Mechanism and relevance of ploidy in neuroblastoma

Neuroblastoma arises in early fetal development and its evolutionary duration predicts outcome

Neuroblastoma, the most frequent solid tumor in infants, shows very diverse outcomes from spontaneous regression to fatal disease. When these different tumors originate and how they evolve are not known. Here we quantify the somatic evolution of neuroblastoma by deep whole-genome sequencing, molecular clock analysis and population-genetic modeling in a comprehensive cohort covering all subtypes. We find that tumors across the entire clinical spectrum begin to develop via aberrant mitoses as early as the first trimester of pregnancy. Neuroblastomas with favorable prognosis expand clonally after short evolution, whereas aggressive neuroblastomas show prolonged evolution during which they acquire telomere maintenance mechanisms. The initial aneuploidization events condition subsequent evolution, with aggressive neuroblastoma exhibiting early genomic instability. We find in the discovery cohort (n = 100), and validate in an independent cohort (n = 86), that the duration of evolution is an accurate predictor of outcome. Thus, insight into neuroblastoma evolution may prospectively guide treatment decisions.

Chromosomal instability in adult-type diffuse gliomas

Chromosomal instability (CIN) is a fundamental property of cancer and a key underlying mechanism of tumorigenesis and malignant progression, and has been documented in a wide variety of cancers, including colorectal carcinoma with mutations in genes such as APC. Recent reports have demonstrated that CIN, driven in part by mutations in genes maintaining overall genomic stability, is found in subsets of adult-type diffusely infiltrating gliomas of all histologic and molecular grades, with resulting elevated overall copy number burden, chromothripsis, and poor clinical outcome. Still, relatively few studies have examined the effect of this process, due in part to the difficulty of routinely measuring CIN clinically. Herein, we review the underlying mechanisms of CIN, the relationship between chromosomal instability and malignancy, the prognostic significance and treatment potential in various cancers, systemic disease, and more specifically, in diffusely infiltrating glioma subtypes. While still in the early stages of discovery compared to other solid tumor types in which CIN is a known driver of malignancy, the presence of CIN as an early factor in gliomas may in part explain the ability of these tumors to develop resistance to standard therapy, while also providing a potential molecular target for future therapies.

MYCN in Neuroblastoma: "Old Wine into New Wineskins"

MYCN Proto-Oncogene, BHLH Transcription Factor (MYCN) has been one of the most studied genes in neuroblastoma. It is known for its oncogenetic mechanisms, as well as its role in the prognosis of the disease and it is considered one of the prominent targets for neuroblastoma therapy. In the present work, we attempted to review the literature, on the relation between MYCN and neuroblastoma from all possible mechanistic sites. We have searched the literature for the role of MYCN in neuroblastoma based on the following topics: the references of MYCN in the literature, the gene's anatomy, along with its transcripts, the protein's anatomy, the epigenetic mechanisms regulating MYCN expression and function, as well as MYCN amplification. MYCN plays a significant role in neuroblastoma biology. Its functions and properties range from the forming of G-quadraplexes, to the interaction with miRNAs, as well as the regulation of gene methylation and histone acetylation and deacetylation. Although MYCN is one of the most primary genes studied in neuroblastoma, there is still a lot to be learned. Our knowledge on the exact mechanisms of MYCN amplification, etiology and potential interventions is still limited. The knowledge on the molecular mechanisms of MYCN in neuroblastoma, could have potential prognostic and therapeutic advantages.

Somatic Sex: On the Origin of Neoplasms With Chromosome Counts in Uneven Ploidy Ranges

Stable aneuploid genomes with nonrandom numerical changes in uneven ploidy ranges define distinct subsets of hematologic malignancies and solid tumors. The idea put forward herein suggests that they emerge from interactions between diploid mitotic and G0/G1 cells, which can in a single step produce all combinations of mono-, di-, tri-, tetra- and pentasomic paternal/maternal homologue configurations that define such genomes. A nanotube-mediated influx of interphase cell cytoplasm into mitotic cells would thus be responsible for the critical nondisjunction and segregation errors by physically impeding the proper formation of the cell division machinery, whereas only a complete cell fusion can simultaneously generate pentasomies, uniparental trisomies as well as biclonal hypo- and hyperdiploid cell populations. The term "somatic sex" was devised to accentuate the similarities between germ cell and somatic cell fusions. A somatic cell fusion, in particular, recapitulates many processes that are also instrumental in the formation of an abnormal zygote that involves a diploid oocyte and a haploid sperm, which then may further develop into a digynic triploid embryo. Despite their somehow deceptive differences and consequences, the resemblance of these two routes may go far beyond of what has hitherto been appreciated. Based on the arguments put forward herein, I propose that embryonic malignancies of mesenchymal origin with these particular types of aneuploidies can thus be viewed as the kind of flawed somatic equivalent of a digynic triploid embryo.

The origins and functions of hepatic polyploidy

Polyploid cells contain more than two homologous sets of chromosomes. The original observations of liver polyploidy date back to the 1940s, but functional roles for polyploid cells are still unclear. Liver polyploidy may influence regeneration, stress response, and cancer, although little evidence has established direct causal links between polyploidy and these biological phenotypes. In this review, we will introduce broad concepts about polyploidy including its distribution in nature and how polyploids form in normal and pathological situations. Then we will examine recent discoveries that have begun to clarify functionality and disease relevance of liver polyploidy. Finally, we will discuss implications and future directions of research about polyploidy in the liver.

Genome instability model of metastatic neuroblastoma tumorigenesis by a dictionary learning algorithm

Background

Metastatic neuroblastoma (NB) occurs in pediatric patients as stage 4S or stage 4 and it is characterized by heterogeneous clinical behavior associated with diverse genotypes. Tumors of stage 4 contain several structural copy number aberrations (CNAs) rarely found in stage 4S. To date, the NB tumorigenesis is not still elucidated, although it is evident that genomic instability plays a critical role in the genesis of the tumor. Here we propose a mathematical approach to decipher genomic data and we provide a new model of NB metastatic tumorigenesis.

Method

We elucidate NB tumorigenesis using Enhanced Fused Lasso Latent Feature Model (E-FLLat) modeling the array comparative chromosome hybridization (aCGH) data of 190 metastatic NBs (63 stage 4S and 127 stage 4). This model for aCGH segmentation, based on the minimization of functional dictionary learning (DL), combines several penalties tailored to the specificities of aCGH data. In DL, the original signal is approximated by a linear weighted combination of atoms: the elements of the learned dictionary.

