Gains, losses and complex karyotypes in myeloid disorders: a light at the end of the tunnel

Hematological OncologyHematol Oncol 2005; 23: 18–25Published online 5 September 2005 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/hon.744

Review Article

Gains, losses and complex karyotypes inmyeloid disorders:a light at the end of the tunnel

Sara Alvarez and Juan C. Cigudosa*

Cytogenetics Unit, Centro Nacional de de Investigaciones Oncologicas (CNIO), Madrid, Spain

Abstract

Complex karyotypes are seen in approximately 15% of de novo MDS/AML and in up to50% of therapy-related MDS/AML. These patients represent a therapeutic challenge forwhich no current treatment approach is satisfactory. Therefore, a large number of genet-ic studies using cytogenetic molecular techniques have been performed to better definethe chromosomal abnormalities in this poor-prognosis group. On the basis of the avail-able data from several studies of AML with complex karyotypes, similar findings onrecurrent breakpoints and frequently lost and gained chromosomal regions have beenobserved. The most frequent rearrangements, in all the published series, were unba-lanced translocations leading to loss of chromosomal material. Overall, loss of 5q and/or 7q chromosomal material seemed the more common event, and losses of 5q, 7q,and 17p in combination were observed in many cases. Overrepresented chromosomalmaterial from 8q, 11q23, 21q and 22q was found recurrently and in several cases thiswas due to the amplification of the MLL (located at 11q23) and AML1/RUNX1 (locatedat 22q22) genes. As a result of these findings, the presence of MLL copy gain/amplifica-tions or losses of the short arm of chromosome 17, in association with 5/5q, have beenfound to be indicators of an extremely poor prognosis. Interestingly, this non-randompattern of DNA gains and losses, that characterizes AML cases with complex karyotypes,affects the gene expression pattern, and a specific expression profile, characterized by theupregulation of genes involved in the DNA repair and chromosome segregation path-ways, has been recently reported. Therefore, a comprehensive genome-wide analysis ofpatients with AML or MDS with complex karyotypes has led to a better characterizationof chromosomal aberrations. These specific alterations could be used in the near futureas therapeutic targets or markers for the risk stratification of patients, detection of mini-mal residual disease and the development of new therapeutic interventions.Copyright # 2005 John Wiley & Sons, Ltd.

Keywords: complex karyotype; myelodysplastic syndromes; acute myeloid leukemia;

M-FISH; SKY; CGH; expression profiling

Abbreviations: AML, acute myeloid leukemia; MDS, myelodysplastic syndromes; AML-

CK, AMLwith complex karyotype; FISH, fluorescence in situ hybridization;M-FISH,multiplex

fluorescence in situ hybridization; SKY, spectral karyotyping; CGH, comparative genomic

hybridization

Introduction

Acute myeloid leukemia (AML) and myelodysplasticsyndromes (MDS) constitute two different entitiesamong myeloid neoplasms. While not all cases ofMDS terminate in AML, these disorders are consideredpre-leukemic diseases, suggesting that both disordersmay be the result of a similar genetic damage.1,2

In addition to insights into the molecular pathophysio-

logy of myeloid disorders, cytogenetic analysis provides

important prognostic information that influences therapy

and outcome of AML and MDS.3–5 Individuals displaying

a normal karyotype in chromosome-banding analysis repre-

sent 40–45% of MDS and AML patients, precluding any

insights into themolecularmechanisms thatmay take place

in their molecular pathogenesis. However several molecu-

lar defects, such as internal tandem duplications of the

MLL gene,6 lengthmutations of theFLT3 gene,7,8 and point

mutations within the AML1,9 CEBPA10 and NPM11 genes,

have been described in AML with normal karyotypes.

Two subgroups can be distinguished among patients

with an acquired cytogenetic aberration: (1) myeloid dis-

orders with a primary balanced chromosome aberration

(approximately 20% of all AML cases, and some

therapy-related MDS), and (2) myeloid disorders with

unbalanced karyotype abnormalities, which are character-

ized by gains and/or losses of usually large regions of

the genome and no known primary balanced abnormality

(35–40% of AML, 50% of the de novo MDS, and more

than 80% of the therapy related MDS/AML).3,12–14

Copyright � 2005 John Wiley & Sons, Ltd.

