Myeloproliferative Neoplasms

Myeloproliferative neoplasms (MPNs) are a group of blood cancers that cause excess blood cell production in the bone marrow and often in the peripheral blood, and are characterized by clonal genetic changes. MPNs include chronic myeloid leukemia (CML), polycythemia vera (PV), essential thrombocythemia (ET), primary myelofibrosis (PMF), chronic neutrophilic leukemia (CNL), and chronic eosinophilic leukemia (CEL). CML, which is discussed separately, is defined by the presence of the BCR-ABL1 fusion gene; the other MPN types are BCR-ABL1 negative. The majority of patients with PV, ET, and PMF have a mutation in the JAK2, CALR, or MPL gene, which carries implications for classification, diagnosis, and prognosis; however, other clonal markers may also be diagnostic for MPN.

Laboratory testing for the evaluation of MPN includes an initial workup of blood counts (CBC). Peripheral blood smear microscopy, bone marrow histology, cytogenetics, and genetic profiling complete the diagnostic testing. A diagnosis is made when results of these studies meet the specific diagnostic criteria for a particular MPN subtype. Distinguishing MPN types and grades is essential because treatments vary and long-term clinical outcomes differ significantly among the subtypes. 

Quick Answers for Clinicians

How do myeloproliferative neoplasms differ from myelodysplastic syndromes/myeloproliferative neoplasms?

Myeloproliferative neoplasms (MPNs) are characterized by an overproduction of red blood cells, platelets, or certain white blood cells; myelodysplastic syndromes (MDSs) are characterized by overproduction of defective, dysplastic myeloid cells, which results in peripheral blood cytopenias. The diseases classified as MDS/MPN exhibit both dysplastic and proliferative features. MDS/MPN disorders include chronic myelomonocytic leukemia (CMML), atypical chronic myeloid leukemia (aCML), juvenile myelomonocytic leukemia (JMML), MDS/MPN with ring sideroblasts and thrombocytosis (MDS/MPN-RS-T), and unclassifiable MDS/MPN. 

What is the testing strategy for diagnosing myeloproliferative neoplasms?

The diagnosis of myeloproliferative neoplasms (MPNs) requires a combination of CBC and peripheral smear examination, bone marrow histology, chromosome analysis, and molecular testing.  The combination of these studies allows clinicians to determine whether results meet corresponding diagnostic criteria. Subclassification often requires a bone marrow biopsy with ancillary cytogenetic and molecular testing.

What is the role of next generation sequencing in the diagnosis of myeloproliferative neoplasms?

Next generation sequencing (NGS) panels that include JAK2, MPL, and CALR genes may be used in place of individual gene tests in the initial diagnostic workup of myeloproliferative neoplasms (MPNs); NGS may also be especially useful to establish clonality in the diagnosis of triple-negative MPNs, in which JAK2, MPL, and CALR gene mutations are not present.  Furthermore, NGS can identify multiple spliceosome genes and can also identify additional prognostically relevant  mutations.  NGS testing is recommended in select patients to evaluate for higher-risk mutations that are associated with disease progression. 

Is further testing recommended after myeloproliferative neoplasm diagnosis is made?

Coagulation testing to evaluate for acquired von Willebrand disease (VWD) and/or other coagulopathies is recommended in patients with an elevated platelet count and/or unexplained bleeding, and in those who are undergoing high-risk surgical procedures.  If hematopoietic cell transplantation is being considered, human leukocyte antigen (HLA) type testing performed on a blood sample is necessary for donor matching. 

Indications for Testing

Along with medical history, symptom assessment, and physical examination, the following nonspecific laboratory tests are recommended as part of the initial evaluation in the diagnostic workup of MPNs: CBC, peripheral blood smear, comprehensive metabolic panel (including lactate dehydrogenase [LDH], liver function, and serum uric acid tests), serum erythropoietin (EPO), and serum iron level measurements.  If the results of these tests suggest the possibility of MPN, molecular testing, chromosome analysis, and bone marrow staining are indicated.

Classification

The following are the major MPN subtypes, not including CML.

