-
Advances in Understanding and Management ofMyeloproliferative
Neoplasms
Alessandro M. Vannucchi, MD1; Paola Guglielmelli, MD2; Ayalew
Tefferi, MD3
AbstractAccording to the 2008 World Health Organization
classication system for hematologic malignancies,
themyeloproliferative neoplasms (MPN) include chronic myelogenous
leukemia, polycythemia vera, essentialthrombocythemia, primary
myelobrosis, mastocytosis, chronic eosinophilic leukemia-not
otherwise specied,chronic neutrophilic leukemia, and MPN,
unclassiable. All of these clinicopathologic entities are
characterized bystem cell-derived clonal myeloproliferation, and
their phenotypic diversity is ascribed to the occurrence of
distinctoncogenic events. In the last 4 years, new JAK2 and MPL
mutations have been added to previously described ABLand KIT
mutations as molecular markers of disease in MPN. These discoveries
have markedly simplied theapproach to clinical diagnosis and have
also provided molecular targets for the development of
small-moleculedrugs. In the current article, the authors provide a
clinically oriented overview of MPNs in terms of their
molecularpathogenesis, classication, diagnosis, and management. CA
Cancer J Clin 2009;59:171-191. 2009 AmericanCancer Society,
Inc.
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successfully completing the online quiz based on this article, goto
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IntroductionIn 1951, William Dameshek1 introduced the term
myeloproliferative disorders (MPD) to encompass polycy-themia vera
(PV), essential thrombocythemia (ET), primary myelobrosis (PMF),2
chronic myelogenous leuke-mia (CML), and Di Guglielmos syndrome
(erythroleukemia). His proposal was based on similarities in
theclinical phenotype of these disorders and on the hypothesis that
a generalized proliferation of bone marrow cells,due to some
unknown stimuli, was the underlying cause. The association of the
Philadelphia (Ph1)-chromosomewith CML in 1960,3 and the subsequent
recognition of erythroleukemia as a variant of acute myeloid
leukemia(AML), distinguished the other three disorders as classic
Ph1-negative MPD.4
The rst systematic attempt to classify MPD and MPD-like
clinicopathologic entities was undertaken by theWorld Health
Organization (WHO) committee for the classication of hematologic
malignancies.5 Accordingto the 2001 WHO classication system, CML,
PV, ET, and PMF were included under the category of
chronicmyeloproliferative diseases (CMPD). The CMPD category also
included other nonclassic MPD-like disorderssuch as chronic
neutrophilic leukemia (CNL), chronic eosinophilic
leukemia/hypereosinophilic syndrome (CEL/HES), and unclassied CMPD.
The identication of BCR-ABL as a CML-specic genetic event, in
thecontext of CMPD, has facilitated accurate molecular diagnosis
and effective targeted therapy. The lack of
1Associate Professor of Hematology, Department of Hematology,
University of Florence, Florence, Italy. 2Research Fellow at the
Department of Hematology,University of Florence, Florence, Italy.
3Professor of Medicine and Hematology, Mayo Clinic College of
Medicine, Rochester, NY.
Corresponding authors: Alessandro M. Vannucchi, MD, Hematology
Unit, Dip. Area Critica, University of Florence, Viale Morgagni 85,
50134 Florence, Italy;[email protected] and Ayalew Tefferi, MD,
Division of Hematology, Mayo Clinic College of Medicine, 200 First
Street SW, Rochester, MN 55905;[email protected]
DISCLOSURES: This study was supported by Associazione Italiana
per la Ricerca sul Cancro, Milano; Istituto Toscano Tumori; MIUR
(COFIN 2006067001_003). Theauthors report no conicts of
interest.
2009 American Cancer Society, Inc. doi:10.3322/caac.20009.
Available online at http://cajournal.org and
http://cacancerjournal.org
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171VOLUME 59 NUMBER 3 MAY/JUNE 2009
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knowledge, until recently, onspecic genetic defects in theother
BCR-ABL-negative classicCMPDs necessitated that diag-nosis rest on
a combination ofbone marrow histology and afew clinical and
laboratory nd-ings to distinguish clonal fromreactive
myeloproliferation andone CMPD from another.6
The last 4 years have wit-nessed fundamental advances
inunderstanding the molecularpathogenesis of classic
BCR-ABL-negative CMPD, cappedby the discovery of specic mo-lecular
abnormalities associatedwith PV, ET, and PMF.7 As aresult, WHO
diagnostic criteriahave been revised,8 and the termCMPD has been
changed tomyeloproliferative neoplasms(MPN).8 It is hoped that
newlydiscovered mutations will also fa-cilitate development of
targeted therapy. At the sametime, large clinical studies continue
to provide practi-cally useful clinical information.
The current review has two main objectives. The rstis to provide
a general overview ofMPN including theirmolecular pathogenesis and
updated WHO classica-tion. The second objective is to describe in
more detailthe criteria for diagnosis, risk stratication, and
man-agement of patients with the classic BCR-ABL-nega-tive MPN
including PV, ET, and PMF.
Molecular Basis of MyeloproliferativeNeoplasmsApart from the
BCR/ABL rearrangement in CML,originated by a reciprocal
translocation betweenchromosomes 9 and 22, t(9;22)(q34; q11),9 or
thechimeric FIP1L1-PDGFRA mRNA in some formsof eosinophilia,10 and
kit mutations in cases withsystemic mastocytosis,11 information
concerning mo-lecular abnormalities of MPN has been scanty
until2005, when a Janus kinase 2 mutation (JAK2V617F)was discovered
in the majority of patients with PVand in 50% or fewer of those
with ET or PMF.12-15
In the following 2 years, additional mutations inJAK216 and
MPL17,18 were reported (Table 1). Thesedifferent mutant alleles all
result in a gain of functiondue to the constitutive activation of
tyrosine kinase-dependent cellular signaling pathways, particularly
ofthe JAK-STAT pathway.19,20 Overall, this wouldsuggest that
mutated kinases represent a commonpathogenetic mechanism in these
disorders and that,as exemplied by the efcacy of the tyrosine
kinaseinhibitor imatinib in CML, they could representvalid targets
for therapy.21,22
Members of the Janus kinase family (JAK1, JAK2,JAK3, and
tyrosine kinase 2-Tyk2) are named afterthe Roman god with two
faces, meaning ending andbeginning, because they contain two
symmetrical ki-nase-like domains: the C-terminal JAK homology
1(JH1) domain possesses tyrosine kinase function,whereas the
immediately adjacent JH2 domain isenzymatically inactive, but it is
credited with nega-tively regulating the activity of JH1.23,24
Ordinarily,JAKs are associated in an inactive state to the
cyto-plasmic tail of type 1 or type 2 cytokine receptors
(eg,erythropoietin receptor, EpoR; thrombopoietin re-ceptor, MPL;
granulocyte colony-stimulating factorreceptor, G-CSFR; and
interferon-gamma receptor,
TABLE 1. Recurrent Molecular Abnormalities Associated with
MyeloproliferativeNeoplasms
GENETIC ABNORMALITY DISEASE FREQUENCY
BCR-ABL Chronic myelogenous leukemia 99%
JAK2V617F Polycythemia vera 95%
Essential thrombocythemia 60%
Primary myelobrosis 60%
MPN, unclassiable 20%
Refractory anemia with sideroblasts andthrombocytosis
(RARS-T)
50%
JAK2 exon 12 Polycythemia vera 2%
MPLW515L/K* Primary myelobrosis 8%
Essential thrombocythemia 8%
Involving PDGFRA Myeloid neoplasms with eosinophilia Unknown
Mast cell disease Unknown
Involving PDGFRB Myeloid neoplasms with eosinophilia Unknown
Involving FGRF1 Myeloid neoplasms with eosinophilia Unknown
Involving KIT (D816V as the most frequent) Mast cell disease
Unknown
MPN indicates myeloproliferative neoplasm.*Other infrequent
mutations, such as W515A or S505N, have been reported.Calculated on
JAK2V617F-negative patients.
