Discussion

My articles are on Myeloid Leukemia 

1. Write a proposal about what the research journal is about (the three articles).minimum of 150 words. 

2. Discuss emerging technologies in healthcare and their application to providing safe and effective care.

Explain a position on the advancement of healthcare informatics and technology in healthcare 250 words/APA style/ References

Review article

The molecular biology of chronic myeloid leukemia
Michael W. N. Deininger, John M. Goldman, and Junia V. Melo

Chronic myeloid leukemia (CML) is probably the most extensively
studied human malignancy. The discovery of the Philadelphia (Ph)
chromosome in 19601 as the first consistent chromosomal abnormal-
ity associated with a specific type of leukemia was a breakthrough
in cancer biology. It took 13 years before it was appreciated that the
Ph chromosome is the result of a t(9;22) reciprocal chromosomal
translocation2 and another 10 years before the translocation was
shown to involve theABL proto-oncogene normally on chromo-
some 93 and a previously unknown gene on chromosome 22, later
termedBCR for breakpoint cluster region.4 The deregulated Abl
tyrosine kinase activity was then defined as the pathogenetic
principle,5 and the first animal models were developed.6 The end of
the millennium sees all this knowledge transferred from the bench
to the bedside with the arrival of Abl-specific tyrosine kinase
inhibitors that selectively inhibit the growth ofBCR-ABL–positive
cells in vitro7,8 and in vivo.9

In this review we will try to summarize what is currently known
about the molecular biology of CML. Because several aspects of
CML pathogenesis may be attributable to the altered function of the
2 genes involved in the Ph translocation, we will also address the
physiological roles ofBCRandABL. We concede that a review of
this nature can never be totally comprehensive without losing
clarity, and we therefore apologize to any authors whose work we
have not cited.

The physiologic function
of the translocation partners

The ABL gene is the human homologue of the v-abl oncogene
carried by the Abelson murine leukemia virus (A-MuLV),10 and it
encodes a nonreceptor tyrosine kinase.11 Human Abl is a ubiqui-
tously expressed 145-kd protein with 2 isoforms arising from
alternative splicing of the first exon.11 Several structural domains
can be defined within the protein (Figure 1). Three SRC homology
domains (SH1-SH3) are located toward the NH2 terminus. The
SH1 domain carries the tyrosine kinase function, whereas the SH2
and SH3 domains allow for interaction with other proteins.12

Proline-rich sequences in the center of the molecule can, in turn,
interact with SH3 domains of other proteins, such as Crk.13 Toward
the 39 end, nuclear localization signals14 and the DNA-binding15

and actin-binding motifs16 are found.
Several fairly diverse functions have been attributed to Abl, and

the emerging picture is complex. Thus, the normal Abl protein is
involved in the regulation of the cell cycle,17,18 in the cellular

response to genotoxic stress,19 and in the transmission of informa-
tion about the cellular environment through integrin signaling.20

(For a comprehensive review of Abl function, see Van Etten21).
Overall, it appears that the Abl protein serves a complex role as a
cellular module that integrates signals from various extracellular
and intracellular sources and that influences decisions in regard to
cell cycle and apoptosis. It must be stressed, however, that many of
the data are based solely on in vitro studies in fibroblasts, not
hematopoietic cells, and are still controversial. Unfortunately, the
generation ofABL knockout mice failed to resolve most of the
outstanding issues.22,23

The 160-kd Bcr protein, like Abl, is ubiquitously expressed.11

Several structural motifs can be delineated (Figure 2). The first
N-terminal exon encodes a serine–threonine kinase. The only
substrates of this kinase identified so far are Bap-1, a member of the
14-3-3 family of proteins,24 and possibly Bcr itself.11 A coiled–coil
domain at the N-terminus of Bcr allows dimer formation in vivo.25

The center of the molecule contains a region withdbl-like and
pleckstrin-homology (PH) domains that stimulate the exchange of
guanidine triphosphate (GTP) for guanidine diphosphate (GDP) on
Rho guanidine exchange factors,26 which in turn may activate
transcription factors such as NF-kB.27 The C-terminus has GTPase
activity for Rac,28 a small GTPase of the Ras superfamily that
regulates actin polymerization and the activity of an NADPH
oxidase in phagocytic cells.29 In addition, Bcr can be phosphory-
lated on several tyrosine residues,30 especially tyrosine 177, which
binds Grb-2, an important adapter molecule involved in the
activation of the Ras pathway.31 Interestingly, Abl has been shown
to phosphorylate Bcr in COS1 cells, resulting in a reduction of Bcr
kinase activity.31,32 Although these data argue for a role of Bcr in
signal transduction, their true biologic relevance remains to be
determined. The fact thatBCR knockout mice are viable and the
fact that an increased oxidative burst in neutrophils is thus far the
only recognized defect33 probably reflect the redundancy of
signaling pathways. If there is a role for Bcr in the pathogenesis of
Ph-positive leukemias, it is not clearly discernible because the
incidence and biology of P190BCR-ABL-induced leukemia are the
same inBCR2/2 mice as they are in wild-type mice.34

Molecular anatomy
of the BCR-ABL translocation

The breakpoints within theABL gene at 9q34 can occur anywhere
over a large (greater than 300 kb) area at its 59 end, either upstream

From the Department of Hematology/Oncology, University of Leipzig,
Germany; and the Department of Haematology, Imperial College School of
Medicine, Hammersmith Hospital, London, United Kingdom.

Submitted November 16, 1999; accepted July 12, 2000.

Supported by grants from Leukaemia Research Fund (UK) and the Dr Ernst
und Anita Bauer Stiftung (Germany).

Reprints: Michael W. N. Deininger, Department of Hematology/Oncology,

University of Leipzig, Johannisallee 32, Leipzig 04103, Germany; e-mail:
deim@medizin.uni-leipzig.de.

The publication costs of this article were defrayed in part by page charge
payment. Therefore, and solely to indicate this fact, this article is hereby
marked ‘‘advertisement’’ in accordance with 18 U.S.C. section 1734.

© 2000 by The American Society of Hematology

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of the first alternative exon Ib, downstream of the second alterna-
tive exon Ia, or, more frequently, between the two35 (Figure 3).
Regardless of the exact location of the breakpoint, splicing of the
primary hybrid transcript yields an mRNA molecule in whichBCR
sequences are fused toABL exon a2. In contrast toABL, break-
points within BCR localize to 1 of 3 so-called breakpoint cluster
regions (bcr). In most patients with CML and in approximately one
third of patients with Ph-positive acute lymphoblastic leukemia
(ALL), the break occurs within a 5.8-kb area spanningBCRexons
12-16 (originally referred to as exons b1-b5), defined as the major
breakpoint cluster region (M-bcr). Because of alternative splicing,
fusion transcripts with either b2a2 or b3a2 junctions can be formed.
A 210-kd chimeric protein (P210BCR-ABL) is derived from this
mRNA. In the remaining patients with ALL and rarely in patients
with CML, characterized clinically by prominent monocytosis,36,37

the breakpoints are further upstream in the 54.4-kb region between
the alternativeBCRexons e29 and e2, termed the minor breakpoint
cluster region (m-bcr). The resultant e1a2 mRNA is translated into
a 190-kd protein (P190BCR-ABL). Recently, a third breakpoint cluster
region (m-bcr) was identified downstream of exon 19, giving rise to
a 230-kd fusion protein (P230BCR-ABL) associated with the rare
Ph-positive chronic neutrophilic leukemia,38 though not in all
cases.39 If sensitive techniques such as nested reverse transcription–
polymerase chain reaction are used, transcripts with the e1a2 fusion
are detectable in many patients with classical P210BCR-ABLCML.40

The low level of expression of these P190-type transcripts com-
pared to P210 indicates that they are most likely the result of
alternative splicing of the primary mRNA. Occasional cases with
other junctions, such as b2a3, b3a3, e1a3, e6a2,41 or e2a2,42 have
been reported in patients with ALL and CML. These “experiments
of nature” provide important information as to the function of the

various parts ofBCR and ABL in the oncogenic fusion protein.
Interestingly,ABL exon 1, even if retained in the genomic fusion, is
never part of the chimeric mRNA. Thus, it must be spliced out
during processing of the primary mRNA; the mechanism underly-
ing this apparent peculiarity is unknown. Based on the observation
that the Abl part in the chimeric protein is almost invariably
constant while the Bcr portion varies greatly, one may deduce that
Abl is likely to carry the transforming principle whereas the
different sizes of the Bcr sequence may dictate the phenotype of the
disease. In support of this notion, rare cases of ALL express a
TEL-ABL fusion gene,43,44 indicating that theBCR moiety can in
principle be replaced by other sequences and still cause leukemia.
Interestingly, a fusion betweenTEL(ETV6) and theABL-related
geneARG has recently been described in a patient with AML.45

Although all 3 major Bcr-Abl fusion proteins induce a CML-like
disease in mice, they differ in their ability to induce lymphoid
leukemia,46 and, in contrast to P190 and P210, transformation to
growth factor independence by P230BCR-ABL is incomplete,47 which
is consistent with the relatively benign clinical course of P230-
positive chronic neutrophilic leukemia.38

One of the most intriguing questions relates to the events
responsible for the chromosomal translocation in the first place.
From epidemiologic studies it is well known that exposure to
ionizing radiation (IR) is a risk factor for CML.48,49 Moreover,
BCR-ABLfusion transcripts can be induced in hematopoietic cells
by exposure to IR in vitro50; such IR-induced translocations may
not be random events but may depend on the cellular background
and on the particular genes involved. Two recent reports showed
that the physical distance between theBCR and theABL genes in
human lymphocytes51 and CD341 cells52 is shorter than might be
expected by chance; such physical proximity could favor transloca-
tion events involving the 2 genes. However, the presence of the
BCR-ABL translocation in a hematopoietic cell is not in itself
sufficient to cause leukemia becauseBCR-ABLfusion transcripts of
M-bcr and m-bcr type are detectable at low frequency in the blood
of many healthy individuals.53,54 It is unclear why Ph-positive
leukemia develops in a tiny minority of these persons. It may be
that the translocation occurs in cells committed to terminal
differentiation that are thus eliminated or that an immune response
suppresses or eliminates Bcr-Abl–expressing cells. Indirect evi-
dence that such a mechanism may be relevant comes from the
observation that certain HLA types protect against CML.55 Another
possibility is thatBCR-ABLis not the only genetic lesion required
to induce chronic-phase CML. Indeed, a skewed pattern of G-6PD

Figure 1. Structure of the Abl protein. Type Ia isoform is slightly shorter than type
Ib, which contains a myristoylation (myr) site for attachment to the plasma mem-
brane. Note the 3 SRC-homology (SH) domains situated toward the NH2 terminus.
Y393 is the major site of autophosphorylation within the kinase domain, and
phenylalanine 401 (F401) is highly conserved in PTKs containing SH3 domains. The
middle of each protein is dominated by proline-rich regions (PxxP) capable of binding
to SH3 domains, and it harbors 1 of 3 nuclear localization signals (NLS). The carboxy
terminus contains DNA as well as G- and F-actin–binding domains. Phosphorylation
sites by Atm, cdc2, and PKC are shown. The arrowhead indicates the position of the
breakpoint in the Bcr-Abl fusion protein.

Figure 2. Structure of the Bcr protein. Note the dimerization domain (DD) and the 2
cyclic adenosine monophosphate kinase homologous domains at the N terminus.
Y177 is the autophosphorylation site crucial for binding to Grb-2. The center of the
molecule contains a region homologous to Rho guanidine nucleotide exchange
factors (Rho-GEF) as well as dbl-like and pleckstrin homology (PH) domains. Toward
the C-terminus a putative site for calcium-dependent lipid binding (CaLB) and a
domain with activating function for Rac-GTPase (Rac-GAP) are found. Arrowheads
indicate the position of the breakpoints in the BCR-ABL fusion proteins.

Figure 3. Locations of the breakpoints in the ABL and BCR genes and structure
of the chimeric mRNAs derived from the various breaks.

