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MP 2.04.60

JAK2 and MPL Mutation Analysis in Myeloproliferative Neoplasms


Medical Policy

Section
Medicine
 
Original Policy Date
01/14/10
Last Review Status/Date
Reviewed with literature search/2:2013
Issue
2:2013
  Return to Medical Policy Index

Disclaimer

Our medical policies are designed for informational purposes only and are not an authorization, or an explanation of benefits, or a contract.  Receipt of benefits is subject to satisfaction of all terms and conditions of the coverage.  Medical technology is constantly changing, and we reserve the right to review and update our policies periodically.


Description

Mutations in the gene coding for the Janus kinase 2 (JAK2) protein and in the gene myeloproliferative leukemia virus oncogene (MPL) coding for the thrombopoietin receptor have been associated with myeloproliferative neoplasms and with acute lymphoblastic leukemia (ALL) in Down syndrome patients. This policy addresses the use of JAK2 and MPL gene mutation testing for diagnosis, prognosis, and treatment selection in patients with myeloproliferative neoplasms. This policy will also address the potential use of JAK2 mutations in the diagnosis or selection of treatment in patients with Down syndrome and acute lymphoblastic leukemia.

Background

Myeloproliferative neoplasms (MPNs) are a category of uncommon overlapping blood diseases characterized by the production of one or more blood cells—chronic myeloid leukemia (CML), polycythemia vera (PV), essential thrombocythemia (ET), primary myelofibrosis (PMF), systemic mastocytosis, chronic eosinophilic leukemia, and others. A common finding in many of the MPNs is clonality, and a central pathogenic feature is the presence of a mutated version of the tyrosine kinase enzyme, such that it is abnormally constitutively activated. The paradigm for use of this information to revolutionize patient management is CML. A unique chromosomal change (the Philadelphia chromosome) and an accompanying unique gene rearrangement (BCR-ABL) resulting in a continuously activated tyrosine kinase enzyme were identified. These led to discovery of a targeted tyrosine kinase inhibitor drug treatment (imatinib) that produces long-lasting remissions.

Diagnosis and monitoring of patients with Philadelphia chromosome-negative MPNs have been challenging because many of the laboratory and clinical features of the classic forms of these diseases—PV, ET, and PMF—can be mimicked by other conditions such as reactive or secondary erythrocytosis, thrombocytosis, or myeloid fibrosis. In addition, these entities can be difficult to distinguish on morphologic bone marrow exam, and diagnosis can be complicated by changing disease patterns: PV and ET can evolve into PMF or undergo leukemic transformations. World Health Organization (WHO) criteria were published as a benchmark for diagnosis in 2001. These have been challenging to use because they involve complex diagnostic algorithms, rely on morphologic assessment of uncertain consistency, and require tests such as endogenous erythroid colony formation that are not well-standardized or widely available.

In March and April of 2005, 4 separate groups using different modes of discovery and different measurement techniques reported the presence of a novel somatic point mutation in the conserved autoinhibitory pseudokinase domain of the gene coding for the Janus kinase 2 (JAK2) protein in patients with classic MPNs. The mutation was noted to cause a valine-to-phenylalanine substitution at amino acid position 617 (JAK2V617F). Loss of JAK2 autoinhibition, caused by JAK2V617F, results in constitutive activation of the kinase and in recruitment and phosphorylation of substrate molecules including signal transducers and activators of transcript (STAT) proteins (so-called JAK-Stat signaling). The result is cell proliferation independent of normal growth factor control. These findings were subsequently confirmed, and additional mutations affecting the JAK2 gene—mutations in exon 12—or involved in complementary pathways such as the thrombopoietin-receptor-pathway mutations in MPL exon 10—were identified. These mutations were seen with varying but reliable frequency in patients with classic MPNs and with uncommon and erratic frequency in other MPNs. In addition, unique cases of JAK2 mutations were reported in a subset of patients with Down syndrome-associated acute lymphoblastic leukemia (ALL).

While these mutations were of importance in better understanding the biology of the MPNs, they were also of immediate interest as laboratory tools to aid in diagnosis and management of disease. To that end, at least 4 potential intended uses for mutation testing have been considered, including:

a. Diagnosis of patients with clinical, laboratory, or pathologic findings suggesting classic MPNs (PV, ET, or PMF);

b. Diagnosis or selection of treatment for patients with Down syndrome ALL;

c. Phenotyping of disease subtypes in patients with MPNs to establish disease prognosis;

d. Identification, selection, and monitoring of treatment.

More than a dozen commercial laboratories currently offer a wide variety of diagnostic procedures for JAK2 gene mutation testing and MPL testing. These tests are available as laboratory developed procedures under the U.S. Food and Drug Administration (FDA) enforcement discretion policy for laboratory developed tests. Variable analytical and clinical performance has been reported, suggesting that the nucleic acid amplification methodologies are more sensitive than mutation sequence analysis. It appears that there can be considerable interassay and interlaboratory variability in the generation of testing results.


Policy

JAK2 tyrosine kinase and MPL mutation testing may be considered medically necessary in the diagnosis of patients presenting with clinical, laboratory, or pathological findings suggesting classic forms of myeloproliferative neoplasms (MPN), that is, polycythemia vera (PV), essential thrombocythemia (ET), or primary myelofibrosis (PMF).

