The utility of spectral karyotyping in the cytogenetic analysis of newly diagnosed pediatric acute lymphoblastic leukemia.

We applied multicolor spectral karyotyping (SKY) to a panel of 29 newly diagnosed pediatric pre B-cell ALLs with normal and abnormal G-banded karyotypes to identify cryptic translocations and define complex chromosomal rearrangements. By this method, it was possible to define all add chromosomes in six cases, a cryptic t(12;21)(p13;q11) translocation in six cases, marker chromosomes in two cases and refine the misidentified aberrations by G-banding in two cases. In addition, we identified five novel non-recurrent translocations - t(2;9)(p11.2;p13), t(2;22) (p11.2;q11.2), t(6;8)(p12;p11), t(12;14)(p13;q32) and t(X;8)(p22.3;q?). Of these translocations, t(2;9), t(2;22) and t(12;14) were identified by G-banding analysis and confirmed by SKY. We characterized a t(12;14)( p13;q32) translocation by FISH, and identified a fusion of TEL with IGH for the first time in ALL. We identified a rearrangement of PAX5 locus in a case with t(2;9)(p11.2;p13) by FISH and defined the breakpoint telomeric to PAX5 in der(9)t(3;9)(?;p13). These studies demonstrate the utility of using SKY in combination with G-banding and FISH to augment the precision with which chromosomal aberrations may be identified in tumor cells.     

SKY reveals a high frequency of unbalanced translocations involving chromosome 6 in t(12;21)-positive acute lymphoblastic leukemia

The G-band cryptic t(12;21)(p13;q22) is the most common chromosomal rearrangement in childhood acute lymphoblastic leukemia (ALL). To investigate the nature of additional chromosomal events in this group of patients spectral karyotyping (SKY) following G-banding analysis was performed in 14 cases. From these cases six showed structural aberrations of chromosome 6, including both simple deletions and unbalanced translocations, and involved both q (n=4) and p (n=3) arms. The results show that rearrangements of 6p are also non-random events t(12;21)-positive ALL. This study illustrates the value of a combined SKY and G-banding approach in identifying novel karyotypic events in childhood ALL.     

Novel cryptic chromosomal rearrangements detected in acute lymphoblastic leukemia detected by application of new multicolor fluorescent in situ hybridization approaches

Routine cytogenetic analysis provides important information on diagnostic and prognostic relevance for hematological malignancies. However, it is often difficult to obtain good karyotypes, especially of cells from cases with acute lymphoblastic leukemia (ALL) because of poor morphology and spreading. Thus, detailed karyotyping can be hampered and even in case of a 'normal karyotype' according to banding cytogenetics doubts remain if the result is reliable. In order to address this problem a series of 37 ALL cases without any detectable numerical or structural chromosomal defects was selected and studied by two recently developed multicolor fluorescence in situ hybridization (FISH) approaches: 1) multitude multicolor banding (mMCB) is a FISH-banding technique, which allows the analyses of inter- and intra-chromosomal rearrangements of the whole human karyotype in one single experiment; 2) chromosome-specific subcentromere/subtelomere-specific multicolor (subCTM-)FISH applies locus-specific subtelomeric and subcentromic probes and enables the characterization of the subtelomeric and peri-centric regions of the chromosomes, not analyzable by other FISH-approaches. Thus, we detected the following recurrent cryptic chromosomal aberrations: del(12)(pter) [8 cases], del(9)(qter) [3 cases], and del(11)(pter) [2 cases]. Moreover, cryptic changes in additional nine subtelomeric and in two subcentromeric regions were observed one time, each. In summary, mMCB and subCTM were proven to be powerful methods in the screening for new cryptic chromosomal aberrations, which considerably increased the accuracy of cytogenetic diagnosis.     