*Correspondence to:Juan C. Cigudosa, CentroNacional de InvestigacionesOncologicas (CNIO), C/MelchorFernandez Almmagro, No. 3,28029 Madrid, Spain.E-mail: [email protected]

Contract/grant sponsor: Consejer-ia de Educacion de la Communi-dad de Madrid; contract/grantnumber: GR/SAL/0219/2004.Contract/grant sponsor: Fondo deInvestigaciones Sanitarias (FIS),Ministerio de Sanidad; contract/grant number: 040555.

Received: 7 July 2005

Accepted: 27 July 2005

The direct involvement of recurring translocations and

inversions in the leukemogenic process is supported by

molecular dissection and cloning of genes adjacent to trans-

locations breakpoints. More than 300 recurring chromoso-

mal translocations in human leukemia cases has provided

fertile ground for the characterization of the molecular

pathogenesis of the disease. More than 100 of these have

been cloned and characterized, and the available data cau-

sally implicates these translocations in the pathogenesis

of leukaemia.15

On the other hand, myeloid disorders with unbalanced

karyotype abnormalities constitute a subtype that has

been classified rather descriptively, partially because these

aberrations frequently occur in the context of complex

karyotypes. The characterization and understanding of the

specific role of these rearrangements has dramatically im-

proved through the application of a spectrum of cytogenetic

and molecular diagnostic techniques. These techniques

include multicolour karyotyping, conventional compara-

tive genomic hybridization (CGH), loss-of-heterozygosity

analysis, CGH arrays, and expression arrays. The biological

and clinical implications of these findings are the subject of

this review.

Characterization of complex karyotypes

Complex karyotypes, defined by the presence of abnorm-alities involving at least three chromosomes, are seen inapproximately 15% of de novo MDS/AML and in up to50% of therapy-related MDS/AML.3,16 These patientsrepresent a considerable therapeutic challenge for whichno current treatment approach is satisfactory.17 There-fore, a large number of genetic studies have been per-formed to better define this poor-prognosis group.Comprehensive analysis of AML cases with complexaberrant karyotypes has been hampered by the difficultyof resolving all abnormalities by conventional chromo-some-banding analysis alone. Along these lines, theintroduction of multicolour karyotyping techniques(spectral karyotyping and multiplex fluorescence in situhybridization) and the development of CGH havemarked a significant improvement. Several recent studiesemploying these techniques have focused on the analysisof AML/MDS cases with complex karyotypes 14,18–23

(Table 1), and on some uncommon AML subtypes, sinceAML-M6 and AML-M7 are often associated with a highcytogenetic complexity.24–26 These analyses havedetected a non-random cytogenetic pattern, character-ized by a high number of unbalanced aberrations, fre-quently leading to a loss of chromosomal material, andsome recurrently gained or amplified regions.

Chromosomal translocations

Unbalanced chromosomal translocations are the mostfrequently observed rearrangement. Only a minority ofaberrations detected by multicolour karyotyping arebalanced. Reciprocal translocations, recently detected

or redefined by SKY or M-FISH, have been describedin nearly every study published. However, for most ofthe novel translocations detected, it is unclear at presentif they constitute recurrent events in AML.27 Furthercharacterization of the genes involved in these aberra-tions are needed in order to identify whether the translo-cated segment might: (1) serve only as a donor of thetelomeric sequences necessary to stabilize termini ofchromosomes that have undergone terminal deletions,thus probably not contributing to leukemogeneis or, (2)might lead to functional fusion proteins.28

The chromosomal breakpointsmost frequently identified

after multicolour hybridization analysis have been: 3q21,

3q26, 5q11-13, 5q35, 7q11.2, 7q22, 11q23, 12p13,

13q11.2, 17p10-11.2, and 22q11.2. Some breakpoints

such as 20q11.2 and 16q12 have been observed mainly in

MDS patients, while others such as 21q11.2 and 21q22

are found predominantly in t-MDS and t-AML. In most

instances, these breakpoints seem to be involved in unba-

lanced translocations or deletions.18,22,23,29 Interestingly,

the distribution of breakpoints in terms of their location

and frequency varies depending on AML subtype. As an

example, we have found a characteristic pattern in the ery-

throleukemia cases (AML-M6) where the most recurrent

breakpoints are located at bands 11p15 and 19q13.1.25

A more precise description of these breakpoints has

allowed the identification and study of several candidate

genes involved in leukemogenesis. Studying myeloid leu-

kemia cells using FISH mapping and exon trapping of a

translocation breakpoint within 20q, we identified the

L3MBTL gene, which codified a polycomb group protein.30

By quantitative RT-PCR we observed decreased or absent

L3MBTL expression in some leukemia cells, however no

functionally significantmutationswere detected.31 In paral-

lel, imprinting of the L3MBTL gene was reported. There-

fore, the absence of L3MBTL expression in some samples

may reflect an epigenetic silencing.32 Given the known

dosage effects of polycomb group proteins in regulating

gene expression, this reduced or absentL3MBTL expression

may be relevant in some cases of MDS/AML.

