MYCN gene overrepresentation detected in primary neuroblastoma tumour cells without amplification

Changes in MYCN expression in human neuroblastoma cell lines following cisplatin treatment may not be related to MYCN copy numbers

Neuroblastoma is a tumor accounting for approximately 10% of all childhood malignancies and 50% of all childhood cancer-related deaths. MYCN gene copy number variation represents the most important prognostic factor in neuroblastoma. Prognostic significance of MYCN gene expression is more complicated and may depend on other factors such as MYCN gene copy number status. In the present study, we assessed MYCN gene expression using real-time RT-PCR following cisplatin treatment in three human neuroblastoma cell lines (UKF-NB-3, UKF-NB-4 and SK-N-AS) and their cisplatin-resistant counterparts. We also examined MYCN gene status and copy number (gain and amplification) variations using interphase and metaphase fluorescent in situ hybridization (FISH) and multiplex ligation-dependent probe amplification (MLPA). Only cisplatin-sensitive UKF-NB-4 cells exhibited decreased MYCN expression following treatment with cisplatin. Other sensitive neuroblastoma cells did not exhibit a change in MYCN expression. In contrast, cisplatin-resistant UKF-NB-4 and SK-N-AS cells exhibited increased MYCN expression irrespective of the number of MYCN copies or concentration of cisplatin in the medium. In MYCN-amplified neuroblastoma cells we did not observe any significant change in the number of MYCN copies after cisplatin treatment, whereas MYCN-non-amplified SK-N-AS cells revealed during cisplatin treatment an increased number of MYCN gene copies caused by 2p gain in the majority of cells by FISH. We postulated that cisplatin treatment does not result directly in altered transcription of MYCN. A functional change in MYCN mRNA levels and increased MYCN expression in cisplatin-resistant neuroblastoma cells do not have a clear relationship to MYCN copy numbers. These findings may further contribute to the understanding of cisplatin chemotherapy in connection with MYCN expression, and the possible copy number variations in MYCN neuroblastoma cells may be of importance since targeting of MYCN is being tested as neuroblastoma therapy.

2p24 Gain region harboring MYCN gene compared with MYCN amplified and nonamplified neuroblastoma: biological and clinical characteristics

Although the role of MYCN amplification in neuroblastoma is well established, the biological and clinical characteristics of the 2p gain region harboring the MYCN gene remain unclear. The aim of this study was to compare the biological and clinical characteristics of these tumors with MYCN amplified and nonamplified neuroblastoma and to determine their impact on disease outcome. Samples from 177 patients were analyzed by fluorescence in situ hybridization, including MYCN, 1p, 17q, and 11q regions; 2p gain was identified in 25 patients, MYCN amplification in 31, and no amplification in 121 patients. Patients with 2p gain had a significantly worse 5-year event-free survival rate than patients with no MYCN amplified (P < 0.001), and an intermediate 5-year overall survival rate difference existed between the MYCN amplified tumors (P = 0.025) and nonamplified (P = 0.003) groups. All of the 2p gain samples were associated with segmental and/or numerical alterations in the other tested regions. The presence of segmental alterations with or without MYCN amplification was recently found to be the strongest predictor of relapse in a multivariate analysis. The results of the present study suggest that the determination of MYCN gene copy number relative to chromosome 2, when evaluating MYCN status at diagnosis, may help to reveal the underlying genetic pattern of these tumors and better understand their clinical behavior.

Molecular biology of neuroblastoma

Neuroblastoma is one of the most frequently occurring solid tumours in children, especially in the first year of life, when it accounts for 50% of all tumours. It is the second most common cause of death in children, only preceded by accidents. The most peculiar characteristic of neuroblastoma is its clinical heterogeneity. Approximately half of the cases are classified as high risk, with overall survival rates around 40% despite intensive multimodal therapy. Nevertheless, other subsets of neuroblastomas will undergo spontaneous regression and others will show very slow progression. Despite many advances in the past three decades, neuroblastoma has remained an enigmatic challenge to clinical and basic scientists. Elucidation of the exact molecular pathways of neuroblastoma will enable researchers and clinicians to stratify the disease and adapt therapy to the risk of relapse or progression. This review focuses on recent advances in our understanding of the biology of this complex paediatric tumour. Neuroblastoma is already one of the first examples for the use of tumoral genetic markers as a tool for defining tumour behaviour and to aid clinical staging.