Applications of SKY in cancer cytogenetics

Clinical and cancer cytogenetics is a rapidly evolving discipline. The past decade has seen a dramatic change in molecular biology and fluorescence microscopy. The use of fluorescence in situ hybridization (FISH) technologies has enabled the rapid analysis of cytogenetic specimens as an adjunct to classical cytogenetic analysis. Spectral karyotyping (SKY) is a 24-color, multi-chromosomal painting assay that allows the visualization of all human chromosomes in one experiment. The ability for SKY analysis to detect equivocal or complex chromosomal rearrangements, as well as to identify the chromosomal origins of marker chromosomes and other extra-chromosomal structures, makes this a highly sensitive and valuable tool for identifying recurrent chromosomal aberrations. The SKY has been applied to various tumor groups including hematological malignancies, sarcomas, carcinomas and brain tumors, with the intent of identifying specific chromosomal abnormalities that may provide insight to the genes involved in the disease process as well as identifying recurrent cytogenetic markers for clinical diagnosis and prognostic assessment. The SKY has also been applied for the mouse genome, enabling investigators to extrapolate information from mouse models of cancer to their human counterparts. This review will address the advances that SKY has facilitated in the field of cancer cytogenetics, as well as its variety of application in the cancer research laboratories.     

Comparison of spectral karyotyping and conventional cytogenetics in 39 patients with acute myeloid leukemia and myelodysplastic syndrome.

Spectral karyotyping (SKY) was performed in patients with acute myeloid leukemia (AML; n = 25), secondary AML (s-AML; n = 7), myelodysplastic syndrome (MDS; n = 6) and s-MDS (n = 1) to complement conventional cytogenetic investigations. According to the results of conventional cytogenetics the patients were subdivided into three groups: group 1, normal karyotype, n = 19 cases, median age = 64 years; group 2, patients displaying either one or two single aberrations, n = 10 cases, median age = 54 years; group 3, patients with > or =3 independent aberrations, n = 10 cases, median age = 61.5 years. SKY identified no abnormal metaphases in group 1. In one patient of group 2 a hidden translocation t(7;14)(q3?1;q2?2) could be revealed with SKY. Conventional cytogenetics had only shown trisomy 8. A similar t(7;14) was also detected in one patient of group 3. SKY was helpful for the delineation of marker chromosomes and additional material. Furthermore, SKY could distinguish between partial and total monosomies or real existing and apparent deletions. The combination of G-banding, FISH and SKY was found very useful for the precise delineation of the karyotype. As a result of our study we recommend SKY investigation as an important additional tool for accurate chromosome analysis. The detected t(7;14) might represent a novel recurrent translocation in acute myeloid leukemias.     

The Application of Spectral Karyotyping in Leukemia

Spectral karyotyping (SKY) is a novel cytogenetic technique, which has been developed to unambiguously display and identify all 24 human chromosomes at one time without previous knowledge of any abnormalities involved. SKY can discern aberrations that fail to be easily detected by conventional banding techniques and by fluorescent in situ hybridization (FISH). Therefore SKY is highly accurate, highly sensitive, and highly prognostic. In this report the featurese and application of SKY in studies of leukemia are reviewed.     

Combined classical and molecular cytogenetic analysis of cancer

While chromosome-banding analysis has set the standard for karyotyping from 1970 onwards, fluorescent in situ hybridisation (FISH) has more recently been used to complement the study of chromosomal rearrangements. Especially useful has been the appearance of FISH methodologies with screening abilities, namely comparative genome hybridisation (CGH), multicolour-FISH (m-FISH), and cross-species colour banding (RxFISH). These FISH-based screening techniques are reviewed here together with methodologies using chromosome- or locus-specific probes. Emphasis is put on the strengths and limitations of these FISH techniques to complement standard chromosome banding analysis. Judicious choice from the molecular cytogenetic techniques now available has significantly improved our ability to characterise the genomic rearrangements of cancer cells.     

Comparison of cytogenetic and molecular cytogenetic detection of chromosome abnormalities in 240 consecutive adult patients with acute myeloid leukemia.

PURPOSE: To prospectively compare cytogenetic and molecular cytogenetic analysis for the detection of the most relevant chromosome abnormalities in a large series of patients with acute myeloid leukemia (AML). PATIENTS AND METHODS: Two hundred forty consecutive adult patients with AML entered onto the multicenter treatment trial AML HD93 were studied. Chromosome banding and fluorescence in situ hybridization (FISH) applying a comprehensive set of genomic DNA probes were performed in a single reference laboratory. RESULTS: Two cases of inv(16), three cases of t(11q23), and three cases of t(8;21)var were only detected by molecular cytogenetics. By FISH, aberrations were identified in three cases with normal karyotypes: inv(16), -Y (in a patient with low metaphase yield on chromosome banding) and a 12p microdeletion. Additional aneuploidies, in particular +8q and +11q, were diagnosed by FISH; however, virtually all these aberrations occurred in patients with complex karyotypes or as an additional abnormality in leukemias with an AML-specific translocation. Finally, aberrations were detected by FISH in eight of 14 patients with no assessable metaphases. CONCLUSION: In most cases of AML, conventional cytogenetic study reliably detects chromosomal abnormalities, and this method should not be replaced by FISH. FISH should be used as a complementary method for the detection of more subtle abnormalities, such as inv(16) and t(11q23), in all patients with newly diagnosed AML and for suspected t(8;21)var. Furthermore, molecular cytogenetics using this comprehensive set of DNA probes provides a valuable diagnostic tool for patients with poor chromosome morphology, low or no yields of metaphase cells, or both.     

