An Ongoing Story of Discovery:An Ongoing Story of Discovery:

Pathophysiology of Chronic Pathophysiology of Chronic Myeloproliferative DisordersMyeloproliferative Disorders

Katy Moran MDKaty Moran MD

August 30, 2005August 30, 2005

““Imagination is more important than Imagination is more important than knowledge, for knowledge is limited knowledge, for knowledge is limited

while imagination embraces the entire while imagination embraces the entire world.”world.”

Albert EinsteinAlbert Einstein

First, some cases. . .First, some cases. . .

Case #1: 63 yo woman presents to clinic with increasing abdominal girth, Case #1: 63 yo woman presents to clinic with increasing abdominal girth, physical – hepatosplenomegaly. CBC reveals a Hct 52% and Platelet count physical – hepatosplenomegaly. CBC reveals a Hct 52% and Platelet count 900,000 cells/mm900,000 cells/mm33. Diagnosis?. Diagnosis?

Polycythemia veraPolycythemia vera

Case #2: 46 yo man presents to clinic with painful unilateral swelling of the Case #2: 46 yo man presents to clinic with painful unilateral swelling of the right lower extremity for 48 hours. No known risk factors for DVT, right lower extremity for 48 hours. No known risk factors for DVT, ultrasound reveals femoral vein DVT. CBC reveals platelet count 1,200,000 ultrasound reveals femoral vein DVT. CBC reveals platelet count 1,200,000 cells/mmcells/mm33. Diagnosis?. Diagnosis?

Essential thrombocytosisEssential thrombocytosis

Case #3: 65 yo man of Jewish ancestry presents with fatigue, low grade Case #3: 65 yo man of Jewish ancestry presents with fatigue, low grade fever. Mild pancytopenia and teardrop-shaped rbcs are noted on blood fever. Mild pancytopenia and teardrop-shaped rbcs are noted on blood smear. Bone marrow biopsy shows atypical megakaryocytes and stromal smear. Bone marrow biopsy shows atypical megakaryocytes and stromal stranding. Diagnosis?stranding. Diagnosis?

Agnogenic Myeloid Metaplasia Agnogenic Myeloid Metaplasia ≈ Idiopathic Myelofibrosis≈ Idiopathic Myelofibrosis

Case #4: 55 yo man presents with complaints of generalized fatigue, weight Case #4: 55 yo man presents with complaints of generalized fatigue, weight loss and abdominal discomfort with early satiety. Physical exam – afebrile, loss and abdominal discomfort with early satiety. Physical exam – afebrile, thin, massive splenomegaly. No adenopathy is identified, liver is normal in thin, massive splenomegaly. No adenopathy is identified, liver is normal in size. CBC reveals neutrophilic leukocytosis. Diagnosis? size. CBC reveals neutrophilic leukocytosis. Diagnosis?

Chronic myelogenous leukemiaChronic myelogenous leukemia

Tefferi, A. N Engl J Med 2000;342:1255-1265

DiseaseDisease CharacteristicsCharacteristics Transformation Transformation

CMLCML Genetic translocation Genetic translocation Philadelphia chromosome Philadelphia chromosome t(9;22) resulting in fusion t(9;22) resulting in fusion of bcr-abl oncogeneof bcr-abl oncogene

>90% will transform to >90% will transform to acute leukemia if acute leukemia if untreateduntreated

Polycythemia veraPolycythemia vera Elevated red cell mass, Elevated red cell mass, hypercellular marrow, hypercellular marrow, independent of independent of erythropoietinerythropoietin

10% myelofibrosis @10 10% myelofibrosis @10 yrsyrs

25% myelofibrosis @ 25 25% myelofibrosis @ 25 yrsyrs

Essential thrombocytosisEssential thrombocytosis Clonal or autonomous Clonal or autonomous thrombocytosisthrombocytosis

<5% will transform to <5% will transform to acute leukemiaacute leukemia

Agnogenic myeloid Agnogenic myeloid metaplasiametaplasia

(Chronic idiopathic (Chronic idiopathic myelofibrosis)myelofibrosis)