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isoenzymes has been detected in Ph-negative Epstein-Barr virus-
transformed B-cell lines derived from patients with CML, suggest-
ing that a Ph-negative pathologic state may precede the emergence
of the Ph chromosome.56

Mechanisms of BCR-ABL –mediated
malignant transformation

Essential features of the Bcr-Abl protein

Mutational analysis identified several features in the chimeric
protein that are essential for cellular transformation (Figure 4). In
Abl they include the SH1, SH2, and actin-binding domains (Figure
1), and in Bcr they include a coiled–coil motif contained in amino
acids 1-63,25 the tyrosine at position 177,57 and phosphoserine–
threonine-rich sequences between amino acids 192-242 and 298-
41358 (Figure 2). It is, however, important to note that essential
features depend on the experimental system. For example, SH2
deletion mutants of Bcr-Abl are defective for fibroblast transforma-
tion,59 but they retain the capacity to transform cell lines to factor
independence and are leukemogenic in animals.60

Deregulation of the Abl tyrosine kinase

Abl tyrosine kinase activity is tightly regulated under physi-
ologic conditions. The SH3 domain appears to play a critical
role in this inhibitory process because its deletion14 or positional
alteration61 activates the kinase; it is replaced by viralgag
sequences in v-abl.62 Both cis- and trans-acting mechanisms
have been proposed to mediate the repression of the kinase.
Several proteins have been identified that bind to the SH3
domain.63-65 Abi-1 and Abi-2 (Abl interactor proteins 1 and 2)
activate the inhibitory function of the SH3 domain; even more
interesting, activated Abl proteins promote the proteasome-
mediated degradation of Abi-166 and Abi-2. Another candidate
inhibitor of Abl is Pag/Msp23. On exposure of cells to oxidative
stress such as ionizing radiation, this small protein is oxidized
and dissociates from Abl, whose kinase is in turn activated.67

These results are in line with previous observations that highly
purified Abl protein is kinase-active,61 suggesting that its
constitutive inhibition derives from a trans-acting mechanism.
Alternatively, the SH3 domain may bind internally to the
proline-rich region in the center of the Abl protein, causing a
conformational change that inhibits interaction with sub-
strates.68 Furthermore, a mutation of Phe401 to Val (within the

kinase domain) leads to the transformation of rodent fibroblasts.
Because this residue is highly conserved in tyrosine kinases with
N-terminal SH3 domains, it may bind internally to the SH3
domain.69 It is conceivable that the fusion of Bcr sequences 59 of
the Abl SH3 domain abrogates the physiologic suppression of
the kinase. This might be the consequence of homodimer
formation; indeed, the N-terminal dimerization domain is an
essential feature of the Bcr-Abl protein but can be functionally
replaced by other sequences that allow for dimer formation,
such as the N-terminus of theTEL (ETV-6) transcription factor
in the TEL-ABL fusion associated with the t(9;12).43,70 It is
possible that deregulated tyrosine kinase activity is a unifying
feature of chronic myeloproliferative disorders. Several other
reciprocal translocations have been cloned from patients with
chronic BCR-ABL–negative myeloproliferative disorders. Re-
markably, most of these turn out to involve tyrosine kinases such
as fibroblast growth factor receptor 171 and platelet-derived
growth factorb receptor (PDGFbR).72

A host of substrates can be tyrosine phosphorylated byBcr-Abl
(Table 1). Most important, because of autophosphorylation, there is
a marked increase of phosphotyrosine onBcr-Abl itself, which
creates binding sites for the SH2 domains of other proteins.
Generally, substrates ofBcr-Abl can be grouped according to their
physiologic role into adapter molecules (such as Crkl and p62DOK),
proteins associated with the organization of the cytoskeleton and
the cell membrane (such as paxillin and talin), and proteins with
catalytic function (such as the nonreceptor tyrosine kinase Fes or
the phosphatase Syp). It is important to note that the choice of
substrates depends on the cellular context. For example, Crkl is the
major tyrosine-phosphorylated protein in CML neutrophils,73

whereas phosphorylated p62DOK is predominantly found in early
progenitor cells.74

Tyrosine phosphatases counterbalance and regulate the effects
of tyrosine kinases under physiologic conditions, keeping cellular
phosphotyrosine levels low. Two tyrosine phosphatases, Syp83 and
PTP1B,84 have been shown to form complexes with Bcr-Abl, and
both appear to dephosphorylate Bcr-Abl. Interestingly, PTP1B
levels increase in a kinase-dependent manner, suggesting that the
cell attempts to limit the impact of Bcr-Abl tyrosine kinase activity.
At least in fibroblasts, transformation by Bcr-Abl is impaired by the
overexpression of PTP1B.85 Interestingly, we recently observed the
up-regulation of receptor protein tyrosine phosphatasek (RPTP-k)
with the inhibition of Bcr-Abl in BV173 cells treated with the

Figure 4. Signaling pathways activated in BCR-ABL –positive cells. Note that this
is a simplified diagram and that many more associations between Bcr-Abl and
signaling proteins have been reported.

Table 1. Substrates of BCR-ABL

Protein Function Reference

P62DOK Adapter 74

Crkl Adapter 73

Crk Adapter 13

Shc Adapter 75

Talin Cytoskeleton/cell membrane 76

Paxillin Cytoskeleton/cell membrane 77

Fak Cytoskeleton/cell membrane 78

Fes Myeloid differentiation 79

Ras-GAP Ras-GTPase 80

GAP-associated proteins Ras activation? 214

PLCg Phospholipase 80

PI3 kinase (p85 subunit) Serine kinase 127

Syp Cytoplasmic phosphatase 83

Bap-1 14-3-3 protein 24

Cbl Unknown 81

Vav Hematopoietic differentiation 82

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tyrosine kinase inhibitor STI571,86 which suggests that the oppo-
site effect may also occur. Thus, though the pivotal role of Bcr-Abl
tyrosine kinase activity is clearly established, much remains to be
learned about the significance of tyrosine phosphatases in the
transformation process.

Activated signaling pathways and biologic properties
of BCR-ABL–positive cells

Three major mechanisms have been implicated in the malignant
transformation byBcr-Abl, namely altered adhesion to stroma cells
and extracellular matrix,87 constitutively active mitogenic signal-
ing88 and reduced apoptosis89 (Figure 5). A fourth possible
mechanism is the recently described proteasome-mediated degrada-
tion of Abl inhibitory proteins.66

Altered adhesion properties

CML progenitor cells exhibit decreased adhesion to bone
marrow stroma cells and extracellular matrix.87,90 In this sce-
nario, adhesion to stroma negatively regulates cell proliferation,
and CML cells escape this regulation by virtue of their perturbed
adhesion properties. Interferon-a (IFN-a), an active therapeutic
agent in CML, appears to reverse the adhesion defect.91 Recent
data suggest an important role forb-integrins in the interaction
between stroma and progenitor cells. CML cells express an
adhesion-inhibitory variant ofb1 integrin that is not found in
normal progenitors.92 On binding to their receptors, integrins are
capable of initiating normal signal transduction from outside to
inside93; it is thus conceivable that the transfer of signals that
normally inhibit proliferation is impaired in CML cells. Because
Abl has been implicated in the intracellular transduction of such
signals, this process may be further disturbed by the presence of
a large pool of Bcr-Abl protein in the cytoplasm. Furthermore,
Crkl, one of the most prominent tyrosine-phosphorylated pro-
teins in Bcr-Abl–transformed cells,73 is involved in the regula-
tion of cellular motility94 and in integrin-mediated cell adhe-
sion95 by association with other focal adhesion proteins such as
paxillin, the focal adhesion kinase Fak, p130Cas,96 and Hef1.97

We recently demonstrated that Bcr-Abl tyrosine kinase up-
regulates the expression ofa6 integrin mRNA,86 which points to
transcriptional activation as yet another possible mechanism by
which Bcr-Abl may have an impact on integrin signaling. Thus,
though there is sound evidence that Bcr-Abl influences integrin
function, it is more difficult to determine the precise nature of
the biologic consequences, and, at least in certain cellular
systems, integrin function appears to be enhanced rather than
reduced by Bcr-Abl.98

Activation of mitogenic signaling

Ras and the MAP kinase pathways.Several links between
Bcr-Abl and Ras have been defined. Autophosphorylation of
tyrosine 177 provides a docking site for the adapter molecule
Grb-2.57 Grb-2, after binding to the Sos protein, stabilizes Ras in its
active GTP-bound form. Two other adapter molecules, Shc and
Crkl, can also activate Ras. Both are substrates of Bcr-Abl73,99 and
bind Bcr-Abl through their SH2 (Shc) or SH3 (Crkl) domains. The
relevance of Ras activation by Crkl is, however, questionable
because it appears to be restricted to fibroblasts.100 Moreover, direct
binding of Crkl to Bcr-Abl is not required for the transformation of
myeloid cells.101 Circumstantial evidence that Ras activation is
important for the pathogenesis of Ph-positive leukemias comes
from the observation that activating mutations are uncommon, even
in the blastic phase of the disease,102 unlike in most other tumors.
This implies that the Ras pathway is constitutively active, and no
further activating mutations are required. There is still dispute as to
which mitogen-activated protein (MAP) kinase pathway is down-
stream of Ras in Ph-positive cells. Stimulation of cytokine
receptors such as IL-3 leads to the activation of Ras and the
subsequent recruitment of the serine–threonine kinase Raf to the
cell membrane.103 Raf initiates a signaling cascade through the
serine–threonine kinases Mek1/Mek2 and Erk, which ultimately
leads to the activation of gene transcription.104 Although some data
indicate that this pathway may be activated only in v-abl– but not in
BCR-ABL–transformed cells,105 this view has recently been chal-
lenged.106 Moreover, activation of the Jnk/Sapk pathway by
Bcr-Abl has been demonstrated and is required for malignant
transformation107; thus, signaling from Ras may be relayed through
the GTP–GDP exchange factor Rac108 to Gckr (germinal center
kinase related)109 and further down to Jnk/Sapk (Figure 6). There is
also some evidence that p38, the third pillar of the MAP kinase
pathway, is also activated in BCR-ABL–transformed cells, and
there are other pathways with mitogenic potential. In any case, the
signal is eventually transduced to the transcriptional machinery of
the cell.

It is also possible that Bcr-Abl uses growth factor pathways in a
more direct way. For example, association with thebc subunit of
the IL-3 receptor110 and the Kit receptor111 has been observed.
Interestingly, the pattern of tyrosine-phosphorylated proteins seenFigure 5. Mechanisms implicated in the pathogenesis of CML.

Figure 6. Signaling pathways with mitogenic potential in BCR-ABL –trans-
formed cells. The activation of individual paths depends on the cell type, but the
MAP kinase system appears to play a central role. Activation of p38 has been
demonstrated only in v-abl–transformed cells, whereas data for BCR-ABL–
expressing cells are missing.

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in normal progenitor cells after stimulation with Kit ligand is
similar to the pattern seen in CML progenitor cells.112 Dok-1
(p62DOK), one of the most prominent phosphoproteins in this
setting, forms complexes with Crkl, RasGAP, and Bcr-Abl. In fact,
there may be a whole family of related proteins with similar
functions—for example, the recently described Dok-2 (p56DOK2).113

Somewhat surprisingly, p62DOK is essential for transformation of
Rat-1 fibroblasts but not for growth-factor independence of my-
eloid cells114; thus, its true role remains to be defined.

Jak-Stat pathway.The first evidence for involvement of the Jak-
Stat pathway came from studies in v-abl–transformed B cells.62 Consti-
tutive phosphorylation of Stat transcription factors (Stat1 and Stat5) has
since been reported in several BCR-ABL–positive cell lines115 and in
primary CML cells,116 and Stat5 activation appears to contribute to
malignant transformation.117Although Stat5 has pleiotropic physiologic
functions,118 its effect in BCR-ABL–transformed cells appears to be
primarily anti-apoptotic and involves transcriptional activation of
Bcl-xL.119,120 In contrast to the activation of the Jak-Stat pathway by
physiologic stimuli, Bcr-Abl may directly activate Stat1 and Stat5
without prior phosphorylation of Jak proteins. There seems to be
specificity for Stat6 activation by P190BCR-ABL proteins as opposed to
P210BCR-ABL.115 It is tempting to speculate that the predominantly
lymphoblastic phenotype in these leukemias is related to this peculiarity.

The role of the Ras and Jak-Stat pathways in the cellular
response to growth factors could explain the observation that
BCR-ABLrenders a number of growth factor–dependent cell lines
factor independent.105,121 In some experimental systems there is
evidence for an autocrine loop dependent on the Bcr-Abl–induced
secretion of growth factors,122 and it was recently reported that
Bcr-Abl induces an IL-3 and G-CSF autocrine loop in early
progenitor cells.123 Interestingly, Bcr-Abl tyrosine kinase activity
may induce expression not only of cytokines but also of growth
factor receptors such as the oncostatin Mb receptor.86 One should
bear in mind, however, that during the chronic phase, CML
progenitor cells are still dependent on external growth factors for
their survival and proliferation,124 though less than normal progeni-
tors.125 A recent study sheds fresh light on this issue. FDCPmix
cells transduced with a temperature-sensitive mutant ofBCR-ABL
have a reduced requirement for growth factors at the kinase
permissive temperature without differentiation block.126 This situa-
tion resembles chronic-phase CML, in which the malignant clone
has a subtle growth advantage while retaining almost normal
differentiation capacity.

PI3 kinase pathway.PI3 kinase activity is required for the
proliferation of BCR-ABL–positive cells.127 Bcr-Abl forms multi-
meric complexes with PI3 kinase, Cbl, and the adapter molecules
Crk and Crkl,95 in which PI3 kinase is activated. The next relevant
substrate in this cascade appears to be the serine–threonine kinase
Akt.128 This kinase had previously been implicated in anti-
apoptotic signaling.129 A recent report placed Akt in the down-
stream cascade of the IL-3 receptor and identified the pro-apoptotic
protein Bad as a key substrate of Akt.130 Phosphorylated Bad is
inactive because it is no longer able to bind anti-apoptotic proteins
such as BclXL and it is trapped by cytoplasmic 14-3-3 proteins.
Altogether this indicates that Bcr-Abl might be able to mimic the
physiologic IL-3 survival signal in a PI3 kinase-dependent manner
(see also below). Ship131 and Ship-2,132 2 inositol phosphatases
with somewhat different specificities, are activated in response to
growth factor signals and by Bcr-Abl. Thus, Bcr-Abl appears to
have a profound effect on phosphoinositol metabolism, which
might again shift the balance to a pattern similar to physiologic
growth factor stimulation.