Comprehensive molecular cytogenetic investigation of chromosomal abnormalities in human medulloblastoma cell lines and xenograft

Cell lines and xenografts derived from medulloblastomas are useful tools to investigate the chromosomal changes in these tumors. Here we used G-banding, fluorescence in situ hybridization (FISH), spectral karyotyping (SKY), and comparative genomic hybridization to study 4 medulloblastoma cell lines and 1 xenograft. Cell line D-425 Med had a relatively simple karyotype, with a terminal deletion of 10q and amplification of MYC in double-minutes (dmins). FISH demonstrated that an apparent isochromosome (17q) by routine karyotyping was actually an unbalanced translocation between 2 copies of chromosome 17. Cell line D-556 Med also had a simple near-diploid stemline with an unbalanced 1;13 translocation resulting in a gain of 1q, an isochromosome (17q), and dmins. These findings were initially described using routine G-banded preparations, and FISH showed that the dmins were an amplification of MYC and the i(17q) was an isodicentric 17q chromosome. The other finding was confirmed by FISH, SKY, and comparative genomic hybridization. Cell lines D-721 Med and D-581 Med had complex karyotypic patterns that could be completely characterized only when FISH and SKY were used. Xenograft D-690 Med also had a complex pattern that FISH and SKY were helpful in completely elucidating. Interestingly, balanced reciprocal translocations were seen as well as complicated unbalanced translocations and marker chromosomes. Comparative genomic hybridization demonstrated only a deletion of 10q22-10q24, supporting the idea that despite the complexity of the chromosomal rearrangements, minimal alterations in the overall chromosomal content had occurred. This study demonstrates that routine cytogenetic preparations are adequate to describe chromosomal abnormalities in occasional medulloblastoma samples, but a broader spectrum of molecular cytogenetic methods is required to completely analyze most of these tumor samples.     

Cytogenetic Profile of De Novo B lineage Acute Lymphoblastic Leukemia: Determination of Frequency,Distribution Pattern and Identification of Rare and Novel Chromosomal Aberrations in Indian Patients

Background: Chromosomal aberrations identified in acute lymphoblastic leukemia (ALL) have an importantrole in disease diagnosis, prognosis and management. Information on karyotype and associated clinical parametersare essential to physicians for planning cancer control interventions in different geographical regions. Materialsand Methods: In this study, we present the overall frequency and distribution patterns of chromosomal aberrationsin both children and adult de novo B lineage ALL Indian patients using conventional cytogenetics, interphaseFISH and multiplex RT-PCR. Results: Among the 215 subjects, cytogenetic results were achieved in 172 (80%)patients; normal karyotype represented 37.2% and abnormal 62.8% with a distribution as follows: 15.3%hypodiploidy; 10.3% hyperdiploidy; 15.8% t(9;22); 9.8% t(1;19); 3.7% t(12;21); 2.8% t(4;11); 2.8% complexkaryotypes. Apart from these, we observed several novel, rare and common chromosomal rearrangements. Also,FISH studies using LSI extra-signal dual-color probes revealed additional structural or numerical changes.Conclusions: These results demonstrate cytogenetic heterogeneity of ALL and confirm that the incidence ofchromosomal abnormalities varies considerably. To the best of our knowledge, this is one of the largest reportedseries of cytogenetic investigations in Indian B-lineage ALL cases. In addition, ongoing cytogenetic studies arewarranted in larger groups of B-lineage ALL cases to identify newly acquired chromosomal abnormalities thatmay contribute to disease diagnosis and management.     