Results

The hierarchical structures for stage 4S shows at the first level of the oncogenetic tree several whole chromosome gains except to the unbalanced gains of 17q, 2p and 2q. Conversely, the high CNA complexity found in stage 4 tumors, requires two different trees. Both stage 4 oncogenetic trees are marked diverged, up to five sublevels and the 17q gain is the most common event at the first level (2/3 nodes). Moreover the 11q deletion, one of the major unfavorable marker of disease progression, occurs before 3p loss indicating that critical chromosome aberrations appear at early stages of tumorigenesis. Finally, we also observed a significant (p = 0.025) association between patient age and chromosome loss in stage 4 cases.

Conclusion

These results led us to propose a genome instability progressive model in which NB cells initiate with a DNA synthesis uncoupled from cell division, that leads to stage 4S tumors, primarily characterized by numerical aberrations, or stage 4 tumors with high levels of genome instability resulting in complex chromosome rearrangements associated with high tumor aggressiveness and rapid disease progression.

Electronic supplementary material

The online version of this article (doi:10.1186/s12920-015-0132-y) contains supplementary material, which is available to authorized users.

RASSF1A methylation may have two biological roles in neuroblastoma tumorigenesis depending on the ploidy status and age of patients

RASSF1A methylation was frequent in neuroblastomas found in infants by mass-screening or infants and children diagnosed clinically, whereas CASP8 and DCR2 methylation was only frequent in tumors in children. When classified according to the ploidy status, RASSF1A and PCDHB methylation was only associated with MYCN amplification and poor outcomes in infants with a clinically diagnosed diploid, not triploid tumor. RASSF1A and PCDHB methylation was associated with poor outcomes in children with triploid and diploid tumors, respectively, and with MYCN amplification in children with diploid tumor. RASSF1A methylation may have two biological roles based on the ploidy status and patient's age.

Intratumour diversity of chromosome copy numbers in neuroblastoma mediated by on-going chromosome loss from a polyploid state

Neuroblastomas (NBs) are tumours of the sympathetic nervous system accounting for 8–10% of paediatric cancers. NBs exhibit extensive intertumour genetic heterogeneity, but their extent of intratumour genetic diversity has remained unexplored. We aimed to assess intratumour genetic variation in NBs with a focus on whole chromosome changes and their underlying mechanism. Allelic ratios obtained by SNP-array data from 30 aneuploid primary NBs and NB cell lines were used to quantify the size of clones harbouring specific genomic imbalances. In 13 cases, this was supplemented by fluorescence in situ hybridisation to assess copy number diversity in detail. Computer simulations of different mitotic segregation errors, single cell cloning, analysis of mitotic figures, and time lapse imaging of dividing NB cells were used to infer the most likely mechanism behind intratumour variation in chromosome number. Combined SNP array and FISH analyses showed that all cases exhibited higher inter-cellular copy number variation than non-neoplastic control tissue, with up to 75% of tumour cells showing non-modal chromosome copy numbers. Comparisons of copy number profiles, resulting from simulations of different segregation errors to genomic profiles of 120 NBs indicated that loss of chromosomes from a tetraploid state was more likely than other mechanisms to explain numerical aberrations in NB. This was supported by a high frequency of lagging chromosomes at anaphase and polyploidisation events in growing NB cells. The dynamic nature of numerical aberrations was corroborated further by detecting substantial copy number diversity in cell populations grown from single NB cells. We conclude that aneuploid NBs typically show extensive intratumour chromosome copy number diversity, and that this phenomenon is most likely explained by continuous loss of chromosomes from a polyploid state.

The role of genetic and epigenetic alterations in neuroblastoma disease pathogenesis

Neuroblastoma is a highly heterogeneous tumor accounting for 15 % of all pediatric cancer deaths. Clinical behavior ranges from the spontaneous regression of localized, asymptomatic tumors, as well as metastasized tumors in infants, to rapid progression and resistance to therapy. Genomic amplification of the MYCN oncogene has been used to predict outcome in neuroblastoma for over 30 years, however, recent methodological advances including miRNA and mRNA profiling, comparative genomic hybridization (array-CGH), and whole-genome sequencing have enabled the detailed analysis of the neuroblastoma genome, leading to the identification of new prognostic markers and better patient stratification. In this review, we will describe the main genetic factors responsible for these diverse clinical phenotypes in neuroblastoma, the chronology of their discovery, and the impact on patient prognosis.

New prognostic markers in neuroblastoma

INTRODUCTION

The hallmark of neuroblastoma is its clinical and biological heterogeneity, with the likelihood of cure varying widely according to age at diagnosis, extent of disease and tumor biology. We hope this review will be useful for understanding part of the unfamiliar neuroblastoma codex.

AREAS COVERED

In the first part of this review, the authors summarize the currently used prognostic factors for risk-adapted therapy, with the focus on clinical management of neuroblastoma patients. In the second part, the authors discuss the evolving prognostic factors for future treatment schemes. A search of online medical research databases was undertaken focusing especially on literature published in the last six years.

EXPERT OPINION

Harnessing the synergy of the various forms of data, including clinical variables and biomarker profiles, would allow mathematical predictive models to be built for the individual patient, which could eventually become molecular targets of specific therapies.

Cancer chromosomal instability: therapeutic and diagnostic challenges

Chromosomal instability (CIN)-which is a high rate of loss or gain of whole or parts of chromosomes-is a characteristic of most human cancers and a cause of tumour aneuploidy and intra-tumour heterogeneity. CIN is associated with poor patient outcome and drug resistance, which could be mediated by evolutionary adaptation fostered by intra-tumour heterogeneity. In this review, we discuss the clinical consequences of CIN and the challenges inherent to its measurement in tumour specimens. The relationship between CIN and prognosis supports assessment of CIN status in the clinical setting and suggests that stratifying tumours according to levels of CIN could facilitate clinical risk assessment.

Gender and ploidy in cancer survival

Background

Females carry a better prognosis than men for many cancer types. We hypothesized that chromosomal changes, in particular numerical alterations of the sex chromosomes or the presence of near-triploidy may contribute to these gender differences.

Methods

To characterize the influence of gender a literature search was performed for survival data of 27 tumor types. All entities were categorized by the strength of evidence for differences in survival between females and males. To test our hypothesis the Mitelman database of chromosomal alterations was evaluated for the major tumor types occurring in both women and men. Numerical gonosome alterations were documented and mean chromosome numbers were converted into histograms to provide insight into the ploidy level of 37 cancer types.