Bone marrow fibrosis not Bone marrow fibrosis not associated with CML or associated with CML or MDSMDS

Mean survival <5 yrsMean survival <5 yrs

AtypicalAtypical Atypical CML, chronic Atypical CML, chronic neutrophilic leukemia, neutrophilic leukemia, systemic mast cell systemic mast cell disease, chronic disease, chronic eosinophilic leukemiaeosinophilic leukemia

VariableVariable

Chronic Myeloproliferative DisordersChronic Myeloproliferative Disorders

Common features:Common features: Overproduction of one or more formed elements in Overproduction of one or more formed elements in

the blood in the absence of an obvious stimulusthe blood in the absence of an obvious stimulus Clonal disorders arising in a single, multipotent Clonal disorders arising in a single, multipotent

progenitor or stem cell progenitor or stem cell proliferates proliferates dominates dominates the marrow and bloodthe marrow and blood

Extramedullary hematopoiesisExtramedullary hematopoiesis Hypercellular marrowHypercellular marrow Hyperplastic megakaryocytes Hyperplastic megakaryocytes myelofibrosis myelofibrosis Clinical tendency toward thrombotic and hemorrhagic Clinical tendency toward thrombotic and hemorrhagic

complicationscomplications

1892 Louis Vasquez of Paris described a pt with cyanotic 1892 Louis Vasquez of Paris described a pt with cyanotic polycythemia, autopsy massive enlargement liver and spleenpolycythemia, autopsy massive enlargement liver and spleen

1903 William Osler at Johns Hopkins reported four patients with 1903 William Osler at Johns Hopkins reported four patients with polycythemia, two with splenomegalypolycythemia, two with splenomegaly

Osler-Vasquez disease (Osler-Vasquez disease ( polycythemia vera) polycythemia vera)

1951 William Dameshek writes an article in 1951 William Dameshek writes an article in BloodBlood grouping PV, grouping PV, idiopathic myelofibrosis, ET, CML, and ‘erythroleukemia’ into a idiopathic myelofibrosis, ET, CML, and ‘erythroleukemia’ into a general category termed myeloproliferative disordersgeneral category termed myeloproliferative disorders

““Perhaps it is possible…not that the various conditions listed are Perhaps it is possible…not that the various conditions listed are different, but that they are closely interrelated. It is possible that these different, but that they are closely interrelated. It is possible that these various conditions – “myeloproliferative disorders”-are all somewhat various conditions – “myeloproliferative disorders”-are all somewhat variable manifestations of proliferative activity of the bone marrow cells, variable manifestations of proliferative activity of the bone marrow cells, perhaps due to a hitherto undiscovered stimulus.”perhaps due to a hitherto undiscovered stimulus.”

SyndromeSyndrome ErythroblastsErythroblasts GranulocyteGranulocyte Mega-Mega-karyocyteskaryocytes

FibroblastsFibroblasts Spleen and Spleen and liverliver

Chronic Chronic Granulocytic Granulocytic

Leukemia Leukemia (CML)(CML)

+/-+/- ++++++ + + to to

++++++

++ ++++

PVPV ++++++ ++++ ++ ++ to to

++++++

+ + to to

++++++

+ + to to

++++++Agnogenic Agnogenic

Myeloid Myeloid MetaplasiaMetaplasia

+/-+/- +/-+/- ++++++ + + to to

++++++

++++++

Mega-Mega-karyocytickaryocytic

LeukemiaLeukemia

+/-+/- +/-+/- ++++++ ++ + + to to

++++++

Dameshek W. Some Speculations on the Myeloproliferative Syndromes. Blood 1951. Adaptation from Table 1:

Myelostimulatory Factor (s)

““Myelostimulatory Factor”Myelostimulatory Factor”

Highly potent since it causes not only normal Highly potent since it causes not only normal bone marrow to become highly proliferative bone marrow to become highly proliferative but also causes activation of sites embryonic but also causes activation of sites embryonic or potential hematopoeisis such as spleen or potential hematopoeisis such as spleen and liverand liver

Theorized of a hormonal or steroid type of Theorized of a hormonal or steroid type of factorfactor

““In the middle of difficulty lies In the middle of difficulty lies opportunity.”opportunity.”

