Transcript JAK2 - College of American Pathologists

Emerging Concepts in the Workup
of Polycythemia and
Thrombocythemia: JAK2
Short Presentations in Emerging
Concepts (SPEC)
Clinical Question
• HGB over 18.5 in ♂ or 16.5 in ♀?
• Platelets over 1 million?
Are the hematologic abnormalities
reactive or the result of an underlying
neoplastic process?
JAK-STAT Pathway
• Cell signaling pathway
• Allows extracellular chemicals to effect
nuclear DNA expression
• Erythropoietin signals through the JAKSTAT pathway.
JAK2
• In Spring 2005, four separate groups
independently published discovery of a point
mutation (V617F) in the JAK2 gene of patients
with the PV and ET
• Subsequent studies have identified JAK2
mutations as key molecular events in development
of the myeloproliferative neoplasms (MPNs)
Incidence of JAK2 Mutation in MPNs
Polycythemia vera (PV)
99%
Essential thrombocythemia (ET)
60%
Primary myelofibrosis (PMF)
40%
Chronic myelogenous leukemia (CML)
<1%
JAK2: wild-type and mutant
EP
O
No signal
Signal
Campbell P, N Engl J Med 2006, 355:2452-2466.
Signal
Clinical Dilemma
• HGB over 18.5 in ♂ or 15.5 in ♀?
– JAK2 abnormal in 99% of PV
JAK2
Testing
• Platelets over 1 million?
– 85% are not Essential Thrombocytosis
(ET)
JAK2
Testing
– JAK2 abnormal in 60% of ET
Detection of JAK2 means neoplastic process.
Mutations
• Most common mutation is V617F
– Substitutes a phenylalanine for valine at codon 617
• Other JAK2 exon 12 mutations (not V617F)
– Found in PV that does not have V617F
– Thus nearly 100% PV have some JAK2 abnormality
• ET and CIMF can also have MPL mutations
– Found in up to 5%
– Not seen in PV
Polycythemia vera: WHO 2008
Diagnosis requires meeting both major criteria and one minor criterion OR
the first major criterion and two minor criteria.
Major criteria
1. Hemoglobin > 18.5 g/dL in men, 16.5 g/dL in women or other evidence of
increased red cell volume.*
2. Presence of JAK2V617F or other functionally similar mutation such as JAK2
exon 12 mutation.
Minor criteria
1. Bone marrow biopsy showing hypercellularity for age with trilineage growth
(panmyelosis) with prominent erythroid, granulocytic, and megakaryocytic
proliferation.
2. Serum erythropoietin level below the reference range for normal.
3. Endogenous erythroid colony formation in vitro.
*Hemoglobin or hematocrit > 99th percentile of method-specific reference range for age, sex, and altitude of residence; or hemoglobin > 17 g/dL in men, 15 g/dL in women if associated with a documented and sustained increase of at least 2 g/dL from an
individual’s baseline value that cannot be attributed to correction of iron deficiency; or elevated red cell mass > 25% above mean
normal predicted value.
PV Dx Algorithm
*Clinical clues for PV include
splenomegaly, thrombosis, aquagenic
pruritus, and erythromelalgia.
Laboratory clues for PV include
thrombocytosis, leukocytosis, and
increased leukocyte alkaline
phosphatase score. Janus kinase 2
(JAK2) screening is to detect the V617F
mutation that occurs in most patients
with PV.
Essential thrombocythemia: WHO
2008
Diagnosis requires meeting all four criteria.
1.Sustained* platelet count ≥ 450 × 109/L.
2.Bone marrow biopsy specimen showing proliferation mainly of the
megakaryocytic lineage with increased numbers of enlarged, mature
megakaryocytes. No signi- ficant increase or left-shift of neutrophil
granulopoiesis or erythropoiesis.
3.Not meeting WHO criteria for polycythemia vera,† primary myelofibrosis,‡
BCR-ABL1–positive chronic myelogenous leukemia,§ or myelodysplastic
syndrome¶ or other myeloid neoplasms.
4.Demonstration of JAK2V617F or other clonal marker, or in the absence of
JAK2V617F, no evidence for reactive thrombocytosis.**
*Sustained during the workup process.
†Requires the failure of iron replacement therapy to increase hemoglobin level to the polycythemia vera range in the presence of
decreased serum ferritin. Exclusion of polycythemia vera is based on hemoglobin and hematocrit levels, and red cell mass measure- ment
is not required.
‡Requires the absence of relevant reticulin fibrosis, collagen fibrosis, peripheral blood leukoerythroblastosis, or markedly hypercellular
marrow accompanied by megakaryocyte morphology that is typical for primary myelofibrosis (small to large megakaryocytes with an
aberrant nuclear/cytoplasmic ratio and hyperchromatic, bulbous, or irregularly folded nuclei and dense clustering). §Requires the absence
of BCR-ABL1.
¶Requires the absence of dyserythropoiesis and dysgranulopoiesis. **Causes of reactive thrombocytosis include iron deficiency,
splenectomy, surgery, infection, inflammation, connective tissue disease, metastatic cancer, and lymphoproliferative disorders. However,
the presence of a condition associated with reactive thrombocytosis does not exclude the possibility of essential thrombocythemia if the
first three criteria are met.
ET DiagnosticAlgorithm
*In addition to clinical history, laboratory tests that are helpful in distinguishing reactive
thrombocytosis from ET include serum ferritin, peripheral blood smear, and C-reactive protein.
JAK2 Testing
• JAK2 V617F Detection
– Performed on peripheral blood or bone
marrow
– Highly sensitive and specific assays
– Should be performed in CAP Accredited lab
• JAK2 Exon 12 Mutation Analaysis
– Used when suspect PV but V617F not
detected
Quantification of JAK2?
diagnosis
“clinical/hematologic/
prognostic correlates”
monitoring
• Detection is
sufficient.
• Quantification not
necessary
• Controversial
• Response to
therapy
• Utility not well
defined clinically
CALR Mutations
• Second most frequent mutation after JAK2
• CALR found in endoplasmic reticulin: protein folding, calcium
homeostasis
• CALR mutations mutually exclusive with JAK2 and MPL
• Found in 73% of ET and MF cases that are JAK2 neg and MPL neg
• CALR not reported in PV
• Can distinguish ET from PV and MF
• Presence of CALR mutation associated with better outcomes (longer
survival, less thrombosis)
Selected Resources
Nangalia J, Massie CE, Baxter EJ, et al. Somatic CALR mutations in
myeloproliferative neoplasms with nonmutated JAK2. N Engl J Med. 2013; 369:
2391-405.
Klampfl T, Gisslinger H, Harutyunyan AS, et al. Somatic mutations of calreticulin in
myeloproliferative neoplasms. N Engl J Med. 2013; 369: 2379-90.
Cross NC. Genetic and epigenetic complexity in myeloproliferative neoplasms.
Hematology Am Soc Hematol Educ Program. 2011;2011:208-14.
Schmidt AE, Pathology Consultation on Myeloproliferative Neoplasms. Oh ST; for
the Education Committee of the Academy of Clinical Laboratory Physicians and
Scientists. Am J Clin Pathol. 2012 Jul;138(1):12-19.
Tefferi A. JAK inhibitors for myeloproliferative neoplasms: clarifying facts from
myths. Blood. 2012 Mar 22;119(12):2721-30. Epub 2012 Jan 25.
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