JAK2 tyrosine kinase and MPL mutation testing may be considered investigational in all other circumstances including, but not limited to, the following situations.

  • Diagnosis of nonclassic forms of MPNs
  • Molecular phenotyping of patients with MPNs
  • Monitoring, management, or selecting treatment in patients with MPNs
  • Diagnosis or selection of treatment in patients with Down syndrome and acute lymphoblastic leukemia


Policy Guidelines

Patients suspected to have polycythemia vera (PV) should first be tested for the most common finding JAK2V617F. If testing is negative, further testing to detect other JAK2 tyrosine kinase mutations, e.g., in exon 12, is warranted.

Patients suspected to have essential thrombocythemia (ET) or primary myelofibrosis (PMF) should first be tested for JAK2 mutations, as noted. If testing is negative, further testing to detect MPL mutations is warranted.

Effective in 2012, there is a specific CPT code for JAK2V617F testing:

81270: JAK2 (Janus kinase 2) (e.g., myeloproliferative disorder) gene analysis, p.Val617Phe (V617F) variant.

If further JAK2 testing is performed, the following code might be reported:

81403: Molecular pathology procedure, Level 4 (e.g., analysis of single exon by DNA sequence analysis, analysis of >10 amplicons using multiplex PCR [polymerase chain reaction] in 2 or more independent reactions, mutation scanning or duplication/deletion variants of 2-5 exons) – which includes JAK2 (Janus kinase 2) (e.g., myeloproliferative disorder), exon 12 sequence and exon 13 sequence, if performed

The following CPT code is available for MPL testing:

81402: Molecular pathology procedure, Level 3 (e.g., >10 SNPs [single-nucleotide polymorphism], 2-10 methylated variants, or 2-10 somatic variants [typically using non-sequencing target variant analysis], immunoglobulin and T cell receptor gene rearrangements, duplication/deletion variants 1 exon, loss of heterozygosity [LOH], uniparental disomy [UPD]) – which includes MPL (myeloproliferative leukemia virus oncogene, thrombopoietin receptor TPOR) (e.g., myeloproliferative disorder), common variants (e.g., W515A, W515K, W515L, W515R)


Benefit Application
BlueCard/National Account Issues

None identified


Rationale

The original policy was based on a literature search using MEDLINE that was performed for the period of March 2005 through November 2009. The search identified 1,313 publications including 150 reviews, 41 clinical trials, 17 editorials, 2 meta-analyses, and 1 observational prospective study. The literature search for the most recent update was performed on January 8, 2013.

Tyrosine Kinase Mutation Analysis and the Diagnosis of Philadelphia Chromosome-Negative Myeloproliferative Neoplasms

Diagnosis of classic myeloproliferative neoplasms

Diagnosis of the various classic forms of myeloproliferative neoplasms (MPNs) has been most recently based on a complex set of clinical, pathological, and biological criteria first introduced by the Polycythemia Vera Study Group (PVSG) in 1996 (1, 2) or the World Health Organization (WHO) in 2001. (3) Both of these classifications use a combination of clinical, pathological, and/or biological criteria to arrive at a definitive diagnosis. Varying combinations of these criteria are used to determine if a patient has polycythemia vera (PV), essential thrombocythemia (ET), or primary myelofibrosis (PMF): MPNs that are Philadelphia chromosome-negative. (An important component of the diagnostic process is a clinical and laboratory assessment to rule out reactive or secondary causes of disease.)

As noted in the Description section, some diagnostic methods (i.e., bone marrow microscopy) are not well-standardized, (4-6) and others (i.e., endogenous erythroid colony formation) are neither standardized nor widely available.

In March 2005, a novel somatic gain-of-function point mutation was discovered in the conserved autoinhibitory pseudokinase domain of the Janus kinase 2 (JAK2) protein in patients with MPNs. The mutation was present in blood and bone marrow from a variable portion of patients with classic BCR-ABL-negative (i.e., Philadelphia chromosome-negative) MPNs including 65% to 97% of patients with PV, 23% to 57% with ET, and 35% to 56% with PMF (see Table 1). It was initially reported to be absent in all normal subjects and in patients studied with secondary erythrocytosis, (6-16) although recently very low levels of mutated cells have been reported to be found in a small subset of the healthy population. (17, 18)

That the JAK2V617F -mutated protein was potentially causal for the disease was suggested by the demonstration that cell lines transfected with JAK2V617F could be maintained in culture for several weeks in the absence of growth factor and that dependency was restored by transduction of wild-type JAK2. In vivo, mice irradiated and then transplanted with bone marrow cells infected with retrovirus containing the mutation developed a myeloproliferative syndrome. (8)

Table 1: Frequency ofJAK2V617FMutations in Patients with Classic Philadelphia Chromosome-Negative MPN 