Concomitant DDX1 and MYCN gain in neuroblastoma

DDX1, a gene mapping to the 2p24 region, has been observed to be co-amplified with MYCN in neuroblastoma. Co-amplification of the DDX1 gene is a consequence of the short physical distance between the two genes. Recently, it has been found that neuroblastoma cells can show a low increase in MYCN gene copy number, defined as MYCN gain. We studied 13 neuroblastomas with MYCN gain to evaluate the status of the DDX1 gene. We investigated DDX1/MYCN gain by double-colour FISH on interphase nuclei. All cases showed concomitant low extra copy number of DDX1 and MYCN. Heterogeneous distribution of nuclei displaying DDX1/MYCN gain was observed in almost all tumours, suggesting a clonal evolution of cells with DDX1/MYCN gain. This is the first report that shows DDX1 co-gained with MYCN in neuroblastoma and indicates that DDX1 over-representation is closely associated with an increase in MYCN copy number in neuroblastoma cells. Since DDX1 has already been found co-amplified with MYCN, DDX1 gain seems to be a further rearrangement due to the physical proximity of the two genes. Moreover, all patients with DDX1/MYCN gain show a good overall survival but a high frequency of adverse events.

Congenital neuroblastoma in a patient with partial trisomy of 2p

We report the fourth example of a patient with germline partial trisomy of 2p21-pter and congenital neuroblastoma. The male infant had a dysmorphic facial expression and presented with congenital heart disease, supernumerary nipples, hypospadias, shawl scrotum, hemilateral persistent hyperplastic primary vitreous, and neuroblastoma. His germline karyotype of 46,XY,der(8)t(2;8)(p21;p23.2) was inherited from a maternal-balanced translocation, which indicates that the proto-oncogene MYCN region of 2p24.3 is tripicated in germline cells. A cytogenetic study of the biopsied tumor cells did not show MYCN amplification, but the DNA index was 2.4 and histologic fluorescent in situ hybridization analysis indicated somatic mutation with near-pentaploidy of the tumor cells. This could be an alternative mechanism of MYCN activation in the process of the tumorigenesis of neuroblastoma.

Chromogenic in situ hybridization-detected hotspot MYCN amplification associates with Ki-67 expression and inversely with nestin expression in neuroblastomas

Since neuroblastomas are intratumorally heterogeneous, the analysis of genetic and biologic features of randomly selected tumor specimen spots may lead to erroneous conclusions. Our purpose was therefore to construct an easily assessable and strictly defined strategy to unify the detection of various molecular markers in paraffin-embedded neuroblastoma samples. We selected tumor specimen spots of highest proliferation activity, that is, hotspots, for the analysis of MYCN amplification status and proliferation-associated molecular markers, such as nestin, which role in neuroblastoma specimens was evaluated for the first time. Using a chromogenic in situ hybridization (CISH) technique, we showed that patients with a MYCN copy number higher than six in anti-Ki-67-detected hotspots have significantly worse overall survival prognosis than patients with low MYCN copy numbers (P = 0.0006). The chosen cutoff value of six was shown to dichotomize MYCN-amplified neuroblastomas at least as specifically as Southern blot hybridization, in which amplification was defined by a copy number of > or = 10. Interestingly, we also detected without difficulty MYCN-amplified neuroblastic cells in bone marrow samples using the CISH technique. The proliferation activity, assessed with an anti-Ki-67-based proliferation index, was significantly higher in MYCN-amplified than in nonamplified hotspots. The proliferation indices of the hotspots had also a significant correlation with the prognosis (International Classification) and histological type, whereas the proliferation accelerator Id2 did not associate with any of the mentioned parameters. The expression of nestin associated inversely with MYCN amplification (P = 0.018), which challenges a previously suggested role of nestin in neuroblastomas. In summary, hotspot focusing provides a means of analyzing proliferation-associated markers in neuroblastomas, and together with the CISH detection of the MYCN copy number enables an easy and reliable examination of MYCN status in neuroblastomas.

Oncogene amplification in the proximal part of chromosome 6 in rat endometrial adenocarcinoma as revealed by combined BAC/PAC FISH, chromosome painting, zoo-FISH, and allelotyping

The inbred BDII rat is a valuable experimental model for the genetic analysis of endometrial adenocarcinoma (EAC). One common aberration detected by comparative genomic hybridization in rat EAC was gain/amplification affecting the proximal part of rat chromosome 6 (RNO6). We applied rat and mouse chromosome painting probes onto tumor cell metaphase preparations in order to detect and characterize gross RNO6 aberrations. In addition, the RNO6q11-q16 segment was analyzed by fluorescence in situ hybridization with probes representing 12 cancer-related genes in the region. The analysis revealed that seven tumors contained large RNO6-derived homogeneously staining regions (HSRs) in addition to several normal or near-normal RNO6 chromosomes. Five tumors (two of which also had HSRs) exhibited a selective increase of the RNO6q11-q16 segment, sometimes in conjunction with moderate amplification of one or a few genes. Most commonly, the amplification affected the region centered around band 6q16 and included the Mycn, Ddx1, and Rrm2 genes. A second region, centering around Slc8a1 and Xdh, also was affected by gene amplification but to a lesser extent. The aberrations in the proximal part of RNO6 were further analyzed using allelotyping of microsatellite markers in all tumors from animals that were heterozygous in the proximal RNO6 region. We could detect allelic imbalance (AI) in 12 of 20 informative tumors, 6 of which were in addition to those already analyzed by molecular cytogenetic methods as described. Our findings suggest that increase/amplification of genes in this chromosome region contribute to the development of this hormone-dependent tumor.