An additional two genes TEL and TP53, located in

12p13, and 17p11.2 respectively, have been extensively stu-

died. The TEL gene, also known as ETV6, which codifies a

transcription factor specifically required for hematopoiesis

within the bone marrow, has been shown to be involved in

41 different translocations.33 In complex karyotypes, TEL

was not involved in balanced translocations, but a monoal-

lelic deletion was observed on the rearranged chromosome

12.23,34,35

Whereas TP53 deletions are rare in de novo AML,36,37

we and others have shown a significant association of

mutation of the TP53 gene with the presence of a complex

karyotype inMDSand t-MDS/AML.18,37–39 In addition, the

refinement by SKYof the cytogenetic abnormalities invol-

ving 17p in the complex karyotype cases allowed us to

identify that the complete inactivation of this gene is

more frequently observed in the presence of translocations

involving 17p11 than in del17p cases.18 Moreover, a strong

association between mutations of the TP53 gene and the

presence of highly rearranged chromosome derivatives

Hematol Oncol 2005; 23: 18–25

Complex karyotypes in myeloid disorders 19

has been established. These results underline the impor-

tance of having a normal gene to maintain the chromosome

stability.29

Loss of chromosomal material as a consequenceof unbalanced aberrations

Overall, losses of chromosomal material seem morecommon than gains/amplifications, with deletions of 5qand 7q being the most frequent aberrations in absoluteterms (Table 1). In most series studied, chromosomalmaterial from total or partial monosomies previouslycharacterized by G-banding has been found in derivativeor marker chromosomes, and multicolour hybridizationanalysis has revealed that some deletions are frequentlyfound to be unbalanced translocations. These findingswere mainly observed for the genomic losses of chromo-some 5 and 20.18,21,23,28,29,35,40,41 Similar observationswere made, though to a lesser extent, for the regions7q, 12p, 13q and 17p. However, most of the monosomiesof chromosomes 7, 18, 17, and 16 were con-firmed.21,27,28,42

A high frequency of a simultaneous loss of 5q, 7q, and

17p has been observed in most cases carrying a complex

karyotype. A significant association of TP53 mutations

with 5q deletion in AML-CK has been reported, and there

is some evidence of a sequence of events, where loss of

5q and 17p precedes TP53 inactivation by mutation of the

second allele.14,22,38,39 Interestingly, it has been suggested

that this sequence of genomic events seems to parallel

the association of certain balanced chromosome abnormal-

ities with a distinct pattern of additional abnormalities

such as the loss of a sex chromosome in AML with

t(8;21)(q22;q22) or trisomy 21 and trisomy 22 in AML

with inv(16)(p13q22).14

Despite years of painstaking research, the functional

significance of hemizygous chromosomal losses in

myeloid malignancies (notably at chromosome arms 5q,

7q, and 20q) remains uncertain because no inactivated

genes have been discovered. In the light of these studies

it has been proposed that future studies should not be lim-

ited to the classical model of tumour-suppressor genes

requiring the inactivation of both alleles. Instead, the

role of haploinsufficiency of one or multiple genes within

these chromosomal regions, as being responsible for the

anomalous hematopoietic proliferation and/or differentia-

tion programmes seen in myeloid disorders, should be

investigated.14,31

Chromosomal segments found to beoverrepresented

The chromosomal regions 8q, 11q23, 21q and 22q havebeen found to be overrepresented in several series.28

Although genomic amplification occurs mainly in solidtumours, we found regions of high-level amplificationin 35% of the cases in a series of 37 MDS patients withcomplex karyotypes. They were detected in both sexchromosomes and in different autosomal chromosomes,

some of them previously identified such as 3q26–27,11q23, 17q12, 18q12–21, and 21q21.19