Myeloproliferative Neoplasms
172 CA: A Cancer Journal for Clinicians
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to name a few). After the engagement of the receptorby
corresponding ligand, JAK undergoes a confor-mational change and
becomes activated via phospho-rylation of key tyrosine residues. In
turn, phospho-rylated JAKs mediate phosphorylation of
tyrosineresidues of the cytoplasmic domain of the receptorsand
create a docking site for the recruitment ofseveral proteins,
ultimately leading to activation ofthe signal transducer and
activator of transcription(STAT), the mitogen-activated protein
(MAP) ki-nase, and the phosphatidylinositol 3-kinase-AKT(PI3K-AKT)
pathways25 (Fig. 1A). ActivatedSTATs dimerize and translocate to
the nucleuswhere they regulate transcription after binding tospecic
consensus sequences in the promoter regionsof several target genes
(Fig. 1A). The entire processis tightly controlled at multiple
levels by proteintyrosine phosphatases, suppressors of cytokine
sig-naling (SOCS), and protein inhibitors of activatedSTAT.26-29
JAK2, and possibly other JAKs, is alsoinvolved in the expression of
cognate receptorsEPOR and MPL at the cell surface by acting as
achaperon and protein stabilizer.30,31
The JAK2V617F mutation is a somatically ac-quired G to T
nucleotide shift at position 1849 inexon 14 that results in a
valine to phenylalaninesubstitution at codon 617; the mutation is
located inthe JH2 pseudo-kinase domain and is believed toresult in
the loss of auto-inhibitory control of JAK2(Fig. 1B). As a
consequence, mutated JAK2 is in aconstitutively phosphorylated
state, independentfrom the binding of ligand to its receptor; in
fact,when the mutation is introduced into cytokine-de-pendent cell
lines it results in a cytokine-independentgrowth of the cells and
their hypersensitivity to cy-tokines,13,14 mimicking the in vitro
growth pattern ofhematopoietic progenitors from MPN patients.
Inparticular, the gain of function of mutated JAK2provides a
mechanistic explanation for the phenom-enon of endogenous erythroid
colony formation(EEC),33,34 ie, the capacity of erythroid
progenitorsto spontaneously produce hemoglobinized coloniesin vitro
in the absence of added erythropoietin, ahallmark of PV and other
classic MPNs. Further-more, transplantation of JAK2V617F mutated
cellsinduced a PV-like phenotype in recipient mice,13,35-38
accompanied by leukocytosis of a different extent andeventually
followed by changes suggestive of myelo-brotic transformation.35-38
More recently, by ma-
nipulating expression levels of the V617F allele, micewith an
ET-like phenotype were also generated inthe presence of low levels
of mutated JAK2.39 Over-
FIGURE 1. (A) In normal hematopoietic cells, signaling is
initiated when cyto-kines bind to and activate their cell surface
type-1 receptors, which havemoleculesof JAK2 associated to the
cytoplasmic domains. After ligand engagement (thepathway activated
by EPO bound to the EPOR is herein schematized) the
receptor-associated JAKsbecomeactivated throughauto-phosphorylation
andon turnphos-phorylate tyrosine residues in the receptor
cytoplasmic tail. The receptor phospho-tyrosines serve as docking
sites for the recruitment of inactive cytoplasmic STATmonomers
through interaction with their SH2 domain. JAK-mediated
phosphoryla-tion of tyrosine residues on the receptor-bound STAT
monomer induces STATsdimerization. The activated dimers translocate
to the nucleus, where they bind tospecic DNA-responsive elements in
the promoters of target genes and therebyinduce unique gene
expression program(s). Activation of JAK2 pathway also resultsin
the recruitment and activation of MAPk signaling proteins and
AKT/mTOR/FOXOpathway that transmit signals for survival,
proliferation, and differentiation oferythroblastic progenitors;
JAK2-independent activation of these pathways mightalso occur.
Negative feedback mechanisms are normally mediated, among
otherregulators, by SOCS proteins. These complex signals are
autonomously activated,in the absence of binding of the cytokine to
its receptor, when JAK2 is mutated(JAK2V617For activatingmutations
in exon12) or the receptor itself ismutated (asis the case of
W515L/K mutation of MPL receptor). (B) Schematic representationof
the most common genetic abnormalities associated with MPN. For
details,please refer to text.STAT indicates signal transducer and
activator of transcription; AKT, protein kinaseB, PKB; FOXO,
forkhead transcription factors; PI3K,
phosphatidylinositol-3-kinase;MAPK, mitogen-activated protein
kinase; mTOR, mammalian target of rapamycin;SOCS, suppressor of
cytokine signaling; JAK2, Janus kinase 2 gene;MPL, thrombo-poietin
receptor gene; FIP1L1-PDGFRA, fusion gene of Fip1-like 1 with
platelet-derived growth factor receptor alpha; kit: stem cell
factor (SCF) receptor gene;FERM: 4-point-1, Erzin, Radixin, Moesin
JAK2 amino-terminal domain; JH1, JAKhomology 1 (active tyrosine
kinase) domain; JH2, JAK homology 2 (catalyticallyinactive
pseudokinase) domain; SH2, SRC homology 2 domain; HRD1, HRD2,
He-matopoietin/cytokine receptor domain1 (negative regulatory
domain) or domain2(ligand binding region); SP, signal peptide; TM,
trans-membrane domain; JM, jux-tamembrane domain; Ig,
Immunoglobuline-like repeat; K1, Kinase domain 1; KI, 76amino acids
kinase insert domain; K2, kinase domain 2.
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all, these models indicated that the JAK2V617F mu-tation is
sufcient to induce a MPN-like phenotypein mice and suggested that
the level of mutated allelemay inuence disease phenotype.40
Mutational frequency of JAK2V617F is estimatedto be more than
95% in PV, 60% in ET or PMF,40% to 50% in refractory anemia with
ringed sidero-blasts and thrombocytosis (RARS-T),41 whereas it
isvery rare in AML or MDS.42-45 In most patients withPV or PMF, as
opposed to a minority of those withET, the mutation is harbored in
a homozygous state,which is accomplished by mitotic
recombination.12-15
In general, the highest V617F allele burden, that is thelevel of
mutated allele relative to normal allele in a cellsuspension such
as granulocytes, is found in patientswith PV followed by PMF and
ET46,47; however, suchvariability in the allele burden does not
represent asufcient criterion for distinguishing among
differentclinical entities, nor does it satisfactorily help to
explainthe apparent paradox of one mutant allele-differentclinical
phenotypes. In fact, how a single V617F mu-tation can be the basis
of different clinical disorders, asin the classic MPN, is still
unclear. Interestingly, singlenucleotide polymorphisms (SNPs) in
JAK2 have beenassociated preferentially with the diagnosis of
PV,48
supporting the contribution of inherited host
geneticcharacteristics to MPN phenotypic variability. Regard-less,
there is evidence to suggest that JAK2V617F maynot be the initial
clonogenic event in MPN and that apre-JAK2 mutated cell may
exist.49,50 In support ofthis is also a nding that leukemic blasts
in patients whoevolve to AML from a pre-existing
JAK2V617F-posi-tive MPN are often negative for the JAK2V617F
mu-tation.51,52 Conversely, JAK2V617F, or other JAK2mu-tations, are
likely a necessary component of the PVphenotype because they are
detected in virtually allpatients with the disease53 and are
sufcient to repro-duce the phenotype in mice. In summary,
JAK2V617Fmutation is integral to the classic MPN, but its
exacthierarchical position in pathogenesis and its role
inphenotypic variability remain to be claried. After all,one could
conclude that PV, ET, and PMF are separatediseases or different
presentations or different phases ofa unique disease. It has been
suggested that the pheno-type of patients with JAK2V617F-positive
ET resem-bles forme fruste of PV.54
In patients with a clinical picture suggestive of PVand who were
found to be negative for theJAK2V617F mutation, several genetic
abnormalities
(ie, mutations, deletions, insertions) have been de-tected in a
short region of JAK2 exon 12 (Fig.1B).16,55 These mutations, which
probably accountfor less than 2% of patients with PV,55 affect
auton-omous cell proliferation and differentiation in a fash-ion
similar to that of the V617F allele.16
Another recurrent molecular abnormality of MPNis represented by
somatic mutations at codon 515 ofMPL,17,18 which, as is the case
with JAK2V617F,involve early myeloid and lymphoid
progenitors.56-58
MPL (named after myeloproliferative leukemia virusoncogene
homolog) is the receptor for the cytokinethrombopoietin (Tpo) and
is highly expressed inearly hematopoietic progenitors and in cells
of themegakaryocytic lineage.59 The two most commonMPL mutations,
which are located in the cytoplasmicjuxtamembrane portion, are
represented by W515L(a tryptophan to leucine substitution) and
W515K (atryptophan to lysine substitution; Fig. 1B). Theyhave been
detected in 5% to 11% of patients withPMF17,18,60 and in up to 9%
of JAK2V617F-negativecases of ET.61,62 Other unusual MPL mutations
(egMPLW515S, W5151A, and MPLS505N, initiallydiscovered in
association with inherited familialthrombocytosis) have also been
reported.63
MPLW515L induced both cytokine-independentgrowth and Tpo
hypersensitivity in cell lines, result-ing in constitutively
activated JAK-STAT/ERK/Aktsignaling pathways,64 and caused a
PMF-like diseasein mice.17 At variance with the JAK2V617F
trans-plantation model, the disease induced byMPLW515L was
characterized by a rapidly fatalcourse, marked thrombocytosis,
leukocytosis, hepa-tosplenomegaly, and bone marrow brosis, all
remi-niscent of PMF.17 Interestingly in some patients,multiple MPL
mutations or the coexistence withJAK2V617F allele were
described.60,62,65
The gene encoding for the receptor of platelet-derived growth
factor A (PDGFRA) is involved in atleast four different genetic
abnormalities associatedwith eosinophilia.66 The most frequent and
bestcharacterized abnormality is due to a karyotypicallyoccult
microdeletion at chromosome 4q12, wherePDGFRA is located, resulting
in a chimeric FIP1L1-PDGFRA fusion gene (Fig. 1B).10 The latter
encodesfor an aberrantly activated tyrosine kinase as
theconsequence of disruption of the autoinhibitory ac-tivity
encoded by PDGFRA exon 12, where thebreakpoint is located; this
constitutively active ty-
Myeloproliferative Neoplasms
174 CA: A Cancer Journal for Clinicians
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rosine kinase drives autonomous eosinophil progen-itor
proliferation,67 possesses transforming propertiesin vitro, and
induces a myeloproliferative disorderwith extensive eosinophil
proliferation when ex-pressed in transplanted mice.68 The fusion
gene hasbeen demonstrated at the level of hematopoietic stemcell
compartment.69 Also the Beta type of PDGFRhas been reported as
being involved in rearrange-ments70 associated with
imatinib-responsive eosino-philia.71 The PDGFRB is located at
chromosome5q31-32 and may fuse with different partners. One ofthe
most common is the ETV6/TEL gene on chro-mosome 12p13, which
encodes for a transcriptionfactor with nonredundant roles in normal
hemato-poiesis.72 The fusion protein constitutively activatesthe
cellular pathways normally associated with PDG-FRB signaling73 and
has transforming propertieswhen expressed in cell lines.