Myc pathway. Overexpression of Myc has been demonstrated
in many human malignancies. It is thought to act as a transcription
factor, though its target genes are largely unknown. Activation of
Myc by Bcr-Abl is dependent on the SH2 domain, and the
overexpression of Myc partially rescues transformation-defective
SH2 deletion mutants whereas the overexpression of a dominant-
negative mutant suppresses transformation.133 The pathway linking
Myc to the SH2 domain of Bcr-Abl is still unknown. However,
results obtained in v-abl–transformed cells suggest that the signal is
transduced through Ras/Raf, cyclin-dependent kinases (cdks), and
E2F transcription factors that ultimately activate the MYC pro-
moter.134 Similar results were reported for BCR-ABL–transformed
murine myeloid cells.135 How these findings relate to human
Ph-positive cells is unknown. It seems likely that the effects of Myc
in Ph-positive cells are probably not different from those in other
tumors. Depending on the cellular context, Myc may constitute a
proliferative or an apoptotic signal.136,137It is therefore likely that
the apoptotic arm of its dual function is counterbalanced in CML
cells by other mechanisms, such as the PI3 kinase pathway.

Inhibition of apoptosis

Expression of Bcr-Abl in factor-dependent murine138 and
human122 cell lines prevents apoptosis after growth-factor with-
drawal, an effect that is critically dependent on tyrosine kinase
activity and that correlates with the activation of Ras.88,139 More-
over, several studies showed thatBCR-ABL–positive cell lines are
resistant to apoptosis induced by DNA damage.89,140 The underly-
ing biologic mechanisms are still not well understood. Bcr-Abl
may block the release of cytochrome C from the mitochondria and
thus the activation of caspases.141,142 This effect upstream of
caspase activation might be mediated by the Bcl-2 family of
proteins. Bcr-Abl has been shown to up-regulate Bcl-2 in a Ras-143

or a PI3 kinase-dependent128 manner in Baf/3 and 32D cells,
respectively. Moreover, as mentioned previously, BclxL is transcrip-
tionally activated by Stat5 inBCR-ABL–positive cells.119,120

Another link betweenBCR-ABLand the inhibition of apoptosis
might be the phosphorylation of the pro-apoptotic protein Bad. In
addition to Akt, Raf-1, immediately downstream of Ras, phosphor-
ylates Bad on 2 serine residues.144,145Two recent studies provided
evidence that the survival signal provided by Bcr-Abl is at least
partially mediated by Bad and requires targeting of Raf-1 to the
mitochondria.146,147It is also possible that Bcr-Abl inhibits apopto-
sis by down-regulating interferon consensus sequence binding
protein (ICSBP).148,149 These data are interesting because ICSBP
knockout mice develop a myeloproliferative syndrome,150 and
hematopoietic progenitor cells from ICSBP2/2 mice show altered
responses to cytokines.151 The connection to interferona, an active
agent in the treatment of CML, is obvious.

It becomes clear that the multiple signals initiated by Bcr-Abl
have proliferative and anti-apoptotic qualities that are frequently
difficult to separate. Thus, Bcr-Abl may shift the balance toward
the inhibition of apoptosis while simultaneously providing a
proliferative stimulus. This is in line with the concept that a
proliferative signal leads to apoptosis unless it is counterbalanced
by an anti-apoptotic signal,152 and Bcr-Abl fulfills both require-
ments at the same time. There is, however, controversy. One report
found 32D cells transfected withBCR-ABLto be more sensitive to
IR than the parental cells,153 whereas 2 other studies failed to detect
any difference between CML and normal primary progenitor cells
with regard to their sensitivity to IR and growth factor with-
drawal.124,154Furthermore, based on results obtained in transfected
cell systems, it was suggested that Bcr-Abl inhibits apoptosis

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mediated by the Fas receptor/Fas ligand system.155 However,
though there may be a role for this system in mediating the clinical
response to interferon-a,156 there is no indication that Fas-triggered
apoptosis is defective in primary CML cells or in “natural”
Ph-positive cell lines.157 Moreover, Bcr-Abl accelerates C2 cer-
amide-induced apoptosis,158 and it does not protect against natural
killer cell-induced apoptosis.159 These inconsistencies may reflect
genuine differences between cell lines and primary cells. On the
other hand, it is debatable whether complete growth-factor with-
drawal and IR constitute stimuli that have much physiologic
relevance. To allow for a representative comparison, it would be
crucial to define the signals that induce apoptosis in vivo.

Degradation of inhibitory proteins.

The recent discovery that Bcr-Abl induces the proteasome-
mediated degradation of Abi-1 and Abi-2,66 2 proteins with
inhibitory function, may be the first indication of yet another way
by which Bcr-Abl induces cellular transformation. Most compel-
ling, the degradation of Abi-1 and Abi-2 is specific for Ph-positive
acute leukemias and is not seen in Ph-negative samples of
comparable phenotype. The overall significance of this observation
remains to be seen, and one must bear in mind that the data refer to
acute leukemias and not to chronic phase CML. It is nevertheless
tempting to speculate that other proteins, whose level of expression
is regulated through the proteasome pathway, may also be de-
graded. A good candidate would be the cell cycle inhibitor p27, but
to our knowledge no data are available yet.

Experimental models of CML

Various experimental systems have been developed to study the
pathophysiology of CML. All of them have their advantages and
shortcomings, and it is probably fair to say that there is still no ideal
in vitro or in vivo model that would cover all aspects of the
human disease.

Cell lines

Fibroblasts. Fibroblast lines have been used extensively in CML
research because they are easy to manipulate. Fibroblast transforma-
tion—that is, anchorage-independent growth in soft agar—is the
standard in vitro test for tumorigenicity.160 However, it became
clear that the introduction ofBCR-ABLinto fibroblasts has diverse
effects, depending on the type of fibroblast used. Thus, though
P210BCR-ABL transforms Rat-1 fibroblasts,161 there is no such effect
in NIH3T3.162 Moreover, transformation to serum-independent
growth occurs only in few cells (permissive cells163), whereas most
undergo growth arrest. These observations show that certain
cellular requirements must be met if a cell is to be transformed by
BCR-ABL. Interestingly, this is also the case for the various parts of
the Bcr-Abl protein. Thus, aBCR-ABLmutant that lacks the SH2
domain retains the capacity to transform hematopoietic 32D cells
to growth factor independence60 but is defective for fibroblast
transformation.59 In addition, there are differences between hemato-
poietic cells and fibroblasts in terms of interactions with other
proteins such as Crkl. The latter is functional in Ras activation and
transformation in fibroblasts100 but not in hematopoietic cells.101

Thus, results obtained from studies in fibroblasts must be inter-
preted with great caution.

Hematopoietic cell lines.Until relatively recently, only a few
BCR-ABL–positive lines derived from CML were available, but

their number has grown considerably in the past few years.164 They
include cell lines with myeloid differentiation, such as the well-
known K562, and lymphoid phenotype, such as BV173. The main
drawback common to all these lines is the fact that they are derived
from blast crisis and, thus, contain genetic lesions in addition to
BCR-ABL. Consequently, they may reflect blast crisis fairly well
but are insufficient models of chronic phase CML. Until now, no
cell line from chronic phase CML has been established, just as no
cell line could be derived from normal human bone marrow. Even
attempts to immortalize Ph-positive B-cells from patients in the
chronic phase of disease were not successful because these lines
have a limited life span,165 in contrast to their Ph-negative
counterparts. One could therefore speculate that the very establish-
ment of a line from a patient with CML would be diagnostic of
advanced disease. In this context, it is surprising that most human
CML lines remain dependent on Bcr-Abl tyrosine kinase activity
for their proliferation and survival, as shown by their susceptibility
to the effects of the Abl-specific tyrosine kinase inhibitor STI571.8

However, the phenotype of these cell lines is that of an acute
leukemia. Therefore great caution is warranted if experimental
results are to be transferred to chronic phase CML. A striking
example is the fact that inhibition of apoptosis by Bcr-Abl is easily
demonstrable in cell lines139 but not in primary cells.124 It should
also be noted that many of the lines used have undergone hundreds,
if not thousands, of rounds of replication, and different laboratories
frequently house lines that have little in common but their names
andBCR-ABLpositivity.

Transformation of factor-dependent cell lines to growth-factor
independence is an important feature of Bcr-Abl, and, in fact, other
oncoproteins that contain an activated tyrosine kinase.43,166 Al-
though it is usually difficult to obtain stable expression of
BCR-ABLin previously immortalized cell lines, this is relatively
easily achieved in factor-dependent lines, presumably because
BCR-ABLexpression is an advantage to the latter but useless or
even detrimental to the former. Murine cell lines such as Baf/3 and
32D and human cell lines such as MO7 were used to study the
effects ofBCR-ABLby direct comparison between transduced and
parental cells. A particular advantage of the murine lines is the fact
that they are derived from normal nonmalignant hematopoietic
cells. Unfortunately, this does not rule out the development of
additional mutations167 that confer a selective growth advantage.
Furthermore, it is not clear how the transformation to complete
factor independence relates to clinical CML in which the cells are
still factor-dependent, though obviously less so than normal
hematopoietic cells.123 The subject of growth factor independence
andBCR-ABLtransformation has been reviewed recently.168

None of the cell lines mentioned above is capable of multilineage
hematopoietic differentiation. Two strategies are promising in overcom-
ing this restraint. A recent report126 shows that murine FDCPmix cells,
transduced with a temperature-sensitive mutant ofBCR-ABL, become
partially factor-independent at the permissive temperature, in analogy to
chronic phase CML. They retain the capacity for terminal differentia-
tion, similar to chronic phase CML cells. Another approach is the study
of embryonic stem (ES) cells transduced withBCR-ABL. In one such
experimental system, it was possible to reproduce one cardinal feature of
the clinical disease in the model, namely the expansion of the myeloid
compartment at the expense of the erythroid compartment.169 Interest-
ingly, the increase in total cell numbers in theBCR-ABL-transduced ES
cells was found to result from increased proliferation though there was
little effect on apoptosis, another finding in line with observations in
primary Ph-positive cells.124,154 In this system, a stromal cell layer is
used on which the ES cells removed from leukemia-inhibitory factor

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(LIF) differentiate into hemangioblasts and then into hematopoietic
cells. This may explain why these results are not strictly comparable to
those of another study, in whichBCR-ABLresulted in the decreased
formation of embryonal bodies along with increased output of all kinds
of hematopoietic progenitors.170 In yet another study,BCR-ABL–
transformed ES cells transplanted into irradiated mice induced a
leukemic syndrome with many features of CML.171If developed further,
these models may well be able to retain the major advantage of cell
lines—their ease of manipulation—while at the same time moving the
in vitro system closer to the clinical disease.

Bearing all these caveats in mind, there is no doubt that the
study of cell lines contributed significantly to our understanding of
CML. Particularly, many of the proteins that interact with Bcr-Abl
were identified in Ph-positive cell lines, where they are more
abundantly expressed than in primary cells. Thus, though these
lines are invaluable tools for screening, it is important to confirm
the results in primary cells.

Primary cells. The study of patient material and its comparison
with normal hematopoietic progenitor cells is certainly the gold
standard of CML research, particularly for the chronic phase of the
disease. Much of the data refer to operationally defined cellular
properties of CML versus normal cells, such as clonogenicity or
adherence to bone marrow stroma; to give a comprehensive
account of the cellular biology of CML would require a review in
its own right. We will therefore focus on some areas in which the
study of primary CML cells has been particularly instrumental to
the study of the molecular biology of the disease.

One of the main problems when studying primary cells is
inherent in the very nature of chronic phase cells—they tend to
mature when placed in culture. Thus, the window of time for in
vitro studies is narrow, and expansion of very primitive cells, the
least prevalent but most interesting population, is difficult and
carries the risk for introducing nonphysiologic alterations.172

Furthermore, there is considerable variation between patients
that frequently results in an overlap rather than a clear distinc-
tion between normal cells and CML cells. Last, results are
unreliable unless clearly defined cell populations such as CD341

cells are studied. To a large extent, these problems can be
overcome by the introduction of retroviralBCR-ABLexpression
vectors to murine or human primary bone marrow cells (see
“Animal models” below).

A striking example of how fruitful the comparison of primary
cell populations can be is the study of tyrosine-phosphorylated
proteins in CD341 cells.112 This study led to the subsequent
identification of p62DOK74;173and SHIP2132 as mediators of Bcr-Abl–
induced transformation. Moreover, it produced the important
notion that Bcr-Abl tyrosine kinase activity may have conse-
quences similar to the activation of the KIT receptor.112 Another
example is the identification of CRKL as the major tyrosine-
phosphorylated protein in CML neutrophils.73

The recent possibility of turning off the Bcr-Abl tyrosine kinase
activity in cell lines and primary cells with STI5717,8 provided the
opportunity to study the effects of theBCR-ABL gene when
expressed from its naturalBCRpromoter at “physiological” levels.
This is certainly an advantage over transduced cell systems; the
drawback, however, is that effects related to inhibition of the KIT
and PDGFRb kinases, and potentially other unidentified tyrosine
kinases, cannot be ruled out. Furthermore, the Bcr-Abl protein,
though kinase-inactive, is still present in the cells and may interfere
with other proteins.