Recurrently amplified and/or overexpressed genes have

been identified in patients carrying 11q or 21q amplifica-

tions. In cases with 11q23 amplification, the MLL gene

was consistently shown to be amplified in approximately

20% of cases with complex karyotypes.14,19,20,23,28,40,43

Using FISHwithMLLflanking probes, two distinct patterns

were identified: MLL amplification on homogeneously

staining regions or double minutes, and MLL low-copy

gain due to the retention ofMLL copies on extra or deriva-

tive chromosomes 11. Interestingly, a detailed FISH and

expression analysis ofMLL and five selected 11q candidate

oncogenes revealed that the 11q23 amplicon invariably

encompassedMLL,DDX6, ETS1 andFLI1whereas expres-

sion analyses identifiedMLL and DDX6 as the most differ-

entially expressed genes. Due to the similarities observed in

the transcriptional programme associated with MLL rear-

rangements andMLL overexpression, this oncogene seems

to be the prime target of the 11q23 amplicon.44

In cases with 21q amplification, AML1, also called

RUNX1, one of the most frequently deregulated genes in

leukemia, has been largely investigated. It has been

reported by several authors that an increase in the copy

number of the AML1 gene correlated with the amount of

21q material gained.18,40,45 However, in cases of de novo

AML, it has been shown to be clearly underrepresented,

relative to the amount of extra 21q. These data suggest

the notion that AML1 gene amplification represents a recur-

rent event only during the development or progression of

AML evolving from MDS.28 This observation has recently

driven an exhaustive study of the 21q amplicon identifying

overexpression of the transcription factors ERG and ETS2,

and theAPP gene on this amplified region, suggesting a role

for these genes in the leukemogenesis process.46

The numerical chromosomal abnormalities observed in

myeloid disorders are usually regarded as secondary

changes. However, abnormalities occurring during clonal

evolution might also be disease specific and help to charac-

terize the cytogenetic profile of a specificmalignancy. Inter-

estingly, using CGH, we have found a different pattern of

numerical abnormalities in the acute megakaryoblastic leu-

kemia subtype (AML-M7), characterized by non-random

gains of chromosomes 19 and 21 that are underestimated

when only conventional cytogenetics was used.24 These

findings are inconsistent with the fact that the distribution

of trisomies observed by conventional G-banding is differ-

ent in AML-M7. In this AML subtype trisomy 8 is not pre-

dominant and trisomies of chromosomes 19 and 21 are the

most frequent gains.26

Clinical implications of the chromosomalcharacterization of complex karyotypes

During the last 30 years, the information provided bycytogenetic analysis has become indispensable for theclinical management of patients with hematological dis-orders. Patients in whom complex karyotypes are diag-nosed have an adverse prognosis under currently usedtreatment protocols, with a survival rate of under 20%

20 S Alvarez et al


at 5 years.17 Improved characterization of the cytoge-netic abnormalities observed in this poor-prognosisgroup has allowed the identification of ‘high risk’ patientsubgroups. As the result of these analyses, the presence

ofMLLgain/amplifications or deletion 17p in associationwith 5q losses have been found to be indicators of anextremely poor prognosis.20,38 Recently, Schoch et al.combined available data on frequently lost and gained

Table 1. Multicolour hybridization and CGH studies in MDS/AML with complex karyotypes

Percentage of cases

with gains and losses of

Reference chromosome material of* Results of FISH validations Rearrangementsy

34N¼ 5 AMLTechn: SKY

�5/del5q in 40% of the casesþ8/8q and 21 in 40% of the casesþ11/11q in 20% of the cases

MLL: amplified in one caseSplit signals in one caseTEL: deleted in one caseTP53: deleted one case

Identification of six markerchromosomes, 11 translocationsand three insertions which wereundetected by G-banding

21N¼ 6MDS and12 AMLTechn: SKY

�5/del5q in 39% of the cases�7/del7q in 44% of the cases

Identification of hidden translo-cations and reconstruction ofcomplex rearrangements

20N¼ 10 MDS and 12 AMLTechn: SKY and CGH

�5/�5q in 73% of the cases�7/�7q in 27% of the cases�17p/�17 and þ8/8q in 41%of the casesþ11/11q in 36% of the cases

MLL: amplified in oneMDS and seven AMLValidation of 5q subtelomericloss in seven cases

101 structural aberrations wereidentified by SKY of which only16% were characterize by G-banding Six structural aberra-tions: 61 unbalanced and sixbalanced

14N¼ 125 AMLTechn: M-FISH

–5q in 80% of the cases�7 in 20% of the cases�12p in 23% of the cases�17p/–17 in 51% of the casesþ8/8q in 33% of the cases

MLL: amplified in 52% of thecasesTP53:deleted in 53% of the casesEGR1(5q31): deleted in 82% ofthe cases