A D816V mutation located in the catalytic domainof the tyrosine
kinase receptor c-Kit occurs in sys-temic mastocytosis (Fig.
1B).11,74 c-Kit is the recep-tor for stem cell factor, a key
cytokine involved in thegeneration and differentiation of mast
cells fromprimitive hematopoietic progenitors; it is encoded bykit,
located at chromosome 4q12. Additional activat-ing kit mutations
other than D816V have also beendescribed in SM, acute leukemia,75
gastrointestinalstromal cell tumors (GIST), and germ cell
tumors.76
The D816V and other homologous mutations inducegrowth factor
independent growth and cell differen-tiation in mast cell lines
through activation ofSTAT5/PI3K/AKT signaling pathways and a
phe-notype resembling human SM in murine models.77
Classication of MyeloproliferativeNeoplasmsThe 2008 WHO
classication for myeloid neo-plasms, which incorporates novel
information de-rived from molecular discoveries in BCR-ABL
neg-ative classic myeloproliferative states and clonaleosinophilic
disorders, includes ve major entities(Table 2)8 as follows: the
Acute Myeloid Leukemia(AML) and the Myelodysplastic Syndromes
(MDS)with their different subtypes, whose listing is outsidethe
scope of this review; the Myeloproliferative Neo-plasms (MPN); the
category of overlapping Myelo-dysplastic/Myeloproliferative
Neoplasms (MDS/MPN); and the Myeloid Neoplasms associated with
eosinophilia and specic molecular abnormalities.AML is dened by
the presence of either20% blastcells in the bone marrow and/or
peripheral blood orcertain characteristic cytogenetic
abnormalities.78
The MDSs are recognized and distinguished fromMPN primarily on
the basis of the presence of tri-lineage dyshematopoiesis in the
absence of monocy-tosis in both bone marrow and peripheral
blood.78
A nontrivial formal modication in the 2008WHO classication has
been the substitution of theattribute neoplasm for disease. In
fact, notwith-standing the analysis of the X chromosome
inactiva-tion pattern in informative females and other cyto-genetic
and/or molecular ndings that establishedboth classic and nonclassic
myeloproliferative dis-orders as being clonal stem cell
disorders,79-89 and thending that evolution to AML is part of their
naturalhistory,90 the neoplastic nature of these conditions
TABLE 2. The 2008 World Health OrganizationClassication for
Myeloid Neoplasms
1. Acute myeloid leukemia (AML) and related precursor
neoplasms
2. Myelodysplastic syndromes (MDS)
3. Myeloproliferative neoplasms (MPN)
3.1. Chronic myelogenous leukemia (CML), BCR-ABL1 positive
3.2. Polycythemia vera (PV)
3.3. Essential thrombocythemia (ET)
3.4. Primary myelobrosis (PMF)
3.5. Chronic neutrophilic leukemia (CNL)
3.6. Chronic eosinophilic leukemia, not otherwise classied
(CEL-NOS)
3.7. Mastocytosis
3.8. Myeloproliferative neoplasm, unclassiable (MPN-u)
4. Myelodysplastic/Myeloproliferative neoplasms (MDS/MPN)
4.1. Chronic myelomonocytic leukemia (CMML)
4.2. Juvenile myelomonocytic leukemia (JMML)
4.3 Atypical chronic myeloid leukemia, BCR-ABL1 negative
4.4. Myelodysplastic/myeloproliferative neoplasm,
unclassiable
4.5. Refractory anemia with ring sideroblasts associated with
markedthrombocytosis
5. Myeloid and lymphoid neoplasms with eosinophilia and
abnormalitiesof PDGFRA, PDGFRB, or FGFR1
5.1. Myeloid and lymphoid neoplasms associated with
PDGFRArearrangement
5.2. Myeloid neoplasms with PDGFRA rearrangement
5.3. Myeloid and lymphoid neoplasms with FGFR1 abnormalities
From Tefferi A and Vardiman JW.136
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has been mostly dismissed until recently. This beliefhas most
likely represented one of the reasons for thetraditionally poor
interest in these neoplasms by can-cer surveillance programs,
agencies granting researchsupport, or pharmaceutical companies.
The four classic MPNs (ie, CML, PV, ET, andPMF) should be
distinguished from the other non-classic MPNs, which include
chronic neutrophilicleukemia (CNL), chronic eosinophilic
leukemia-nototherwise specied (CEL-NOS), systemic mastocy-tosis
(SM), and unclassiable forms of MPN.91
CML presents very unique characteristics, and it willnot be
further discussed herein; recent excellent re-views on molecular
and therapeutic issues have beenpublished.92-94
Chronic Neutrophilic LeukemiaCNL is a rare disorder of elderly
people characterizedby neutrophilic leukocytosis (greater than 25
109/L)made up of greater than 80% mature granulocytes,splenomegaly,
and an absence of the Philadelphia chro-mosome/BCR-ABL fusion gene.
Bone marrow biopsyreveals hyperplasia of granulocytic lineage
without in-volvement of other series, and there is an absence
ofbrosis or myelodysplastic features. Given the potentialfor
evolution to acute leukemia or progressive refractoryleukocytosis,
allogeneic stem cell transplantation may beappropriate for younger
patients.95,96
Chronic Eosinophilic Leukemia andHypereosinophilic
SyndromePatients who have a persistent absolute eosinophilcount of
at least 1.5 109/L, after exclusion of re-active eosinophilias or
other hematologic disorders,suffer from one of the different forms
of primaryeosinophilia.97,98 Many patients with nonclonalforms of
eosinophilia fall within the category of id-iopathic
hypereosinophilia; the possibility of a T-cell mediated
eosinophilia, generally via increasedlevels of interleukin-5, can
be ruled out with ade-quate studies of T-cell immunophenotyping and
T-cell receptor antigen gene rearrangement.99 Con-versely, nding a
cytogenetic or molecularabnormality would indicate a clonal,
myeloprolifera-tive, eosinophilic disorder.98 Diagnosis of CEL
nototherwise (molecularly) specied rests on the dem-onstration of a
cytogenetically abnormal proliferation
of eosinophilic precursors with a myeloblast count of5% to 19%
in the bone marrow or greater than 2% inperipheral blood, usually
accompanied by evidence oforgan damage.97 However, because of
intrinsic dif-culties in establishing the presence of a clonal
disor-der when the most frequent molecular abnormalitiesassociated
with eosinophilia are lacking (see below),it is likely that many
forms of CEL-NOS actually fallimproperly within the idiopathic
hypereosinophilicsyndrome (HES) category.100 Documentation of
tar-get organ damage is necessary for a patient to beconsidered as
suffering from HES. Clinical manifes-tations are related to
eosinophilic inltration of targettissues and may range from almost
asymptomaticdisease to fatal endomyocardial tissue brosis.