Study Mutation Detection Method PV ET PMF Normals Secondary Erythrocystosis Comment
Baxter 2005 (6) DNA Sequencing, PCR 71/73 (97%) 29/51 (57%) 8/16 (50%) 90/90 (0%)   Case series
Levine 2005 (7) DNA Sequencing 121/164 (74%) 37/115 (32%) 16/46 (35%) 0/269 (0%)    Case series
James 2005 (8) DNA Sequencing 40/45 (88%) 9/21 (43%) 3/7 (43%) 0/15 (0%) 0/35 (0%) Case series
Kravolics 2005 (9) DNA Sequencing 83/128 (65%) 21/94 (23%) 13/23 (56%) 0/142 (0%) 0/11 (9%) Case series
Jones 2005 (10) PCR Testing 58/72 (81%) 24/59 (41%) 15/35 (43%) 0/160 (0%) 0/4 (0%) Case series
Tefferi 2006 (11) PCR Testing 36/38 (95%) 12/46 (55%) 3/10 (30%)   0/19 (0%) Case series
Zhoa 2005 (12) DNA Sequencing 20/24 (83%)     0/12 (0%)    Case series
Campbell 2005 (13) PCR Testing   414/776 (53%)          Prospective, case series
Wolanski 2005 (14) PCR Testing    73/150 (49%)          Case series
Campbell 2005 (15) PCR Testing       83/152 (55%)       Case series
Tefferi 2005 (16) PCR Testing       80/157 (51%)       Case series

Although almost all studies reported were retrospective and/or cross-sectional case series and although both analytical and clinical performances appear dependent on the laboratory method used to detect the mutation, there has been impressive consistency across studies in demonstrating that the JAK2V617F mutation is a highly specific marker for clonal evidence of an MPN.

Early reports suggested that specificity was 100%, although sensitivity was variable (as high as 97% in patients with PV but only 30% to 50% in patients with ET or PMF). A result of the extraordinary specificity observed was that in the setting of evaluating a patient with a suspected Philadelphia chromosome-negative MPN, the predictive value of a positive test also approached 100%. It was recognized within months of the discovery of this mutation, that JAK2V617F testing could dramatically expedite diagnosis by reducing the need for complex workups of secondary or reactive causes of the observed proliferative process in the JAK2V617F-positive patients. (19) Two important caveats should be noted in use of this test. A negative result cannot be used to rule out a classic MPN. A positive result is excellent evidence that a classic MPN is present but alone is insufficient to subclassify the disease category present.

In recognition of the value of use of this new marker in refining the diagnostic workup of patients suspected of having Philadelphia chromosome-negative MPNs, several reports recommending new algorithms for diagnosis were published.(20, 21) The 2001 World Health Organization (WHO) criteria were revised in 2008 to reflect incorporation of the test in patient workup.(22, 23)

It is important to note that the 2008 WHO revision represents expert consensus and is not based on independent validation of the 2008 criteria compared to earlier diagnostic criteria or on clinical outcomes. Since these previous criteria were themselves based on expert consensus alone, the importance of such comparative studies may be a moot point. However, 2 small cross-sectional comparative studies have been performed that evaluate JAK2V617F testing directly against previously established PVSG or WHO criteria.

In 2005, James et al. (20) compared PV diagnosed using WHO or PVSG criteria with a streamlined diagnostic approach for PV using a 2-step algorithm (elevated hematocrit and the presence of the JAK2V617F mutation). Although the study group was small (45 patients with a PVSG diagnosis of PV and 61 patients meeting WHO criteria), use of the 2-step algorithm resulted in a correct diagnosis in 96% (PVSG criteria) or 93% (WHO criteria) of patients with PV.

In 2008, Kondo et al. (24) compared the 2001 WHO classification and the 2008 classification in a small study of 75 patients undergoing evaluation for MPN. Using the 2001 criteria, 57 patients were diagnosed with MPNs, including 16 with PV, 37 with ET, and 4 with PMF. Using the 2008 criteria, 59 patients were diagnosed with MPNs. The PV and PMF categories were in complete agreement. The 2008 criteria caused reclassification of 2 patients (1 with erythrocytosis and 1 with thrombocytosis) into the ET category.

Ongoing studies of new drugs targeted to treat the mutated tyrosine kinase in patients with MPN are expected to cast additional light on the functionality of the observed JAK2V617F mutation and are likely to contribute not only to refined treatment choices but to improved insight into the diagnostic role of this important marker.

Diagnosis of nonclassical forms of MPNs

While the most common Philadelphia-negative MPNs include what are commonly referred to as classic forms of this disorder (PV, ET, and PMF), patients may rarely show unusual manifestations of this proliferative hematopoietic disorder including nonclassical forms of MPNs such as chronic myelomonocytic leukemia, hypereosinophilic syndrome, systemic mastocytosis, chronic neutrophilic leukemia, or others. Reports have appeared that identify JAK2V617 F mutations in some of these cases. (10, 25) Due to the paucity of data about the significance or use of JAK2V617F or MPL mutations in these disease settings, use of the test in patients with these diseases should be considered investigational.

 

Other tyrosine kinase or related mutations

In 2007, Scott et al. (26) identified 4 somatic gain-of-function mutations in the JAK2 exon 12 section of 10 of 11 PV patients without the JAK2V617F mutation. Patients with a JAK2 exon 12 mutation differed from those with the JAK2V617F mutations, presenting at a younger age with higher hemoglobin levels and lower platelet and white cell counts. Erythroid colonies could be grown from their blood samples in the absence of exogenous erythropoietin, and mice treated with transfected bone marrow transplants developed a myeloproliferative syndrome.