Results

In general, a survival advantage of women could be shown for most, but not all cancer types. In addition, 36.859 karyograms were analyzed. Numerical gonosome alterations were more frequent in males than females indicating a potential link with gender differences in survival. Neartriploidy was a common phenomenon in many cancer types suggesting that it represents a metastable condition of the cancer genome. It was not related to gender differences in survival. However, the extent of triploidy and aneuploidy was associated with poor prognosis in carcinomas. There was no single case in the Mitelman database with normal chromosome number (n = 46) that did not carry at least one structural or numerical aberration.

Conclusions

Our study highlights the importance of chromosomal changes in tumor formation and progression. In addition, it suggests potential associations with gender specific differences in survival.

Electronic supplementary material

The online version of this article (doi:10.1007/s13402-011-0013-0) contains supplementary material, which is available to authorized users.

Systems biology and modeling in neuroblastoma: practicalities and perspectives

Neuroblastoma (NB) is a common pediatric malignancy characterized by clinical and biological heterogeneity. A host of prognostic markers are available, contributing to accurate risk stratification and appropriate treatment allocation. Unfortunately, outcome is still poor for many patients, indicating the need for a new approach with enhanced utilization of the available biological data. Systems biology is a holistic approach in which all components of a biological system carry equal importance. Systems biology uses mathematical modeling and simulation to investigate dynamic interactions between system components, as a means of explaining overall system behavior. Systems biology can benefit the biomedical sciences by providing a more complete understanding of human disease, enhancing the development of targeted therapeutics. Systems biology is largely contiguous with current approaches in NB, which already employ an integrative and pseudo-holistic approach to disease management. Systems modeling of NB offers an optimal method for continuing progression in this field, and conferring additional benefit to current risk stratification and management. Likewise, NB provides an opportunity for systems biology to prove its utility in the context of human disease, since the biology of NB is comprehensively characterized and, therefore, suited to modeling. The purpose of this review is to outline the benefits, challenges and fundamental workings of systems modeling in human disease, using a specific example of bottom-up modeling in NB. The intention is to demonstrate practical requirements to begin bridging the gap between biological research and applied mathematical approaches for the mutual gain of both fields, and with additional benefits for clinical management.

Aurora A is a negative prognostic factor and a new therapeutic target in human neuroblastoma

We studied expression of the Aurora A gene and its clinical significance in a cohort of neuroblastoma patients. In addition, we investigated the antitumor activity of MLN8054, a novel small-molecule inhibitor of Aurora A kinase, on cultured NB cell lines in vitro. Aurora A mRNA expression was assessed by quantitative real-time PCR in tumor tissue specimens from 67 patients at diagnosis and in 9 human neuroblastoma cell lines. Western blot assays for Aurora A protein were done on tumor tissue of 53 patients. The results were correlated with various prognostic factors of neuroblastoma. Aurora A mRNA and protein expression were identified in 9 of 9 neuroblastoma cell lines. Overexpression of Aurora A mRNA in neuroblastoma tumor tissue is associated with high risk (P = 0.019), high-stage (International Neuroblastoma Staging System III and IV) tumors (P = 0.007), unfavorable histology (P = 0.007), MYCN amplification (P = 0.017), disease relapse (P = 0.019), and decreased progression-free survival (P < 0.0001) but not correlated with the age at diagnosis (P = 0.877). Similarly, Aurora A protein expression also significantly correlated with high risk (P = 0.011), high stage (P = 0.0028), unfavorable histology (P = 0.0006), MYCN amplification (P = 0.0029), and disease relapse (P = 0.044). Small interfering RNA-mediated knockdown of the endogenous Aurora A gene causes a proliferation defect and enhances chemosensitivity in human neuroblastoma cell lines. In support of these observations, the Aurora A kinase inhibitor, MLN8054, markedly inhibited growth of cultured neuroblastoma cell lines through an apoptosis-dependent pathway. Overexpression of Aurora A is associated with disease progression in neuroblastoma. Inhibition of this kinase is a promising modality for neuroblastoma treatment.

The emerging molecular pathogenesis of neuroblastoma: implications for improved risk assessment and targeted therapy

Neuroblastoma is one of the most common solid tumors of childhood, arising from immature sympathetic nervous system cells. The clinical course of patients with neuroblastoma is highly variable, ranging from spontaneous regression to widespread metastatic disease. Although the outcome for children with cancer has improved considerably during the past decades, the prognosis of children with aggressive neuroblastoma remains dismal. The clinical heterogeneity of neuroblastoma mirrors the biological and genetic heterogeneity of these tumors. Ploidy and MYCN amplification have been used as genetic markers for risk stratification and therapeutic decision making, and, more recently, gene expression profiling and genome-wide DNA copy number analysis have come into the picture as sensitive and specific tools for assessing prognosis. The applica tion of new genetic tools also led to the discovery of an important familial neuroblastoma cancer gene, ALK, which is mutated in approximately 8% of sporadic tumors, and genome-wide association studies have unveiled loci with risk alleles for neuroblastoma development. For some of the genomic regions that are deleted in some neuroblastomas, on 1p, 3p and 11q, candidate tumor suppressor genes have been identified. In addition, evidence has emerged for the contribution of epigenetic disturbances in neuroblastoma oncogenesis. As in other cancer entities, altered microRNA expression is also being recognized as an important player in neuroblastoma. The recent successes in unraveling the genetic basis of neuroblastoma are now opening opportunities for development of targeted therapies.

When the genome plays dice: circumvention of the spindle assembly checkpoint and near-random chromosome segregation in multipolar cancer cell mitoses

Background

Normal cell division is coordinated by a bipolar mitotic spindle, ensuring symmetrical segregation of chromosomes. Cancer cells, however, occasionally divide into three or more directions. Such multipolar mitoses have been proposed to generate genetic diversity and thereby contribute to clonal evolution. However, this notion has been little validated experimentally.

Principal Findings

Chromosome segregation and DNA content in daughter cells from multipolar mitoses were assessed by multiphoton cross sectioning and fluorescence in situ hybridization in cancer cells and non-neoplastic transformed cells. The DNA distribution resulting from multipolar cell division was found to be highly variable, with frequent nullisomies in the daughter cells. Time-lapse imaging of H2B/GFP-labelled multipolar mitoses revealed that the time from the initiation of metaphase to the beginning of anaphase was prolonged and that the metaphase plates often switched polarity several times before metaphase-anaphase transition. The multipolar metaphase-anaphase transition was accompanied by a normal reduction of cellular cyclin B levels, but typically occurred before completion of the normal separase activity cycle. Centromeric AURKB and MAD2 foci were observed frequently to remain on the centromeres of multipolar ana-telophase chromosomes, indicating that multipolar mitoses were able to circumvent the spindle assembly checkpoint with some sister chromatids remaining unseparated after anaphase. Accordingly, scoring the distribution of individual chromosomes in multipolar daughter nuclei revealed a high frequency of nondisjunction events, resulting in a near-binomial allotment of sister chromatids to the daughter cells.