Albert EinsteinAlbert Einstein

1974 NEJM Prchal and Axelrad demonstrate that in 1974 NEJM Prchal and Axelrad demonstrate that in patients with PV erythroid progenitor cells from marrow patients with PV erythroid progenitor cells from marrow or peripheral blood proliferate in serum-containing or peripheral blood proliferate in serum-containing culture in the absence of exogenous erythropoietin culture in the absence of exogenous erythropoietin termed “Endogenous Erythroid Colony” formationtermed “Endogenous Erythroid Colony” formation

1977 J Clin Invest Zanjani shows this phenomenon really 1977 J Clin Invest Zanjani shows this phenomenon really is hypersensitivity to erythropoietin in the culture serum is hypersensitivity to erythropoietin in the culture serum rather than a erythropoietin independent resposerather than a erythropoietin independent respose

1989 Cell D’Andrea – Cloning of EPO receptor1989 Cell D’Andrea – Cloning of EPO receptor No recognizable intracellular signals/pathway No recognizable intracellular signals/pathway

compared with other known receptors such as insulin compared with other known receptors such as insulin

1989 Research continues on a new class of receptors, called type I 1989 Research continues on a new class of receptors, called type I cytokine receptorscytokine receptors

GM-CSF, multiple interleukin receptors, and others are identifiedGM-CSF, multiple interleukin receptors, and others are identified Mechanism via novel kinase/signal transduction pathway Mechanism via novel kinase/signal transduction pathway

1992 Cell Valezquez describe this novel pathway as JAK 1992 Cell Valezquez describe this novel pathway as JAK receptor/signal transducer and activator of transcription (STAT)receptor/signal transducer and activator of transcription (STAT)

JAK – “Just another kinase”JAK – “Just another kinase” Janus kinase – named for Roman god of gates and passagesJanus kinase – named for Roman god of gates and passages

Studies in 1992-1994 demonstrate hypersensitivity of PV erythroid Studies in 1992-1994 demonstrate hypersensitivity of PV erythroid progenitor cells with a variety of growth factors such as IL-3, GM-progenitor cells with a variety of growth factors such as IL-3, GM-CSF, IGF-1CSF, IGF-1

? Downstream effect ? Downstream effect

Tyrosine KinasesTyrosine Kinases

Enzymes that catalyze transfer of Enzymes that catalyze transfer of phosphate from ATP to tyrosine residues phosphate from ATP to tyrosine residues in polypeptidesin polypeptides

2 Classes2 Classes Receptor TK – Transmembrane Protein with Receptor TK – Transmembrane Protein with

extracellular domainextracellular domain Nonreceptor TK – Intracellular - found in Nonreceptor TK – Intracellular - found in

cytosol, nucleuscytosol, nucleus

Janus Kinase ProteinJanus Kinase Protein

Kinase domain (JH1)+ catalytically inactive Kinase domain (JH1)+ catalytically inactive pseudokinase domain (JH2) which acts as a pseudokinase domain (JH2) which acts as a regulatorregulator

Intermediate between membrane receptors and Intermediate between membrane receptors and signaling moleculessignaling molecules

Cytoplasmic region of a membrane receptor – Cytoplasmic region of a membrane receptor – when receptor is activated (for example a when receptor is activated (for example a cytokine binds) JAK is phosphorylated and cytokine binds) JAK is phosphorylated and activated initiating signalling cascade via the activated initiating signalling cascade via the STAT moleculesSTAT molecules STAT molecules enter the nucleus STAT molecules enter the nucleus transcription transcription

Four members of JAK familyFour members of JAK family JAK 1JAK 1 JAK 2JAK 2

• Activated particularly when receptor binds to Activated particularly when receptor binds to hematopoietic growth factors, including hematopoietic growth factors, including erythropoietin, GM-CSF, G-CSF, and erythropoietin, GM-CSF, G-CSF, and thrombopoietinthrombopoietin