Evidence of chromosomal instability in prostate cancer determined by spectral karyotyping (SKY) and interphase fish analysis

The way in which cytogenetic aberrations develop in prostate cancer (CaP) is poorly understood. Spectral karyotype (SKY) analysis of CaP cell lines has shown that they have unstable karyotypes and also have features associated with chromosomal instability (CIN). To accurately determine the incidence of de novo structural and numerical aberrations in vitro in CaP, we performed SKY analysis of three independent clones derived from one representative cell line, DU145. The frequent generation of new chromosomal rearrangements and a wide variation in the number of structural aberrations within two to five passages suggested that this cell line exhibited some of the features associated with a CIN phenotype. To study numerical cell-to-cell variation, chromosome 8 aneusomy was assessed in the LNCaP, DU145, and PC-3 cell lines and a patient cohort of 15 CaP primary tumors by interphase fluorescence in situ hybridization (FISH). This analysis showed that a high frequency of numerical alteration affecting chromosome 8 was present in both in vitro and in CaP tissues. In comparison to normal controls, the patient cohort had a statistically significant (P<.05), greater frequency of cells with one and three centromere 8 copies. These data suggest that a CIN-like process may be contributing towards the generation of de novo numerical and structural chromosome abnormalities in CaP.     

Chromosomal aberrations of multiple myeloma in Chinese patients at diagnosis: a study by combined G-banding and multicolor spectral karyotyping

Cytogenetic investigation of multiple myeloma (MM) has been difficult by conventional methods and most of the data have been derived from western population where incidence of MM is much higher as compared to that of Asians. The current study represents the first report of chromosomal aberrations of multiple myeloma in Chinese. We investigated 25 consecutive Chinese patients with MM for chromosomal aberrations at diagnosis using G-banding and multicolor spectral karyotyping (SKY). Of the 21 patients successfully analyzed by G-banding, 11 patients revealed cytogenetic abnormalities showing complex numerical and structural aberrations, which were further characterized with SKY. An abnormal karyotype significantly associated with blastic MM was observed. Consistent with the western literature, structural rearrangements involving chromosomes 1, 6, 8, 19, numerical abnormalities of gains in chromosomes 9, 3, and 5, and losses in chromosomes 13 and 14 were observed. However, there were notably higher incidences of -22/22q- (4/11) and structural aberrations of chromosome X but a lower incidence of -X. The biological implications of these findings, if confirmed, deserve further evaluation.     

Multicolor karyotyping in acute myeloid leukemia

Cytogenetic data have significantly contributed to our understanding of the heterogeneity of acute myeloid leukemia (AML). In AML, numerous recurrent chromosomal aberrations have been identified, and several of them, e.g. t(8;21)(q22;q22), t(15;17)(q22;q11-12), inv(16)(p13q22), are specific for distinct subgroups. Furthermore, chromosomal aberrations have proved to be of paramount prognostic importance for remission induction and survival. Chromosome analysis using classical cytogenetic banding techniques often fails to completely resolve complex karyotypes and cryptic translocations not identifiable by these techniques have been detected using molecular cytogenetic methods. While fluorescence in situ hybridization (FISH) has become an indispensable tool for screening and follow-up of known aberrations, the techniques of spectral karyotyping (SKY) and multiplex-fluorescence in situ hybridization (M-FISH) allow for the simultaneous visualization of all chromosomes of a metaphase in a single hybridization step, and thereby enable screening for the aberrations present without their prior knowledge. Therefore, with the introduction of these techniques in 1996 the comprehensive analysis of complex karyotypes and the identification of new, hitherto cryptic translocations and, ultimately, the identification of new disease subgroups seemed possible. Since, more than 600 cases of AML and MDS have been analyzed. Herein, we attempt to summarize the data published and discuss what has been achieved towards realization of these goals.     

Importance of FISH combined with Morphology,Immunophenotype and Cytogenetic Analysis of Childhood/ Adult Acute Lymphoblastic Leukemia in Omani Patients