Animal models

Thus far, no animals other than mice have been used for the study
of CML in vivo. Various approaches have been taken.

Engraftment of BCR-ABL–transformed cell lines in synge-
neic mice. Murine factor-dependent cell lines such as 32D trans-
duced withBCR-ABLgive rise to an aggressive leukemia when
transplanted into syngeneic recipients.60,174 This is an excellent in
vivo model to test the efficacy of new drugs, such as the tyrosine
kinase inhibitor STI571, in vivo. Furthermore, the impact on
leukemogenicity of modifications within the Bcr-Abl protein and
modifications to the respective cell lines (such as the introduction
of co-stimulatory molecules174) can be tested. The main drawback
is that the disease is a form of acute leukemia and is thus far from
chronic phase CML.

Engraftment of immunodeficient mice with human BCR-ABL–
positive cells.Cell lines derived from human CML blast crisis are
relatively easily propagated in severe combined immunodeficiency
(SCID) mice.175 The distribution of the leukemia cells is fairly
similar to the human disease, that is, they home to bone marrow and
peripheral blood before they metastasize to nonhematopoietic
tissues. More recently, it was shown that SCID mice can be
engrafted with chronic phase CML cells if the cell inoculum is
large enough (in the range of 13 108 cells).176 Up to 10% human
cells were detectable in the recipient bone marrow and showed
multilineage differentiation. Interestingly, most colonies were
BCR-ABL negative and thus were derived from the patient’s
residual normal hematopoiesis. This is reminiscent of long-term
bone marrow cultures of CML177 and shows that host factors
modify the disease to a great extent, a problem that will persist,
even if higher percentages of engraftment can eventually be
achieved. A step into this direction is the use of nonobese
diabetes-SCID mice. In addition to the SCID defect in V(D)J
recombination, these animals lack functional natural killer cells.
Chronic phase CML cells and, even more so, cells from accelerated
phase or blast crisis readily engraft in these mice, and there is a
significant correlation between engraftment and disease state.178

Interestingly, the cells were exclusively Ph-positive in most cases,
in contrast to cells engrafted in SCID mice, as mentioned above.
This may be attributed to technical reasons but may also reflect a
genuine difference between the different strains of mice. We can
anticipate that these murine models will be useful for studying
certain aspects of CML, such as the response to novel forms of
treatment. Their value in investigating the human disease will be
limited because it is difficult to see how disease modification by
host factors could ever be ruled out.

Transgenic mouse models.Attempts to useBCR-ABLtrans-
genic mice as a CML model go back to the late 1980s, when a
full-length cDNA of BCR-ABL was not yet available and an
artificial construct of human BCR sequences fused to v-abl was
used instead.179 Since then, a number of studies have been
published that clearly prove the oncogenic potential ofBCR-ABL.
Several different promoters were used to direct the expression to
the desired target tissues. However, some problems were encoun-
tered. First, it became clear that Bcr-Abl has a toxic effect on
embryogenesis,180 perhaps the consequence of a cytostatic effect in
nonhematopoietic tissues.181 Recently, the expression ofBCR-ABL
from a tetracycline-repressible promoter effectively overcame this
problem.182 Most striking, the leukemia in these transgenic mice is
completely reversible on re-addition of tetracycline. The second
problem with transgenic mice is that the P210BCR-ABLvariant
relevant to CML is difficult to study because it is less efficient in

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inducing leukemia than P190, a finding that was again confirmed in
a recent study.47 Third and most important, the types of leukemia
that developed in these mice were acute and of either B- or
T-lymphoid phenotype, regardless of whether they arose in P190 or
P210 transgenic animals. Thus, they resembledBCR-ABL–positive
ALL but not chronic-phase CML183,184. In fact, myeloid leukemias
developed rarely, if at all. A recent report185 may represent a major
advance in this respect. In this study,BCR-ABLwas expressed from
the Tec promoter, a cytoplasmic tyrosine kinase predominantly
expressed in hematopoietic cells. Although the founder mice
exhibited excessive proliferation of lymphoblasts, their progeny
developed a CML-like disease, albeit after a relatively long latency
period of approximately 10 months. Thus, it is likely that the
problems of the transgenic models will eventually be resolved if the
gene is targeted to the appropriate cell.

Transduction of murine bone marrow cells with BCR-ABL
retroviruses. In 1990, several groups reported that a CML-like
myeloproliferative syndrome could be induced when P210BCR-
ABL–infected marrow was transplanted into syngeneic recipi-
ents.6,186,187 Transplantation into secondary recipients frequently
produced an identical disease while some mice developed acute
leukemias of T- or B-cell phenotype, analogous to the development
of lymphoid blast crisis in the clinical disease. Clonality was
demonstrated in many cases. Roughly a quarter of the mice showed
the myeloproliferative disease, whereas other recipients developed
other distinct hematologic malignancies, such as macrophage
tumors, B-ALL, T-ALL, and erythroleukemia. Most likely, these
different diseases are the consequence of infection of different
committed progenitor cells that, after transformation, give rise to
the respective progeny. Not surprisingly, the infection conditions
have a major impact on the disease phenotype.188 Building on the
foundations of this early work, major improvements to the
transduction–transplantation system have been made in the past
few years. High-titerBCR-ABLretroviral stocks can be produced
rapidly by transient transfection of packaging lines; the culture
conditions have been refined, and the murine stem cell virus LTR
has been introduced that allows for more efficient expression of
BCR-ABLin the desired target cell. Combining all 3 improvements,
2 recent studies189,190 reported the induction of a transplantable
CML-like disease in 100% of recipients. Pulmonary hemorrhage, a
complication not found in human CML, was a frequent cause of
death in both studies, demonstrating that these novel models,
though a major step forward, may have their own distinct problems.
Nevertheless, bone marrow transduction–transplantation most faith-
fully reproduces human CML, and further improvements are likely
in the near future.

Transformation to blast crisis

Clinically, chronic-phase CML does not represent a major manage-
ment problem because the elevated white blood cell count is readily
controlled with cytotoxic agents in most patients, and neutrophil
and platelet functions are largely normal. However, the disease
progresses inexorably to acceleration and blast crisis, often within
5 years of diagnosis. The mechanisms underlying this evolution
remain enigmatic. Deletion or inactivation of p16,191 p53,192 and
the retinoblastoma gene product193 have been reported but occur
relatively rarely and, similar to the overexpression ofEVI-1,194 are
not specific for blast crisis CML. This probably indicates that a
wide variety of lesions, possibly multiple “cooperating” lesions,
are required to induce the phenotype of blast crisis. Perhaps even

more intriguing is why the cells acquire these additional lesions in
the first place. A recent report shows that Bcr-Abl enhances the
mutation rate in the Na-K-ATPase and in the HPRT genomic loci,
both commonly used markers to measure mutation frequency.
Along with this goes enhanced expression of DNA polymeraseb,
the mammalian DNA polymerase with the least fidelity.195 P210BCR-

ABL , but not P190BCR-ABL, phosphorylates and potentially interacts
with xeroderma pigmentosum group B protein (XPB); as a result,
the catalytic function of XPB may be reduced, and DNA repair may
be impaired.196 In a recent study p210BCR-ABL transgenic mice were
cross-mated with p53 heterozygous mice. In the offspring, the
remaining p53 was rapidly lost because of somatic mutation, and
the mice developed a disease that resembled blast crisis.197

Although this is still not a perfect model of human CML because
the blasts are of T lineage, it strongly supports the concept of
genomic instability inBCR-ABL–transformed cells. How Bcr-Abl
leads to these phenomena is unclear, but they might form the basis
of the presumed genomic instability of chronic phase CML. It is
also possible that the alleged anti-apoptotic effect of Bcr-Abl
favors inaccurate DNA repair where apoptosis would ensue in
normal cells. In line with this concept, a prolonged G2 arrest after
IR has been observed inBCR-ABL–expressing cell lines exposed to
DNA-damaging agents.140This arrest could allow for DNA (mis)re-
pair, whereas in a normal cell the damage would induce apoptosis.
Over time this could lead to the accumulation of mutations in
BCR-ABL–positive cells that finally result in blastic transforma-
tion. There is no doubt that the excessive proliferation, with its high
cell turnover, must be a risk factor per se for additional ge-
netic lesions.

Molecular targets for therapy

Attempts at designing therapeutic tools for CML based on our
current knowledge of the molecular and cell biology of the disease
have concentrated on 3 main areas—the inhibition of gene
expression at the translational level by “antisense” strategies, the
stimulation of the immune system’s capacity to recognize and
destroy leukemic cells, and the modulation of protein function by
specific signal transduction inhibitors. The antisense oligonucleo-
tide198,199 and ribozyme200 approaches received much attention in
the last decade but have in general failed to fulfill their theoretical
promises. New modifications to the system, such as the use of
BCR-ABLjunction-specific catalytic subunits of RNase P,201 may
revitalize the field. The issue of immunologic stimulation, be it in
the form of adoptive immunotherapy by donor lymphocyte infu-
sions202 or of BCR-ABLjunction peptide vaccination,203 is another
avenue being extensively explored for the treatment of CML.

Perhaps the most exciting of the molecularly designed therapeu-
tic approaches was brought about by the advent of signal transduc-
tion inhibitors (STI), which block or prevent a protein from
exerting its role in the oncogenic pathway. Because the main
transforming property of the Bcr-Abl protein is effected through its
constitutive tyrosine kinase activity, direct inhibition of such
activity seems to be the most logical means of silencing the
oncoprotein. To this effect, several tyrosine kinase inhibitors have
been evaluated for their potential to modify the phenotype of CML
cells. The first to be tested were compounds isolated from natural
sources, such as the iso-flavonoid genistein and the antibiotic
herbimycin A.204 Later, synthetic compounds were developed
through a rational design of chemical structures capable of
competing with the adenosine triphosphate (ATP) or the protein

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substrate for the binding site in the catalytic center of the kinase205

(Figure 7).
The most promising of these compounds is the 2-phenylamin-

opyrimidine STI571 (formerly CGP57418B; Novartis Pharmaceu-
tics, Basel, Switzerland), which specifically inhibits Abl tyrosine
kinase at micromolar concentrations.206 Inhibition of the Bcr-Abl
kinase activity by this compound results in the transcriptional
modulation of various genes involved in the control of the cell
cycle, cell adhesion, and cytoskeleton organization, leading the
Ph-positive cell to an apoptotic death.86 Furthermore, STI571
selectively suppresses the growth of CML primary cells and cell
lines in vitro7,8 and in mice.7,207 Its remarkable specificity and
efficacy led to consideration of the drug for therapeutic use. Thus,
in the spring of 1998, a phase 1 clinical trial was initiated in the
United States in which patients with CML in chronic phase
resistant to IFN-a were treated with STI571 in increasing doses.
The drug showed little toxicity but proved to be highly effective.
All patients treated with 300 mg/d or more entered a complete
hematologic remission. Even more striking, many of the patients
had cytogenetic responses.9 This might mean that STI571 changes
the natural course of the disease, though it is far too early to arrive
at any definite conclusions. Altogether, the results were convincing
enough to justify the initiation of phase 2 studies that included
patients with acute Ph-positive leukemias (CML in blast crisis and
Ph-positive ALL) and, at a later stage, a large cohort of interferon-
intolerant or -resistant patients. These studies are ongoing. It turned
out that STI571 is effective in many patients with acute Ph-positive
leukemia, particularly of lymphoid phenotype. Although in many
patients the remissions are not sustained, the advent of an effective
oral medication with little toxicity represents a major step forward
in this very poor risk group. Clearly, elucidation of the mechanisms
underlying the resistance208 will be of critical importance for the
development of further treatment strategies, such as a combination
of STI571 with conventional cytotoxic drugs or, perhaps, with
other STIs (see below). In this context, the most interesting
question is whether STI571 will be able to eradicate the malignant
clone, at least in some patients with chronic-phase CML. From
what we know about the disease, this seems unlikely—colony
formation by CML progenitor cells is much reduced but not
abrogated in the presence of STI5717,8—which might mean that a
subset of these cells proliferates independently of Bcr-Abl tyrosine

kinase activity and still relies on external growth factors. There is
no doubt, however, that the clinical efficacy and low toxicity of
STI571 sets a precedent for the further development of targeted
forms of therapy in malignant disease.