JAK 3JAK 3 TYK 2 (tyrosine kinase 2)TYK 2 (tyrosine kinase 2)

Region of JH2 interacts with the activation Region of JH2 interacts with the activation loop of the kinase domain. A specific site loop of the kinase domain. A specific site mutation in the JH2 domain results in mutation in the JH2 domain results in constitutive kinase activity of JH1constitutive kinase activity of JH1

Mutation has been mapped to position 617 Mutation has been mapped to position 617 on the pseudokinase domainon the pseudokinase domain Guanine to thiamine substitution –>Amino Guanine to thiamine substitution –>Amino

acid acid ΔΔ valine to phenylalanine valine to phenylalanine Termed V617FTermed V617F

Goldman, J. M. N Engl J Med 2005;352:1744-1746

Expression of an isolated JAK-2 JH1 kinase domain leads to its constitutive activity

Addition of pseudokinase JH2 domain greatly reduces the level of autoactivation

Schwartz, R. N Engl J Med 2002;347:462-463

Mutation found only in hematopoietic cellsMutation found only in hematopoietic cells Acquired somatic mutationAcquired somatic mutation

• Present in DNA from granulocytes but absent in T Present in DNA from granulocytes but absent in T cellscells

Mechanism for loss of heterozygosity at Mechanism for loss of heterozygosity at chromosome 9pchromosome 9p• Deletion of telomeric part of wild-type chromosome Deletion of telomeric part of wild-type chromosome

9p9p• Events during mitotic recombinationEvents during mitotic recombination

Kralovics R, Passamonti F, Buser AS, et al. A gain-of-function mutation of JAK2 in Kralovics R, Passamonti F, Buser AS, et al. A gain-of-function mutation of JAK2 in myeloproliferative disorders. N Engl J Med. 2005; 352: 1779-1790.myeloproliferative disorders. N Engl J Med. 2005; 352: 1779-1790.

Mechanism of Loss of Mechanism of Loss of Heterozygosity at Chromosome 9pHeterozygosity at Chromosome 9p

What are the implications of What are the implications of this mutation among the this mutation among the chronic myeloproliferative chronic myeloproliferative disorders?disorders?

StudyStudy PurposePurpose PVPV ET ET MFMFCambridge, UK

Baxter EJ, Scott LM, Campbell PJ, et al. Acquired mutation of the tyrosine kinase JAK2 in human myeloproliferative diseases. Lancet. 2005; 365: 1054-1061.

Focused on the key role of Focused on the key role of JAK2 in signal transduction JAK2 in signal transduction from multiple hematopoietic from multiple hematopoietic growth factor receptorsgrowth factor receptors

97%97%

N=73N=73

57%57%

N=51N=51

50% 50%

N=16N=16

BostonBostonLevine RL, Wadleigh M, Cools J, et Levine RL, Wadleigh M, Cools J, et al. Activating mutation in the al. Activating mutation in the tyrosine kinase JAK2 in tyrosine kinase JAK2 in polycythemia vera, essential polycythemia vera, essential thrombocytosis, and myeloid thrombocytosis, and myeloid metaplasia with myelofibrosis. metaplasia with myelofibrosis. Cancer Cell (in press).Cancer Cell (in press).

DNA sequence analysis of DNA sequence analysis of activation loops and activation loops and autoinhibitory domains of 85 autoinhibitory domains of 85 tyrosine kinasestyrosine kinases

74% 74%

N=164N=164

32% 32%

N=115N=115

35% 35%

N=46N=46

ParisParisJames C, Ugo V, Le Couedic J-P, et James C, Ugo V, Le Couedic J-P, et al. A unique clonal JAK2 mutation al. A unique clonal JAK2 mutation leading to constitutive signalling leading to constitutive signalling causes polycythemia vera. Nature causes polycythemia vera. Nature (in press).(in press).