Identification of MYCN Gene Amplification in Neuroblastoma Using Chromogenic In Situ Hybridization (CISH)

Chromogenic in situ hybridization (CISH) is a recently developed technique, which utilizes the general principles of in situ hybridization and a detection system similar to immunohistochemistry. To assess the utility of CISH for analysis of MYCN gene amplification, we compared this assay with established diagnostic assays such as Southern blot analysis (SB) and fluorescent in situ hybridization (FISH). CISH was performed on 67 cases of neuroblastoma using tissue microarray (65 cases) and whole tissue sections (2 cases). Unequivocal, high-level amplification (> or =10 gene copies per tumor nucleus) was identified in 19 of 67 (28.4%) tumors. Two (3%) tumors showed low-level amplification (6-9 gene copies per tumor nucleus). No amplification was seen in 46 of 67 (68.6%) tumors. SB data were available in 44 tumors. Forty-one of the 44 tumors (93%) showed concordant results between CISH and SB. Three tumors showed MYCN amplification by CISH but no amplification by SB, most likely due to dilution effect of nonneoplastic tissue in the test samples. Two of these three tumors also showed MYCN amplification by FISH, and the third tumor was not analyzed by FISH. FISH data were available in total of 30 tumors. All 30 tumors showed concordant results between CISH and FISH for classifying a tumor as MYCN amplified or not amplified. We conclude that CISH is an accurate method for determining MYCN gene amplification, with added advantages that make it a more practically useful method.

Relationship between MYCN copy number and expression in rhabdomyosarcomas and correlation with adverse prognosis in the alveolar subtype

PURPOSE

Amplification of the transcription factor MYCN is an important molecular diagnostic tool in stratifying treatment for neuroblastoma. Increased copy number and overexpression of MYCN in the pediatric cancer rhabdomyosarcoma has been described in a number of small studies with conflicting conclusions about its association with clinicopathologic characteristics. We aimed to study the phenomenon in the largest series to date.

PATIENTS AND METHODS

Using quantitative polymerase chain reaction, we measured MYCN copy number and expression levels in rhabdomyosarcoma samples from 113 and 92 individuals with a confirmed diagnosis of rhabdomyosarcoma, respectively.

RESULTS

Increased copy number of MYCN was found to be a feature of both the embryonal and alveolar subtypes. The copy number and expression levels were significantly greater in the alveolar subtype, although the range of expression in both subtypes spanned several orders of magnitude. MYCN copy number showed a significant correlation with expression in the alveolar subtype; this relationship between copy number and expression could be modeled as a logarithmic function. It is notable that relatively high expression frequently occurred in embryonal rhabdomyosarcoma without high copy number and that low expression was found in some cases with high copy number. In patients with alveolar rhabdomyosarcoma, overexpression (greater than median) or gain of genomic copies of MYCN were significantly associated with adverse outcome.

CONCLUSION

MYCN deregulation is a feature of rhabdomyosarcoma tumorigenesis, defines groups of patients with a poor prognosis, and is a potential target for novel therapies.

Evolution of unbalanced gain of distal chromosome 2p in neuroblastoma

Neuroblastoma, one of the most common tumors of childhood, presents at diagnosis with a vast number of recurrent chromosomal imbalances that include hyperdiploidy for whole chromosomes, partial loss of 1p, 3p, 4p, 11q, 14q, partial gain of 1q, 7q, 17q and amplification of MYCN. These abnormalities are nonrandomly distributed in neuroblastoma as loss of 3p and 11q rarely occur in MYCN amplified neuroblastomas. Here, we report on a patient who had a non-MYCN amplified 3p-/11q- neuroblastoma at diagnosis who subsequently developed a high level of MYCN amplification in bone marrow metastases 41 months after induction of complete remission. The tumor at diagnosis had low level unbalanced gain of distal 2p. In order to assess the frequency of low level gain of distal 2p in neuroblastoma, we examined the comparative genomic hybridization results from 60 neuroblastomas. Among non-MYCN amplified neuroblastomas, 8/45 (18%) had low level gain of distal 2p. Low level gain for a segment of 2p (i.e. a region larger than the 2p23-->p24 undergoing amplification) was also detected in five of the 15 tumors that had high level MYCN amplification. The possibility that low level gain of distal 2p is a risk factor for high level MYCN amplification is discussed.