Findings were subsequently confirmed by a number of investigators who identified additional mutations with similar functional consequences in patients with PV and in patients with idiopathic erythrocytosis. (27, 28) Based on these findings, it was concluded that the identification of JAK2 exon 12 mutations provides a diagnostic test for JAK2V617F -negative patients who present with erythrocytosis (see Policy Guidelines). Of note, different mutations in the same gene appear to have different effects on signaling, resulting in distinct clinical phenotypes. (26) This perhaps explains the surprise findings of a series of JAK2 mutations in patients with Down syndrome-associated acute lymphoblastic lymphoma (ALL).

In 2006, Pikman et al. (29) surveyed JAK2 mutation-negative patients with suspected ET and PMF to determine if mutations in pathways complementary to Janus kinase 2 signaling could be identified. A mutation of the thrombopoietin receptor gene (MPL) at codon 515 (exon 10) causing a change from tryptophan to leucine (MPLW515L) was discovered.

Subsequent studies identified additional mutations including MPLS505N, MPLW515Ki, and MPLW515Kii in a small but growing number of patients with ET and PMF (see Table 2). (30-33) While this mutation can be found in both JAK2V617F- positive and -negative patients, it is of particular value in the latter in helping to establish a clonal basis of the observed disease process.

Table 2: Frequency of MPL 515 Mutations in Patients with Philadelphia Chromosome-Negative MPN

Study Mutation
Detection
Method
PV ET PMF Normals Other
MPNs
Comment
Pikman et
al. 2006
(29)

DNA
Sequencing

0/10
(0%)
0/50
(0%)
4/45
(8.8%)
0/270
(0%)
  JAK2
Negative
Pardanani
et al. 2006
(30)
Site 1: PCR
with DNA
sequencing;

Site 2: DNA
sequencing
0/38
(0%)


0/204
(0%)
2/167
(1%)


2/151
(1%)
8/198
(4%)


5/92
(5%)
0/64
(0%)
3/118
(2.5%)
  
Beer et al.
2008 (31)
PCR testing   Preliminary
3/88
(3.4%)

Prospective
32/776
(4.1%)
Preliminary
8/112
(7.1%)



      
Pancrazzi
et al. 2008
(32)
PCR testing 0/50
(0%)
  19/217
(8.7%)
0/60
(0%)
    
Ruan et al.
2009 (33)
PCR testing 0/32
(0%)
7/199
(3.5%)
3/24
(12.5%)
0/52
(0%)
0/29
(0%)
  
Schnittger
et al. 2009
(34)
PCR testing    19/356
(5.3%)
10/193
(5.2%)
   2/269
(0%)
 

Similar to the observations made on the JAK2V617F-negative mutations involving exon 12, the MPL exon 10 mutations appeared to demonstrate an autoinhibitory role leading to receptor activation in the absence of thrombopoietin binding. Expression of the MPL allele resulted in cytokine-independent growth of three independent cell lines, and transplantation of mice with bone marrow expressing this allele results in a distinctive myeloproliferative disorder. (30)

Although the data sets are small, the JAK2 exon 12 and MPL exon 10 mutations are unique, appear to be associated with MPNs, and exhibit in vitro and murine model behavior consistent with a causative role in MPNs. The 2008 WHO criteria specifically cite testing for JAK2 exon 12 mutations in patients with suspected PV (presumably in patients who are JAK2V617F -negative), specifically cite testing for MPLW515L/K in patients with PMF (presumably in patients who are JAK2V617F -negative), and suggest patients with ET be subject to testing for JAK2V617F or other clonal markers, such as MPL testing in patients with ET (see Policy Guidelines).

Mutations of JAK2 in acute lymphoblastic leukemias associated with Down syndrome
Children with Down syndrome have a 10- to 20-fold increased risk of developing acute leukemia. The mechanisms for this are unknown; interestingly, the disease process appears to be exclusively B cell in origin. In 2007, Malinge et al. published a case report (35) describing a novel JAK2 mutation in a patient with Down syndrome and B-cell precursor acute lymphoblastic lymphoma. Speculating that this finding might relate to the role the JAK/signal transducer and activator of transcription (STAT) signaling pathway played in early B-cell development, Bercovich et al. (36) studied 88 patients with Down syndrome-acquired acute lymphoblastic leukemia (ALL) for JAK2 mutations and compared these to 216 patients with sporadic ALL. Five mutant alleles were identified in 16 (18%) of the patients with Down syndrome, all at a highly conserved arginine residue (R683) on exon 16. These mutations immortalized primary mouse hematopoietic progenitor cells in vitro. Only a single non-Down syndrome patient exhibited this mutation, and this patient was found to have an isochromosome 21Q. This finding was subsequently confirmed by Gaikwad et al. (37) who found that 20% of patients with Down syndrome with ALL exhibited a point mutation at this location. The role of this abnormality and efforts to consider treatment modifications based on its finding remain subjects for future study.