Identification of 537 unbalancedand 19 balanced translocations

þ11q in 17% of the casesþ21 in 15% of the cases

D7S522 (7q31): deleted in 46%of the cases

23N¼ 13 MDS and 23 AMLTechn: M-FISH

�5/del5q in 86% of the cases�7/del7q in 47% of the cases

MLL: amplified in 17% of thecasesTEL: deleted in five cases with12 rearrangementsAML1: amplified in one case

Identification 146 unbalancedand 15 balanced aberrations

28N¼ 29 AMLTechn: SKY

�5/del5q in 45% of the cases�7/del7q in 34% of the cases�17p in 45% of the casesþ8/8q in 3% of the casesþ11/11q in 24% of the casesþ21 in 28% of the cases

AML1: in only one out of eightcases with 21q amplification,AML1 seems to correspond tothe degree of 21q

Reinterpretation of 136 unba-lanced aberrations and discov-ery of three aberrations hiddenin apparently normal chr.Identification of 22 balancedtranslocations

18N¼ 23 MDSTechn: SKY

�5/del5q in 57% of the cases�7/del7q in 30% of the cases�17p in 26% of the casesþ8/8q in 26% of the casesþ11/11q in 13% of the cases

MLL: amplified in one caseTP53: analysis of nine cases withcytogenetic aberrations of 17p:TP53 was found fully inactivatedin three cases, partially in two, andnormal in threeAML1: amplified in one caseHER2/neu: amplified in one case

Identification of 84 unbalancedand eight balanced structuralaberrations

19N¼ 37 MDSTechn: CGH

�5/del5q in 73% of the cases�7/del7q in 38% of the cases�17p in 19% of the casesþ8/8q in 24% of the casesþ11/11q in 38% of the cases

MLL: amplified in 1 caseTP53: deleted or rearranged in16 casesAML1: amplified in three casesBCL2: amplified in one caseBCL6: amplified in one case

A frequent involvement of sub-telomeric regions was detectedby CGH. However, thisabnormality was only confirmedin a few cases

22N¼ 23 MDS and 5 AMLTechn: CGH

�5/del5q in 96.5% of the cases�7/del7q in 57% of the cases�17p in 57% of the casesþ11/11q in 14% of the casesþ21q in 11% of the cases

MLL: amplified in four casesTP53: deletion of one allelein 15 casesRearrangement of one allelein one caseAML1: amplified in two casesDeletion of one allele in one case

Unbalanced rearrangementswere observed in 96% of thecases. Cryptic translocationswere found in 13 cases

N, number of cases analysed; Techn, technique used; *The percentage of abnormalities has been approximately calculated with theavailable data in the published articles.yDetected rearrangements using multicolour hybridizations.



chromosomal regions to define a group of ‘typical com-plex karyotypes’ characterized by the absence ofbalanced translocations, losses of at least 5q, 7q, or 17pregions, plus either losses of 18q21–22, 12p13, or16q22q24 or gains of 11q23q25, 1p33p36, 8q22q24, or21q11q22. Using Cox regression analysis, they found ashorter overall survival significantly associated with the‘typical complex karyotypes’.42 Similar studies in differ-ent cohorts are needed.

In summary, a comprehensive genome-wide analysis of

patients with AML and MDS with complex karyotypes

has allowed a better characterization of the relevant chro-

mosomal aberrations. These specific alterations could be

used in the near future as markers for the risk stratification

of patients, detection of minimal residual disease, and the

development of new therapeutic interventions.

Effect of unbalanced abnormalities in thetranscriptome

Expression profiling of AML with a complexaberrant karyotype

Two groups have recently provided evidence via analysisof gene expression data, that AML-CK has a specifictranscriptional pattern, which allow it to be distinguishedfrom other AML cytogenetic subgroups.42,47 Lindvallet al. identified 169 genes that were differentiallyexpressed in AML-CK compared to AML with normalkaryotypes. The upregulated genes included thoseinvolved in DNA repair (CASPG6, BTG2), chromosomesegregation (CFP1, CSPG6) and in the actin cytoskele-ton.47

A similar signature characterized by a higher expression

of genes involved in DNA repair and DNA-damage-

induced checkpoint signalling in AML with a complex

aberrant karyotype compared to all other subtypes has

been reported by Schoch et al.48 Overexpression of the

genes RAD21, RAD1, RAD9A, RAD23B, RAD51AP1

(RAD51 interacting protein), NBS1, MSH6, SUMO1, and

PARP2was reported. These data have led to the speculation

that the upregulation of these pathways allows cells with

complex aberrant karyotypes to survive instead of under-

going apoptosis after DNA damage, and that this may be

the same mechanism that prevents the cells from under-

going apoptosis after cytotoxic treatment.42

Effect of DNA gains and losses on theexpression profile

To test whether there is a correlation between genomicimbalances and changes in gene expression, severalgroups have investigated whether the transcription ofgenes mapped to the deleted or gained chromosomalregions shows significantly different levels of expres-sion ratios than those located within the unchangedregions.

