Comparison of different techniques for the detection of genetic risk-identifying chromosomal gains and losses in neuroblastoma

The Detection of Genetic Parameters for Prognostic Stratification of Neuroblastoma Using Multiplex Ligation-Dependent Probe Amplification Technique

BACKGROUND

Neuroblastoma (NB) is a neoplasm of the sympathetic nervous system and the most frequent extra cranial solid tumor of early childhood. These tumors display a wide range of clinical behavior and are characterized by complex chromosomal changes, some of which are associated with distinct clinical phenotypes. We investigated the contribution of genetic variables to staging and histology by logistic regression analyses.

METHODS

We used multiplex ligation-dependent probe amplification (MLPA) to detect segmental genomic imbalances and gene copy number changes in 202 primary NBs.

RESULTS

Cases with NB were categorized into four distinct groups based on the genomic changes. Group 1 (48 cases, 23.7%) contained tumors with a 1p deletion and/or MYCN gene amplification (MNA). Group 2 included 46 cases (22.8%) with 3p and/or 11q deletions without 1p deletion and MYCN gene amplification. Tumors harboring at least two commonly observed deletions with or without MNA were classified as Group 3 (25 cases, 12.4%). Tumors with chromosomal imbalance other than MYCN gene amplification and 1p, 3p, and 11q deletions were in Group 4 (83 cases, 41.1%). MYCN gene amplification and 17q gain were significant predisposing factors for unfavorable histology. Significant correlations were detected between 1p deletion and MYCN gene amplification; 3p and 11q deletions; and 11q deletion and 17q gain.

CONCLUSION

MLPA can be used effectively to simultaneously detect multiple genomic imbalances and these changes can be utilized to classify neuroblastomas by prognostic subtypes. The genetic changes detected in NB in this study and their associations with clinical characteristics are in line with previously published reports.

Detection of MDM2/CDK4 amplification in lipomatous soft tissue tumors from formalin-fixed, paraffin-embedded tissue: comparison of multiplex ligation-dependent probe amplification (MLPA) and fluorescence in situ hybridization (FISH)

In this study, the detection of MDM2 and CDK4 amplification was evaluated in lipomatous soft tissue tumors using multiplex ligation-dependent probe amplification (MLPA), a PCR-based technique, in comparison with fluorescence in situ hybridization (FISH). These 2 techniques were evaluated in a series of 77 formalin-fixed, paraffin-embedded lipomatous tumors (27 benign adipose tumors, 28 atypical lipomatous tumors/well-differentiated liposarcomas, 18 dedifferentiated liposarcomas, and 4 pleomorphic liposarcomas). Using MLPA, with a cut-off ratio of >2, 36/71 samples (22 atypical lipomatous tumors/well-differentiated liposarcomas, and 14 dedifferentiated liposarcomas) showed MDM2 and CDK4 amplification. Using FISH as gold standard, MLPA showed a sensitivity of 90% (36/40) and a specificity of 100% (31/31) in detecting amplification of MDM2 and CDK4 in lipomatous soft tissue tumors. In case of high-level amplification (MDM2-CDK4/CEP12 ratio >5), concordance was 100%. Four cases of atypical lipomatous tumor/well-differentiated liposarcoma (4/26, 15%) with a low MDM2 and CDK4 amplification level (MDM2-CDK4/CEP12 ratio ranging between 2 and 2.5) detected by FISH showed no amplification by MLPA, although gain of MDM2 and CDK4 (ratios ranging between 1.6 and 1.9) was seen with MLPA. No amplification was detected in benign lipomatous tumors and pleomorphic liposarcomas. Furthermore, there was a very high concordance between the ratios obtained by FISH and MLPA. In conclusion, MLPA proves to be an appropriate and straightforward technique for screening MDM2/CDK4 amplification in lipomatous tumors, especially when a correct cut-off value and reference samples are chosen, and could be considered a good alternative to FISH to determine MDM2 and CDK4 amplification in liposarcomas. Moreover, because MLPA, as a multiplex technique, allows simultaneous detection of multiple chromosomal changes of interest, it could be in the future a very reliable and fast molecular analysis on paraffin-embedded material to test for other diagnostically, prognostically, or therapeutically relevant genomic mutations in lipomatous tumors.