Bonemarrow biopsy reveals eosinophilia without involve-ment of
other cell lines, absence of immature myeloidcells or dysplasia,
and a normal number of mast cells.Therapy is based on
corticosteroids as rst-line ther-apy, interferon-alpha, or
hydroxyurea in refractory orsteroid-dependent patients; some
patients may re-spond to imatinib.101 Use of monoclonal
antibodiesto interleukin-5 (mepolizumab)102 or CD52 (the re-ceptor
for interleukin 2; alemtuzumab)103 has pro-duced appreciable
results in refractory cases.66
Mast Cell DiseaseMast cell disease, which is dened by tissue
inltra-tion by abnormal mast cells, can be broadly classiedinto
cutaneous mastocytosis (CM) and systemic mas-tocytosis (SM); the
latter might have an indolent oran aggressive clinical course
depending on the ab-sence or presence, respectively, of impaired
organfunction.104 Life expectancy is nearly normal in in-dolent
forms of SM but is signicantly shortened inaggressive SM. The bone
marrow is almost univer-sally involved in SM and is characterized
by dense,multifocal aggregates of morphologically and
immu-nophenotypically abnormal mast cells, preferentiallyin a
perivascular location, and is often accompaniedby increased
eosinophils. Serum levels of tryptase aretypically high and
represent a clinically useful dis-ease-related marker. By using
adequately sensitivemolecular techniques (such as allele-specic
poly-merase chain reaction [PCR] amplication of DNA)and mast
cell-enriched sources (such as bone marrowaspirate or biopsied
lesional material), the kit D816Vmutation is detected in virtually
all patients with
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176 CA: A Cancer Journal for Clinicians
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SM.105 In addition to its diagnostic value, clinicalrelevance of
searching the D816V kit mutation lies inthe almost universally
reported refractoriness of mu-tated patients to imatinib.106
Conversely, rare pa-tients with other mutations that are located in
thec-Kit juxtamembrane portion may respond to treat-ment with
imatinib. Treatment of systemic mastocy-tosis is highly
individualized and largely palliative,aiming to prevent or reduce
symptoms due to mastcell degranulation or organ inltration.
Therapeuticoptions are represented by interferon-alpha or
cyto-toxic drugs, such as cladribine, but clinical responsesare
limited.107
Myelodysplastic/MyeloproliferativeNeoplasmsMDS/MPN neoplasms are
dened by simultaneouspresence of both myelodysplastic and
myeloprolifer-ative features that exclude them from being
catego-rized as either MDS or MPN alone.108 MDS/MPNneoplasms
comprise chronic myelomonocytic leuke-mia (CMML), juvenile MML (of
pediatric interestand, thus, not further discussed here), atypical
CML,and unclassied MDS/MPN. The clinical and he-matologic
presentation of MDS/MPN is pleomor-phic, with cytopenia and
dysplasia of any cell lineageeventually becoming associated with
elevated leuko-cyte or platelet count. Symptoms may be attributedto
cytopenias (anemia, infections, hemorrhage)and/or to
myeloproliferation (organomegaly, sys-temic symptoms,
cardiovascular events).91 The mo-lecular basis of these disorders
is largely unknown,apart from the involvement of ras pathway with
mu-tations of RAS109 in CMML and PTPN11110 muta-tions in JMML, or
the uncommon presence ofJAK2V617F mutation.111 Therefore, diagnosis
relieson a combination of hematological, clinical, and
his-tological criteria.
The typical manifestation of CMML is peripheralblood monocytosis
greater than 1 106/L and apercentage of monocytes in the white
blood cellcount of greater than 10%. Monocytes may or maynot
display signs of dysplasia, but the percentage ofimmature monocytes
(promonocytes) and mono-blasts in peripheral blood is less than
20%. Bothmonocytic and granulocytic hyperplasia are found in
the bone marrow with a total blast count of less than20%; signs
of erythroid and megakaryocytic dysplasiaare variably present.
Random cytogenetic abnormal-ities can be discovered in 20% to 40%
of these pa-tients. The prognosis is unfavorable with a
mediansurvival of only 2-4 years; a major determinant ofsurvival is
the percentage of blood and bone marrowblasts.91 Hypomethylating
agents like decitabine andazacitidine are now approved for treating
CMML.112
Response rate varies from 10% to 30%, depending onthe drug and
the schedule used, with best resultsreported for decitabine when a
high-dose intensityregimen is used.113-115 Treatment is well
toleratedwith relatively few nonmyelosuppressive complica-tions and
has become a valuable therapeutic optionfor a disease where just a
few years ago the standardof care was merely supportive.
Atypical CML is a rare, aggressive disorder with amedian
survival of 1-2 years and usually affects el-derly patients. It
presents features typical of classicCML, but unlike classic CML, it
is BCR/ABL neg-ative and displays manifest signs of
dysgranulopoiesiswith nuclear aberrations and cytoplasmic
hypogranu-lation.108 JAK2V617F mutation is absent.116 Thebone
marrow is hypercellular; dysplasia of myeloidlineage with less than
20% blasts is a constant feature,whereas other lineages are
variably involved. Thedisease terminates in AML in up to 40% of
thesepatients.
Refractory anemia with ring sideroblasts andthrombocytosis
(RARS-T) is a rare syndrome char-acterized by anemia with
dyserythropoiesis and ringsideroblasts in the bone marrow,
associated withthrombocytosis and increased number of
largemegakaryocytes. These morphologic features ofmegakaryocytes
are distinct from the appearance typ-ically associated with the 5q-
abnormality.117 A highproportion of patients have the JAK2V617F
muta-tion,118 although a few harbor the MPL mutation.119
RARS-T is a disease with a relatively good progno-sis,120 and it
shares many aspects with classic MPN.
Finally, when myelodysplastic and myeloprolifer-ative features
simultaneously present in bone marrowaspirate do not t into any of
the previous categories,and after any known molecular or
cytogenetic abnor-mality is excluded, the disorder is dened as
MDS/MPN unclassiable, with a comment describing theatypical
features.108
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Myeloid Neoplasms Associated withEosinophilia and Specic
MolecularAbnormalitiesBoth the alpha (PDGFRA) and beta
(PDGFRB)types of platelet-derived growth factor receptor(PDGFR)
genes may be involved in genetic abnor-malities associated with
eosinophilia.121 Eosinophiliaassociated with FIP1L1-PDGFRA
rearrangementhas a strikingly male predominance. In addition to
anexpanded eosinophilic lineage, the bone marrow of-ten contains an
increased number of mast cells that,together with ndings of raised
serum levels oftryptase, sometimes make problematic the
differen-tial diagnosis with SM.122 However, at variance withkit
D816V-mutated forms of SM, presence of theFIP1L1-PDGFRA mutation
reliably predicts hema-tologic and molecular remission when
imatinib isused at doses lower than those used for CML (100mg daily
is generally efcacious).123 The rate of com-plete molecular
response may be as high as 95%, anda prospective multicenter study
showed it to be stableand durable during a median follow-up of 25
monthsbut to be dependent on treatment continuation. Inthree
patients who discontinued imatinib, molecularnegativity was lost
and then regained after imatinibwas resumed.124 A denitely lower
proportion ofpatients with imatinib-responsive eosinophilia
haverearrangements involving the PDGFRB gene. Fi-nally,
translocations involving the broblast growthfactor receptor-1 gene
(FGFR1), which is located atchromosome 8p11, and several different
gene part-ners are at the basis of the 8p11
myeloproliferativesyndrome.125 This is also called stem cell
leukemia/lymphoma syndrome because of the clinical pheno-type that
is characterized by features of both lym-phoma and eosinophilic
myeloproliferation. Thedisease results from constitutive activation
of the ty-rosine kinase domain of FGFR1 after its juxtapositionwith
any partner gene. Prognosis is very poor with mostpatients
progressing to overt AML or lymphoblasticlymphoma with 1-2 years of
diagnosis.126
The Classic MyeloproliferativeNeoplasmsAmong classic MPNs, PV
and ET are relativelyindolent disorders,127 resulting in a modest
reductionof lifespan compared with a control population; how-
ever, most patients ultimately suffer from one ormore severe and
potentially fatal complications di-rectly attributable to the
disease. Conversely, PMFhas a severe course in most cases, and
survival issignicantly affected. The three clinical entities
shareseveral common features,6 such as their origin in amultipotent
hematopoietic stem cell, a relatively nor-mal cellular maturation,
a striking overlap in clinicalpresentation (apart from PMF, which
has its ownpeculiar manifestations), and in cases of PV and ET,the
propensity to evolve into post-polycythemic orpost-thrombocythemic
myelobrosis (or less fre-quently each into the other), and the
possibility totransform into AML.90
EpidemiologyClassic MPNs are among the most frequent
hema-tologic neoplasms, usually affecting the adult
elderlypopulation; however, they can also be found in chil-dren,
and in this instance, they raise specic diag-nostic and management
issues128,129 that are beyondthe scope of this review. A recent
study,130 based onthe North American Association of Central
CancerRegistries (NAACCR) encompassing 82% of totalUS population,
reported an average 2001-2003 an-nual age-adjusted incidence rate
of 2.1 per 100,000and estimated that there were 6,328 new cases in
thetotal US population in 2004. Furthermore, becauseof their
relatively smooth clinical course, it is likelythat many classic
MPN cases actually go undetectedor are not reported to registries.