Conclusion

The capability of multipolar mitoses to circumvent the spindle assembly checkpoint system typically results in a near-random distribution of chromosomes to daughter cells. Spindle multipolarity could thus be a highly efficient generator of genetically diverse minority clones in transformed cell populations.

Heterogeneous subgroups in human neuroblastoma for clinically relevant risk stratification

Neuroblastoma is a heterogeneous tumor and that may have a favorable or unfavorable prognosis. In Japan, a nation-wide neuroblastoma mass-screening (MS) project assessed 6-month-old infants between 1985 and 2003, and almost all neuroblastomas, including regressing or maturing tumors were thought to be detected in this period. To evaluate the heterogeneity of neuroblastoma subgroups, we analyzed patients with neuroblastoma who had been diagnosed during this period. The clinical courses of 4,209 patients with neuroblastoma, including 1,560 MS detected patients, whose tumors had been diagnosed between 1971 and 1995 were registered. The 2,520 cases registered between 1985 and 1995 were compared to 1,050 cases registered between 1971 and 1980 and analyzed by a multi-gene target model to determine the age distribution of neuroblastoma incidence. We hypothesized that three target genes were responsible for the progression of neuroblastoma: one pair of tumor suppressor gene alleles, one oncogene, and one gene controlling regression/differentiation. This simulation study revealed that the age distribution at initial diagnosis of neuroblastoma was divided into four groups based on post-fertilization age: 20-40, 40-50, 60-90, and 160-200 weeks. Since neuroblatoma in the first group occurred prenatal, post-natal clinical neuroblastoma can be classified into three age groups: 0-6 months, 1-2 years, and 3-4 years. The 0- to 6-month group consisted of mostly benign tumors, and the two older groups had predominantly malignant phenotypes. Our proposed model could explain qualitatively the distribution of neuroblastoma consisting of one subgroup with a favorable prognosis and two subgroups with unfavorable prognosis. For clinically relevant risk stratification, an age cutoff should be considered by the age distribution of these heterogeneous subgroups.

Distinct evolutionary mechanisms for genomic imbalances in high-risk and low-risk neuroblastomas

BACKGROUND

Neuroblastoma (NB) is the most common extracranial solid tumour of childhood. Several genomic imbalances correlate to prognosis in NB, with structural rearrangements, including gene amplification, in a near-diploid setting typically signifying high-risk tumours and numerical changes in a near-triploid setting signifying low-risk tumours. Little is known about the temporal sequence in which these imbalances occur during the carcinogenic process.

METHODS

We have reconstructed the appearance of cytogenetic imbalances in 270 NBs by first grouping tumours and imbalances through principal component analysis and then using the number of imbalances in each tumour as an indicator of evolutionary progression.

RESULTS

Tumours clustered in four sub-groups, dominated respectively by (1) gene amplification in double minute chromosomes and few other aberrations, (2) gene amplification and loss of 1p sequences, (3) loss of 1p and other structural aberrations including gain of 17q, and (4) whole-chromosome gains and losses. Temporal analysis showed that the structural changes in groups 1-3 were acquired in a step-wise fashion, with loss of 1p sequences and the emergence of double minute chromosomes as the earliest cytogenetic events. In contrast, the gains and losses of whole chromosomes in group 4 occurred through multiple simultaneous events leading to a near-triploid chromosome number.

CONCLUSION

The finding of different temporal patterns for the acquisition of genomic imbalances in high-risk and low-risk NBs lends strong support to the hypothesis that these tumours are biologically diverse entities, evolving through distinct genetic mechanisms.

Comprehensive analysis of tumoral DNA content reveals clonal ploidy heterogeneity as a marker with prognostic significance in locoregional neuroblastoma

The clinical management of locoregional neuroblastoma (LR NB) is controversial. In a previous study we showed that diploidy was a strong prognostic predictor of outcome and detected the existence of clonal ploidy heterogeneity in a select group of cases. The aims of this study were (1) to assess the frequency of ploidy heterogeneity in LR NB, (2) to ascertain the best method to detect heteterogeneity, and (3) to correlate ploidy populations with clinical outcome. We undertook a comprehensive analysis of tumoral DNA content in 38 LR NBs comparing (1) flow cytometry (FCM), (2) karyotyping, (3) interphase fluorescence in situ hybridization, and (4) laser-scanning cytometry (LSC). Tumor ploidy heterogeneity was found by all methodologies. By FCM, all tumors with aneuploid peaks had detectable diploid DNA peaks. By LSC, all tumors with diploid and hyperploid peaks were GD2-positive in both, consistent with their tumoral origin. A predominant near-triploid clonal population (ratio diploid vs. triploid, <2.5) was observed in most nonprogressing LR NB tumors, and a predominant diploid clone (ratio di- vs. triploid, >2.5) in most progressing LR NB cases. Multivariate analysis was performed to evaluate the prognostic value of tumor ploidy assayed by different methods versus age, INSS (International Neuroblastoma Staging System) stage, and MYCN status. FCM was the most powerful prognostic factor related to poor prognosis (overall survival, P = 0.02; progression-free survival, P = 0.01). These results provide strong evidence for clonal ploidy heterogeneity in LR NB and clonal evolution toward diploidy in progressing LR NB.

DRAQ5: improved flow cytometric DNA content analysis and minimal residual disease detection in childhood malignancies

BACKGROUND

The majority of flow cytometric DNA content analyses are performed on whole peripheral blood, bone marrow or tumor samples containing significant numbers of non-malignant cells which hamper specific DNA content analysis. Simultaneous analysis of DNA content and immunophenotype greatly improves the specificity of DNA-ploidy measurements. Therefore, a three-color flow cytometric assay using DRAQ5 was developed and validated.

METHODS

The results of DNA content analysis using DRAQ5 and propidium iodide were compared using peripheral blood samples of 15 healthy volunteers. The reproducibility of the multiparameter DRAQ5 assay was assayed in 10 analytical runs and the sensitivity was evaluated with addition experiments.