An alternative or a supplement to direct inhibition of Bcr-Abl is
interference with proteins that are critical for Bcr-Abl–induced
transformation (Figure 4). One of these proteins is Grb2, whose
SH2 domain binds directly to Bcr-Abl through the phosphorylated
tyrosine 177 within the Bcr portion of the chimera57 and is essential
for activation of the Ras pathway (Figure 6).209 Another good
candidate is Ras itself, whose activity depends on its attachment to
the cell membrane through a prenyl (usually a farnesyl) group.
Thus, farnesyl transferase inhibitors (FTI) have been studied for
their effect in inhibiting the proliferation of ALL210 and juvenile
myelomonocytic leukemia cells,211 and they may be useful for the
control of CML cells. Additional targets worth considering are
represented by PI-3 and Src kinases, of which the available
inhibitors have been shown to suppress colony formation of
primary progenitors,127 proliferation ofBCR-ABL–transfected cell
lines, or both.212,213It is envisaged that the progressive unraveling
of which pathways are really essential for the development of the
disease, coupled to rapid advances in biotechnology, will bring us
the ideal combination of rationally designed drugs that can tip the
balance toward the re-establishment of normal hematopoiesis
in CML.

Conclusion

Though this be madness, yet there is method in it.(Shakespeare W.,
Hamlet.Act 2, scene 2.)

There are 2 ways to conclude this review after going through the
vast amount of data presented. Surely one could argue that despite
all these data, there is still no clear picture emerging and each piece
of additional information adds only more confusion. Alternatively,
what might help us against capitulation in the face of complexity is
to try to simplify without oversimplification.

Can we build a model of CML that incorporates all the scientific
data available but still retains clarity? In other words, could we
explain how Bcr-Abl works in a few sentences to somebody who
has never heard of it? Perhaps the most promising approach might
be to try to link the biologic behavior of a CML cell to the
underlying molecular events (Figure 5). Crucially, we should be
able to picture this scenario relying onBCR-ABLalone because, at
least until now, there is no unequivocal evidence that additional
genetic lesions are present during chronic phase. We do not know
how long it takes to move from the initial genetic event to fully
established chronic-phase CML, but there is good reason to believe
that the proliferative advantage of CML over normal cells is
limited. Together with the largely normal differentiation capacity
and function of CML blood cells, one feels that Ph-positive
hematopoiesis cannot be so much different from normal hematopoi-
esis until the disease accelerates. Thus, Bcr-Abl is likely to hijack
pathways that normally increase blood cell output in response to
physiologic stimuli rather than to interrupt or replace them with
pathways that are not normally used in hematopoietic cells. Indeed,
there is plenty of experimental evidence to support this notion.
Importantly, Bcr-Abl is capable of activating survival pathways
along with proliferative stimuli without the need for a second
cooperating genetic lesion; in this way, the apoptotic response that
would otherwise follow an isolated proliferative stimulus is

Figure 7. Mechanism of action of tyrosine kinase inhibitors. The drug competes
with ATP for its specific binding site in the kinase domain. Thus, whereas the
physiologic binding of ATP to its pocket allows Bcr-Abl to phosphorylate selected
tyrosine residues on its substrates (left diagram), a synthetic ATP mimic such as
STI571 fits this pocket equally well but does not provide the essential phosphate
group to be transferred to the substrate (right diagram). The downstream chain of
reactions is then halted because, with its tyrosines in the unphosphorylated form, this
protein does not assume the necessary conformation to ensure association with
its effector.

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avoided. The sustained dependence on growth factors is an
indication that Bcr-Abl is not a complete substitute; rather, it tips
the balance to provide a limited growth advantage in vivo. This
growth advantage is also dependent on specific survival conditions:
transient regeneration of Ph-negative hematopoiesis is often ob-
served after autografting, even when the autograft seems to be
comprised exclusively of Ph-positive stem cells, and long-term
cultures initiated from patients with chronic-phase CML become
dominated byBCR-ABL–negative cells after some time.177 Thus,
there appears to be a specific interaction (or noninteraction) of
CML progenitor cells with their microenvironment that is crucial to
maintain their proliferative advantage. Whether this interaction is
stimulatory for CML over normal progenitor cells or inhibitory for
normal over CML progenitor cells remains to be seen. Similarly,
we can look at extramedullary hematopoiesis as a loss of function
(ie, loss of the capacity to respond to negative signals) or a gain of
function (ie, acquisition of a capacity to respond to positive signals
that are not provided in the bone marrow) phenomenon. Much of
the evidence implicates integrins in mediating these abnormal
interactions, but other proteins may also play a role. Overall, it
appears that the organization of cell membrane and cytoskeleton is
more profoundly perturbed in CML progenitor cells than might be
anticipated from the largely normal function of their progeny.
Furthermore, Bcr-Abl may interfere with the “wiring” between
integrin receptors on the cell surface and the nucleus and so disturb
the communication of the cell with its environment. Another
mechanism may also be important: Bcr-Abl appears to induce the
degradation of certain inhibitory proteins. This might thwart
cellular counter-reactions that would otherwise be activated, rather
like cutting the telephone cable before the police can be called in.

Many questions remain unanswered. Why is there a predomi-
nantly myeloid expansion when all 3 lineages carry the translo-

cation? What is the biologic basis for the extraordinary variabil-
ity in the clinical course of a disease that appears to carry just a
single genetic lesion? What is the molecular basis for the
genomic instability that we see clinically as relentless progres-
sion to blast crisis?

Where do we go from here? The more we learn about the
pathogenesis of CML, the more we realize its extraordinary
complexity. Perhaps one should not be too surprised because it
has become clear that cellular processes tend to rely on
integrated networks rather than on straight unidirectional path-
ways. Only in this way can the cell achieve the flexibility
required to respond to the various stimuli within a multicellular
organism. Clearly, some components must be more important,
and some less so, in the transformation network operated by
Bcr-Abl. Absolutely essential features may be restricted to
functional domains and to certain residues of the Bcr-Abl
protein itself, and downstream effectors may be able to substi-
tute for each other, at least to some extent. In this respect, the
use of knockout mice that lack specific downstream molecules
will allow one to define their precise relevance for Bcr-Abl–
mediated cellular transformation. It may turn out that the
combined elimination of several components abrogates transfor-
mation by Bcr-Abl, whereas each component individually is of
limited significance. Chronic phase CML operates very much by
exploiting physiologic pathways, perhaps by gently “coaxing”
hematopoiesis toward the classical CML phenotype; neverthe-
less it prepares the ground for blast crisis. Thus, to understand
CML, we must study its chronic phase. We must move away
from artificial systems, such as transduced fibroblasts, and take
on the demanding task of studying signal transduction in
primary progenitor cells.

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original article

T h e n e w e n g l a n d j o u r n a l o f m e d i c i n e

n engl j med 355;23 www.nejm.org december 7, 20062408

Five-Year Follow-up of Patients Receiving
Imatinib for Chronic Myeloid Leukemia

Brian J. Druker, M.D., François Guilhot, M.D., Stephen G. O’Brien, M.D., Ph.D.,
Insa Gathmann, M.Sc., Hagop Kantarjian, M.D., Norbert Gattermann, M.D.,

Michael W.N. Deininger, M.D., Ph.D., Richard T. Silver, M.D.,
John M. Goldman, D.M., Richard M. Stone, M.D., Francisco Cervantes, M.D.,
Andreas Hochhaus, M.D., Bayard L. Powell, M.D., Janice L. Gabrilove, M.D.,
Philippe Rousselot, M.D., Josy Reiffers, M.D., Jan J. Cornelissen, M.D., Ph.D.,

Timothy Hughes, M.D., Hermine Agis, M.D., Thomas Fischer, M.D.,
Gregor Verhoef, M.D., John Shepherd, M.D., Giuseppe Saglio, M.D.,
Alois Gratwohl, M.D., Johan L. Nielsen, M.D., Jerald P. Radich, M.D.,
Bengt Simonsson, M.D., Kerry Taylor, M.D., Michele Baccarani, M.D.,

Charlene So, Pharm.D., Laurie Letvak, M.D.,
and Richard A. Larson, M.D., for the IRIS Investigators*

Address reprint requests to Dr. Druker at
the Oregon Health and Science University
Cancer Institute, L592, 3181 SW Sam Jack-
son Park Rd., Portland, OR 97239, or at
drukerb@ohsu.edu.

* Authors’ affiliations and investigators in
the International Randomized Study of
Interferon and STI571 (IRIS) are listed in
the Appendix.

N Engl J Med 2006;355:2408-17.
Copyright © 2006 Massachusetts Medical Society.

A B S T R A C T

Background

The cause of chronic myeloid leukemia (CML) is a constitutively active BCR-ABL tyro-
sine kinase. Imatinib inhibits this kinase, and in a short-term study was superior to
interferon alfa plus cytarabine for newly diagnosed CML in the chronic phase. For
5 years, we followed patients with CML who received imatinib as initial therapy.

Methods

We randomly assigned 553 patients to receive imatinib and 553 to receive interferon
alfa plus cytarabine and then evaluated them for overall and event-free survival; pro-
gression to accelerated-phase CML or blast crisis; hematologic, cytogenetic, and mo-
lecular responses; and adverse events.

Results

The median follow-up was 60 months. Kaplan–Meier estimates of cumulative best
rates of complete cytogenetic response among patients receiving imatinib were 69%
by 12 months and 87% by 60 months. An estimated 7% of patients progressed to
accelerated-phase CML or blast crisis, and the estimated overall survival of patients
who received imatinib as initial therapy was 89% at 60 months. Patients who had a
complete cytogenetic response or in whom levels of BCR-ABL transcripts had fallen
by at least 3 log had a significantly lower risk of disease progression than did pa-
tients without a complete cytogenetic response (P<0.001). Grade 3 or 4 adverse events diminished over time, and there was no clinically significant change in the profile of adverse events.

Conclusions

After 5 years of follow-up, continuous treatment of chronic-phase CML with imatinib
as initial therapy was found to induce durable responses in a high proportion of pa-
tients. (ClinicalTrials.gov number, NCT00006343.

)

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Chronic myeloid leukemia (cml) is a myeloproliferative disorder characterized by the expansion of a clone of hematopoi-
etic cells that carries the Philadelphia chromo-
some (Ph).1 The Ph chromosome results from a
reciprocal translocation between the long arms
of chromosomes 9 and 22, t(9;22)(q34;q11).2 The
molecular consequence of this translocation is a
novel fusion gene, BCR-ABL, which encodes a con-
stitutively active protein, tyrosine kinase.3-5 Ima-
tinib (Gleevec, Novartis; formerly called STI571) is
a relatively specific inhibitor of the BCR-ABL tyro-
sine kinase and has efficacy in CML.6-11

Before the availability of imatinib, interferon
alfa plus cytarabine was considered standard ther-
apy for patients with CML who were not plan-
ning to undergo allogeneic hematopoietic stem-
cell transplantation.12,13 A randomized trial that
compared imatinib with interferon alfa plus cyta-
rabine in the chronic phase of CML demonstrated
the significant superiority of imatinib in all stan-
dard indicators of the disease within a median
follow-up of 19 months.14 The trial was designed
as a crossover study, and given the superior results
with imatinib, a large proportion of patients in
the interferon group switched to imatinib. In ad-
dition, at the time of Food and Drug Administra-
tion approval of imatinib, many patients who were
assigned to receive interferon alfa plus cytarabine
left the study. Consequently, the trial has evolved
into a long-term study of the result of treating
newly diagnosed patients in the chronic phase of
CML with imatinib. We now report 60 months of
follow-up data and focus on patients who received
imatinib as a primary treatment.

M e t h o d s

Study Design

The design of the study has been described pre-
viously.14 The International Randomized Study
of Interferon and STI571 (IRIS) was a multicenter,
international, open-label, phase III randomized
study. Eligible patients had to be between 18 and
70 years of age, must have been diagnosed with
Ph-positive CML in chronic phase within 6 months
before study entry, and must not have received
treatment for CML, except for hydroxyurea or ana-
grelide.

Patients were recruited from June 2000 through
January 2001 and were randomly assigned to re-

ceive imatinib at a dose of 400 mg orally per day
or subcutaneous interferon alfa at a daily tar-
get dose of 5 million U per square meter of body-
surface area, plus 10-day cycles of cytarabine at
a daily dose of 20 mg per square meter every
month. Patients receiving imatinib who did not
have a complete hematologic response within
3 months or whose bone marrow contained more
than 65% Ph-positive cells at 12 months could
have a stepwise increase in the dose of imatinib
to 400 mg orally twice daily as long as there were
no dose-limiting adverse events. Patients were al-
lowed to cross over to the other treatment group
if they did not achieve either a complete hema-
tologic response after 6 months of therapy or a
major cytogenetic response after 12 months or if
they had a relapse or an increase in white-cell
count or could not tolerate treatment. All cross-
over requests were made anonymously and con-
sidered weekly by the study management com-
mittee (see the Appendix).