Genetic changes associated with acute lymphoblastic leukemia (ALL) provide very important diagnostic andprognostic information with a direct impact on patient management. Detection of chromosome abnormalities byconventional cytogenetics combined with fluorescence in situ hybridization (FISH) play a very significant rolein assessing risk stratification. Identification of specific chromosome abnormalities has led to the recognition ofgenetic subgroups based on reciprocal translocations, deletions and modal number in B or T-cell ALL. In the lasttwelve years 102 newly diagnosed childhood/adult ALL bone marrow samples were analysed for chromosomalabnormalities with conventional G-banding, and FISH (selected cases) using specific probes in our hospital.G-banded karyotype analysis found clonal numerical and/or structural chromosomal aberrations in 74.2% ofcases. Patients with pseudodiploidy represented the most frequent group (38.7%) followed by high hyperdiploidygroup (12.9%), low hyperdiploidy group (9.7%), hypodiploidy (<46) group (9.7%) and high hypertriploidygroup (3.2%). The highest observed numerical chromosomal alteration was high hyperdiploidy (12.9%) withabnormal karyotypes while abnormal 12p (7.5%) was the highest observed structural abnormality followed byt(12;21)(p13.3;q22) resulting in ETV6/RUNX1 fusion (5.4%) and t(9;22)(q34.1;q11.2) resulting in BCR/ABL1fusion (4.3%). Interestingly, we identified 16 cases with rare and complex structural aberrations. Application ofthe FISH technique produced major improvements in the sensitivity and accuracy of cytogenetic analysis withALL patients. In conclusion it confirmed heterogeneity of ALL by identifying various recurrent chromosomalaberrations along with non-specific rearrangements and their association with specific immunophenotypes. Thisstudy pool is representative of paediatric/adult ALL patients in Oman.     

Multicolor spectral karyotyping identifies novel translocations in childhood acute lymphoblastic leukemia.

We used a recently described molecular cytogenetic method, spectral karyotyping (SKY), to analyze metaphase chromosomes from 30 pediatric patients with acute lymphoblastic leukemia (ALL). This group included 20 patients whose leukemic blast cells lacked chromosomal abnormalities detected by conventional cytogenetics and 10 patients whose blast cells had multiple chromosomal abnormalities that could not be completely identified by G-banding analysis. In two of the 20 patients (10%) with apparently normal karyotypes, SKY identified three cryptic translocations: a t(7;8)(q34-35;q24.1) in one patient and a t(13;17)(q22;q21) and a der(19)t(17;19)(q22;p13) in another. Fluorescence in situ hybridization using subtelomeric probes proved the latter translocation to be a t(17;19). SKY analysis was also successful in defining the nature of the chromosomal abnormalities in four of the 10 patients with marker and derivative chromosomes. The identified abnormalities in the latter group included three novel translocations: a der(X)t(X;5)(p11.4;q31), a der(21)t(X;21)(p11.4;p11.2) and a t(X;9)(p11.4;p13). The presence of the t(X;9) was suggested by conventional cytogenetics. The application of fluorescence in situ hybridization using chromosome-specific painting probes and locus-specific probes complemented the SKY analysis by confirming the nature of the chromosome rearrangements defined by SKY and by identifying the amplification of the AML1/CBFA2 gene in one patient with a duplicated 21q. Our study demonstrates the utility of SKY in identifying novel translocations and in refining the identity of chromosomal abnormalities in leukemias.     

Cytogenetic analysis of the bipotential murine pre-B cell lymphoma, P388, and its derivative macrophage-like tumor, P388D1, using SKY and CGH.

Spectral karyotyping (SKY) and comparative genomic hybridization (CGH) were used to elucidate the divergent cytogenetic make-up of the prototypical bilineage lymphoblastic pre-B lymphoma, P388, and its progenitor macrophage-like tumor, P388D1. P388 was found to be diploid and genomically stable. P388D1 was triploid, highly unstable and characterized by numerous marker chromosomes (Chrs) and composite rearrangements. The karyotype of P388D1 was so complex that its clonal relatedness to P388 would have remained questionable without confirmation by molecular analysis of the clonotypic immunoglobulin heavy-chain and light-chain gene recombinations that coexisted in both tumors. The intrinsic instability of the P388D1 genome was indicated by the observation that only four out of 42 aberrations uncovered by SKY (in a total of 27 metaphases) occurred consistently (100% incidence), whereas 27 changes occurred non-randomly (27 to 96% incidence) and 11 alterations randomly (4 to 11% incidence). Persistent cytogenetic instability was also observed in P388 'macrophages' after phorbol ester- and ionomycin-induced conversion in vitro of P388 lymphoma cells. The 'cytogenetic noise' in these cells was manifested by a multiplicity of sporadic chromosomal aberrations; ie 25 distinct changes were identified by SKY in 40 metaphases. The results in P388D1 and P388 'macrophages' were interpreted to indicate that the myeloid differentiation program in the bipotential pre-B cell lymphoma P388 is invariably characterized by karyotypic instability. The study presented here demonstrates the power of the combined SKY and CGH approach to resolve complicated karyotypes of important and widely used mouse tumors.     