Distinguishing Characteristics of Myeloproliferative Neoplasms
Subtype Characteristics
PV High number of RBCs (high hemoglobin, red cell mass)

Risk of post-PV MF with poor outcome

ET High number of platelets and increased numbers of large, atypical megakaryocytes in the bone marrow

Fibrosis is rare; can indicate initial misdiagnosis of early-phase PMF

PMF De novo MF (rather than from the transformation of PV to MF)

Leukoerythroblastic blood smear with dacryocytes if marrow is fibrotic

Bone marrow fibrosis might be absent or minimal in early-stage/prefibrotic PMF

Reticulin or collagen fibrosis is considerable in overt PMF

CNL Sustained mature neutrophilia in peripheral blood, hepatosplenomegaly, and hypercellularity in bone marrow due to neutrophilic granulocyte proliferation

CSF3R mutations are common but not specific

CEL, NOS Eosinophilia is the dominant hematologic abnormality caused by autonomous, clonal proliferation of eosinophil precursors

Evidence of clonality; abnormal bone marrow morphology common

MPN-U Designated for cases with features of an MPN but which do not meet diagnostic criteria, whether because distinguishing features are not fully developed or because the subtype is obscured by an advanced stage or another condition
MF, myelofibrosis; MPN-U, MPN, unclassifiable; NCCN, National Comprehensive Cancer Network; NOS, not otherwise specified; RBC, red blood cell; WHO, World Health Organization

Sources: NCCN,  WHO 

Diagnostic Criteria

The diagnosis of MPN should be based on the 2017 WHO diagnostic criteria.  Criteria include specific findings from the CBC, blood smear, and bone marrow analysis, correlated with clinical history as well as the presence of certain molecular markers and the exclusion of other disorders.  

Laboratory Testing

Diagnosis

Molecular Testing

Testing for BCR-ABL1 Mutation

Testing of peripheral blood or bone marrow by fluorescence in situ hybridization (FISH) is best for initial screening because it will detect rare breakpoints that may not always be detected by molecular methods. Multiplex reverse transcriptase polymerase chain reaction (RT-PCR) can also be used to confirm and monitor the BCR-ABL1­ fusion gene, the presence of which is diagnostic for CML in the appropriate context; the absence of BCR-ABL1 by FISH essentially excludes CML, and testing for other MPN mutations should be performed.  For testing specific to CML, see the Chronic Myelogenous Leukemia topic.

Testing for Other Mutations

Molecular testing is used to assess clonality and to detect MPN-specific mutations.  Molecular testing of blood should be performed first for the JAK2 V617F mutation in all patients because it is the most common mutation and occurs in most patients (>95%) with PV.   If the JAK2 V617F mutation is not detected, testing for CALR and then MPL mutations should follow for patients with ET or PMF.  If PV is still suspected in those with negative JAK2 V617F mutation results, testing should be performed for JAK2 exon 12 mutations. In those with ET or PMF but without JAK2, MPL, or CALR mutations (triple-negative MPNs), testing for mutations in ASXL1, CBL, CSF3R, DNM3TA, EZH2, IDH1, IDH2, LINK/SH2B3, SF3B1, SRSF2, TET2, TP53, and U2AF1 genes should then be considered. A comprehensive next generation sequencing (NGS) myeloid panel can be useful for this testing. 

Patients with molecular evidence of PDGFRA, PDGFRB, FGRF1, or PCM1-JAK2 rearrangements are considered to have myeloid/lymphoid neoplasms of a different classification from MPN.

Testing using a multigene NGS panel that includes JAK2, CALR, and MPL may be used instead of single-gene tests.  NGS provides the benefit of identifying additional mutations that may have prognostic importance.

Genetic Abnormalities Associated with MPNs
Gene Frequency Prognostic Significance
JAK2 V617F PV: >90%

ET: 60%

PMF: 60%

Intermediate prognosis in PMF

Higher risk of thrombosis compared with CALR mutation

JAK2 exon 12 PV: 2-3% Rates of thrombosis, evolution to MF or leukemia, and death similar to rates for JAK2 V617F mutation
CALR ET: 20-35%

PMF: 20-35%

Improved survival compared with JAK2 mutation and triple-negative PMF

Lower risk of thrombosis compared with JAK2 mutation

Same overall survival or rate of myelofibrotic or leukemic transformation as in JAK2-mutated ET

MPL ET: 1-4%

PMF: 5-8%

PV: rare

Intermediate prognosis in PMF

Higher risk of thrombosis compared with CALR mutation

Triple-negative MPNs

(ASXL1, CBL, CSF3R, DNM3TA, EZH2, IDH1, IDH2, LNK/SH2B3, SF3B1, SRSF2, TET2, TP53, U2AF1)

ET: 10%

PMF: 10%

Independently associated with worse overall survival and leukemia-free survival
CSF3R CNL: 90% Variable survival but usually progressive disease
Sources: NCCN,  WHO 