End Points

The primary end point was event-free survival,
which was referred to in previous presentations
and articles as the time to progression, or progres-
sion-free survival. Events were defined by the first
occurrence of any of the following: death from any
cause during treatment, progression to the acceler-
ated phase or blast crisis of CML, or loss of a com-
plete hematologic or major cytogenetic response.
Secondary end points were the rate of complete he-
matologic response (defined as a leukocyte count
<10×109 per liter, a platelet count of <450×109 per liter, <5% myelocytes plus metamyelocytes, no blasts or promyelocytes, no extramedullary involve- ment, and no signs of the accelerated phase or blast crisis of CML); a cytogenetic response in mar- row cells, categorized as complete (no Ph-positive metaphases), partial (1 to 35% Ph-positive meta- phases), or major (complete plus partial responses) on the basis of G-banding in at least 20 cells in metaphase per sample; progression to the acceler- ated phase or blast crisis; overall survival; safety; and tolerability. Signs of a molecular response were sought every 3 months after a complete cytoge- netic response was obtained with the use of real- time quantitative polymerase chain reaction to measure the ratio of BCR-ABL transcripts to BCR transcripts. Results were expressed as “log reduc- tions” below a standardized baseline derived from

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10

a median ratio of BCR-ABL to BCR obtained from
30 untreated patients with chronic-phase CML.15

Ethics and Study Management

The study was conducted in accordance with the
Declaration of Helsinki. The study protocol was
reviewed by the ethics committee or institutional

review board at each participating center. All pa-
tients gave written informed consent, according
to institutional regulations. The academic inves-
tigators and representatives of the sponsor, No-
vartis, designed the study. Data-management and
statistical-support staff at a contract research or-
ganization collected the data, which were ana-
lyzed and interpreted by a biostatistician from No-
vartis in close collaboration with the investigators.
The study management committee and all aca-
demic investigators had access to the raw data. The
study management committee, composed of four
academic investigators, served as the writing com-
mittee. Along with the Novartis biostatistician,
they vouch for the accuracy and completeness of
the data.

Statistical Analysis

The study is ongoing, but January 31, 2006, was
the cutoff date for this analysis. This date marked
5 to 5.5 years after patients started to receive ima-
tinib treatment. We followed all 553 patients who
were assigned to receive imatinib for an analysis
of safety and efficacy until they stopped taking
imatinib, and we have continued to follow all pa-
tients until death, loss to follow-up, or withdraw-
al of consent. Survival data were also collected on
patients who underwent bone marrow transplan-
tation after imatinib treatment. We performed
analyses of survival and event-free survival, using
the Kaplan–Meier method according to the inten-
tion-to-treat principle and using all data available,
regardless of whether crossover occurred. Differ-
ences between subgroups of patients receiving
imatinib were calculated by the log-rank test. Cu-
mulative rates of complete hematologic and cyto-
genetic responses were estimated according to the
Kaplan–Meier method, in which data from patients
receiving imatinib who did not have an adequate
response, who had switched to interferon alfa plus
cytarabine, or who had discontinued treatment for
reasons other than progression of CML were cen-
sored at the last follow-up visit. For the estimation
of cumulative response rates, we censored data
from patients with progressive CML at maximum
follow-up. We used the life-table method to deter-
mine yearly event probabilities. The safety of ima-
tinib was analyzed for 551 patients who received
at least one dose of the study drug during the trial.
For the 553 patients assigned to receive interfer-
on alfa plus cytarabine, disposition and overall sur-
vival were summarized.

Table 1. Enrollment, Outcomes, and Reasons for Crossover
and Discon tinuation.*

Variable
Imatinib

(N = 553)

Interferon Alfa
plus Cytarabine

(N = 553)

no. of patients (%)

Assignment of patients

Continued first-line treatment 382 (69) 16 (3)

Discontinued first-line treatment 157 (28) 178 (32)

Crossed over to other treatment 14 (3) 359 (65)

Discontinued second-line treatment 14 (3) 108 (20)

Reason for crossover

Other than progression

Intolerance of treatment† 4 (<1) 144 (26)

No complete hematologic
response at 6 mo

0 41 (7)

No major cytogenetic response
at 12 mo

1 (<1) 49 (9)

Other 0 48 (9)

Progression only

Increase in white-cell count† 2 (<1) 25 (5)

Loss of complete hematologic
response

5 (<1) 29 (5)

Loss of major cytogenetic
response

2 (<1) 23 (4)

Reason for discontinuation‡

Adverse event 23 (4) 35 (6)

Death 10 (2) 2 (<1)

Unsatisfactory therapeutic effect 59 (11) 29 (5)

Stem-cell transplantation 16 (3) 7 (1)

Protocol violation 15 (3) 17 (3)

Loss to follow-up 5 (<1) 6 (1)

Withdrawal of consent 25 (5) 76 (14)

Other 4 (<1) 6 (1)

* The first patient entered the study on June 16, 2000, and enrollment ended
January 30, 2001.

† The crossover of patients with this condition to the other treatment group
needed previous approval by the study management committee.

‡ A total of 157 patients who received imatinib and 178 patients who received
interferon alfa plus cytarabine discontinued therapy.

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R e s u l t s

Patients

Five years after the last of 1106 patients had started
treatment, and with a median of 60 months of
follow-up, 382 of 553 patients (69%) in the ima-
tinib group and 16 of 553 patients (3%) in the
group given interferon alfa plus cytarabine con-
tinued with their initially assigned treatment (Ta-
ble 1). Of the patients given interferon plus cyta-
rabine, 359 (65%) had crossed over to imatinib,
whereas 14 patients (3%) in the imatinib group
had switched to the alternative treatment. The most
common reason for crossover among patients
given interferon plus cytarabine was intolerance
of treatment (26%). Of these patients, 90 (16%)
switched because they did not achieve a complete
hematologic or major cytogenetic response by the
designated target dates, as did 77 patients (14%)
with disease progression. An additional 178 pa-
tients (32%) given interferon alfa plus cytarabine
discontinued therapy. The reasons most common-
ly reported were withdrawal of consent (14%) and
adverse events (6%). In the imatinib group, 23 pa-
tients (4%) discontinued therapy owing to an ad-
verse event, and 25 patients (5%) withdrew con-
sent (Table 1).

Since few patients were still receiving inter-
feron alfa plus cytarabine at 60 months, the re-
mainder of this report focuses on the long-term
follow-up of patients who received imatinib as
the initial therapy for CML. They had been treated
with imatinib for a mean (±SD) of 50±19 months
(median, 60 months). Among the 382 patients

who continued receiving imatinib, the mean daily
dose during this reporting period was 382±50 mg.
In 82% of these patients, the last reported daily
dose was 400 mg; 6% were receiving 600 mg, 4%
were receiving 800 mg, and 8% were receiving
less than 400 mg.

Table 2. Proportion of Patients Receiving First-Line Imatinib Therapy with Grade 3 or Grade 4 Adverse Events.

Hematologic or Hepatic Condition Grade 3 or Grade 4

Adverse Events

Total Events
(N = 551)

Years 1 and 2
(N = 551)

Years 3 and 4
(N = 456)

After Year 4
(N = 409)

percent

Neutropenia 17 14 3* 1*

Thrombocytopenia 9 8 1* <1*

Anemia 4 3 1† <1‡

Elevated liver enzymes 5 5 <1* 0*

Other drug-related adverse event 17 14 4* 2*

* P<0.001 for the comparison of events in years 3 and 4 and after 4 years with those in years 1 and 2. † The difference between events in years 3 and 4 and those in years 1 and 2 did not reach statistical significance.

‡ P<0.01 for the comparison of events after 4 years with those in years 1 and 2.

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Complete hematologic response

Major cytogenetic response

Complete cytogenetic response

Figure 1. Kaplan–Meier Estimates of the Cumulative Best Response
to Initial Imatinib Therapy.

At 12 months after the initiation of imatinib, the estimated rates of having
a response were as follows: complete hematologic response, 96%; major
cytogenetic response, 85%; and complete cytogenetic response, 69%. At
60 months, the respective rates were 98%, 92%, and 87%. Data for pa-
tients who discontinued imatinib for reasons other than progression and
who did not have an adequate response were censored at the last follow-up
visit. Data for patients who did not have an adequate response and who
stopped imatinib because of progression were censored at maximum fol-
low-up.

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n engl j med 355;23 www.nejm.org december 7, 20062412

Adverse Events

After a median follow-up of 60 months, the ad-
verse events reported were similar to those report-
ed previously.14 The most commonly reported ad-
verse events were edema (including peripheral and
periorbital edema) (60%), muscle cramps (49%),
diarrhea (45%), nausea (50%), musculoskeletal
pain (47%), rash and other skin problems (40%),
abdominal pain (37%), fatigue (39%), joint pain
(31%), and headache (37%). Grade 3 or 4 adverse
events consisted of neutropenia (17%), throm-
bocytopenia (9%), anemia (4%), elevated liver en-
zymes (5%), and other drug-related adverse events
(17%). Congestive heart failure was reported as
being drug-related in one patient (<1%). Newly oc- curring or worsening grade 3 or 4 hematologic or biochemical adverse events were infrequent after both 2 and 4 years of therapy (Table 2).

Efficacy

Figure 1 shows the estimated cumulative rates
of complete hematologic remission: 96% at 12
months and 98% at 60 months. The best observed
rate of complete hematologic response was 97%.

At 12 months, the estimated rate of major cyto-
genic response was 85% and that of complete cy-
togenetic response was 69%. At 60 months, the
estimated rates were 92% and 87%, respectively.
With a median follow-up of 60 months, the best
observed rate of major cytogenetic response was
89%, and the best rate of complete cytogenetic
response was 82%. Of the 382 patients who still
received imatinib at 60 months, 368 (96%) had a
complete cytogenetic response.

There were significant differences in the rates
of cytogenetic response, according to a scoring
system devised by Sokal and colleagues,16 which
divides patients with CML into low-risk, interme-
diate-risk, and high-risk groups. In patients who
were deemed to be at low risk on the Sokal scor-
ing system, the rate of complete cytogenetic re-
sponse was 89%; the rate among patients at in-
termediate risk was 82%; and for those at high
risk, the rate was 69% (P<0.001).

Among 124 patients who had a complete cy-
togenetic response and whose blood samples tak-
en at 1 and 4 years were available, BCR-ABL tran-
scripts in the blood samples were measured. After
1 year, levels of BCR-ABL transcripts had fallen by
at least 3 log in 66 of 124 patients (53%); after
4 years, levels had fallen in 99 of 124 patients
(80%) (P<0.001). The proportion of patients with a reduction of at least 4 log in transcript levels increased from 22 to 41% between 1 and 4 years (P<0.001). The median log reduction of BCR-ABL transcripts was 3.08 at 1 year and 3.78 at 4 years (P<0.001).

Long-term Outcomes

At 60 months, the estimated rate of event-free sur-
vival was 83% (95% confidence interval [CI], 79
to 87), and an estimated 93% of patients (95% CI,
90 to 96) had not progressed to the accelerated
phase or blast crisis (Fig. 2). Of the 553 patients
receiving imatinib, 35 (6%) progressed to the ac-
celerated phase or blast crisis, 14 (3%) had a he-
matologic relapse, 28 (5%) had a loss of major cy-
togenetic response, and 9 (2%) died from a cause
unrelated to CML. The estimated annual rate of
treatment failure after the start of imatinib ther-
apy was 3.3% in the first year, 7.5% in the second
year, 4.8% in the third year, 1.5% in the fourth
year, and 0.9% in the fifth year. The correspond-
ing annual rates of progression to the accelerated
phase or blast crisis were 1.5%, 2.8%, 1.6%, 0.9%,
and 0.6%, respectively. In the 454 patients who had

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Progression

All events

No. of Events
Progression
All events
No. at Risk
Progression
All events

8
18

513
505

22
55

461
447

29
76

431
414

33
82

409
395

35
85

280
274

Figure 2. Kaplan–Meier Estimates of the Rates of Event-free Survival
and Progression to the Accelerated Phase or Blast Crisis of CML for Pa-
tients Receiving Imatinib.

At 60 months, the estimated rate of event-free survival was 83%. At that
time, 93% of the patients had not progressed to the accelerated phase or
blast crisis. The following were considered events: death from any cause
during treatment, progression to the accelerated phase or blast crisis, loss
of a complete hematologic response, loss of a major cytogenetic response,
or an increasing white-cell count. The number of patients with events and
the number of patients available for analysis are shown.

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a complete cytogenetic response, the annual rates
of treatment failure were 5.5% in the first year,
2.3% in the second year, 1.1% in the third year,
and 0.4% in the fourth year after a response was
achieved. The corresponding annual rates of pro-
gression to the accelerated phase or blast crisis
were 2.1%, 0.8%, 0.3%, and 0%, respectively, in
these patients.

Effect of Response on Outcome

Cytogenetic and molecular responses had signifi-
cant associations with event-free survival and de-
terrence against progression to the accelerated
phase or blast crisis (Fig. 3). A landmark analysis
of the 350 patients who had had a complete cyto-
genetic response at 12 months after the initiation
of imatinib treatment revealed that at 60 months,
97% of the patients (95% CI, 94 to 99) had not
progressed to the accelerated phase or blast crisis.
For the 86 patients with a partial cytogenetic re-
sponse, the estimate was 93% (95% CI, 87 to 99);
for the 73 patients who did not have a major cy-
togenetic response within 12 months, the esti-
mate was 81% (95% CI, 70 to 92) (overall, P<0.001; P<0.001 for the comparison between patients with a complete response and those without a com- plete response, and P = 0.20 for the comparison between patients with a complete response and those with a partial response) (Fig. 3A).