Molecular profiling – phenotype/genotype associations and impact on prognosis
While there has been great interest in the use of the JAK2V617F test as a front line diagnostic test in the evaluation of myeloproliferative patients, there has also been a growing effort to link the presence of this mutation and the quantitative measurement of its allele burden with clinical features and biological behavior. Unfortunately, due to differences in disease definitions, differences in methods of testing, differences in sample type (bone marrow versus circulating blood cells), and differences in study design, the literature in this area is conflicting and inconclusive.

Since the vast majority of patients with PV do exhibit the mutation, attention has been focused in this disease on differences in its presence in the homozygous versus heterozygous state and on whether allele burden correlates with clinical or laboratory features, Studies have suggested a range of findings including association of homozygous states with older age, higher hemoglobin level at diagnosis, leukocytosis, more frequent pruritus, increased incidence of fibrotic transformation, and larger spleen volumes. (38,39) Studies that compare quantitative measurements of allele burden with disease manifestations have demonstrated both a positive and a lack of association with thrombosis, fibrotic transformation, and need for chemotherapy. (40,41)

The impact of the presence of JAK2V617F in patients with ET is also controversial. In several studies, the presence of this mutation has been associated with advanced age, higher hemoglobin levels, increased leukocyte count, lower platelet count, and a higher rate of transformation to PV. (13, 14) Discrepant results have been reported for thrombotic events and for fibrotic transformation. (42) A recent meta-analysis by Dahabreh et al. (43) surveyed 394 studies on the subject of outcomes in ET. Dahabreh et al. concluded that thrombosis but not myelofibrosis or leukemia appeared to be influenced by the presence of JAK2 mutations. Dahabreh et al. cautioned that there was a need for prospective studies to determine how this information might be used in treatment choices.

Thrombotic effects have been reported to be most pronounced for splanchnic vascular events, (44) and there has been little support for use of testing in patients with more general thrombosis or primary thrombocytosis. (45) Results for splanchnic events have been contradictory. In one retrospective study performed looking at JAK2V617F in patients treated for thrombosis in ET and in unselected patients with splanchnic vein thrombosis (46) JAK2 V617F mutations did occur with increased frequency in patients with splanchnic vein thrombosis and appeared to identify a subset of patients who might benefit from antiplatelet therapy. However, the outcome of routine testing in both settings remained unclear. In recent international collaborative studies of patients with ET, patients with JAK2 V617F mutations appeared at risk for arterial thrombosis but not for venous thrombosis. (47)

A recent report by Hussein et al. (48) demonstrated that although there was significant overlap in JAK2V617 F allele burden among various MPN entities, quantitative measurements suggested discriminatory differences between patients with ET and the prefibrotic stage of PMF.

JAK2V617F mutational status and allele burden appear particularly poorly defined in patients with PMF. In a series of confusing and non-congruent articles, it has been concluded that

  • Patients with JAK2V617F mutations required fewer blood transfusions but exhibited poorer overall survival than those without the mutation. (15)
  • Patients with JAK2V617F mutations did not show differences in the incidence of thrombosis, overall survival, or leukemia-free survival.(29)
  • Patients with homozygous JAK2V617F mutations showed an increased evolution toward large splenomegaly, need of splenectomy, and leukemic transformation. (49)
  • Patients with low allele burdens appeared to exhibit shortened survival, perhaps because they represented a myelodepleted subset of affected patients. (29, 50)

Treatment

Due to the strong epidemiologic and biologic literature linking JAK2 pathway mutations to occurrence of MPNs, there has been considerable recent attention on using JAK2 as a molecular target for drug discovery. In preclinical and early clinical studies, a number of promising JAK2 inhibitors have been identified, and reports have suggested some of these are useful in symptom relief. (51) Many patients with these diseases have a good response to other therapies with cytotoxic drugs, and the natural course of disease, particularly for PV and ET, can be quite indolent. Considerable study will be required to sort through issues of safety and efficacy of these new treatments before they enter routine clinical use. Several early phase and preliminary treatment trials evaluating the safety and efficacy of tyrosine kinase inhibitors in patients with JAK2V617F -positive myeloproliferative neoplasms have been reported. (52-54) It has recently been noted that benefits from tyrosine kinase therapy may not be specific for JAK2V617F -positive myeloproliferative neoplasms but may be observed in wild-type disease as well. (55)

While the identification of a drug producing long-term remissions such as imatinib in chronic myeloid leukemia (CML) is the ultimate goal, it will likely be complicated by the complexity of molecular processes occurring in patients with these other MPNs and the fact that JAK2V617F alone does not appear to be a unique or absolutely necessary event in many patients with these diseases. The role of JAK2V617F in selecting or monitoring patients for new treatments or residual neoplasia remains undefined.

