Prior authorization is recommended. To authorize, call Blue Cross and Blue Shield of Montana (BCBSMT) Customer Service at 1-800-447-7828 or fax your request to the Medical Review Department at 406-441-4624. A retrospective review is performed if services are not prior authorized.
BCBSMT may consider JAK2 (Janus kinase 2 ) tyrosine kinase mutation testing (e.g., JAK2, JAK2V617F) and MPL (myeloproliferative leukemia virus oncogene) mutation testing 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).
NOTE: Generally, patients suspected to have 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. Also, patients suspected to have ET or PMF should first be tested for a JAK2 mutation. If testing is negative, further testing to detect MPL mutations is warranted.
BCBSMT considers JAK2 tyrosine kinase and MPL mutation testing experimental, investigational and unproven in all other circumstances including, but not limited to, the following situations:
- Diagnosis of nonclassic forms of myeloproliferative neoplasms (MPNs);
- Molecular phenotyping of patients with MPNs;
- Monitoring, management, or selecting treatment in patients with MPNs; or
- Diagnosis or selection of treatment in patients with Down syndrome and acute lymphoblastic leukemia (ALL).
Federal mandate prohibits denial of any drug, device, or biological product fully approved by the FDA as investigational for the Federal Employee Program (FEP). In these instances coverage of these FDA-approved technologies are reviewed on the basis of medical necessity alone. Call the BCBSMT FEP Customer Service Department at 1-800-634-3569 for benefit information.
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.
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-STAT signaling pathway played in early B-cell development, Bercovich et al. (36) studied 88 patients with Down syndrome-acquired ALL for JAK2 mutations and compared these to 216 patients with sporadic ALL. Five mutant alleles were identified in 16 (18%) of the Down syndrome patients, 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 20% of Down syndrome patients 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, the literature in this area is conflicting and inconclusive, due to differences in disease definitions, in methods of testing, in sample type (bone marrow versus circulating blood cells), and 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 comparing 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 some 394 studies on the subject of outcomes in ET. Dahabreh concluded thrombosis but not myelofibrosis or leukemia appeared to be influenced by the presence of JAK2 mutations. Dahabreh 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) JAK2V617F 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 JAK2V617F 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 JAK2V617F 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 show 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)
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 suggesting 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)
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
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 MLNs. In almost a dozen reports (all case series), JAK2V617F has been found as a unique clonal finding in patients with PV, ET, or 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 (see Table 1) test specificity is virtually 100%. Patients with PV tested using 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), it is not surprising that there was widespread enthusiasm for use of this test in the workup of patients with PV. The presence of this marker biologically and clinically is a convincing substitute for the need to rule out reactive causes of erythrocytosis.
While multiple reports have replicated the finding of high specificity in patients with ET and PMF, unfortunately these diseases appear more heterogeneous than PV, and the mutation can be identified in only 30% to 50% of cases. However, high specificity assures that even in the absence of high sensitivity, the predictive value of a positive test approaches 100%. As with PV, increasing numbers of cases of patients with ET and PMF are now being described with new additional mutations in the complementary thrombopoietin pathway (MPL genetic mutations of exon 10.) Identification of an appropriate mutation obviates the need for clinical, morphological or other evaluation to demonstrate a reactive cause of disease.
It is important to note that the testing done to establish clinical performance for these genetic markers is not without flaws. With rare exceptions, studies have been observational, performed on retrospective or cross-sectional sampling. Given the rarity of the diseases of interest, most cases have been selected from patients referred to specialty centers of excellence. However, even these special centers are challenged by the vagaries of the existing Gold Standard for diagnosis—the comprehensive but complicated WHO 2001 diagnostic criteria. Reproducibility of these criteria is unknown and in instances in which morphology is a basis for diagnostic truth, it is well-established that the Gold Standard is imperfect.
In 2007, an ad hoc group of experts in the area of MPNs formed a working group to reformulate the 2001 WHO diagnostic criteria for classic cases of MPN. This group recommended the use of JAK2 testing for diagnosis of all three common Philadelphia chromosome-negative MPN variants—PV, ET, and PMF. Revised criteria were published by WHO in 2008.
This reformulation of diagnostic criteria was performed using expert consensus. Since identification of a mechanistic basis for disease is now the target for therapeutic intervention, it is likely that additional information on testing and its clinical use will be gathered. It is not clear if targeted therapies directed at functional aberrations caused by the JAK2 mutation will require testing for patient selection, for assessment of patient phenotype (disease prognosis), and/or for monitoring treatment. In fact the value of treatment itself remains uncertain and is likely to be complicated by the finding that the JAK2 mutation alone may not be necessary or sufficient to cause clinically relevant disease.
Reports have appeared in the literature linking JAK2 mutations to patients with Down syndrome developing ALL. This information is of uncertain diagnostic value and to date has no prognostic or therapeutic use.
While measurements of JAK2 and related mutations (MPL mutations) have been studied in a somewhat non-standardized manner using different methodologies and different study designs, the consensus-driven WHO criteria appear to be supported by multiple epidemiologic, biologic, and clinical studies of classic MPN disorders. Testing for these mutations appears medically necessary in the diagnosis of patients with signs and symptoms of suspected PV, ET, or PMF.
Testing in patients with Down syndrome ALL is not needed to establish this diagnosis and has no known prognostic or treatment use.
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. Based on current data, use of testing for these purposes is considered experimental, investigational and unproven. 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.