At 60 months, the estimated risk of disease
progression was significantly higher for the high-
risk group of patients, according to the Sokal
scoring system (P = 0.002); the estimated rates for
patients in the high-risk, intermediate-risk, and
low-risk groups were 17%, 8%, and 3%, respec-
tively. However, the Sokal score was not associ-
ated with disease progression in patients who had
a complete cytogenetic response (95%, 95%, and
99% in the high-risk, intermediate-risk, and low-
risk groups, respectively) (P = 0.20 overall; P = 0.92
for the comparison between the intermediate-risk
group and the high-risk group, and P = 0.16 for the
comparison between the low-risk group and the
high-risk group).

The molecular responses at 12 and 18 months
were also associated with long-term outcomes. At
60 months, the patients who had a complete cyto-
genetic response and a reduction of at least 3 log
in levels of BCR-ABL transcripts in bone marrow
cells after 18 months of treatment had an esti-
mated rate of survival without progression of CML
of 100%. In the group with a reduction of less

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Complete cytogenetic response
with ≥3 log reduction
Complete cytogenetic response
with <3 log reduction

No complete cytogenetic response

A

B

Complete cytogenetic response

Partial cytogenetic response

No major cytogenetic response

Response at 12 Mo

Response at 18 Mo

Figure 3. Rate of Progression to the Accelerated Phase or Blast Crisis
on the Basis of Cytogenetic Response after 12 Months or Molecular
Response after 18 Months of Imatinib Therapy.

Panel A shows that at 60 months, of the 350 patients with a complete cyto-
genetic response after 12 months of imatinib therapy, an estimated 97%
had not progressed to the accelerated phase or blast crisis. The corre-
sponding rates for 86 patients with a partial cytogenetic response and for
73 patients who did not have a major cytogenetic response were 93% and
81%, respectively (P<0.001; P = 0.20 for the comparison between patients with a complete cytogenetic response and those with a partial response). At 12 months, 44 patients had discontinued imatinib and thus were not included in this analysis. Panel B shows that at 60 months, of the 139 pa- tients with a complete cytogenetic response and a reduction in levels of BCR-ABL transcripts of at least 3 log, 100% were free from progression to the accelerated phase or blast crisis. The corresponding rate for 54 patients with a complete cytogenetic response and a reduction in levels of BCR-ABL transcripts of less than 3 log was 98%; the rate for 88 patients without a complete cytogenetic response was 87% (P<0.001; P = 0.11 for the compari- son between patients with a major molecular response and those without a major molecular response). At 18 months, 86 patients had discontinued imatinib and 186 patients had achieved a complete cytogenetic response but did not have a PCR result available.

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than 3 log in levels of BCR-ABL transcripts, the es-
timated rate was 98% (P = 0.11). However, in the
absence of a complete cytogenetic response, the
rate was 87% (P<0.001) (Fig. 3B). No patient who had a complete cytogenetic response and reduc- tion of at least 3 log in levels of BCR-ABL transcripts at 12 months had progressed to the accelerated phase or blast crisis at 60 months.

Overall Survival

By the cutoff date for this analysis, 57 patients
(10%) who received imatinib had died; 5 of these
patients had switched to interferon alfa plus cy-
tarabine. The estimated overall survival rate at 60
months was 89% (95% CI, 86 to 92) (Fig. 4). Allo-
geneic hematopoietic stem-cell transplantation
was carried out in 44 patients who discontinued
imatinib: 11 had progressed to the accelerated
phase or blast crisis, 15 had had a hematologic or
cytogenetic relapse, and 18 had stopped therapy
for other reasons (including safety and withdrawal
of consent). Of the 44 patients who underwent
transplantation, 14 (32%) died. At 60 months, with
data censored at the time of transplantation, the
estimated overall survival rate was 92% (95% CI,
89 to 95). After data were censored for patients

who had died from causes unrelated to CML or
transplantation, the overall estimated survival rate
was 95% (95% CI, 93 to 98) at 60 months (Fig. 4).

D i s c u s s i o n

The initial analysis of this study, performed at a
median follow-up of 19 months, showed a high
rate of response and an acceptable rate of side ef-
fects of imatinib as initial therapy for newly diag-
nosed chronic-phase CML.14 The present analysis,
with a median follow-up of 60 months, showed
an estimated relapse rate of 17% at 60 months, and
an estimated 7% of all patients progressed to the
accelerated phase or blast crisis. The 5-year esti-
mated overall survival rate for patients who re-
ceived imatinib as initial therapy (89%) is higher
than that reported in any previously published pro-
spective study of the treatment of CML.17

This trial allowed patients to cross over to the
alternate treatment, and most patients in the in-
terferon group either switched to imatinib or dis-
continued interferon. On the basis of an inten-
tion-to-treat analysis, there was no significant
difference in overall survival between the group
of patients who began their treatment with inter-
feron and those who began their treatment with
imatinib (data not shown). Previous randomized
studies of interferon alfa plus cytarabine, per-
formed before the availability of imatinib, showed
a 5-year overall survival of 68 to 70%.12,13 With the
use of historical comparisons, a survival advan-
tage for initial therapy with imatinib over inter-
feron alfa can be demonstrated.18

In a landmark analysis, 97% of patients with
a complete cytogenetic response within 12 months
after starting imatinib did not progress to the ac-
celerated phase or blast crisis by 60 months. No-
tably, patients who were deemed to be at high risk
on the basis of Sokal scores had a lower rate of
complete cytogenetic response (69%) than did pa-
tients who were at low risk or intermediate risk
(89% and 82%, respectively). However, the risk of
relapse in patients who had a cytogenetic response
was not associated with the Sokal score. With
interferon treatment, by contrast, the Sokal score
was important even among patients with a com-
plete cytogenetic response.19

Remarkably, no patient who had a complete
cytogenetic response and a reduction in levels of
BCR-ABL transcripts of at least 3 log at 12 or 18
months after starting imatinib had progression

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JOB: ISSUE:
4-C
H/T
RETAKE
SIZE
ICM
CASE
EMail Line
H/T
Combo
Revised
AUTHOR, PLEASE NOTE:
Figure has been redrawn and type has been reset.
Please check carefully.
REG F
Enon

1st
2nd

3rd
Druker

4 of 4

12-07-06
ARTIST: ts
35523

CML-related deaths

All deaths

No. of Deaths
Related to CML
All deaths
No. at Risk
Related to CML
All deaths

3
6

536
542

11
22

498
518

16
41

474
492

19
52

450
475

23
57

322
333

Figure 4. Overall Survival among Patients Treated with Imatinib Based
on an Intention-to-Treat Analysis.

The estimated overall survival rate at 60 months was 89%. After the cen-
soring of data for patients who died from causes unrelated to CML or trans-
plantation, the estimated overall survival was 95% at 60 months. At the
time of analysis, 57 patients had died. The number of patients with events
and the number of patients available for analysis are shown.

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n engl j med 355;23 www.nejm.org december 7, 2006 2415

of CML by 60 months. Only 2% of patients who
had a complete cytogenetic response and a reduc-
tion in levels of BCR-ABL transcripts of less than
3 log at 18 months had progressed to the accel-
erated phase or blast crisis at 60 months.

It is currently recommended that imatinib
therapy be continued indefinitely. Anecdotal re-
ports suggest that the discontinuation of imatinib,
even in patients with undectectable levels of BCR-
ABL transcripts, results in relapse.20-24 Although
it is not known why imatinib is not able to eradi-
cate the malignant clone, potential mechanisms
include drug efflux25 and amplification or muta-
tion of the BCR-ABL gene.26 It is also possible that
imatinib cannot completely inhibit BCR-ABL ki-
nase activity; low levels of activity would allow
cells to survive but not proliferate. As an alterna-
tive, the malignant clone could persist through
mechanisms that are independent of the BCR-ABL
kinase.27

Initial studies of two new inhibitors of the
BCR-ABL kinase that are more potent than ima-
tinib — dasatinib and nilotinib — showed high
response rates in patients who had had a relapse
during imatinib therapy.28,29 Despite their poten-
cy, these inhibitors cannot eradicate all CML cells
in vitro.30 As was the case in patients in our study,
it is assumed that in patients receiving these drugs
a durable response can be achieved even without
disease eradication if there is a reduction in lev-
els of BCR-ABL transcripts of at least 3 log.

Notably, the rate of disease progression in pa-
tients in our study is apparently trending down-
ward, although the trend has not reached statis-
tical significance. If it persists, such a trend would
be consistent with the findings that mutations
in the BCR-ABL gene are the major cause of relapse
in patients treated with imatinib.31 If we presume
that mutations precede imatinib therapy (as the
data suggest),32,33 the emergence of resistance to

the drug would depend on the size of the mutant
clone at the start of therapy and its doubling
time. Since most mutated and unmutated BCR-
ABL clones have similar doubling times,34 a pa-
tient with a mutant clone should be at highest risk
for relapse during the first several years of thera-
py. This prediction is in line with the apparent
downward trend in the risk of disease progres-
sion observed in our study.

Dr. Druker’s institution is the site of clinical trials sponsored
by Novartis, but neither he nor his laboratory reports receiving
funds from Novartis. Dr. Guilhot reports receiving consulting
and lecture fees from Novartis; Dr. O’Brien, consulting fees from
Novartis and Bristol-Myers Squibb and lecture fees from Novar-
tis; Ms. Gathmann, being an employee of and having equity
ownership in Novartis; Dr. Kantarjian, consulting fees from No-
vartis, Bristol-Myers Squibb, and MGI Pharma; Dr. Gattermann,
consulting and lecture fees from Novartis and Pharmion; Dr.
Deininger, consulting and lecture fees from Novartis and Bris-
tol-Myers Squibb; Dr. Silver, consulting fees from Novartis; Dr.
Goldman, lecture fees from Novartis; Dr. Stone, consulting and
lecture fees and grant support from Novartis and Bristol-Myers
Squibb; Dr. Cervantes, consulting fees from Novartis and lec-
ture fees from Novartis and Bristol-Myers Squibb; Dr. Hochhaus,
consulting and lecture fees from Novartis and Bristol-Myers
Squibb; Dr. Powell, lecture fees from Pharmion; Dr. Gabrilove,
consulting fees from Novartis; Dr. Rousselot, lecture fees from
Novartis Oncology; Dr. Cornelissen, consulting fees from Novar-
tis Oncology; Dr. Hughes, consulting and lecture fees from No-
vartis; Dr. Fischer, consulting fees from LymphoSign and Novar-
tis and lecture fees from Novartis; Dr. Saglio, consulting and
lecture fees from Novartis; Dr. Gratwohl, consulting fees from
Novartis, Pfizer, and Amgen and lecture fees from Novartis; Dr.
Radich, consulting fees from Novartis and Bristol-Myers Squibb
and lecture fees from Novartis; Dr. Simonsson, consulting fees
from Novartis and Bristol-Myers Squibb; Dr. Taylor, consulting
fees from Amgen, Novartis, Bristol-Myers Squibb, and Celgene
and lecture fees from Novartis; Dr. Baccarani, consulting fees
from Novartis, Bristol-Myers Squibb, Merck, and Pfizer and
lecture fees from Novartis, Bristol-Myers Squibb, Schering, and
Pfizer; Dr. So, being an employee of Novartis and having equity
ownership in Novartis and Pfizer; Dr. Letvak, being an employee
of and having equity ownership in Novartis; and Dr. Larson,
consulting and lecture fees from Novartis. No other potential
conflict of interest relevant to this article was reported.

We thank the coinvestigators; the members of the medical,
nursing, and research staff at the trial centers; the clinical trial
monitors and the data managers and programmers at Novartis
for their contributions; and Tillman Krahnke and Manisha
Mone for their invaluable collaboration.

Appendix
From the Oregon Health and Science University Cancer Institute, Portland (B.J.D.); Centre Hospitalier Universitaire, Poitiers, France
(F.G.); University of Newcastle, Newcastle, United Kingdom (S.G.O.); Novartis, Basel, Switzerland (I.G.); M.D. Anderson Cancer Center,
Houston (H.K.); Heinrich Heine University, Dusseldorf, Germany (N.G.); Universität Leipzig, Leipzig, Germany (M.W.N.D.); Weill–Cor-
nell Medical Center, New York (R.T.S.); National Heart, Lung, and Blood Institute, Bethesda, MD (J.M.G.); Dana–Farber Cancer Institute,
Boston (R.M.S.); Hospital Clinic I Provincial, Barcelona (F.C.); University of Heidelberg, Mannheim, Germany (A.H.); Wake Forest Uni-
versity Baptist Medical Center, Winston-Salem, NC (B.L.P.); Mount Sinai School of Medicine, New York (J.L.G.); Hôpital Saint Louis,
Paris (P.R.); Centre Hospitalier Universitaire de Bordeaux, Pessac, France (J.R.); Erasmus Medical Center, Rotterdam, the Netherlands
(J.J.C.); Royal Adelaide Hospital, Adelaide, Australia (T.H.); Universitätsklinik für Innere Medizin I, Vienna (H.A.); Johannes Gutenberg
Universität, Mainz, Germany (T.F.); University Hospital Gasthuisberg, Leuven, Belgium (G.V.); Vancouver Hospital, Vancouver, BC, Cana-
da (J.S.); Azienda Ospedaliera S. Luigi Gonzaga, Orbassano, Italy (G.S.); University Hospital Basel, Switzerland (A.G.); Aarhus
Amtssygehus, Aarhus, Denmark (J.L.N.); Fred Hutchinson Cancer Research Center, Seattle (J.P.R.); Akademiska Sjukhuset, Uppsala, Swe-
den (B.S.); Mater Hospital, Brisbane, Australia (K.T.); Policlinico S. Orsola–Malpighi, Bologna, Italy (M.B.); Novartis, Florham Park, NJ
(C.S., L.L.); and University of Chicago, Chicago (R.A.L.).

