Role of JAK2 in Polycythemia Vera

How does the presence of the JAK2 V617F mutation affect the diagnosis and classification of myeloproliferative neoplasms?

Dr. Richard: The JAK2 V617F mutation is found in > 90% of patients with polycythemia vera (PV). The remaining patients with PV have mutations in a different portion of the JAK2 gene. Since JAK2 mutations are found in virtually all patients with PV, having the mutation helps make the diagnosis, but does not carry prognostic significance. Some studies suggest that the allele burden of the mutated JAK2 V617F could be used to identify aggressive disease, but that finding is not universally accepted across all health care entities or practitioners. Variations in acceptance may be due to factors such as evolution of knowledge based on the latest evidence, clinical practice variability and priorities, availability of testing, and complexity of disease management.

This is not true of the 2 other classical myeloproliferative neoplasms (MPNs) that we see commonly in our clinics: essential thrombocytosis (ET) and myelofibrosis (MF). The CALR mutation can be seen in patients with ET and MF and signals a less aggressive form of the disease.

The presence of JAK2 V617F is critical for prognosis. Although it does not directly help to inform the patient of what to expect, identifying the mutation provides us with important information about the patient’s prognosis, which helps guide treatment decisions such as the intensity of therapy and monitoring for thrombotic events.

What are the potential implications of the JAK2 V617F mutation in the treatment of PV?

Dr. Richard: The discovery of the JAK2 V617F mutation in MPNs in 2005 led to the hope that perhaps there would be targeted therapy that could result in disease remissions. We had all hoped that the spectacular responses observed in patients with chronic myelogenous leukemia (CML) treated with imatinib could be replicated with JAK2 inhibitors. It turned out that blocking JAK2 was insufficient to reverse the disease. Studies are still ongoing whether drugs that can decrease the JAK2 V617F allele burden could be used to achieve a type of remission. Perhaps combination therapies will need to be developed.

I am hopeful that in the future we do see advancements that provide improved diagnosis and monitoring to help facilitate early detection, personalized treatment approaches to offer more effective and well tolerated therapies, risk stratification and prognostication to help identify higher risk progression, combination therapies to possibly improve efficacy and adherence, and novel therapeutic targets to help discover new treatments and provide improved outcomes.

How can JAK2 V617F lead to 3 different forms of myeloproliferative neoplasms?

Dr. Richard: The short answer is no one knows exactly. The phenotypic differences between PV and the other 2 MPN variants are most likely determined by the integration of other signaling pathways that are activated by the corresponding driver mutation, and interactions with other mutations. What also seems to matter is the sequence in which the individual mutations are acquired.

There have been documented cases of post-polycythemic leukemia that no longer have the JAK2 V617F mutation. However, at some point that mutation was lost, and the cells acquired other driver mutations that resulted in leukemia.

What we do know now is that there are several potential interactions that can coexist with JAK2 V617F. There is MPL mutation, which contributes to disease pathogenesis and thrombotic risk. Independent of JAK2 V617F pathways is CALR mutation, which is another driver of MPNs. In addition are other JAK mutations, epigenetic alterations, and microenvironmental factors. All of these have the potential to influence clinical manifestations by impacting clinical outcomes, affecting expression patterns and signaling inflammation within the bone marrow microenvironment.

Are there any ongoing research efforts or clinical trials exploring targeted therapies that specifically address the JAK2 V617F mutation in patients with PV?

Dr. Richard: The ongoing research efforts to address JAK2-targeted therapies are looking at options like novel JAK inhibitors, combination therapies, resistance mechanisms, improved safety profiles, biomarker identification, exploring new indications, and preclinical studies that involve the development and testing of new JAK inhibitors.

Other JAK2-targeted therapies continue to be in development. At this time, we have ruxolitinib, pacritinib, fedratinib, and momelotinib. None of them appear to be a magic bullet the way imatinib was with CML. Perhaps a better disease comparison is chronic lymphocytic leukemia (CLL). In CLL, targeted therapies against Bruton tyrosine kinase and BCL2 are being combined to result in many years of disease control. JAK2 inhibition may need to be combined with another active drug, perhaps against a mutation or pathway that has not yet been identified.