Advanced age, malesex, and white race were identied as risk
factors.Among individuals aged 80 years or older, the rate wasas
high as 13.3 per 100,000. Familial clustering of thesedisorders is
known, and even before the discovery ofJAK2V617F mutation, 131 this
observation led to asuggestion of predisposition allele(s).132 This
hypoth-esis gained substantial support from a large studyrecently
completed in Sweden.133 Relatives of pa-tients with MPN had a 5.7
relative risk (RR) ofhaving PV, an RR 7.4 for ET, and an RR of 7.5
forunclassied forms of MPN, together with a border-line increased
RR of CML. The higher risk observedamong siblings would suggest a
model of recessiveinheritance, although whether presentation of
diseaseoccurs at an even younger age than in parents
isdebatable.133,134 Accordingly, thorough investigationof family
history is mandatory in the initial workup ofpatients with classic
MPN, and appropriate counsel-
Myeloproliferative Neoplasms
178 CA: A Cancer Journal for Clinicians
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ing should be provided. The coexistence of differentclinical
entities and of JAK2V617F-positive andJAK2V617F-negative diseases
in the same family isnoteworthy.131,134,135
DiagnosisBecause of similarities with reactive forms
character-ized by an increased count of mature peripheral
bloodcells on one side, and the signicant phenotypicoverlapping
among them on the other, diagnosis ofdifferent MPNs has
traditionally been challenging;the availability of the new
molecular markers is ex-pected to facilitate diagnosis (Table 3).
As a matter offact, molecular genotyping is integral to the 2008WHO
diagnostic criteria,136 and tests for JAK2 orMPL mutation already
have become a standard toolin the diagnostic work up of MPN (Fig.
2).137 In fact,detection of one of these mutations
unequivocallyestablishes by itself the presence of a clonal MPN
andrules out the possibility of reactive
erythrocytosis,thrombocytosis, or myelobrosis. Unfortunately,they
are of no help in distinguishing among thedifferent forms of MPNs,
although JAK2 exon12
FIGURE 2. Rationale for using JAK2V617F genotyping in the
diagnosticwork-up of suspected MPN. See text for details.
TABLE 3. 2008 WHO Diagnostic Criteria for classic MPN
CRITERIA POLYCYTHEMIA VERA ESSENTIAL THROMBOCYTHEMIA PRIMARY
MYELOFIBROSIS
Major criteria 1. Hgb 18.5 g/dL (men) or 16.5 g/dL(women)
or Hgb or Hct 99th percentile ofreference range for age, sex,
oraltitude of residence
or Hgb 17 g/dL (men) or 15 g/dL(women) if associated with
adocumented and sustained increaseof 2 g/dL from baseline
thatcannot be attributed to correction ofiron deciency
or elevated red cell mass 25% abovemean normal predicted
value
2. Presence of JAK2V617F or similarmutation
1. Sustained platelet count 450 x 109/L2. BM showing
proliferation mainly of themegakaryocytic lineage with
increasednumbers of enlarged, maturemegakaryocytes. No signicant
increase orleft-shift of neutrophil granulopoiesis
orerythropoiesis3. Not meeting the WHO criteria for PV,PMF, CML, or
MDS or other myeloidneoplasm4. Demonstration of JAK2V617F or
otherclonal marker
or no evidence of reactive thrombocytosis
1. Megakaryocyte proliferation and atypia*accompanied by either
reticulin and/or collagenbrosis
or In the absence of reticulin brosis, themegakaryocyte changes
must be accompaniedby increased marrow cellularity,
granulocyticproliferation and often decreasederythropoiesis (ie,
pre-brotic cellular-phasedisease)
2. Does not meet WHO criteria for CML, PV, MDS,or other myeloid
neoplasm3. Demonstration of JAK2V617F or other clonalmarker
or no evidence of reactive marrow brosis
Minor criteria 1. BM showing hypercellularlity for ageand
trilineage growth (panmyelosis)
1. Leukoerythroblastosis
2. Subnormal serum Epo level 2. Increased serum LDH
3. EEC growth 3. Anemia
4. Palpable splenomegaly
Diagnosticcombinations
Both major criteria 1 minor criterionor rst major criterion 2
minor
criteria
All 4 criteria must be met All 3 major criteria 2 minor
criteria
WHO indicates World Health Organization; MPN, myeloproliferative
neoplasm; CML, BCR-ABL1 chronic myelogenous leukemia; PV,
polycythemia vera; PMF, primarymyelobrosis; MDS, myelodysplastic
syndrome; BM, bone marrow biopsy specimen; Epo, erythropoietin;
EEC, endogenous erythroid colonies; LDH, lactate
dehydro-genase.*Small to large megakaryocytes with an aberrant
nuclear/cytoplasmic ratio and hyperchromatic, bulbous, or
irregularly folded nuclei and dense clustering.
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mutations have not yet been reported outside PV,and no patient
with PV has been found to harbor anMPL mutation.
In patients with evidence of increased red cellmass, according
to WHO criteria,136 demonstrationof JAK2V617F mutation allows a
diagnosis in greaterthan 95% of cases, as less than 2% of PV
patientsharbor JAK2 exon 12 abnormalities.16 It is debatedwhether a
diagnosis of PV can still be tenable in theabsence of JAK2
mutation.138,139
The compelling criterion for a diagnosis of ET isa sustained
platelet count of greater than 450 109/L. Notably, this value is
lower than the one originallyused by the 2001 WHO classication
system(600 109/L),5 because the latter might have led
toinadvertently overlooking classic ET cases with alower platelet
count.140 This assumption is supportedby the discovery of the
JAK2V617F mutation in somesubjects who have a platelet count lower
than600 109/L.47 Diagnosis of ET requires exclusionof reactive
thrombocytosis141,142 as well as of otherMPNs that present with
thrombocytosis. In partic-ular, exclusion of CML with FISH or PCR
analysisfor BCR-ABL rearrangement is mandatory. Positivityfor
JAK2V617F or MPL mutation cumulatively ac-count for 60% to 70% of
ET cases. Therefore, theassessment of bone marrow morphology
remains keyto the diagnosis of ET; bone marrow cellularity isnormal
or slightly increased, with abundance of large,mature-appearing
megakaryocytes devoid of mor-phological abnormalities and generally
dispersedthroughout the biopsy. This appearance is distinctfrom
both the panmyelosis typical of PV or thepredominant granulocytic
hyperplasia with highly bi-zarre megakaryocytes, often found in
abnormallytight clusters, with aberrant nuclear to cytoplasmicratio
and hyperchromatic, bulbous, or irregularlyfolded nuclei that are
found in PMF, even in initialstages without overt
brosis.137,143
Bone marrow histology is required for the diagno-sis of PMF.