Endogenous erythroid Endogenous erythroid colonies inhibitorscolonies inhibitors

88% 88%

N=45N=45

smallsmall smallsmall

Switzerland-ItalySwitzerland-ItalyKralovics R, Passamonti F, Buser Kralovics R, Passamonti F, Buser AS, et al. A gain-of-function AS, et al. A gain-of-function mutation of JAK2 in mutation of JAK2 in myeloproliferative disorders. N Engl myeloproliferative disorders. N Engl J Med. 2005; 352: 1779-1790.J Med. 2005; 352: 1779-1790.

Observed patients with PV Observed patients with PV had loss of heterozygosity in had loss of heterozygosity in chromosome 9p that chromosome 9p that included the site of the JAK2 included the site of the JAK2 genegene

65% 65%

N=128N=128

23%23%

N=93N=93

57%57%

N=23N=23* Carriers of the mutation had more complications such as fibrosis, hemorrhage, and thrombosis and were more likely to receive cytoreductive therapy.

Adaptation from Table 1: Jones A, et al. Widespread occurrence of the JAK2 Adaptation from Table 1: Jones A, et al. Widespread occurrence of the JAK2 V617F mutation in chronic myeloproliferative disorders. Blood 2005 (in press).V617F mutation in chronic myeloproliferative disorders. Blood 2005 (in press).

Disease Disease SubtypeSubtype

NN V617F V617F Positive Positive

number (%)number (%)

V617F V617F Negative Negative

number (%)number (%)

V617F V617F homozygotes homozygotes number (% of number (% of

mutants)mutants)

PVPV 7272 58 (81%)58 (81%) 14 (19%)14 (19%) 24 (41%)24 (41%)

ETET 5959 24 (41%)24 (41%) 35 (59%)35 (59%) 4 (17%)4 (17%)

IMFIMF 3535 15 (43%)15 (43%) 20 (67%)20 (67%) 10 (67%)10 (67%)

Idiopathic Idiopathic Hyper-Hyper-

eosinophilic eosinophilic syndromesyndrome

134134 2 (1.5%)2 (1.5%) 132 (99%)132 (99%) 2 (100%)2 (100%)

MastocytosisMastocytosis 2828 00 -- --

CML-like CML-like MPDsMPDs

9999 17 (17%)17 (17%) 82 (93%)82 (93%) 8 (47%)8 (47%)

Unclassified Unclassified MPDMPD

5353 12 (25%)12 (25%) 40 (75%)40 (75%) 7 (54%)7 (54%)

TotalTotal 480480 129 (27%)129 (27%) 351 (73%)351 (73%) 55 (43%)55 (43%)

Further evidence of V617 mutation Further evidence of V617 mutation contribution to CMPDscontribution to CMPDs

Introduction of mutant clone into irradiated mice led to Introduction of mutant clone into irradiated mice led to substantial erythrocytosissubstantial erythrocytosis

Erythroid progenitor cells carrying the mutation were Erythroid progenitor cells carrying the mutation were able grow in the absence of exogenous erythropoietin able grow in the absence of exogenous erythropoietin

Homozygosity Homozygosity Arise from recombination of chromatids during mitosis rather Arise from recombination of chromatids during mitosis rather

than a second mutation the mutant heterozygous linethan a second mutation the mutant heterozygous line Loss of heterozygosity results in a proliferative advantageLoss of heterozygosity results in a proliferative advantage

• Individuals with one mutant and one wild type gene have reduced Individuals with one mutant and one wild type gene have reduced cellular autonomous JAK2 activity and growth factor independent cellular autonomous JAK2 activity and growth factor independent behavior compared with homozygous individualsbehavior compared with homozygous individuals

James C, Ugo V, Le Couedic J-P, et al. A unique clonal JAK2 mutation leading to constitutive signalling James C, Ugo V, Le Couedic J-P, et al. A unique clonal JAK2 mutation leading to constitutive signalling causes polycythemia vera. Nature (in press).causes polycythemia vera. Nature (in press).

