion of PV, PMF, CML, MDS, or other myeloid neoplasm
  • Clonal marker (JAK2 V617F (50%), or exclusion of reactive causes if negative); soon, calreticulin gene mutations will be incorporated into diagnostic algorithms
• Clinical concerns:
  
  • Many are asymptomatic!
  • Vasomotor symptoms-often due to platelet activation
    
    • headache
    • dizziness
    • syncope
    • visual disturbance
    • erythromelalgia
  • Large vessel thrombosis (venous or arterial)
  • Bleeding (acquired Von Willebrand’s with extreme thrombocytosis)
  • Splenomegaly is usually mild, and leukocytosis can be seen
  • Disease transformation
• Prognosis: Survival often similar to age-matched controls

Question 17

What is the treatment of essential thrombocytosis?

Answer 17

• Aspirin
• Chemotherapy: (Hydroxyurea)—often in those over 60, or with prior thrombosis
• Anagrelide: Decrease platelet production
• Pegylated Interferon-Potential disease modifying effects

Question 18

What are the unique features and epidemiology of Primary Myelofibrosis (or secondary, after long history of ET or PV)?

Answer 18

• Unique features:
  
  • Marrow fibrosis with subsequent failure, extramedullary hematopoeisis, highest rate of AML transformation and worst prognosis
  • De novo, or as an evolution from ET or PV
• Epidemiology:
  
  • 0.2 per 100,000 new cases; often male, often around age 65

Question 19

What is the differential diagnosis, diagnosis, clinical concerns, and prognosis of primary myelofibrosis?

Answer 19

• Differential diagnosis:
  
  • Exclude other causes of marrow fibrosis:
    
    • Acute myelofibrosis (more akin to leukemia)
    • MDS with fibrosis
    • CML
    • Other malignancies: Hodgkin’s, Hairy Cell, Mastocytosis, Eosinophilic leukemia, Metastatic Carcinoma
    • Infection
    • Autoimmune disease
• Diagnosis (Proposed per the WHO revisions):
  
  • Major:
    
    • Megakaryocyte proliferation and atypia, with reticulin or collagen fibrosis
    • Exclude CML, PV, MDS, other myeloid neoplasms
    • Clonal marker (JAK2 V617F in 50%, MPL in 10%); if negative, exclude secondary causes
  • Minor:
    
    • Leukoerythroblastosis (immature WBC, tear drop, and nucleated RBC’s on the smear)
    • High LDH
    • Anemia
    • Splenomegaly
• Clinical concerns:
  
  • Constitutional symptoms prominent (cytokine –mediated hypercatabolic state)
  • Extramedullary hematopoiesis (often manifest as massive splenomegaly)
  • Anemia
  • Leukocytosis and/or thrombocytosis
  • Complications of bone marrow failure
  • Leukemic transformation
• Prognosis: 5-6 years median survival but can be quite variable

Question 20

What is the treatment of primary myelofibrosis?

Answer 20

• Allogeneic transplantation (curative, but high morbidity/mortality
• Palliative/Supportive:
  
  • Anemia-directed therapies—androgen, erythropoeitic stimulating agents, immunomodulatory agents (thalidomide and other)
  • JAK-inhibitors (address symptoms and splenomegaly)
  • Extramedullary hematopoeisis: Hydroxyurea, Splenectomy, Splenic Radiation