MYCN-status in neuroblastoma: characteristics of tumours showing amplification, gain, and non-amplification

While the role of MYCN-amplification (MNA) for risk assessment in neuroblastoma is undisputed, the phenomenon of gene copy excess below the amplification threshold is rarely described. To discuss biological characteristics and the clinical impact of the so-called MYCN-gain versus amplified or non-amplified cases, we investigated the MYCN status of 659 patients uniformly analysed by fluorescence in situ hybridisation. The number of MYCN-amplified tumours in our cohort was 18% (116/659); an additional 38 tumours (6%) displayed MYCN-gain. Both alterations were associated with an advanced stage disease, an increased patient age and further chromosomal alterations. Most of the amplified neuroblastomas displayed 1p aberrations, whereas MYCN-gain tumours correlated with 11q alterations. In contrast to the amplified cases, tumours with gain displayed no increased MYCN RNA levels. MNA versus non-amplification discriminated between good and poor outcomes, independent of stage, age and the degree of amplification. However, patients with amplified tumours showed a significantly better outcome when this was combined with non-stage 4 disease and age <1 year versus stage 4 and age < 1 year. Although MYCN-gain was associated with poor event-free-survival (EFS) in stages 1-3, 4S (P=0.005), this might be related to associated genetic aberrations and not to the MYCN-gain itself. A survival difference between neuroblastomas with gain and single copy MYCN could not be delineated. In conclusion, MNA predicts a poor outcome for neuroblastoma patients of all stages and age. MYCN-gain is also a characteristic feature of advanced stage tumours and older patients, but is not associated with higher MYCN expression and appears not to be discriminative in predicting patient outcome.

Alternative pathways of MYCN gene copy number increase in primary neuroblastoma tumors

Neuroblastomas, tumors of the sympathetic nervous system, account for 7-10% of the cancers of childhood. Genetic studies have shown, and this study has confirmed, that neuroblastomas are very heterogeneous; no single genetic change common to all neuroblastomas has yet been identified. One genetic aberration found frequently in this pediatric tumor is MYCN gene amplification. Recently we identified a new subset of tumors showing MYCN gain (small increases in gene number arising from unbalanced translocation). To investigate whether gain precedes amplification or is an independent event, we surveyed 200 primary tumors for MYCN copy number with fluorescence in situ hybridization; 152 of 200 (76%) were MYCN single-copy tumors, whereas 48 of 200 (24%) tumors harbored MYCN abnormalities: 36 of the 48 (75%) had MYCN amplification and 12 (25%) had MYCN gain. Among the 36 with MYCN amplified gene, we found four that also showed gain. In three tumors exhibiting simultaneous gain and amplification, these two events were detected in neighboring cells. In the fourth case we detected only MYCN gain in metastatic neuroblasts in the bone marrow, but both MYCN amplification and gain in the primary tumor. The detailed study of these four cases suggests that there may be several different mechanisms leading to increase in MYCN copy number. Further studies in other human malignancies are necessary to determine whether simultaneous gain and amplification are specific to neuroblastoma or constitute a general mechanism by which tumor cells can acquire selective growth advantage.

Neuroblastoma: Management, recurrence, and follow-up

The clinical use of N-myc amplification in neuroblastoma management has served as a paradigm for "bench to bedside" medicine. It is hoped that the quest for molecular markers such as neurotrophin, TrkA, and TrkB will continue to advance the understanding of neuroblastoma. In addition, animal models of neuroblastoma (N-myc transgenic mice, and neuroblastoma xenografts) have been established to assess the efficacy of novel treatments. These advances are likely to improve clinical practice in the future.

Neuroblastoma: biology and molecular and chromosomal pathology

Neuroblastoma is the most frequently occurring solid tumour in children, with an incidence of 1.3 cases per 100000 children aged 0-14 years. Despite many advances during the past three decades, neuroblastoma has remained an enigmatic challenge to clinical and basic scientists. 20 years ago, the MYCN gene was found to be amplified in neuroblastomas, and research since then has focused on the search for other genetic markers. It has emerged that neuroblastoma cells, like cells of many other tumour types, often suffer from extensive, non-random genetic damage at multiple genetic loci. Elucidation of the exact molecular make-up of neuroblastomas will enable researchers to analyse how much specific markers, alone or in combination, can help to stratify disease in prospective studies; at present, stratification is based on age, stage, MYCN, and Shimada pathology. Neuroblastoma may be one of the first examples of the use of genetic tumour markers as a tool for defining tumour behaviour and to aid clinical staging.