Although advanced reticulin or colla-genic brosis is typically
associated with classic stagesof PMF, some degree of reticulin
brosis can befound as well as in PV, or more occasionally in
ET.Therefore, brosis by itself is not synonym for PMF,and diagnosis
of PMF can be made even in theabsence of overt brosis.8 Also the
leukoerythroblas-tic features of blood smears, with immature
myeloidprecursors, nucleated red cells, and abnormally
shaped erythrocytes (tear-drop cells), is very charac-teristic,
but not diagnostic, of PMF. CML should beruled out through BCR-ABL
rearrangement analysis,while nding a positive JAK2V617F or MPL
muta-tion allows exclusion of reactive forms of myelobro-sis (such
as in infectious or inammatory processes,metastatic cancer, and
lymphoid disorders). Somecytogenetic abnormalities, such as
del(13)(q12;q22),are frequently encountered and may be
diagnosticallyspecic in this context.144 Anemia, palpable
spleno-megaly, and raised lactate dehydrogenase levels
areadditional diagnostic criteria.8
Clinical Course and Risk StraticationThrombosis, hemorrhage,
evolution to post-polycy-themic or post-thrombocythemic
myelobrosis, andAML transformation represent the most
clinicallyrelevant issues in the course of classic MPN.145-147
Most thrombotic events occur at or in the two yearsbefore
diagnosis.148 However, epidemiologic infer-ence from the European
Collaboration on Low-doseAspirin in Polycythemia (ECLAP)
study146,149 andthe UK Medical Research Council Primary
Throm-bocythemia-1 (MRC PT-1) study150 suggested thatthe cumulative
rate of thrombosis during the diseasecourse ranged from 2.5% to
5.0% and from 1.9% to3% per patient-year in PV and ET,
respectively,depending on whether the patient was in a low-riskor
high-risk category.146,150 In a large retrospectivestudy of PV or
ET patients who had suffered from aprevious cardiovascular event,
the calculated recur-rence rate was 5.6% patient-year with a
cumulativeprobability of 49.9% at 10 years.151 Arterial throm-bosis
accounts for 60% to 70% of all cardiovascularevents and includes
acute myocardial infarction, isch-emic stroke, and peripheral
arterial occlusion. Eventsinvolving the venous system, more common
amongPV patients, are represented by lower extremity deepvenous
thrombosis, pulmonary embolism, andsplanchnic vein thromboses (SVT,
which includesportal vein thrombosis, mesenteric thrombosis,
andthrombosis of the hepatic veins causing Budd-Chiarisyndrome).
The prevalence of SVT is unusually highamong MPN patients152;
however, diagnosis is oftencomplicated by the hemodilution
resulting from hy-persplenism that makes blood cell counts
unreliable,in particular as concerns evidence of increased red
cellmass necessary for the diagnosis of PV.153 Recentdata indicate
that at least 40% of patients with SVT
Myeloproliferative Neoplasms
180 CA: A Cancer Journal for Clinicians
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not attributable to other causes actually harbor theJAK2V617F
mutation; therefore, JAK2V617F geno-typing represents a rst-line
test for these condi-tions.154,155 Occasional SVT patients
harboring MPLmutation have also been reported.156 Conversely,
in-volvement of the microcirculatory system is moretypically
associated with ET and manifests as eryth-romelalgia (a rare
disorder characterized by burningpain, warmth, and redness of the
extremities due toarteriolar brosis and occlusion with
plateletthrombi, typically aspirin-sensitive),157 transientischemic
attacks, visual or hearing transitory defects,recurrent headache,
and peripheral paresthesia; how-ever, because of the lack of
objective diagnostic cri-teria, true incidence of microvessel
disturbances isdifcult to assess.158 Pathogenesis of thrombosis
inclassic MPNs is multifactorial; rheologic abnormali-ties due to
increased red cell mass in PV, abnormalfunction of platelets and
their enhanced interactionwith leukocytes and endothelial cells,
are all possiblecontributing factors159; however, neither
thrombocy-tosis nor increased hematocrit (at least until 52%)
areclearly associated with occurrence of thrombosis.160
Mortality rate is age-dependently increased in PV,being 1.6-fold
and 3.3-fold higher than in the refer-ence population in patients
younger or older than 50years, respectively.161 Conversely,
survival of ET pa-tients is reduced by about 2-fold compared with
thegeneral population starting from the rst decade
afterdiagnosis.162 Major causes of shortened survival inPV or ET
are represented by thrombotic events andtransformation to
myelobrosis or AML, which ac-count for 41% and 13% of total deaths
among 1,638PV patients that were included in the observationalarm
of the ECLAP study.146,163 An age of greaterthan 60 years and
leukocytosis were incorporated in apredictive model for survival in
ET that discrimi-nated groups of patients with median survivals of
25,17, and 10 years, respectively.162 Therefore, becauseof the
nding that thrombosis represents the mostcommon event that
complicates the courses of PVand ET, and eventually is the leading
cause of death,it seems appropriate to use this clinical endpoint
asthe criterion for stratifying patients according to theirrisk.164
Older age (greater than 60 years) and a pre-vious history of
thrombosis are standard risk factorsfor thrombosis in both PV and
ET (Table 4), whichhave been validated in several
studies.146,148,165 In thepresence of either of these, a patient is
at high-risk,
whereas when neither of these is present, the diseaseis
low-risk. The role of generic cardiovascular riskfactors, such as
hypertension, diabetes, hyperlipid-emia, smoking, or genetic
alterations of hemostaticfactors, is still controversial; however,
patients whopresent with any of these abnormalities are
pruden-tially considered to belong to an
intermediate-riskcategory,158,166 and both specic medical
interventionand correction of life style issues, particularly
smok-ing, should be aggressively pursued. Recent studieshave
demonstrated that leukocytosis is an additionalindependent risk
factor for thrombosis,162,167,168 par-ticularly for acute
myocardial infarction in PV. Fur-thermore, low-risk ET patients
could be separatedinto two categories with a respective overall
preva-lence of thrombosis of 55% and 20% depending onthe presence,
or not, of an absolute leukocyte countgreater than 8.7 109/L.169
Finally, there is alsoevidence that JAK2V617F mutated status
inET,47,170,171 and a high V617F allelic burden in bothET47,172 and
PV172-173 are associated with increasedrisk of thrombosis.
Therefore, both leukocytosis andJAK2V617F mutated status represent
novel, power-ful, disease-associated, risk factors; however,
beforethey are included in current risk stratication
criteriaoutlined in Table 4, they need validation in prospec-tive
studies.
Life expectancy in PMF is 31% lower than in anage-matched and
sex-matched population, with amedian survival of 5 years, although
younger patientsmay experience longer survival.161,174,175 Major
causesof death are represented by the sequelae of
portalhypertension or hepatic-splenoportal thrombosis,thromboses in
various anatomic sites, heart failuredue to splenic pooling,
infections, pulmonary hyper-tension, bleeding caused by
thrombocytopenia or he-mostatic defects, and transformation to
AML.147
Prognostic staging systems for PMF have been de-veloped that
allow separation of patients with low-
TABLE 4. Risk-Stratication of Patients with PolycythemiaVera or
Essential Thrombocythemia
RISK CATEGORY
AGE >60 YEARSOR HISTORY OFTHROMBOSIS
GENERIC CARDIOVASCULARRISK FACTORS
Low No No
Intermediate No Yes
High Yes Irrelevant
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risk and high-risk disease associated with signi-cantly
different survival times (Table 5). The mostused Lille score
includes anemia and abnormal leuko-cyte count as variables and
effectively distinguishes pa-tients with survival times that range
from 1-8 years.176
Stratication according to risk is of particular impor-tance in
younger patients who may potentially exploitthe curative efcacy of
allogeneic hematopoietic stemcell transplantation (HSCT). In this
regard, Cer-vantes175 and Mayo ad hoc scoring systems for pa-tients
aged younger than 55 years or 60 years have beendeveloped177 and
represent useful instruments to aidboth physician and patient to
make the most appropri-ate therapeutic decision (Table 5). Presence
of aJAK2V617F mutated state independently predictedleukemic
transformation in a longitudinal prospectiveseries of PMF
patients,178 whereas presence ofMPLW5151L/K mutation was associated
with moresevere anemia.60 However, because of conicting
resultsreported in similar studies,179 these markers need fur-ther
validation before being operationally incorporatedinto prognostic
systems.
Transformation to post-polycythemic or post-thrombocytemic
myelobrosis represents the natural
evolution of PV and ET, occurring late in the clinicalcourse.
The estimated rate is about 5% after 15 yearsfrom diagnosis of
PV,146 whereas data are scanty in ET.Criteria for the diagnosis of
evolution to myelobrosishave recently been proposed by the
InternationalWorking Group for Myelobrosis Research and Treat-ment
(IWG-MRT; Table 6).180 Survival is probablyshortened by the
development of myelobrosis, andmay be predicted by hemoglobin level
and platelet andleukocyte counts according to a dynamic
prognosticmodel recently developed in PV patients.183
Evolution to AML occurred in 1.3% of PV patientsincluded in
ECLAP study, at a median time of 8.4years after diagnosis163;
however, because of the shortfollow up, a precise estimate cannot
be made, andinformation about ET is not yet available. Survival
timeis dismal, less than 6 months, although recipients ofallogeneic
HSCT may experience longer remission.184
Advanced age, elevated leukocyte count, and longerdisease
duration were factors associated with increasedrisk of leukemic
transformation.163 An increased risk ofAML was reported in patients
who were treated withradioactive phosphorus or chlorambucil in the
PVSGtrial.185 In addition, sequential or combined use of more
TABLE 5. Prognostic Scoring Systems Used for Risk Assessment in
Patients with PMF
PROGNOSTIC SCORING SYSTEM PROGNOSTIC FACTORS
NO. OF PROGNOSTIC FACTORS BY RISKCATEGORY
NO. OF MONTHS OF SURVIVAL BY RISKCATEGORY
LOW INTERMEDIATE HIGH LOW INTERMEDIATE HIGH
All patients
Lille Hb 10 g/dLWBC 4 or30x109/L
0 1 2 93 26 13
Cervantes Hb 10 g/dLPB Blasts 1%Constitutionalsymptoms
0-1 2-3 99 21
Mayo Hb 10 g/dLWBC 4 or30x109/LPlt 100x109/LMonocytes
1x109/L
0 1 2 173 61 26
Younger patients
Cervantes, aged 55 y Hb 10 g/dLPB Blasts 1%Constitut.
symptoms
0-1 2-3 176 33
Dingli, aged 60 y Hb 10 g/dLWBC 4 or30x109/LPlt 100x109/L
0 1 2-3 155 69 24
Constitutional symptoms included unexplained fever, night
sweats, or weight loss of greater than 10% of baseline value in the
last 6 months.