RESULT

Using DRAQ5, slightly wider CVs of the G0/G1 peak were obtained (average CV=3.29%). When DRAQ5 staining and immunophenotyping were combined, the within- and between-run imprecision was 1.98% and 1.67%, respectively and the DNA content of 25 DNA-hyperdiploid tumor cells (DNA-index=1.16) per 4.10(4) mononuclear cells (0.06%) could be determined.

CONCLUSIONS

The multiparameter DRAQ5 assay has a superior sensitivity and specificity compared to the propidium iodide based method. Since at least 25 DNA-hyperdiploid cells per 10(4) DNA-diploid mononuclear cells could be detected, multiparameter DRAQ5 DNA content analysis could be used to study minimal residual disease.

Favorable outcome of triploid neuroblastomas: a contribution to the special oncogenesis of neuroblastoma

There is a well-known association between patient outcome and tumor ploidy in neuroblastoma. To date, however, most clinical trials have not used this parameter for therapy stratification. Using conventional cytogenetics and fluorescence in situ hybridization (FISH), we investigated 36 tumors in terms of ploidy and chromosome 1 copy number (polysomy). In addition, interphase FISH for polysomy was performed on a second cohort of 440 neuroblastomas, together with the status of 1p, MYCN, and 11q. The main goals were as follows: (1) to assess the reliability of FISH to determine ploidy; (2) to illustrate associations between somy 1 and clinical/biologic factors; and (3) to investigate the role of somy 1 for predicting outcome. The comparison between karyotyping and FISH in the smaller cohort revealed 86% consistency between ploidy and polysomy (31/36). According to FISH, trisomic tumors in the second cohort showed structural chromosomal aberrations less frequently compared to di-/tetrasomic tumors (15 vs. 60%, P < 0.001). The portion of trisomic neuroblastomas was higher in stages 1, 2, and 4S versus stages 3 and 4 (55 vs. 24%, P < 0.001) and in children 18 months or younger versus those older than 18 months (55 vs. 19%, P < 0.001). Prognosis was significantly better for trisomic tumors versus di-/tetrasomic in the whole cohort [event-free (EFS) and overall survival (OS), P < 0.001]. In the subgroup without abnormalities of other molecular markers, EFS of trisomic neuroblastomas was better (P = 0.048), but was most likely due to an unequal stage distribution. In further subgroups, in terms of age and stage, significance between the somy groups was not reached, neither for EFS nor OS. The multivariate analyses including age, stage, chromosomal markers, and somy 1 confirmed the lack of independent prognostic power for the copy number of chromosome 1. This study demonstrates the following: (1) FISH is a practical alternative to other more labor-intensive techniques for determining ploidy; (2) trisomic tumors correlate with younger age at diagnosis, localized stage, and the lack of structural alterations; and (3) polysomy is not an independent prognostic marker. The sharp decline of trisomic tumors after the age of 18 months supports the idea of different genetic tumor entities.

Biology of neuroblastomas that were found by mass screening at 6 months of age in Japan

BACKGROUND

Mass screening (MS) of neuroblastoma has been carried out by measuring the urinary catecholamine metabolites in infants at the age of 6 months in Japan. We assessed the incidence of neuroblastoma that may be a target for MS by studying tumor biology.

PROCEDURE

FISH on chromosome 1 and MYCN analysis was performed on 453 patients that were classified into three clinical groups (287 infants found by MS, 51 infants < 12 months diagnosed clinically, and 115 children >or=12 months diagnosed clinically). The relationship between the biological types of tumors and the clinical outcome was examined.

RESULTS

Type 1 (trisomy 1 and normal MYCN), type 2 (disomy 1/tetrasomy 1 and normal MYCN), and type 3 (disomy 1/tetrasomy 1 and amplified MYCN) tumors were found in 88.2%, 10.5%, and 1.4% of infants found by MS, in 68.0%, 24.0%, and 8.0% of infants diagnosed clinically, and in 23.4%, 42.3%, and 34.2% of children diagnosed clinically (P < 0.001). Infants with type 1 tumors found by MS or diagnosed clinically had earlier stages of the disease (P < 0.0001 and P = 0.0005) and better overall survival (P < 0.001 and P = 0.005) than children with type 1 tumors diagnosed clinically. Infants with type 2 tumors found by MS, had earlier stages (P = 0.06 and P < 0.0001) and better overall survival (P = 0.014 and P < 0.001) than infants or children with type 2 tumors diagnosed clinically. All three clinical groups of patients with type 3 tumors had advanced stages and dismal prognoses.

CONCLUSIONS

About 12% of tumors found by MS showed unfavorable biological (types 2 and 3) characteristics.

Chromosome nondisjunction yields tetraploid rather than aneuploid cells in human cell lines

Although mutations in cell cycle regulators or spindle proteins can perturb chromosome segregation, the causes and consequences of spontaneous mitotic chromosome nondisjunction in human cells are not well understood. It has been assumed that nondisjunction of a chromosome during mitosis will yield two aneuploid daughter cells. Here we show that chromosome nondisjunction is tightly coupled to regulation of cytokinesis in human cell lines, such that nondisjunction results in the formation of tetraploid rather than aneuploid cells. We observed that spontaneously arising binucleated cells exhibited chromosome mis-segregation rates up to 166-fold higher than the overall mitotic population. Long-term imaging experiments indicated that most binucleated cells arose through a bipolar mitosis followed by regression of the cleavage furrow hours later. Nondisjunction occurred with high frequency in cells that became binucleated by furrow regression, but not in cells that completed cytokinesis to form two mononucleated cells. Our findings indicate that nondisjunction does not directly yield aneuploid cells, but rather tetraploid cells that may subsequently become aneuploid through further division. The coupling of spontaneous segregation errors to furrow regression provides a potential explanation for the prevalence of hyperdiploid chromosome number and centrosome amplification observed in many cancers.

Inferring a tumor progression model for neuroblastoma from genomic data

PURPOSE

The knowledge of the key genomic events that are causal to cancer development and progression not only is invaluable for our understanding of cancer biology but also may have a direct clinical impact. The task of deciphering a model of tumor progression by requiring that it explains (or at least does not contradict) known clinical and molecular evidence can be very demanding, particularly for cancers with complex patterns of clinical and molecular evidence.

MATERIALS AND METHODS

We formalize the process of model inference and show how a progression model for neuroblastoma (NB) can be inferred from genomic data. The core idea of our method is to translate the model of clonal cancer evolution to mathematical testable rules of inheritance. Seventy-eight NB samples in stages 1, 4S, and 4 were analyzed with array-based comparative genomic hybridization.