Prognostic significance of karyotype at diagnosis in childhood acute lymphoblastic leukemia [corrected]

Acute lymphoblastic leukemia (ALL) is the most frequent childhood cancer. The disease is heterogeneous. The leukemic cells in childhood ALL patients show various karyotypic abnormalities, express diverse phenotypes, and respond variably to treatment. Identification of prognostic factors will make it possible to predict treatment outcome and to identify the patients that require different therapeutic approaches. The important prognostic implications of chromosome number and of the presence of several well defined structural chromosomal aberrations have been established by several groups. We analyzed 145 children with ALL at diagnosis for cytogenetic features. In 135 cases cytogenetic analysis was successful. Of these, 101 showed abnormal karyotype (70%). Structural chromosomal rearrangements were detected in 71 out of 135 cases investigated (53%), i.e. 71% of the cytogenetically abnormal cases. These cytogenetic findings were correlated with clinical outcome. In our series the ploidy of the karyotype appeared to be of prognostic importance. Our findings concerning karyotype, phenotype, and treatment outcome of this subgroup were in most cases in agreement with earlier reports from other investigators. We observed an increased risk for central nervous system relapse in childhood ALL patients with abnormalities involving the short arm of chromosome 12 in combination with pre-B or common ALL phenotype.     

Cytogenetic analysis of 298 newly diagnosed cases of acute lymphoblastic leukaemia in Tunisia

Genetic changes associated with Acute Lymphoblastic Leukaemia (ALL) provide diagnostic and prognostic information with a direct impact on patient management. We report the cytogenetic analysis of 298 Tunisian patients with ALL, including 183 children and 115 adults. Chromosome abnormalities have been detected in 68.2% of our patients associating clonal numerical and/or structural rearrangements. Some chromosomal abnormalities especially hyperdiploidy, 19p13 abnormalities, 8q24 translocations, 12p, 6q deletions and TCR rearrangements occur at a lower incidence compared to that reported in other populations. ALL cases (5.7%) had miscellaneous clonal abnormalities. We also found in our Tunisian series a higher incidence for T-lineage ALL more than usually described. Among structural chromosomal abnormalities, t(9;22)(q34;q11) resulting in the BCR/ABL fusion and the t(12;21)(p13;q22) resulting in the TEL/AML1 fusion were studied by FISH providing additional diagnostic and prognostic information. We conclude that although the incidence of our cytogenetic results are slightly different, their clinical significance is similar to that described in the literature.     

Identification of cryptic aberrations and characterization of translocation breakpoints using array CGH in high hyperdiploid childhood acute lymphoblastic leukemia.

High hyperdiploidy, characterized by non-random trisomies, is the largest cytogenetic subgroup in childhood acute lymphoblastic leukemia (ALL). It is not known whether the gained chromosomes are sufficient for leukemogenesis or if additional genetic aberrations are necessary. However, the suboptimal chromosome morphology of hyperdiploid ALLs makes detection of structural abnormalities difficult if using cytogenetic techniques; alternative methods are, therefore, needed. We performed array comparative genome hybridization (CGH) analyses, with a resolution of 100 kb, of eight cases of high hyperdiploid childhood ALL to characterize structural abnormalities found with G-banding/multicolor fluorescence in situ hybridization (FISH) and to detect novel changes. The non-centromeric breakpoints of four rearrangements, including three translocations and one 1q duplication, were narrowed down to <0.2 Mb. Furthermore, four submicroscopic imbalances involving 0.6-2.7 Mb were detected, comprising two segmental duplications involving 1q22 and 12q24.31 in one case and two hemizygous deletions in 12p13.2-31 - including ETV6 - and in 13q32.3-33.1 in another case. Notably, FISH analysis of the latter revealed an associated reciprocal t(3;13)(q?;32.2-33.1). In conclusion, the array CGH analyses revealed putative leukemia-associated submicroscopic imbalances and rearrangements in 2/8 (25%) hyperdiploid ALLs. The detection and characterization of these additional genetic aberrations will most likely increase our understanding of the pathogenesis of high hyperdiploid childhood ALL.