How does the presence of the JAK2 V617F mutation affect the diagnosis and classification of myeloproliferative neoplasms?

Dr. Richard: The JAK2 V617F mutation is found in > 90% of patients with polycythemia vera (PV). The remaining patients with PV have mutations in a different portion of the JAK2 gene. Since JAK2 mutations are found in virtually all patients with PV, having the mutation helps make the diagnosis, but does not carry prognostic significance. Some studies suggest that the allele burden of the mutated JAK2 V617F could be used to identify aggressive disease, but that finding is not universally accepted across all health care entities or practitioners. Variations in acceptance may be due to factors such as evolution of knowledge based on the latest evidence, clinical practice variability and priorities, availability of testing, and complexity of disease management.

This is not true of the 2 other classical myeloproliferative neoplasms (MPNs) that we see commonly in our clinics: essential thrombocytosis (ET) and myelofibrosis (MF). The CALR mutation can be seen in patients with ET and MF and signals a less aggressive form of the disease.

The presence of JAK2 V617F is critical for prognosis. Although it does not directly help to inform the patient of what to expect, identifying the mutation provides us with important information about the patient’s prognosis, which helps guide treatment decisions such as the intensity of therapy and monitoring for thrombotic events.

What are the potential implications of the JAK2 V617F mutation in the treatment of PV?

Dr. Richard: The discovery of the JAK2 V617F mutation in MPNs in 2005 led to the hope that perhaps there would be targeted therapy that could result in disease remissions. We had all hoped that the spectacular responses observed in patients with chronic myelogenous leukemia (CML) treated with imatinib could be replicated with JAK2 inhibitors. It turned out that blocking JAK2 was insufficient to reverse the disease. Studies are still ongoing whether drugs that can decrease the JAK2 V617F allele burden could be used to achieve a type of remission. Perhaps combination therapies will need to be developed.

I am hopeful that in the future we do see advancements that provide improved diagnosis and monitoring to help facilitate early detection, personalized treatment approaches to offer more effective and well tolerated therapies, risk stratification and prognostication to help identify higher risk progression, combination therapies to possibly improve efficacy and adherence, and novel therapeutic targets to help discover new treatments and provide improved outcomes.

How can JAK2 V617F lead to 3 different forms of myeloproliferative neoplasms?

Dr. Richard: The short answer is no one knows exactly. The phenotypic differences between PV and the other 2 MPN variants are most likely determined by the integration of other signaling pathways that are activated by the corresponding driver mutation, and interactions with other mutations. What also seems to matter is the sequence in which the individual mutations are acquired.

There have been documented cases of post-polycythemic leukemia that no longer have the JAK2 V617F mutation. However, at some point that mutation was lost, and the cells acquired other driver mutations that resulted in leukemia.

What we do know now is that there are several potential interactions that can coexist with JAK2 V617F. There is MPL mutation, which contributes to disease pathogenesis and thrombotic risk. Independent of JAK2 V617F pathways is CALR mutation, which is another driver of MPNs. In addition are other JAK mutations, epigenetic alterations, and microenvironmental factors. All of these have the potential to influence clinical manifestations by impacting clinical outcomes, affecting expression patterns and signaling inflammation within the bone marrow microenvironment.

Are there any ongoing research efforts or clinical trials exploring targeted therapies that specifically address the JAK2 V617F mutation in patients with PV?

Dr. Richard: The ongoing research efforts to address JAK2-targeted therapies are looking at options like novel JAK inhibitors, combination therapies, resistance mechanisms, improved safety profiles, biomarker identification, exploring new indications, and preclinical studies that involve the development and testing of new JAK inhibitors.

Other JAK2-targeted therapies continue to be in development. At this time, we have ruxolitinib, pacritinib, fedratinib, and momelotinib. None of them appear to be a magic bullet the way imatinib was with CML. Perhaps a better disease comparison is chronic lymphocytic leukemia (CLL). In CLL, targeted therapies against Bruton tyrosine kinase and BCL2 are being combined to result in many years of disease control. JAK2 inhibition may need to be combined with another active drug, perhaps against a mutation or pathway that has not yet been identified.