Baxter EJ, Scott LM, Campbell PJ, et al. Acquired mutation of the tyrosine kinase JAK2 in human myeloproliferative diseases. Lancet. 2005; 365: 1054-1061

Duration of disease was significantly longer Duration of disease was significantly longer among homozygotes compared to among homozygotes compared to heterozygotesheterozygotes

Patients testing negative for the mutation had Patients testing negative for the mutation had the shortest duration of diseasethe shortest duration of disease Homozygous – mean 48 monthsHomozygous – mean 48 months Heterozygous – mean 23 monthsHeterozygous – mean 23 months Wild type – mean 15 monthsWild type – mean 15 months

Phenotype may be expressed without the Phenotype may be expressed without the mutationmutation

Suggests acquiring the mutation and then Suggests acquiring the mutation and then homozygosity are likely stepwise processes homozygosity are likely stepwise processes

Kralovics R, Passamonti F, Buser AS, et al. A gain-of-function mutation of JAK2 in myeloproliferative Kralovics R, Passamonti F, Buser AS, et al. A gain-of-function mutation of JAK2 in myeloproliferative disorders. N Engl J Med. 2005; 352: 1779-1790.disorders. N Engl J Med. 2005; 352: 1779-1790.

In patients that are found to be positive for In patients that are found to be positive for this mutation by genetic testing, diagnostic this mutation by genetic testing, diagnostic and possibly prognostic information may and possibly prognostic information may be obtained be obtained

Specific therapeutic target at the level of Specific therapeutic target at the level of the mutant kinasethe mutant kinase

More questions. . .More questions. . .

““If the facts don't fit the theory, change If the facts don't fit the theory, change the facts.”the facts.”

Albert EinsteinAlbert Einstein

How does one mutation give rise to these various How does one mutation give rise to these various disorders?disorders?

Additional genetic alterations? Pre-existing or acquired after the Additional genetic alterations? Pre-existing or acquired after the JAK2?JAK2?

Dependent on the subtype of progenitor cell in which the Dependent on the subtype of progenitor cell in which the mutation first arises?mutation first arises?

What is the mechanism for disease in patients who do What is the mechanism for disease in patients who do not carry the V617 mutation?not carry the V617 mutation?

Some answers may lie in further exploration of genes that are Some answers may lie in further exploration of genes that are activated by STAT (signal transducer and activator of activated by STAT (signal transducer and activator of transcription) cascade transcription) cascade

Recently, members of the JAK and STAT families have been Recently, members of the JAK and STAT families have been implicated in cellular decisions on whether to proliferate or enter implicated in cellular decisions on whether to proliferate or enter apoptosisapoptosis

One family of genes called suppressor of cytokine signaling One family of genes called suppressor of cytokine signaling (SOCS) encode proteins that bind to JAKs and receptor sites (SOCS) encode proteins that bind to JAKs and receptor sites and then BLOCK further signalingand then BLOCK further signaling

Receptor JAK STAT SOCS Programmed blockade of further JAK signals

Why do some patients progress from Why do some patients progress from indolent CMPDs such as PV to acute indolent CMPDs such as PV to acute leukemia?leukemia?

Rational approach to therapy?Rational approach to therapy? Tyrosine kinases as potential targetsTyrosine kinases as potential targets Broad spectrum of malignancy mediated via Broad spectrum of malignancy mediated via

this family of proteinsthis family of proteins• Examples: Fms-like tyrosine kinase 3 (FLT3) in Examples: Fms-like tyrosine kinase 3 (FLT3) in

acute myeloid leukemia, epidermal growth factor acute myeloid leukemia, epidermal growth factor receptor in subset NSCLC, c-KIT mutation in GISTreceptor in subset NSCLC, c-KIT mutation in GIST

JAKs mediate intracellular signaling in other JAKs mediate intracellular signaling in other pathways and diseasespathways and diseases Leptin receptorLeptin receptor Growth hormone receptorGrowth hormone receptor Interleukin receptorsInterleukin receptors Cardiovascular signaling systemsCardiovascular signaling systems Inherited JAK3 deficiency has been implicated in Inherited JAK3 deficiency has been implicated in

cases of severe combined immunodeficiencycases of severe combined immunodeficiency