There are several reports that suggest JAK2V617F-positive patients are more sensitive to treatment with hydroxyurea than negative patients. (42) In one study of hydroxyurea treatment in patients with PV or ET harboring the JAK2V617F gene, serial changes in allele burden were observed. However, the value of these findings was unclear, and the authors concluded serial testing in patients on this drug should be confined to clinical studies. (56)

On November 16, 2011, the U.S. Food and Drug Administration (FDA) approved ruxolitinib (a JAK kinase inhibitor) for the treatment of intermediate- and high-risk myelofibrosis (including primary myelofibrosis, post-polycythemia vera myelofibrosis, and post-essential thrombocythemia myelofibrosis) due to results from 2 randomized controlled trials (RCTs). One, a double-blind RCT in patients with intermediate- to high-risk myelofibrosis, (57) randomized participants to twice-daily oral ruxolitinib (n=155) or placebo (n=154) and followed patients for 76 weeks. The primary outcome, reduction in spleen volume of 35% or more at 24 or more weeks, was observed in 41.9% of patients treated with ruxolitinib compared with 0.7% in the placebo group (p<0.001). Survival analysis by Kaplan Meier curves estimated 13 deaths in the ruxolitinib group (8.4%) and 24 in the placebo group (15.6%) over a median follow-up of 51 weeks (p=0.04). This significant association was not observed at the prospectively defined data cutoff of median 32 weeks’ follow-up (p=0.33). A myelofibrosis symptom score at 24 weeks showed an improvement of 45.9% in patients who received ruxolitinib compared with 5.3% in placebo patients. Discontinuation in the ruxolitinib and placebo groups due to adverse events was similar (11% to 10.6%, respectively). Ad hoc subgroup analyses on patients with JAK2V617F mutations indicated reduction in spleen volume of 34.6% compared to an increase of 8.1% in placebo. Patients with JAK2V617F mutation improved total symptom score by 52.6% in ruxolitinib compared to a worsening of 42.8% at 24 weeks in the placebo arm.

A second trial by Harrison et al. (NCT00934544) reached similar conclusions. Patients with intermediate- or high-risk primary myelofibrosis, post-polycythemia vera myelofibrosis, or post-essential thrombocythemia myelofibrosis received oral ruxolitinib (n=146) or best available therapy (n=73). (58) No difference in overall survival was observed between the 2 groups at 48 weeks. Twenty-eight percent of patients in the ruxolitinib group had at least a 35% reduction in spleen volume at 48 weeks compared to 0% in the best available treatment group (p<0.001). Among the subgroup of patients who were JAKV617F-positive, spleen reduction was 33% in the ruxolitinib group and 0% in the best available therapy group. In the ruxolitinib group, patients had an improved overall quality of life and a reduction in myelofibrosis symptoms compared to no benefit that was observed in the control group. Serious adverse events were similar between groups: anemia occurred in 5% of patients in the ruxolitinib group and 4% in the best-available-therapy group, pneumonia occurred in 1% of ruxolitinib group and 5% in the best-available-therapy group, and discontinuation of treatment in the ruxolitinib group occurred in 8% of patients and 5% in the best-available-therapy group.

Summary

There is an extensive and growing body of literature providing information on the clinical validation of the JAK2V617F as a distinctive marker of patients with Philadelphia chromosome-negative classic myeloproliferative neoplasms (MPNs). In almost a dozen reports (all case series), JAK2V617F has been found as a unique clonal finding in patients with polycythemia vera (PV), essential thrombocythemia (ET), or primary myelofibrosis (PMF). While the association between defined diseases and the presence of the marker has been rather variable depending on the detection methods used and the study designs applied, test specificity is virtually 100%. Patients with PV tested using polymerase chain reaction (PCR) methodology appear to have a test sensitivity that also may approach 100% (reports up to 97%), and in the subset of patients with suspected PV who are JAK2V617F -negative, there is compelling evidence in several case series to suggest other JAK2 mutations (involving exon 12) may be identified.

Given the difficulty in using classic criteria (morphology and complex tests such as erythropoietin measurements or measurements of endogenous erythroid colony formation), JAK2 testing will facilitate the diagnostic workup. The presence of this marker biologically and clinically is a convincing substitute for the need to rule out reactive causes of erythrocytosis. Testing for this marker is recommended in clinical practice guidelines for patients with all of the most common MPNs that are Philadelphia chromosome-negative. Therefore, JAK2 testing may be considered medically necessary as a diagnostic test for patients with signs and symptoms of MPN.

Mutations testing to establish disease phenotype (such as disease prognosis) or to select or monitor therapy remains an area of intense interest with a growing number of studies, in particular drug trials. Recently multiple additional mutations have been identified in patients with various MPN disorders. These appear to have less specificity than the JAK2 and MPL mutations, and their use in understanding, diagnosing and treating disease remains a matter requiring further study. It is currently unclear if these carry a broad, albeit nonspecific pathogenetic relevance to MPNs or whether they are simply passenger mutations with little or no functional relevance. JAK2 testing for prognosis or to direct therapy is considered investigational.

Practice Guidelines and Position Statements

WHO criteria for MPN (2008)

PV – Major criteria: presence of JAK2V617F or other functionally similar mutation such as JAK2 exon 12 mutation

ET- Major criteria: demonstration of JAK2V617F or other clonal marker, or in the absence of a clonal marker, no evidence for reactive thrombocytosis

PMF- Major criteria: demonstration of JAK2V617F or other clonal marker (e.g., MPLW515K or MPLW515L) or in the absence of a clonal marker, no evidence of bone marrow fibrosis due to underlying inflammatory or other neoplastic disease

Medicare National Coverage

No national coverage determination.