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Copyright © 2006 Massachusetts Medical Society. All rights reserved.

T h e n e w e n g l a n d j o u r n a l o f m e d i c i n e

n engl j med 355;23 www.nejm.org december 7, 20062416

The following investigators participated in IRIS: Australia — Royal Brisbane Hospital, Herston: S. Durrant; Monash Medical Centre, Mel-
bourne: A. Schwarer; Sir Charles Gairdner Hospital, Perth: D. Joske; Australian Leukemia and Lymphoma Group, Melbourne: J. Seymour; Royal Mel-
bourne Hospital, Parkville: A. Grigg; St. Vincent’s Hospital, Darlinghurst: D. Ma; Royal North Shore Hospital, St. Leonards: C. Arthur; Westmead Hos-
pital, Westmead: K. Bradstock; Royal Prince Alfred Hospital, Sydney: D. Joshua. Belgium — A.Z. Sint-Jan, Brugge: A. Louwagie; Institut Jules Bordet,
Brussels: P. Martiat; Cliniques Universitaires, Yvoir: A. Bosly. Canada — McGill University, Montreal: C. Shustik; Princess Margaret Hospital, Toronto:
J. Lipton; Queen Elizabeth II Health Sciences Centre, Halifax, NS: D. Forrest; McMaster University Medical Centre, West Hamilton, ON: I. Walker; Uni-
versité de Montréal, Montreal: D.-C. Roy; CancerCare Manitoba, Winnipeg: M. Rubinger; Ottawa Hospital Regional Cancer Centre, Ottawa: I. Bence-
Bruckler; University of Calgary and Tom Baker Cancer Centre, Calgary, AB: D. Stewart; London Regional Cancer Centre, London, ON: M. Kovacs; Cross
Cancer Center, Edmonton, AB: A.R. Turner. Denmark — Kobenhavns Amts Sygehus i Gentofte, Hellerup: H. Birgens; Danish University of Pharmaceuti-
cal Sciences and University of Southern Denmark, Copenhagen: O. Bjerrum. France — Hôpital Claude Huriez, Lille: T. Facon; Hôtel Dieu Hospital, Nantes:
J.-L. Harousseau; Henri Mondor Hospital, Creteil: M. Tulliez; Centre Hospitalier Universitaire (CHU) Brabois, Vandoeuvre-les-Nancy: A. Guerci; Insti-
tut Paoli-Calmettes, Marseille: D. Blaise; Hopital Civil, Strasbourg: F. Maloisel; CHU la Milétrie, Poitiers: M. Michallet. Germany — University of
Regensburg, Regensburg: R. Andreesen; Krankenhaus Muenchen Schwabing, Munich: C. Nerl; Universitätsklinikum Rostock, Rostock: M. Freund;
Heinrich Heine University, Düsseldorf: N. Gattermann; Carl-Gustav Carus Universität, Dresden: G. Ehninger; Leipzig University Hospital, Leipzig: M.
Deininger; Medizinische Klinik III, Frankfurt: O. Ottmann; Clinical Center Rechts der Isar, Munich: C. Peschel; University of Heidelberg, Heidelberg: S.
Fruehauf; Philipps-Universität Marburg, Baldingerstraße, Marburg: A. Neubauer; Humboldt Universität, Berlin: P. Le Coutre; Robert Bosch Hospital,
Stuttgart: W. Aulitzky. Italy — University Hospital, Udine: R. Fanin; San Orsola Hospital, Bologna: G. Rosti; Università La Sapienza, Rome: F.
Mandelli; Istituto di Ricovero e Cura a Carattere Scientifico (IRCCS) Policlinico San Matteo, Pavia: M. Lazzarino; Niguarda Ca’ Granda Hospital, Milan:
E. Morra; Azienda Ospedaliera e Cliniche Universitarie San Martino, Largo R Benzi, Genoa: A. Carella; University of Pisa, Pisa: M. Petrini; Azienda Os-
pedaliera Bianchi-Malacrino-Morelli, Reggio Calabria: F. Nobile; University of Bari, Policlinico, Bari: V. Liso; Cardarelli Hospital, Naples: F. Ferrara;
University of Parma, Parma: V. Rizzoli; Ospedale Civile, Pescara: G. Fioritoni; Institute of Hematology and Medical Oncology Seragnoli, Bologna: G.
Martinelli; Università degli Studi di Firenze, Florence: V. Santini. the Netherlands — Vrije Universiteit Academic Medical Center, Amsterdam: G. Os-
senkoppele. New Zealand — University of Auckland, Auckland: P. Browett. Norway — Medisinsk Avdeling, Rikshospitalet, Oslo: T. Gedde-Dahl;
Ullevål Sykehus, Oslo: J.-M. Tangen; Hvidovre Hospital, Betalende: I. Dahl. Spain — Hospital Clinic, Villarroel, Barcelona: J. Odriozola; University of
Barcelona, Barcelona: J.C. Hernández Boluda; Hospital Universitario de la Princesa, Madrid: J.L. Steegman; Hospital Universitario de Salamanca,
Salamanca: C. Cañizo; San Carlos Clinical Hospital, Madrid: J. Diaz; Institut Català d’Oncología, Barcelona: A. Granena; Hospital Lluis Alcanyis, Cta
Xativa-Silla: M.N. Fernández. Sweden — Karolinska Hospital, Stockholm: L. Stenke; Huddinge Sjukhus, Huddinge: C. Paul; Medicinkliniken Uni-
versitetssjukhuset, Örebro: M. Bjoreman; Regionsjukhuset, Linköping: C. Malm; Sahlgrenska Hospital, Göteborg: H. Wadenvik; Endokrinsekt/Medklin
Universitetssjukhuset, Lund: P.-G. Nilsson; Universitetssjukhuset Malmo University Hospital, Malmo: I. Turesson. Switzerland — Kantonsspital, St.
Gallen: U. Hess; University of Bern, Bern: M. Solenthaler. United Kingdom — University of Nottingham and Nottingham City Hospital, Nottingham:
N. Russell; Kings College, London: G. Mufti; St. George’s Hospital, Medical School, London: J. Cavenagh; Royal Liverpool University Hospital, Liverpool:
R.E. Clark; Cambridge Institute for Medical Research, Cambridge: A.R. Green; Glasgow Royal Infirmary, Glasgow: T.L. Holyoake; Manchester Royal
Infirmary, Manchester: G.S. Lucas; Leeds General Infirmary, Leeds: G. Smith; Queen Elizabeth Hospital, Edgbaston, Birmingham: D.W. Milligan; Der-
riford Hospital, Plymouth: S.J. Rule; University Hospital of Wales, Cardiff: A.K. Burnett; United States — Walt Disney Memorial Cancer Institute, Or-
lando, FL: R. Moroose; Roswell Park Cancer Center, Buffalo, NY: M. Wetzler; Gibbs Cancer Center, Spartanburg, SC: J. Bearden; Ohio State University
School of Medicine, Columbus: S. Cataland; University of New Mexico Health Sciences Center, Albuquerque: I. Rabinowitz; University of Maryland Cancer
Center, Baltimore: B. Meisenberg; Montgomery Cancer Center, Montgomery, AL: K. Thompson; State University of New York Upstate Medical Center,
Syracuse: S. Graziano; University of Alabama at Birmingham, Birmingham: P. Emanuel; Hematology and Oncology, Inc., Dayton, OH: H. Gross;
Billings Oncology Associates, Billings, MT: P. Cobb; City of Hope National Medical Center, Duarte, CA: R. Bhatia; Cancer Center of Kansas, Wichita: S.
Dakhil; Alta Bates Comprehensive Cancer Center, Berkeley, CA: D. Irwin; Cancer Research Center of Hawaii, Honolulu: B. Issell; University of Nebraska
Medical Center, Omaha: S. Pavletic; Columbus Community Clinical Oncology Program, Columbus, OH: P. Kuebler; Michigan State University Hematol-
ogy/Oncology, Lansing: E. Layhe; Brown University School of Medicine, Providence, RI: P. Butera; Loyola University Medical Center, Shreveport, LA: J.
Glass; Duke University Medical Center, Durham, NC: J. Moore; University of Vermont, Burlington: B. Grant; University of Tennessee, Memphis: H. Niell;
University of Louisville Hospital, Louisville, KY: R. Herzig; Sarah Cannon Cancer Center, Nashville: H. Burris; University of Minnesota, Minneapolis: B.
Peterson; Cleveland Clinic Foundation, Cleveland: M. Kalaycio; Fred Hutchinson Cancer Research Center, Seattle: D. Stirewalt; University of Utah, Salt
Lake City: W. Samlowski; Memorial Sloan-Kettering Cancer Center, New York: E. Berman; University of North Carolina School of Medicine, Charlotte: S.
Limentani; Atlanta Cancer Center, Atlanta: T. Seay; University of North Carolina School of Medicine, Chapel Hill: T. Shea; Indiana Blood and Marrow
Institute, Beech Grove: L. Akard; San Juan Regional Cancer Center, Farmington, NM: G. Smith; University of Massachusetts Memorial Medical Center,
Worcester: P. Becker; Washington University School of Medicine, St. Louis: S. Devine; Veterans Affairs Medical Center, Milwaukee: R. Hart; Louisiana
State University Medical Center, New Orleans: R. Veith; Decatur Memorial Hospital, Decatur, IL: J. Wade; Rocky Mountain Cancer Centers, Denver: M.
Brunvand; Oncology-Hematology Group of South Florida, Miami: L. Kalman; Memphis Cancer Center, Memphis, TN: D. Strickland; Henry Ford Hospi-
tal, Detroit: M. Shurafa; University of California, San Diego, Medical Center, La Jolla: A. Bashey; Western Pennsylvania Cancer Institute, Pittsburgh: R.
Shadduck; Tulane Cancer Center, New Orleans: H. Safah; Southbay Oncology Hematology Partners, Campbell, CA: M. Rubenstein; University of Texas
Southwest Medical Center, Dallas: R. Collins; Cancer Care Associates, Tulsa, OK: A. Keller; Robert H. Lurie Comprehensive Cancer Center, Chicago: M.
Tallman; Northern New Jersey Cancer Center, Hackensack: A. Pecora; University of Pittsburgh Medical Center, Hillman Cancer Center, Pittsburgh: M. Agha;
Texas Oncology, Dallas: H. Holmes; and New Mexico Oncology Hematology Consultants, Albuquerque: R. Guidice. Study Management Committee:
Oregon Health and Science University Cancer Institute Research and Patient Care, Portland: B.J. Druker; University Hospital, Poitier, France: F. Guilhot;
University of Chicago, Chicago: R.A. Larson; University of Newcastle upon Tyne, Newcastle upon Tyne, UK: S.G. O’Brien. Independent Data Monitor-
ing Board: Rambam Medical Center, Haifa, Israel: J. Rowe; Wayne State University, Barbara Ann Karmanos Cancer Institute, Detroit: C.A. Schiffer;
International Drug Development Institute, Brussels: M. Buyse. Protocol Working Group: Policlinico San Orsola–Malpighi, Bologna, Italy: M. Bacca-
rani; Hospital Clinic, Barcelona: F. Cervantes; Erasmus Medical Center, Rotterdam, the Netherlands: J. Cornelissen; Johannes Gutenberg Universität,
Mainz, Germany: T. Fischer; Universität Heidelberg, Mannheim, Germany: A. Hochhaus; Hanson Institute Centre for Cancer, Adelaide, Australia: T.
Hughes; Medical University of Vienna, Vienna: K. Lechner; Aarhus Amtssygehus, Aarhus, Denmark: J.L. Nielsen; CHU de Bordeaux, Pessac, France: J.
Reiffers; Hôpital Saint Louis, Paris: P. Rousselot; San Luigi Gonzaga Hospital, Turin, Italy: G. Saglio; Vancouver Hospital, Vancouver, BC, Canada:
J. Shepherd; Akademiska Sjukhuset, Uppsala, Sweden: B. Simonsson; University Hospital, Basel, Switzerland: A. Gratwohl; Imperial College,
London: J.M. Goldman; University of Michigan Health System, Ann Arbor: M. Talpaz; Mater Misericordiae Public Hospital, Brisbane, Australia: K.
Taylor; and University Hospital Gasthuisberg, Leuven, Belgium: G. Verhoef.

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n engl j med 355;23 www.nejm.org december 7, 2006 2417

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