Schoch et al.48 demonstrated that the majority of the

genes located on 5q and chromosome 7, when deleted,

showed significantly lower expression in the majority of

AML-CKcases compared to thosewithAMLwith a normal

karyotype. Similarly, overexpression of the genes located

on the respective gained chromosomal regions has been

demonstrated for chromosomes 8, 11, 13, and 21. These

observations are consistent with a gene-dosage effect for

genes located on chromosomal gained regions associated

with leukaemogenesis.44,46,48,49 We have recently investi-

gated the genomic and expression of chromosome 19 on

10 AML-M7 cell lines by simultaneously hybridizing

DNAand c-DNA over a c-DNA array and found a higher fre-

quency of overexpressed clones. We also found 36 clones

that were recurrently amplified and overexpressed, identi-

fying eight genes with at least three occurrences of greater

expression in at least two cell lines. The dendogram of the

unsupervised analysis of these eight genes gave three

main arms that discriminated according to the status of

genomic chromosome 19. Three of the selected genes

(KCNK6,NR2F6, andAPOC1) showed significant differen-

tial levels of expression depending on the Chr.19 status

(Figure 1).50 Several recent studies have identified

APOC1 as one of the genes recurrently overexpressed in

acute megakaryoblastic leukaemia.51,52

Furthermore, the effect of gene dosage on the global gene

expression signature has been evaluated. In cases with

del5q and monosomy 7, of the 50 probes that showed

most statistically different levels of expression, between

AML with complex karyotypes and other AML subtypes,

29 and 90% respectively were located on the deleted

region.48 Similar results have been reported by Lindvall

et al. who observed that among the 30 genes most signifi-

cantly downregulated in AML with complex karyotypes

compared to normal karyotypes, 12 (40%) were located

on either 5q or 7q.47 These may therefore constitute new

candidate genes and their role in the pathogenesis of malig-

nancies with unbalanced karyotypes needs to be clarified.48

In contrast to chromosomal loss, the gain of an entire chro-

mosome does not dominate the specific gene expression

signature. Virtaneva et al. showed that while AML samples

could be clearly distinguished from CD34þ samples on the

basis of their expression profiles, class prediction techni-

ques indicated that the identification of molecular patterns

to distinguish AML with normal karyotype from AML

with trisomy 8 is more difficult.49 Interestingly, Schoch et

al. found that the 50 most differentially expressed probe

sets of genes detected in cases with trisomies 8, 11, and

13 versus all other subtypes were equally distributed over

the genome.48 To explain the absence of the position effect,

it has been suggested that the genes on the gained chromo-

somes whose overexpression is critical to AML may use

different mechanisms of overexpression such as chromoso-

mal duplication, gene amplification or differences in the

transcriptional regulation of the genes.53

In conclusion, a common pattern of chromosomal

changes, characterized by the presence of unbalanced trans-

locations leading to loss of chromosomal material and gain/

amplification of selected genes, has been identified in

AML-CK. Furthermore, a specific transcriptional pattern

that distinguishes these groups of leukemias from other

AML cytogenetic groups has been described. These find-

ings should allow a better stratification of these patients

22 S Alvarez et al


for clinical trials. Interestingly, new studies have emerged

that investigate the role of haploinsufficiency of genes

located on the lost chromosomal regions, the identification

of targets of the gained/amplified chromosomes and the

analysis of the pathways leading to chromosomal instabil-

ity. Nevertheless, new approaches based on the analysis

of the samples at the functional and protein level are

needed.

Acknowledgements

SaraAlvarez is in receipt of a Post doctoral Contract from the Con-

sejeria de Educacion de la Comunidad deMadrid, Grant GR/SAL/

0219/2004. This work is being partially supported by Grant

040555, from the Fondo de Investigaciones Sanitarias (FIS), Min-

isterio de Sanidad.

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Gains, losses and complex karyotypes in myeloid disorders: a light at the end of the tunnel