RESULTS

The pattern of recurrent genomic alterations in NB is strongly stage dependent and it is possible to identify traces of tumor progression in this type of data.

CONCLUSION

A tumor progression model for neuroblastoma is inferred, which is in agreement with clinical evidence, explains part of the heterogeneity of the clinical behavior observed for NB, and is compatible with existing empirical models of NB progression.

Mutant KRAS, chromosomal instability and prognosis in colorectal cancer

The RAS gene family provides a global effect on gene expression by encoding small GTP-binding proteins which act as molecular switches connecting extracellular signals with nuclear transcription factors. While wild type RAS proteins are switched off shortly after activation, mutant RAS proteins remain constitutively activated leading to complex interactions among their downstream effectors. For some human tumor types, these interactions were shown to contribute to cancer genesis and progression by inducing changes in cell survival, apoptosis, angiogenesis, invasion and metastasis. This review addresses the controversial link of KRAS mutations in colorectal cancer with chromosomal instability and patient prognosis.

Gene profiling of high risk neuroblastoma

Neuroblastoma, a cancer of young children, is well known for its diverse pattern of presentation. Approximately one-half of children have localized tumors that can be cured with surgery alone. The remaining children have widespread metastatic disease or quite large, aggressive, localized tumors. These children have a poor long-term survival rate of approximately 30%. We review the prognostically significant histologic and molecular features of high risk neuroblastoma and propose an algorithm to dissect further the differentially expressed genes that define the phenotype of this disease. Over the past 25 years, much effort has gone into establishing reliable prognostic indicators of high risk disease. For neuroblastoma, age, stage, and histopathology have time and again correlated well with outcomes. Chromosomal number, or ploidy, and amplification of the MYCN oncogene have proved to be equally as important and are commonly used to stratify patient risk. Other potentially lucrative markers include chromosome 1p deletion, chromosome 17q gain, receptor tyrosine kinases A and B (trk-A, trk-B), CD44, CXCR4, and multidrug resistance associated protein (MRP). With the onset of new technology, expression microarrays are now being used to profile advanced-stage neuroblastoma on a larger scale. Genes particular to cell cycle control, DNA/RNA replication, ribosomal synthesis, neuronal differentiation, and intracellular/extracellular signal transduction have been identified through differential expression analysis. We present our research on the MYCN transcription factor and target gene, MCM7, to show the utility of this approach.

Multiple numerical chromosome aberrations in cancer: what are their causes and what are their consequences?

Several neoplastic tumor types are cytogenetically characterized by multiple numerical chromosome abnormalities without concomitant structural karyotypic changes. At present, no good gene-level theories are at hand to explain the pathogenetic effect of these changes during tumorigenesis, nor is it known how they arise or what causes them. Genetic instability is often invoked as an underlying cause, but actual data favoring this explanation are meager or non-existing. Numerical chromosome changes and ploidy shifts allow the simultaneous alteration of multiple cancer-relevant genes, thereby reducing the number of independent genomic events necessary for carcinogenesis and the need for postulating genomic instability as a necessity in cancer development.

The biologic basis for neuroblastoma heterogeneity and risk stratification

PURPOSE OF REVIEW

Neuroblastoma serves as the paradigm for the clinical utility of tumor-specific biologic data for prognostication. This review will describe the genetic and biologic basis for the diverse clinical phenotypes observed in neuroblastoma patients. It will also discuss the current approach to risk classification and how this may change in the future.

RECENT FINDINGS

The biologic basis of neuroblastoma has come into clearer focus. PHOX2B is the first bona fide neuroblastoma predisposition gene identified, but is mutated in only a small subset of cases. Somatically acquired alterations at chromosome arms 3p and 11q are highly correlated with acquisition of metastases in the absence of MYCN amplification and may be useful as prognostic markers. The Children's Oncology Group risk classification system has been validated, with current emphasis on further refinement such as reevaluation of the age cutoff used to stratify therapy, and incorporation of additional molecular genetic markers is being studied prospectively. High-throughput genome scale analyses of neuroblastomas are further clarifying the genetic basis of this heterogeneous disease.

SUMMARY

Neuroblastoma remains a significant challenge as high-risk patients are treated with intensive multimodal therapies but cure rates remain suboptimal. There is remarkable heterogeneity observed in tumor phenotype, ranging from spontaneous regression to relentless progression. There are literally dozens of clinical and biologic markers that have been proposed as being predictive of disease outcome, but large clinical correlative studies are sharpening the focus of which markers can be used by the clinician to optimize therapy for an individual patient.

Characterization of karyotypic events and evolution in neuroblastoma

BACKGROUND

Neuroblastoma (NB) is cytogenetically characterized by a number of non-random events. However, knowledge is limited concerning the timing of occurrence and inter-action of many of these events.

METHODS

Karyotypic patterns were obtained from a study group of 49 NB tumors that had been analyzed by conventional cytogenetics combined with FISH and in some instances SKY.

RESULTS

All chromosomes were involved in a numerical and structural aberration in at least one tumor. There was a positive correlation between the occurrence of MYCN and del(1p) and between del(1p) and 17q. Aberrations involving chromosomes X, 3, 19, and del(1p) could be considered early events, whereas those involving chromosomes 9, 13, 15, 18, 20, and 21 were often late events.

CONCLUSIONS

This study suggests that the karyotypic patterns characterizing NB are complex. There are aberrations that can be grouped into early or late karyotypic events, but others, such as gain of 17q, are variable.

Inverse correlation between genetic aberrations and malignancy grade in ependymal tumors: a paradox?

OBJECTIVE

The goal of our study was to investigate the inverse correlation between number of genetic aberrations and malignancy grade in ependymal tumors at the ploidy level.

METHODS

we examined seven myxopapillary ependymomas (mpEs) (WHO grade I), 28 spinal and cerebral ependymomas (Es) (WHO grade II), and 18 cerebral anaplastic ependymomas (aEs) (WHO grade III) using image DNA cytometry. The ploidy status was correlated with clinicopathological characteristics and with the results obtained by comparative genomic hybridization (CGH) analysis that we performed in about half of these tumors.

RESULTS

mpEs were exclusively located in the spinal cord and aEs in the cerebrum only, whereas Es were located in both the spinal cord and brain. We found aneuploidy or tetraploidy to be common in the group of mpEs (6 out of 7) and much less frequent in Es (6 out of 28) and aEs (4 out of 18). Three-year postoperative survival was 100% for mpEs, 100% for spinal Es, 92% for cerebral Es, and 33% for aEs. Our CGH results in a selection of these tumors revealed the highest number of genetic aberrations in the mpEs (average 16; n = 2), a lower number in Es (average 12; n = 11) and the lowest number in aEs (average 5; n = 6). Interestingly, in the group of Es and aEs, a high number of genetic aberrations as detected by CGH was not correlated with aneuploidy or tetraploidy. Three patients, all with mpEs had local seeding.