References:

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  2. Pearson TC, Messinezy M. The diagnostic criteria of polycythaemia rubra vera. Leuk Lymphoma 1996; 22 Suppl 1:87-93.
  3. Vardiman JW, Harris NL, Brunning RD. The World Health Organization (WHO) classification of the myeloid neoplasms. Blood 2002; 100(7):2292-302.
  4. Tefferi A, Thiele J, Vardiman JW. The 2008 World Health Organization classification system for myeloproliferative neoplasms: order out of chaos. Cancer 2009; 115(17):3842-7.
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  6. Baxter EJ, Scott LM, Campbell PJ et al. Acquired mutation of the tyrosine kinase JAK2 in human myeloproliferative disorders. Lancet 2005; 365(9464):1054-61.
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  8. James C, Ugo V, Le Couedic JP et al. A unique clonal JAK2 mutation leading to constitutive signalling causes polycythaemia vera. Nature 2005; 434(7037):1144-8.
  9. Kralovics R, Passamonti F, Buser AS et al. A gain-of-function mutation of JAK2 in myeloproliferative disorders. N Engl J Med 2005; 352(17):1779-90.
  10. Jones AV, Kreil S, Zoi K et al. Widespread occurrence of the JAK2 V617F mutation in chronic myeloproliferative disorders. Blood 2005; 106(6):2162-8.
  11. Tefferi A, Sirhan S, Lasho TL et al. Concomitant neutrophil JAK2 mutation screening and PRV-1 expression analysis in myeloproliferative disorders and secondary polycythaemia. Br J Haematol 2005; 131(2):166-71.
  12. Zhao R, Xing S, Li Z et al. Identification of an acquired JAK2 mutation in polycythemia vera. J Biol Chem 2005; 280(24):22788-92.
  13. Campbell PJ, Scott LM, Buck G et al. Definition of subtypes of essential thrombocythaemia and relation to polycythaemia vera based on JAK2 V617F mutation status: a prospective study. Lancet 2005; 366(9501):1945-53.
  14. Wolanskyj AP, Lasho TL, Schwager SM et al. JAK2 mutation in essential thrombocythaemia: clinical associations and long-term prognostic relevance. Br J Haematol 2005; 131(2):208-13.
  15. Campbell PJ, Griesshammer M, Dohner K et al. V617F mutation in JAK2 is associated with poorer survival in idiopathic myelofibrosis. Blood 2006; 107(5):2098-100.
  16. Tefferi A, Lasho TL, Schwager SM et al. The JAK2(V617F) tyrosine kinase mutation in myelofibrosis with myeloid metaplasia: lineage specificity and clinical correlates. Br J Haematol 2005; 131(3):320-8.
  17. Xu X, Zhang Q, Luo J et al. JAK2(V617F): Prevalence in a large Chinese hospital population. Blood 2007; 109(1):339-42.
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  19. Steensma DP. JAK2 V617F in myeloid disorders: molecular diagnostic techniques and their clinical utility: a paper from the 2005 William Beaumont Hospital Symposium on Molecular Pathology. J Mol Diagn 2006; 8(4):397-411; quiz 526.
  20. James C, Delhommeau F, Marzac C et al. Detection of JAK2 V617F as a first intention diagnostic test for erythrocytosis. Leukemia 2006; 20(2):350-3.
  21. McMullin MF, Reilly JT, Campbell P et al. Amendment to the guideline for diagnosis and investigation of polycythaemia/erythrocytosis. Br J Haematol 2007; 138(6):821-2.
  22. Tefferi A, Thiele J, Orazi A et al. Proposals and rationale for revision of the World Health Organization diagnostic criteria for polycythemia vera, essential thrombocythemia, and primary myelofibrosis: recommendations from an ad hoc international expert panel. Blood 2007; 110(4):1092-7.
  23. Vardiman JW, Thiele J, Arber DA et al. The 2008 revision of the World Health Organization (WHO) classification of myeloid neoplasms and acute leukemia: rationale and important changes. Blood 2009; 114(5):937-51.
  24. Kondo T, Okuno N, Naruse H et al. Validation of the revised 2008 WHO diagnostic criteria in 75 suspected cases of myeloproliferative neoplasm. Leuk Lymphoma 2008; 49(9):1784-91.
  25. Steensma DP, Dewald GW, Lasho TL et al. The JAK2 V617F activating tyrosine kinase mutation is an infrequent event in both "atypical" myeloproliferative disorders and myelodysplastic syndromes. Blood 2005; 106(4):1207-9.
  26. Scott LM, Tong W, Levine RL et al. JAK2 exon 12 mutations in polycythemia vera and idiopathic erythrocytosis. N Engl J Med 2007; 356(5):459-68.
  27. Pardanani A, Lasho TL, Finke C et al. Prevalence and clinicopathologic correlates of JAK2 exon 12 mutations in JAK2V617F-negative polycythemia vera. Leukemia 2007; 21(9):1960-3.
  28. Siemiatkowska A, Bieniaszewska M, Hellmann A et al. JAK2 and MPL gene mutations in V617F-negative myeloproliferative neoplasms. Leuk Res 2010; 34(3):387-9.
  29. Tefferi A, Lasho TL, Huang J et al. Low JAK2V617F allele burden in primary myelofibrosis, compared to either a higher allele burden or unmutated status, is associated with inferior overall and leukemia-free survival. Leukemia 2008; 22(4):756-61.
  30. Pardanani AD, Levine RL, Lasho T et al. MPL515 mutations in myeloproliferative and other myeloid disorders: a study of 1182 patients. Blood 2006; 108(10):3472-6.
  31. Beer PA, Campbell PJ, Scott LM et al. MPL mutations in myeloproliferative disorders: analysis of the PT-1 cohort. Blood 2008; 112(1):141-9.
  32. Pancrazzi A, Guglielmelli P, Ponziani V et al. A sensitive detection method for MPLW515L or MPLW515K mutation in chronic myeloproliferative disorders with locked nucleic acid-modified probes and real-time polymerase chain reaction. J Mol Diagn 2008; 10(5):435-41.
  33. Ruan GR, Jiang B, Li LD et al. MPL W515L/K mutations in 343 Chinese adults with JAK2V617F mutation-negative chronic myeloproliferative disorders detected by a newly developed RQ-PCR based on TaqMan MGB probes. Hematol Oncol 2010; 28(1):33-9.
  34. Schnittger S, Bacher U, Haferlach C et al. Characterization of 35 new cases with four different MPLW515 mutations and essential thrombocytosis or primary myelofibrosis. Haematologica 2009; 94(1):141-4.
  35. Malinge S, Ben-Abdelali R, Settegrana C et al. Novel activating JAK2 mutation in a patient with Down syndrome and B-cell precursor acute lymphoblastic leukemia. Blood 2007; 109(5):2202-4.
  36. Bercovich D, Ganmore I, Scott LM et al. Mutations of JAK2 in acute lymphoblastic leukaemias associated with Down's syndrome. Lancet 2008; 372(9648):1484-92.
  37. Gaikwad A, Rye CL, Devidas M et al. Prevalence and clinical correlates of JAK2 mutations in Down syndrome acute lymphoblastic leukaemia. Br J Haematol 2009; 144(6):930-2.
  38. Tefferi A, Lasho TL, Schwager SM et al. The clinical phenotype of wild-type, heterozygous, and homozygous JAK2V617F in polycythemia vera. Cancer 2006; 106(3):631-5.
  39. Vannucchi AM, Antonioli E, Guglielmelli P et al. Clinical profile of homozygous JAK2 617V>F mutation in patients with polycythemia vera or essential thrombocythemia. Blood 2007; 110(3):840-6.
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Codes