Developing inhibitors that act Developing inhibitors that act specificallyspecifically on on V617F without causing side effects in other V617F without causing side effects in other signaling systems may be challengingsignaling systems may be challenging

SummarySummary Advances in the field of molecular/cell biology Advances in the field of molecular/cell biology

and specifically describing JAK2 have provided and specifically describing JAK2 have provided a valuable window into the mechanism of a valuable window into the mechanism of chronic myeloproliferative diseases including chronic myeloproliferative diseases including PV, ET, and IMF among othersPV, ET, and IMF among others

This information has diagnostic and prognostic This information has diagnostic and prognostic clinical relevance clinical relevance

Tyrosine kinases are vital proteins which have Tyrosine kinases are vital proteins which have broad implications broad implications

Ongoing research in this field will impact how Ongoing research in this field will impact how medicine is practiced for years to comemedicine is practiced for years to come

““If we knew what we were doing, it If we knew what we were doing, it wouldn't be called research, would wouldn't be called research, would

it?” it?”

Albert EinsteinAlbert Einstein

ReferencesReferences Tefferi, A. N Engl J Med 2000;342:1255-1265 Dameshek W. Some Speculations on the Myeloproliferative Syndromes. Blood 1951. Goldman, J. M. N Engl J Med 2005;352:1744-1746 Schwartz, R. N Engl J Med 2002;347:462-463 Baxter EJ, Scott LM, Campbell PJ, et al. Acquired mutation of the tyrosine kinase JAK2 in human

myeloproliferative diseases. Lancet. 2005; 365: 1054-1061. Levine RL, Wadleigh M, Cools J, et al. Activating mutation in the tyrosine kinase JAK2 in polycythemia vera, Levine RL, Wadleigh M, Cools J, et al. Activating mutation in the tyrosine kinase JAK2 in polycythemia vera,

essential thrombocytosis, and myeloid metaplasia with myelofibrosis. Cancer Cell (in press).essential thrombocytosis, and myeloid metaplasia with myelofibrosis. Cancer Cell (in press). James C, Ugo V, Le Couedic J-P, et al. A unique clonal JAK2 mutation leading to constitutive signalling causes James C, Ugo V, Le Couedic J-P, et al. A unique clonal JAK2 mutation leading to constitutive signalling causes

polycythemia vera. Nature (in press).polycythemia vera. Nature (in press). Kralovics R, Passamonti F, Buser AS, et al. A gain-of-function mutation of JAK2 in myeloproliferative disorders. Kralovics R, Passamonti F, Buser AS, et al. A gain-of-function mutation of JAK2 in myeloproliferative disorders.

N Engl J Med. 2005; 352: 1779-1790.N Engl J Med. 2005; 352: 1779-1790. Jones A, et al. Widespread occurrence of the JAK2 V617F mutation in chronic myeloproliferative disorders. Jones A, et al. Widespread occurrence of the JAK2 V617F mutation in chronic myeloproliferative disorders.

Blood 2005Blood 2005 MKSAP Review Hematology and OncologyMKSAP Review Hematology and Oncology Up to DateUp to Date Krause, DS, Etten RA. Tyrosine Kinases as Targets for Cancer Therapy. N. Engl J Med. 2005; 353: 172-187.Krause, DS, Etten RA. Tyrosine Kinases as Targets for Cancer Therapy. N. Engl J Med. 2005; 353: 172-187. Tefferi A, Gilliland DG. The JAK2 Tyrosine Kinase Mutation in MPD: Status report. Mayo Clin. Proc. July 2005: Tefferi A, Gilliland DG. The JAK2 Tyrosine Kinase Mutation in MPD: Status report. Mayo Clin. Proc. July 2005:

80 (7): 947-958.80 (7): 947-958. Kaushansky K. On the molecular origins of the chronic myeloproliferative disorders: it all makes sense. Blood. Kaushansky K. On the molecular origins of the chronic myeloproliferative disorders: it all makes sense. Blood.

June 2005. 105: 4187-4190.June 2005. 105: 4187-4190.