Cytogenetics

Cytogenetic analysis is important in distinguishing MPN subtypes. The chromosome analysis also serves to provide evidence of clonality and clonal evolution over time, and to assess the success of treatment. Chromosomal evaluation (eg, karyotype) is performed with or without FISH and should be done with bone marrow biopsy when possible.  The Philadelphia chromosome, which results from a reciprocal translocation of chromosomes 9 and 22 and affects the BCR-ABL1 fusion gene, is the hallmark of CML. Although specific chromosomal abnormalities have not been identified for MPNs other than CML, abnormalities range from <5-30% and are varied.  Complex karyotypes are defined as three or more unrelated chromosomal abnormalities, or one or two abnormalities that include trisomy 8, 7/7q-, i(17q), 5/5q-, 12p-, inv(3), or 11q23 rearrangement. These abnormalities have prognostic significance and may predict the transformation of MPN to acute myeloid leukemia (AML). 

Bone Marrow Staining

Bone marrow evaluation is used to confirm a diagnosis of MPN and to assess the blast percentage and any evidence of fibrosis, which help to determine the prognosis. Trichrome and reticulin staining of bone marrow aspirate or biopsy is necessary to accurately assess the degree of fibrosis.  Bone marrow histology should be assessed to rule out disease progression to MF before starting cytoreductive therapy. 

Prognosis

The overall survival of patients with MPNs is variable depending on the subtype.  Several scoring systems and prognostic models have been developed for the risk stratification of patients with MPNs. See the National Comprehensive Cancer Network Clinical Practice Guidelines in Oncology for Myeloproliferative Neoplasms  for recommendations on risk stratification.

Monitoring

Monitoring of Treatment Effects

Ruxolitinib has been associated with increased levels of total cholesterol, low-density lipoprotein cholesterol, and triglycerides; thus, assessment of lipid profiles should be performed 8-12 weeks following initiation of ruxolitinib.  Patients with high lipid levels should be monitored and treated according to clinical guidelines for hyperlipidemia.  See Atherosclerotic Cardiovascular Disease Risk Markers for information on screening and testing for dyslipidemia.

Patients should be monitored for additional risks associated with ruxolitinib use, including :

  • Renal impairment
  • Hepatic impairment
  • Bacterial, mycobacterial, fungal, and viral infections
  • Tuberculosis
  • Hepatitis B
  • Progressive multifocal leukoencephalopathy
  • Herpes zoster
  • Nonmelanoma skin cancer

Patients receiving danazol for the management of MF-associated anemia should be screened for prostate cancer and monitored with liver function tests. 

ARUP Lab Tests

Molecular Testing

BCR-ABL1 Testing

Detect the presence of a BCR-ABL1 fusion gene to diagnose or exclude CML

Monitor for minimal residual disease (MRD)

Panel/Reflex Tests

Assess for somatic variants in genes associated with myeloid malignancies that are relevant for diagnosis, prognosis, or clinical management in patients with MPN, MDS/MPN, and related disorders

In addition to the above, evaluate for important genomic abnormalities in MPN that may have diagnostic, prognostic, and/or therapeutic significance, such as loss/gain of DNA or loss of heterozygosity (LOH)

Evaluate for mutations when diagnosis of ET or PMF is suspected

JAK2 Mutation Tests

Evaluate for the JAK2 V617F mutation in peripheral blood or bone marrow

Quantitate JAK2 V617F allele frequency to aid in risk stratification and therapeutic monitoring 

Evaluate for mutations when diagnosis of PV is suspected

Evaluate for PV in cases of high suspicion but negative JAK2 V617F mutation status

CALR Mutation Test

Determine diagnosis and prognosis of MPN in patients with JAK2-negative mutation

MPL Mutation Test

Evaluate for ET or PMF when suspected in individuals who are negative for JAK2 V617F  and CALR mutations

Cytogenetics

Karyotyping

Diagnose and monitor MPN and determine prognosis

Diagnose and monitor MPN and determine prognosis when bone marrow cannot be obtained

FISH

Limited role in the workup of MPNs in the setting of an otherwise optimal cytogenetic study

Use to order individual or multiple oncology FISH probes if standard FISH panels are not desired

Bone Marrow Staining

Use to assess fibrosis in the bone marrow

Trichrome stain is used for collagen fibrosis

Erythropoietin Testing

Initial screen for evaluation of polycythemia

Medical Experts

Contributor

Karner

Kristin Hunt Karner, MD
Assistant Professor of Clinical Pathology, University of Utah
Medical Director, Hematopathology and Molecular Oncology, ARUP Laboratories

References

Additional Resources
Resources from the ARUP Institute for Clinical and Experimental Pathology®
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