CONCLUSION

These results underline that mpEs are distinctly different from Es and aEs at the genetic level and that extensive genomic alterations and aneuploidy in ependymal tumors are not in itself an indicator of malignant behavior.

From polyploidy to aneuploidy, genome instability and cancer

Polyploidy is a frequent phenomenon in the eukaryotic world, but the biological properties of polyploid cells are not well understood. During evolution, polyploidy is thought to be an important mechanism that contributes to speciation. Polyploid, usually non-dividing, cells are formed during development in otherwise diploid organisms. A growing amount of evidence indicates that polyploid cells also arise during a variety of pathological conditions. Genetic instability in these cells might provide a route to aneuploidy and thereby contribute to the development of cancer.

Neural crest development and neuroblastoma: the genetic and biological link

Neuroblastoma is one of the most common pediatric solid tumors originating from the sympathoadrenal lineage of neural crest. The tumor shows extremely different clinical phenotypes such as spontaneous regression on one hand and aggressive growth on the other hand. The different biological behavior of neuroblastoma appears to be determined by the genetic abnormalities including amplification of MYCN oncogene, DNA ploidy and some allelic imbalances. However, the spontaneous regression of neuroblastoma mimics the programmed cell death normally occurring in developing sympathetic cells expressing both TrkA tyrosine kinase A and p75NTR neurotrophin receptor. Indeed, TrkA expression is the most important factor related to the induction of tumor cell differentiation and/or programmed cell death because without its expression spontaneous regression of neuroblastoma never occurs. Thus, the enigmatic clinical behaviors of neuroblastoma are strictly linked to the molecular mechanism of neural crest development.

Cytogenetic heterogeneity and progression of esophageal squamous cell carcinoma

It is widely believed that most human tumors, including esophageal squamous cell carcinoma (ESCC), arise through multistep genetic and cytogenetic alterations. The time sequence of these alterations, however, is still unknown. The present study was designed to differentiate common early changes from uncommon later ones with combined comparative genomic hybridization (CGH) and ploidy analyses in multiple or single samples of 12 ESCCs. We first demonstrated that the mean copy numbers of chromosomes 3 and 11, determined directly by fluorescence in situ hybridization, showed linear correlation with the mean copy numbers calculated from the G/R ratio of CGH and DNA ploidy (R(2)=0.714, P<0.0001). On this basis, we estimated the absolute copy numbers of chromosomal parts by applying the ploidy-dependent threshold criteria to the G/R ratio data after the criteria were corrected by the percentage of tumor cells in each sample. One-copy changes in the DNA-diploid stage may give large shifts of the G/R ratio, even after tetraploidization, whereas those after tetraploidization undergo small shift. Using the tumors with multiple samples, it was actually demonstrated that most of the gains common to the samples in individual tumors showed the large shifts. Though early changes varied from tumor to tumor in the nine informative cases, it was found that gains of 3q (5/7: number of cases with large-shift 3q+/total number of cases with 3q+), 8q (3/4), 11q13 (4/5), and 14q (3/4) were early events, while losses of 3p (2/8), 5q (1/5), 13q (1/5), and 21q (1/5), and gains of 1p (1/4) and Xq (1/4) were later events in progression of individual tumors.

FISH analyses for alterations in chromosomes 1, 2, 3, and 11 define high-risk groups in neuroblastoma

BACKGROUND

The prognostic chromosomal markers 1p loss and MYCN amplification (MNA) are only present in a subgroup of approximately 30% of neuroblastomas. To further characterize high and low risk subsets we investigated alterations in chromosome arms 3p and 11q, additional changes in 1p and MYCN as well as the somy-status of chromosome 1 in the same sample.

PROCEDURE

Fluorescence in situ hybridization (FISH) was used as an alternative technique to PCR/LOH- or comparative genomic hybridization (CGH) analyses. Alterations in chromosomes 3p and 11q were investigated in 182 unselected tumors, 1p loss and MNA in 174 and 179 of these, respectively. The somy-status of chromosome 1 was determined in 165 tumors as it highly correlates with the tumor ploidy.

RESULTS

Alterations in the four chromosomal regions were found in the following frequencies: 3p26: 19%, 11q23: 29%, 1p36: 29%, MNA: 19%. Fifty-two percent of all cases displayed structural aberrations in at least one chromosomal region, 83% in stage 4 and 30% in stages 1-3, 4s. All aberrations were thus correlated with stage 4 disease but were also present in a substantial subset of localized and 4s tumors. Trisomy of chromosome 1 was found in 38% of the tumors, disomy or tetrasomy in 62%. Patients with alterations in any of the four chromosomes and di/tetrasomy 1 showed a significantly increased age at diagnosis. Loss in 1p and MNA were closely associated with each other, as well as 3p and 11q aberrations but not the groups 1p/MNA versus 3p/11q. Only a small portion of trisomic tumors showed aberrations in at least one of the four chromosomal regions (14%) in contrast to the majority of the di/tetrasomic cases (74%). As already known the MYCN status discriminated between good and poor outcome in localized and metastatic stage 4 tumors. In addition alterations in 1p or 11q, deletion in 3p and di/tetrasomy 1 were associated with an unfavorable prognosis in MYCN single copy tumors of stages 1-3, 4s. Multivariate analysis revealed 11q alterations and MNA as the most important chromosomal prognostic factors in all stages.

CONCLUSION

FISH analyses for chromosomal alterations in 3p and 11q as well as in 1p and MYCN allows to define different groups with an increased risk for disease progression.

Neuroblastoma: biological insights into a clinical enigma

Neuroblastoma is a tumour derived from primitive cells of the sympathetic nervous system and is the most common solid tumour in childhood. Interestingly, most infants experience complete regression of their disease with minimal therapy, even with metastatic disease. However, older patients frequently have metastatic disease that grows relentlessly, despite even the most intensive multimodality therapy. Recent advances in understanding the biology and genetics of neuroblastomas have allowed classification into low-, intermediate- and high-risk groups. This allows the most appropriate intensity of therapy to be selected - from observation alone to aggressive, multimodality therapy. Future therapies will focus increasingly on the genes and biological pathways that contribute to malignant transformation or progression.