Analysis of genomic alterations in neuroblastoma by multiplex ligation-dependent probe amplification and array comparative genomic hybridization: a comparison of results

In cases of neuroblastoma, recurring genetic alterations--losses of the 1p, 3p, 4p, and 11q and/or gains of 1q, 2p, and 17q chromosome arms--are currently used to define the therapeutic strategy in therapeutic protocols for low- and intermediate-risk patients. Different genome-wide analysis techniques, such as array comparative genomic hybridization (aCGH) or multiplex ligation-dependent probe amplification (MLPA), have been suggested for detecting chromosome segmental abnormalities. In this study, we compared the results of the two technologies in the analyses of the DNA of tumor samples from 91 neuroblastoma patients. Similar results were obtained with the two techniques for 75 samples (82%). In five cases (5.5%), the MLPA results were not interpretable. Discrepancies between the aCGH and MLPA results were observed in 11 cases (12%). Among the discrepancies, a 18q21.2-qter gain and 16p11.2 and 11q14.1-q14.3 losses were detected only by aCGH. The MLPA results showed that the 7p, 7q, and 14q chromosome arms were affected in six cases, while in two cases, 2p and 17q gains were observed; these results were confirmed by neither aCGH nor fluorescence in situ hybridization (FISH) analysis. Because of the higher sensitivity and specificity of genome-wide information, reasonable cost, and shorter time of aCGH analysis, we recommend the aCGH procedure for the analysis of genomic alterations in neuroblastoma.

Use of the MLPA assay in the molecular diagnosis of gene copy number alterations in human genetic diseases

Multiplex Ligation-dependent Probe Amplification (MLPA) assay is a recently developed technique able to evidence variations in the copy number of several human genes. Due to this ability, MLPA can be used in the molecular diagnosis of several genetic diseases whose pathogenesis is related to the presence of deletions or duplications of specific genes. Moreover, MLPA assay can also be used in the molecular diagnosis of genetic diseases characterized by the presence of abnormal DNA methylation. Due to the large number of genes that can be analyzed by a single technique, MLPA assay represents the gold standard for molecular analysis of all pathologies derived from the presence of gene copy number variation. In this review, the main applications of the MLPA technique for the molecular diagnosis of human diseases are described.

Genetic stratification of neuroblastoma for treatment tailoring

Neuroblastoma is the most common extracranial tumor of childhood. The clinical behavior is variable, ranging from spontaneous regression to fatal progression despite aggressive therapy. The most highly statistically significant and clinically relevant factors that are currently used for classification include stage, age, histopathologic category, MYCN oncogene status, chromosome 11q status and DNA ploidy. These genetic markers were analyzed separately by classical methods until recently: mainly fluorescence in situ hybridization or loss of heterozygosity. The development of genome-wide techniques such as comparative genomic hybridization, array comparative genomic hybridization and single nucleotide polymorphism allows the analysis of copy number variations through the whole genome in one step. This enabled the investigators to refine different genetic subtypes for the better comprehension of neuroblastoma tumor behavior and reach the conclusion that these data together with a genomic profile based on gene expression should be included in future treatment stratification.

Prognostic value of partial genetic instability in neuroblastoma with ≤50% neuroblastic cell content

AIMS

Better understanding of neuroblastoma genetics will improve with genome-wide techniques. However, performing these analyses in samples with <60% neuroblast cells is not adequate. We evaluated the utility of fluorescence in situ hybridization (FISH) on tissue microarrays (TMA) in detecting partial genetic instability (PGI), focusing on samples with ≤50% neuroblast cells.

METHODS AND RESULTS

Alterations of 11q and 17q were detected by FISH on 369 neuroblastoma samples in TMA. Status of the MYCN gene and 1p36 region has been established previously by FISH diagnosis. Partial genetic instability (PGI) was defined as the ratio between segmental genetic alterations detected and number of genetic markers diagnosed in each tumour. Of primary tumours, 14.6% harboured 11q deletions, whereas 42.6% showed 17q gain. PGI was established in 260 primary tumours, 67 of which contained ≤50% neuroblasts. Outcomes were statistically worse for patients whose tumours presented high PGI (P < 0.0001). Multivariate analysis revealed moderate and high PGI as prognostic factors.