PMF indicates primary myelobrosis; Hb, hemoglobin; WBC, white
blood cell count; PB Blasts, percentage of blasts in peripheral
blood smears; Plt, platelet count.
Myeloproliferative Neoplasms
182 CA: A Cancer Journal for Clinicians
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than one chemotherapeutic agent, including hydroxy-urea (HU),
signicantly increased the rate of evolutionto AML in PV patients in
the observational arm ofECLAP study.186
Management of Classic MPNOver the years, there has been a
shortage of clinicalstudies specically devoted to classic MPN.
Mostavailable information derives from a limited numberof
randomized clinical trials performed within na-tional or
international collaborative groups that in-clude the Polycythemia
Vera Study Group(PVSG),165,186 the ECLAP study,146,149 the Ber-gamo
trial,187 and the PT-1 trial150; however, theinformation they have
provided represents the foun-dation for current treatment
indications189-192 as well
as the basis for future studies(Table 7). Standardized
criteriafor assessing clinical and hema-tologic responses in PMF
havebeen published193,194 and will beof particular relevance for
evalu-ation of novel molecularly targetdrugs. Conversely, similar
crite-ria for patients with PV or ETare still lacking.
Cytoreductive Therapy in PVand ETTreatment of patients with PVor
ET should adhere to the stan-dard risk stratication outlinedabove
(Table 4). Phlebotomy isthe cornerstone of treatment inlow-risk
patients with PV,aimed at reaching and maintain-ing a target
hematocrit of lessthan 45% in men and less than42% in women,
according tostandard recommendations.165
The ultimate goal of this prac-tice is to limit availability of
ironto erythropoiesis, but often itwill cause symptoms due to
se-vere and prolonged iron de-ciency; fatigue is being recog-nized
as one major burden forquality of life in patients withPV.127 In
fact, there is wide vari-
ability in opinions and attitudes among US andnon-US physicians
concerning the optimal hemato-crit target to be attained with
phlebotomies.195 Con-versely, high-risk patients should receive
myelosup-pressive therapy, eventually in association
withphlebotomy, and hydroxyurea (HU) is the drug ofchoice (Table
7). HU is an antimetabolite thatprevents synthesis of DNA. It is
also approved forthe treatment of sickle cell anemia because of
itscapacity to reactivate synthesis of hemoglobin F,resulting in a
signicant decrease of occlusive andhemolytic events.196 Superiority
of HU comparedwith phlebotomy was suggested in a
comparativeanalysis of the PVSG in the 1980s,185 but norandomized
trial to address this issue has yet beenundertaken.
TABLE 6. Criteria for Establishing the Diagnosis of Evolution to
Post-polycythemicor Post-thrombocythemic Myelobrosis According to
IWG-MRT Criteria180
CRITERIA FOR POST-POLYCYTHEMIC MYELOFIBROSIS
Required criteria
1. Documentation of a previous diagnosis of polycythemia vera as
dened by WHO criteria136
2. Bone marrow brosis grade 2-3 (according to the European
classication181) or grade 3-4 (accordingto standard
classication182)
Additional criteria
1. Anemia (below the reference range for appropriate age, sex,
and altitude considerations) or sustainedloss of either phlebotomy
(in the absence of cytoreductive therapy) or cytoreductive
treatmentrequirement for erythrocytosis
2. A leucoerythroblastic peripheral blood picture
3. Increasing splenomegaly of 5 cm (distance of the tip of the
spleen from the left costal margin) orthe appearance of a newly
palpable splenomegaly
4. Development of 1 of 3 constitutional symptoms: 10% weight
loss in 6 months, night sweats,unexplained fever (37.5C)
CRITERIA FOR POST-THROMBOCYTHEMIC MYELOFIBROSIS
Required criteria
1. Documentation of a previous diagnosis of essential
thrombocythemia as dened by WHO criteria136
2. Bone marrow brosis grade 2-3 (according to the European
classication181) or grade 3-4 (accordingto standard
classication182)
Additional criteria
1. Anemia (below the reference range for appropriate age, sex,
and altitude consideration) and a 20g/L decrease from baseline
hemoglobin level
2. A leucoerythroblastic peripheral blood picture.
3. Increasing splenomegaly of 5 cm (distance of the tip of the
spleen from the left costal margin) orthe appearance of a newly
palpable splenomegaly
4. Increased LDH (above reference level)
5. Development of 1 of 3 constitutional symptoms: 10% weight
loss in 6 months, night sweats,unexplained fever (37.5C)
Diagnosis is made on the basis of meeting all required criteria
plus two additional criteria.
WHO indicates World Health Organization; LDH, lactate
dehydrogenase.
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The use of low-dose aspirin in PV was exploited inthe ECLAP
study that randomized 518 low-riskpatients in a double-blind,
placebo-controlled trial.149
The primary study endpoint (cardiovascular death,nonfatal
myocardial infarction, nonfatal stroke, andmajor venous
thromboembolism) was signicantlylowered by aspirin (RR, 0.40; 95%
condence inter-val [CI] 0.18 to 0.91; P .02), with only a
small,nonsignicant increase of major hemorrhage (RR,1.62; 95% CI,
0.27 to 9.71; P .60); total andcardiovascular mortality were also
reduced by 46%and 59%, respectively. Therefore, in the absence of
ahistory of major bleeding, allergy to the drug orsevere asthma, or
gastric intolerance, low-dose aspi-rin (100 mg daily) is
recommended regardless of riskcategory for all patients with
PV.149
Low-risk patients with asymptomatic ET do notneed therapy,
although high-risk patients have thesame indications for the use of
HU as patients withPV.197 In the Bergamo trial, which randomized
114high-risk patients to HU versus no treatment, thepercentage of
patients who developed thrombosisdecreased from 24% to 3.6%.188 HU
was also superiorto anagrelide, a nonmyelosuppressive
platelet-lower-ing drug, in preventing arterial thrombosis in
therandomized MRC-PT-1 trial, which included 809high-risk patients,
although venous thrombosis wasreduced in the anagrelide arm.54
Interestingly,JAK2V617F-positive patients had a better responseand
required lower doses of HU to control throm-bocytosis compared with
patients who did not havethis mutation.54 The target level at which
the plateletcount should be maintained with therapy in
high-riskpatients is currently set at 400-450 109/L, but thisis not
based on evidence.197,198 Also, there is littlerationale for the
use of cytoreductive treatment toreduce extreme thrombocytosis
(platelet countgreater than 1,000 109/L) in an otherwise low-
risk, asymptomatic patient.199
Unlike PV, the safety and ef-cacy of low-dose aspirin use forET
has not formally beenproven, but most patients in
in-termediate-risk or high-risk cat-egories are currently advised
touse the drug. Higher doses, upto 500 mg daily, may be requiredfor
acute symptoms because ofmicrovascular disturbances, in
particular erythromelalgia. Conversely, extremethrombocytosis is
considered a contraindication foraspirin use because of a possibly
increased bleedingtendency due to acquired Von Willebrand
dis-ease.158,200-202
There has been some debate about potential leuke-mogenicity of
HU, but although current evidence doesnot attribute to the drug a
denite risk in this regard, itis appropriate to reserve HU use for
patients at high riskof developing complications and in whom benets
ex-pected from treatment overcome potential unwantedeffects.
Actually, transformation to AML is consideredpart of the natural
history of MPN.186
Noncytotoxic Drugs for PV and ETInterferon-alpha (IFN-), a
nonleukemogenic agent,has multiple potential activities against
hematopoieticprogenitor cell proliferation and differentiation
whichmay justify its use in the youngest of patients with PVand ET.