Chromosomes that show partial loss or gain in near-diploid tumors coincide with chromosomes that show whole loss or gain in near-triploid tumors: evidence suggesting the involvement of the same genes in the tumorigenesis of high- and low-risk neuroblastomas

We performed two-color fluorescence in situ hybridization analysis to detect the numbers of chromosomes 1 and 17, 1p deletion, and 17q gain in 177 neuroblastomas, including 101 tumors that were found by a mass-screening program for infants. Sixty-eight tumors with disomy 1 or tetrasomy 1 were classified as the Dis1 group, and 109 tumors with trisomy 1, pentasomy 1, or a mixed population of cells with trisomy 1 and cells with tetrasomy 1 were classified as the Tris1 group. 17q gain was the most frequent genetic event, followed by 1p deletion, and MYCN amplification in both Dis1 and Tris1 tumors. However, the incidence of all the genetic events was higher in Dis1 tumors than in Tris1 tumors. These findings suggest that Tris1 tumors are more resistant to acquiring the genetic events than are Dis1 tumors. In addition, there was an accumulation of genetic events in more advanced stages, with the exception of a high incidence of 17q gain in the stage IVS Tris1 tumors. Comparative genomic hybridization analysis, which was performed in 59 of the 177 tumors, showed that chromosomes partially lost or gained in Dis1 tumors coincided with chromosomes totally lost or gained in Tris1 tumors. Dis1 and Tris1 tumors were considered to have near-diploid/tetraploid and near-triploid/pentaploid chromosome numbers, respectively. These findings suggest that the same tumor-suppressor genes or oncogenes may be involved in the development and progression of both high- and low-risk neuroblastomas, and that the ploidy state of the tumor plays a fundamental role in the heterogeneous behavior.

Genetic parameters of neuroblastomas

Neuroblastoma is a malignant childhood tumor of migrating neuroectodermal cells derived from the neural crest and destined for the adrenal medulla and the sympathetic nervous system. The biological behavior of neuroblastomas is extremely variable and in some respects unique. Neuroblastomas tend to regress spontaneously in a portion of infants or to differentiate into a benign ganglioneuroma in some older patients. Unfortunately, in the majority of patients neuroblastoma is metastatic at the time of diagnosis, and it usually undergoes rapid progression with a fatal outcome. The mechanisms leading to this diverse clinical behavior of neuroblastomas are largely unclear. From the analysis of tumors at the cytogenetic and molecular level non-random genetic changes have been identified, including ploidy changes, amplification of the oncogene MYCN, deletions of chromosome 1p, gains of chromosome arm 17q, and deletions of 11q as well as of other genomic regions that allow tumors to be classified into subsets with distinct biological features and clinical behavior. MYCN status is widely accepted for therapy stratification. Additional genetic parameters are currently under investigation to refine risk assessment, but so far the molecular monitoring tools for prediction of therapy response and disease outcome are still incomplete. This should lead to more risk-adapted therapies according to the clinical-genetic parameters by which individual tumors are characterized. This review aims at discussing the role of genomic changes in neuroblastomas of diverse biological and clinical types.

Interphase fluorescence in situ hybridization detection of chromosome 17 and 17q region gains in neuroblastoma: are they secondary events?

Gains of chromosome 17 and 17q region are the most frequent chromosomal abnormalities in neuroblastoma and have been associated with established prognostic indicators. Interphase fluorescence in situ hybridization (FISH) was used to define the status of chromosome 17 in near-triploid (3n) and near-diploid/tetraploid (2n/4n) primary tumors. Gains of chromosome 17 and 17q were detected in 22 and 26 tumors, respectively, in which the ploidy status was determined mainly by the copy number of chromosome 1. Four different types of gains were detected: gain of whole chromosome 17 (+17) and three partial gains (17q11.2 approximately qter, 17q21.1 approximately qter, and 17q21.3 approximately qter). The 17q11.2 approximately qter gains were found in both the 2n/4n and the 3n tumors. Gains of 17q21.1 approximately qter and 17q21.3 approximately qter were found only in the 2n/4n group, and the latter was involved always as a der(22)t(17;22)(q21;q13). A high association was found between chromosome 17 gains and 3n ploidy: +17 was detected in 93% of the 3n group and was not observed in the 2n/4n group. The +17 clone or clones were always present in combination with a clone with normal copies of chromosome 17 and, in the majority, with a +17q11.2 approximately qter clone. We conclude that interphase FISH is a sensitive method for detecting whole and partial chromosome 17 gains in neuroblastoma and can demonstrate the simultaneous presence of several clones with different status of chromosome 17 in 3n neuroblastomas. We suggest that chromosome 17 and 17q gains are not a primary event in the development of neuroblastoma.

Distinct cytogenetic pathways of advanced-stage neuroblastoma tumors, detected by spectral karyotyping

Molecular studies of advanced-stage neuroblastoma (NBL) have revealed a marked genetic heterogeneity. In addition to MYCN amplification and chromosome 1 short-arm deletions/translocations detected by conventional cytogenetics, application of fluorescence in situ hybridization has disclosed a high prevalence of 17q gain, whereas allelotyping and comparative genomic hybridization techniques also have revealed loss of 11q and of other chromosomal material. Using the recently developed technique of spectral karyotyping (SKY), we sought to refine the cytogenetic information, identify hidden recurrent structural chromosomal abnormalities, and compare them to the molecular findings. Thirteen samples of metaphase spreads from 11 patients with advanced-stage NBL were analyzed by SKY. Most of them were found to have complex karyotypes (more than three changes per metaphase) and complex unbalanced rearrangements. Recurrent aberrations leading to 17q gain, deletion of 1p, MYCN amplification, and loss of 11q appeared in 7, 4, 4, and 5 patients, respectively, in simple and complex karyotypes. Chromosome 3 changes and gain of 1q and 7q appeared in 6, 5, and 4 patients, respectively, in complex karyotypes only, reflecting later changes. A strikingly high prevalence of the unbalanced translocation der(11)t(11;17), leading to concomitant 11q loss and 17q gain in 4 patients, delineated a distinct cytogenetic group, none having 1p deletion and/or MYCN amplification. der(11)t(11;17) was associated with complex karyotypes with changes in chromosomes 3 and 7q. The 17q translocations with partners other than 11q were associated with 1p deletion and/or MYCN amplification. The distinct cytogenetic subgroups identified by SKY confirm and extend the recent molecular observations, and suggest that different genes may interact in the der(11)t(11;17) pathway of NBL development and progression.