CONCLUSIONS

In the cohort examined in this study, univariate and multivariate analysis confirmed the effect of PGI in patient outcome. PGI established by FISH on TMA is a useful method to identify high-risk patients even if tumours have a cell content of ≤50% neuroblast cells.

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.

Multiplex Amplicon Quantification (MAQ), a fast and efficient method for the simultaneous detection of copy number alterations in neuroblastoma

Background

Cancer genomes display characteristic patterns of chromosomal imbalances, often with diagnostic and prognostic relevance. Therefore assays for genome-wide copy number screening and simultaneous detection of copy number alterations in specific chromosomal regions are of increasing importance in the diagnostic work-up of tumors.

Results

We tested the performance of Multiplex Amplicon Quantification, a newly developed low-cost, closed-tube and high-throughput PCR-based technique for detection of copy number alterations in regions with prognostic relevance for neuroblastoma. Comparison with array CGH and the established Multiplex Ligation-dependent Probe Amplification method on 52 neuroblastoma tumors showed that Multiplex Amplicon Quantification can reliably detect the important genomic aberrations.

Conclusion

Multiplex Amplicon Quantification is a low-cost and high-throughput PCR-based technique that can reliably detect copy number alterations in regions with prognostic relevance for neuroblastoma.

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.

International consensus for neuroblastoma molecular diagnostics: report from the International Neuroblastoma Risk Group (INRG) Biology Committee

Neuroblastoma serves as a paradigm for utilising tumour genomic data for determining patient prognosis and treatment allocation. However, before the establishment of the International Neuroblastoma Risk Group (INRG) Task Force in 2004, international consensus on markers, methodology, and data interpretation did not exist, compromising the reliability of decisive genetic markers and inhibiting translational research efforts. The objectives of the INRG Biology Committee were to identify highly prognostic genetic aberrations to be included in the new INRG risk classification schema and to develop precise definitions, decisive biomarkers, and technique standardisation. The review of the INRG database (n=8800 patients) by the INRG Task Force finally enabled the identification of the most significant neuroblastoma biomarkers. In addition, the Biology Committee compared the standard operating procedures of different cooperative groups to arrive at international consensus for methodology, nomenclature, and future directions. Consensus was reached to include MYCN status, 11q23 allelic status, and ploidy in the INRG classification system on the basis of an evidence-based review of the INRG database. Standardised operating procedures for analysing these genetic factors were adopted, and criteria for proper nomenclature were developed. Neuroblastoma treatment planning is highly dependant on tumour cell genomic features, and it is likely that a comprehensive panel of DNA-based biomarkers will be used in future risk assignment algorithms applying genome-wide techniques. Consensus on methodology and interpretation is essential for uniform INRG classification and will greatly facilitate international and cooperative clinical and translational research studies.

Analysis of biological prognostic factors using tissue microarrays in neuroblastic tumors

BACKGROUND

Neuroblastic tumors (NT) are pediatric neoplasms with a heterogeneous genetic profile. They present genotypic alterations of prognostic value, the study of which is mandatory in designing therapeutic management. Tissue microarrays (TMA) from paraffin material allow the analysis of a large number of cases with minimal costs. The main purpose of the present study is to analyze specific genetic markers of neuroblastic tumors included in TMAs and determine their prognostic value. We compare the results obtained by different molecular techniques at different substrates to evaluate the feasibility of these assays.

PROCEDURE

One hundred thirty-nine samples were included in four different TMAs. We performed FISH assays to determine the status of MYCN gene, 1p36 region and 17q23 arm. The prognostic value of the genetic markers as well as the statistical correlation among clinical variables and outcome were analyzed by SPSS.

RESULTS

MYCN amplification was detected in 35.3% of the cases, whereas 1p36 deletion and 17q23 gain was observed in 46.8% and 58.3% of the cases, respectively. An adverse prognosis was noted among these patients. Other adverse factors were age (>18 months) as well as high stage of disease (stage 4). Phenotypic signs of differentiation correlated with good outcome.

CONCLUSION

Retrospective studies using paraffin-embedded tissues assembled in TMA are a useful tool for the analysis of prognostic factors in NT.