However, tolerance is often poor because ofacute and chronic side
effects that cause discontinuationof the drug in one-third of
patients. IFN- has beenshown to effectively reduce the hematocrit
or plateletcount to a target level in the majority of cases,203,204
andno thrombohemorragic events were recorded among 55patients with
PV who were followed for a median of 13years.205 Progressive
decrease of JAK2V617F burdenhas been suggested in one study,206
whereas changeswere minimal in another study.207 Notably, a
recent,phase 2, multicenter study that used pegylated-IFN-in 40
patients with PV reported complete molecularremission in 7 of these
patients.208 Finally, becauseIFN- is not teratogenic and does not
cross the pla-centa, it is recommended whenever there is the need
forcytoreduction during pregnancy, according to
currentguidelines.209
Anagrelide has widely been used to control plateletcount in
patients with ET in all risk categories210; the
TABLE 7. Risk-Oriented Therapy in Polycythemia Vera (PV) and
EssentialThrombocythemia (ET)
RISK CATEGORY RISK FACTORS PV ET
Low Age 60 y and no priorcardiovascular event Phlebotomies plus
low-dose
aspirin
Nil, or low-dose aspirin(no consensus)
Intermediate Generic cardiovascularrisk factors
Low-dose aspirin (noconsensus)
High Age 60 y and/or priorcardiovascular event
MyelosuppressionPhlebotomies Myelosuppression
Low-dose aspirin Low-dose aspirin
Myeloproliferative Neoplasms
184 CA: A Cancer Journal for Clinicians
-
majority of patients achieved adequate control ofthrombocytosis,
although cardiovascular side effects(mainly palpitations and
headache, less frequentlycongestive heart failure) may require
early discontin-uation of treatment.211,212 The drug is
considereddevoid of any leukemogenic potential, but it shouldnot be
prescribed during pregnancy. On the basis ofresults of the PT-1
trial, anagrelide is not recom-mended in high-risk patients as an
alternative to HU,and its rationale in otherwise low-risk or
intermedi-ate-risk patients should be carefully evaluated case
bycase.213 However, according to recently publishedguidelines,214
anagrelide could be successfully used inplatelet count control in
patients with PV or ET whoare refractory and/or resistant, or who
show poortolerance, or who develop side effects to HU.
Management of PMFThe only approach that has resulted in a
prolongationof survival time in PMF and has the potential to
becurative is allogeneic HSCT.215 At present, it should bereserved
for patients with high-risk disease after carefulclinical
evaluation and thorough patient counseling,particularly considering
the option of inclusion in trialswith innovative drugs.
Bothmyeloablative and reduced-intensity conditioning regimens have
been used, withsimilar efcacy in terms of survival (3-year
event-freesurvival in the range of 50% to 60%) but lower
mortalityrate with the use of the latter in older patients.216
Therefore, a myeloablative strategy may be consideredas the most
appropriate for younger patients, whereasthe reduced-intensity
regimen would be the best forolder patients. Furthermore, in
patients who relapseafter HSCT, a graft-versus-myelobrosis effect
couldbe demonstrated after donor-lymphocyte infusion witha
remarkable reduction of bone marrow brosis.217,218
Factors that have been reported as having a favorableimpact on
overall survival after HSCT include a con-ditioning regimen with
busulfan/cyclophosphamide,younger age, high platelet count, low
comorbidity in-dex, low risk according to the Dupriez score,
normalkaryotype, hemoglobin of greater than 100 g/L, absenceof
circulating blasts, and absence of osteosclerosis.219-221
The usefulness of pretransplant splenectomy still re-mains
controversial.215,222,223
Given that a conventional drug therapy does notsignicantly
modify disease course and is largely in-effective, it is reserved
for patients who presenteither with symptomatic anemia or
splenomegaly.
Androgens,224 prednisone,224 erythropoiesis-stimulat-ing
agents,225-227 and danazol228,229 are all variably usedwith
measurable effect in a few patients. Low-dosethalidomide in
combination with prednisone improvesanemia or thrombocytopenia in
30% to 50% of cas-es.230-234 Lenalidomide, a thalidomide analog,
has pro-duced excellent and durable responses in the
relativelyinfrequent PMF patients who have the del(5q)
abnor-mality,235 and it can be recommended as rst-line ther-apy in
this patient subset. When there is the need tocontrol excessive
myeloproliferation, ie, leukocytosis,thrombocytosis, or progressive
splenomegaly, HU is thecurrent drug of choice.236 Several other
drugs, includingbusulfan,237 melphalan,238 and
2-chlorodeoxyade-nosine,239 have been used particularly in
HU-refractorypatients, but results are generally dismal.
Splenectomyhas a role for alleviating mechanical symptoms due
toextreme splenomegaly and can also ameliorate anemiain
approximately 25% of transfusion-dependent pa-tients.240 However,
splenectomy in PMF bears an ap-proximately 10% procedure-related
mortality, and itshould be performed by experienced surgeons.
Further-more, up to 25% of patients present with
acceleratedhepatomegaly and extreme thrombocytosis after
sple-nectomy, and these patients require further
cytoreduc-tion.240,241 Splenic irradiation is reserved for
patientswho cannot undergo splenectomy for any reason, butthe
efcacy of this therapy is poor, and subsequentcytopenias are often
severe. Conversely, radiation ther-apy has a dened role in the
treatment of nonhepato-splenic extramedullary hematopoiesis, such
as in casesof spinal cord compression by foci of eterotopic
hema-topoiesis.242-245
Prospect for Molecularly Targeted Therapy inClassic MPNThe
involvement of JAK-STAT pathways in most pa-tients who have classic
MPN and harbor mutations inJAK2 or MPL and the experimental
evidence that sug-gests that the same signaling abnormalities may
be atthe basis of mutation-negative patients20 are behindactive
efforts to develop anti-JAK2 drugs. Many mol-ecules have undergone
preclinical testing, in vitro andalso in vivo, and some have
already been introduced intoclinical trials.246-252 A very
incomplete list of moleculesthat may or may not have selective
anti-JAK2 activity isreported in Table 8. Concerning selective JAK2
inhib-itors, we have listed only those that are already inclinical
trials or whose activity has been demonstrated in
CA CANCER J CLIN 2009;59:171-191
185VOLUME 59 NUMBER 3 MAY/JUNE 2009
-
JAK2V617F-mutated murine models (TG101348).248
Among these, INCB018424, XL019, CEP-701, andTG101348 are
currently undergoing clinical trials inpatients with advanced
stages of PMF, post-PV/ETmyelobrosis, PV, and JAK2V617F-positive
ET.253-256
Preliminary results have been encouraging in terms ofactivity
against splenomegaly and constitutional symp-toms,253 with minimal
toxicity. Although the numberof patients treated until now is less
than 100 with anysingle drug and, thus, prevents us from making
anydenitive comment, the hope that this molecularly tar-
geted approach may nally result in improving qualityof life and
possibly the chance of cure for patients withclassic MPN is
enormous.
Patient ResourcesDuring the last few years, we have witnessed a
re-newed interest in the MPN eld among scienticcommunities and
pharmaceutical companies; at thesame time, the patient community is
growing inawareness and strength. There are several
focusedresources for patient information and support thatinclude
the Myeloproliferative Disorders ResearchConsortium (MPD-RC, an
international researchconsortium funded by the National Cancer
Institute;http://www.mpd-rc.org), theMyeloproliferative Dis-orders
Foundation (committed to promoting focusedresearch and
international expert cooperation andalso devoted to patient
education and support; http://www.mpdinfo.org), the Mastocytosis
Society (http://www.tmsforacure.org), and several online
supportgroups (such as http://www.acor.org;
http://www.mpdsupport.org). Among non-US resources arethe
Myeloproliferative Disorders Australia (MPD-Oz;
http://www.mpd-oz.org), the Italian Mielo-brosi Insieme (for
patients with PMF; http://www.myelobrosis.net), and the Gruppo
Italiano perle Malattie Ematologiche Maligne dellAdulto-GIMEMA
(http://www.gimema.org).
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TABLE 8. Innovative Therapies for Classic MPN
DRUG MAIN TARGETSIN CLINICALTRIAL
JAK2 selective inhibitors
INCB018424 JAK2 Yes
XL019 JAK2 Yes
TG101348 JAK2 Yes
Non-JAK2 selective inhibitors
CEP-701 (Leustartinib) FLT3 Yes
MK-0457 Aurora Kinase, FLT3, BCR-ABL Yes
Erlotinib EGFR Yes
ITF2357 Histone deacetylases Yes
Tipifarnib FT Yes
MPN indicates myeloproliferative neoplasm; FLT3, FMS-like
tyrosine kinase 3;EGFR, epidermal growth factor receptor; FT,
farnesyl transferase.
Myeloproliferative Neoplasms
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