Number

Description

CPT  81270 JAK2 (Janus kinase 2) (e.g., myeloproliferative disorder) gene analysis, p.Val617Phe (V617F) variant (new code 1/1/12)
  81402 Molecular pathology procedure, Level 3 (e.g., >10 SNPs, 2-10 methylated variants, or 2-10 somatic variants [typically using non-sequencing target variant analysis], immunoglobulin and T-cell receptor gene rearrangements, duplication/deletion variants 1 exon) – which includes MPL (myeloproliferative leukemia virus oncogene, thrombopoietin receptor TPOR) (e.g., myeloproliferative disorder), common variants (e.g., W515A, W515K, W515L, W515R) (new code 1/1/12)
  81403 Molecular pathology procedure, Level 4 (e.g., analysis of single exon by DNA sequence analysis, analysis of >10 amplicons using multiplex PCR in 2 or more independent reactions, mutation scanning or duplication/deletion variants of 2-5 exons) – which includes JAK2 (Janus kinase 2) (e.g., myeloproliferative disorder), exon 12 sequence and exon 13 sequence, if performed (new code 1/1/12)
  83912 molecular diagnostics; interpretation and report
ICD-9 Diagnosis  202.60-202.68 Malignant mast cell tumors (includes chronic systemic mastocytosis)
  205.10-205.12 Chronic myeloid leukemia (includes chronic eosiniphilic leukemia)
  238.4 Polycythemia vera
  238.71 Essential thrombocythemia
  238.76 Myelofibrosis with myeloid metaplasia (includes primary myelofibrosis)
ICD-10-CM (effective 10/1/14) C96.2 Malignant mast cell tumors
  C92.10 -C92.12 Chronic myeloid leukemia code range
  D45 Polycythemia vera
   D47.3 Essential thrombocythermia
   D47.4 Osteomyelofibrosis
ICD-10-PCS (effective 10/1/14)   Not applicable. ICD-10-PCS codes are only used for inpatient services. There are no ICD procedure codes for laboratory tests.


Index

JAK2


Policy History

Date Action Reason

01/14/10

Add to Medicine section

New Policy

01/13/11 Replace policy Policy updated with literature; references 52-63 added. No change to policy statements
1/12/12 Replace policy Policy updated with literature search; references 46, 47 and 56 added. Policy title changed to reflect that MPL is not a tyrosine kinase. No change to policy statements
2/14/13 Replace policy Policy updated with literature search; references 57 and 58 added.