How does the presence of the JAK2 V617F mutation affect the diagnosis and classification of myeloproliferative neoplasms?

Dr. Richard: The JAK2 V617F mutation is found in > 90% of patients with polycythemia vera (PV). The remaining patients with PV have mutations in a different portion of the JAK2 gene. Since JAK2 mutations are found in virtually all patients with PV, having the mutation helps make the diagnosis, but does not carry prognostic significance. Some studies suggest that the allele burden of the mutated JAK2 V617F could be used to identify aggressive disease, but that finding is not universally accepted across all health care entities or practitioners. Variations in acceptance may be due to factors such as evolution of knowledge based on the latest evidence, clinical practice variability and priorities, availability of testing, and complexity of disease management.

This is not true of the 2 other classical myeloproliferative neoplasms (MPNs) that we see commonly in our clinics: essential thrombocytosis (ET) and myelofibrosis (MF). The CALR mutation can be seen in patients with ET and MF and signals a less aggressive form of the disease.

The presence of JAK2 V617F is critical for prognosis. Although it does not directly help to inform the patient of what to expect, identifying the mutation provides us with important information about the patient’s prognosis, which helps guide treatment decisions such as the intensity of therapy and monitoring for thrombotic events.

What are the potential implications of the JAK2 V617F mutation in the treatment of PV?

Dr. Richard: The discovery of the JAK2 V617F mutation in MPNs in 2005 led to the hope that perhaps there would be targeted therapy that could result in disease remissions. We had all hoped that the spectacular responses observed in patients with chronic myelogenous leukemia (CML) treated with imatinib could be replicated with JAK2 inhibitors. It turned out that blocking JAK2 was insufficient to reverse the disease. Studies are still ongoing whether drugs that can decrease the JAK2 V617F allele burden could be used to achieve a type of remission. Perhaps combination therapies will need to be developed.

I am hopeful that in the future we do see advancements that provide improved diagnosis and monitoring to help facilitate early detection, personalized treatment approaches to offer more effective and well tolerated therapies, risk stratification and prognostication to help identify higher risk progression, combination therapies to possibly improve efficacy and adherence, and novel therapeutic targets to help discover new treatments and provide improved outcomes.

How can JAK2 V617F lead to 3 different forms of myeloproliferative neoplasms?

Dr. Richard: The short answer is no one knows exactly. The phenotypic differences between PV and the other 2 MPN variants are most likely determined by the integration of other signaling pathways that are activated by the corresponding driver mutation, and interactions with other mutations. What also seems to matter is the sequence in which the individual mutations are acquired.

There have been documented cases of post-polycythemic leukemia that no longer have the JAK2 V617F mutation. However, at some point that mutation was lost, and the cells acquired other driver mutations that resulted in leukemia.

What we do know now is that there are several potential interactions that can coexist with JAK2 V617F. There is MPL mutation, which contributes to disease pathogenesis and thrombotic risk. Independent of JAK2 V617F pathways is CALR mutation, which is another driver of MPNs. In addition are other JAK mutations, epigenetic alterations, and microenvironmental factors. All of these have the potential to influence clinical manifestations by impacting clinical outcomes, affecting expression patterns and signaling inflammation within the bone marrow microenvironment.

Are there any ongoing research efforts or clinical trials exploring targeted therapies that specifically address the JAK2 V617F mutation in patients with PV?

Dr. Richard: The ongoing research efforts to address JAK2-targeted therapies are looking at options like novel JAK inhibitors, combination therapies, resistance mechanisms, improved safety profiles, biomarker identification, exploring new indications, and preclinical studies that involve the development and testing of new JAK inhibitors.

Other JAK2-targeted therapies continue to be in development. At this time, we have ruxolitinib, pacritinib, fedratinib, and momelotinib. None of them appear to be a magic bullet the way imatinib was with CML. Perhaps a better disease comparison is chronic lymphocytic leukemia (CLL). In CLL, targeted therapies against Bruton tyrosine kinase and BCL2 are being combined to result in many years of disease control. JAK2 inhibition may need to be combined with another active drug, perhaps against a mutation or pathway that has not yet been identified.