Cytogenetic findings in malignant peripheral nerve sheath tumors

Malignant peripheral nerve sheath tumor: models, biology, and translation

Malignant peripheral nerve sheath tumors (MPNSTs) are aggressive, invasive cancer that comprise around 10% of all soft tissue sarcomas and develop in about 8-13% of patients with Neurofibromatosis Type 1. They are associated with poor prognosis and are the leading cause of mortality in NF1 patients. MPNSTs can also develop sporadically or following exposure to radiation. There is currently no effective targeted therapy to treat MPNSTs and surgical removal remains the mainstay treatment. Unfortunately, surgery is not always possible due to the size and location of the tumor, thus, a better understanding of MPNST initiation and development is required to design novel therapeutics. Here, we provide an overview of MPNST biology and genetics, discuss findings regarding the developmental origin of MPNST, and summarize the various model systems employed to study MPNST. Finally, we discuss current management strategies for MPNST, as well as recent developments in translating basic research findings into potential therapies.

Establishment and genomic characterization of a sporadic malignant peripheral nerve sheath tumor cell line

Malignant peripheral nerve sheath tumors (MPNSTs) are aggressive Schwann cell-derived neoplasms that occur sporadically or in patients with neurofibromatosis type 1 (NF1). Preclinical research on sporadic MPNSTs has been limited as few cell lines exist. We generated and characterized a new sporadic MPNST cell line, 2XSB, which shares the molecular and genomic features of the parent tumor. These cells have a highly complex karyotype with extensive chromothripsis. 2XSB cells show robust invasive 3-dimensional and clonogenic culture capability and form solid tumors when xenografted into immunodeficient mice. High-density single nucleotide polymorphism array and whole exome sequencing analyses indicate that, unlike NF1-associated MPNSTs, 2XSB cells have intact, functional NF1 alleles with no evidence of mutations in genes encoding components of Polycomb Repressor Complex 2. However, mutations in other genes implicated in MPNST pathogenesis were identified in 2XSB cells including homozygous deletion of CDKN2A and mutations in TP53 and PTEN. We also identified mutations in genes not previously associated with MPNSTs but associated with the pathogenesis of other human cancers. These include DNMT1, NUMA1, NTRK1, PDE11A, CSMD3, LRP5 and ACTL9. This sporadic MPNST-derived cell line provides a useful tool for investigating the biology and potential treatment regimens for sporadic MPNSTs.

GTPases, genome, actin: A hidden story in DNA damage response and repair mechanisms

The classical small Rho GTPase (Rho, Rac, and Cdc42) protein family is mainly responsible for regulating cell motility and polarity, membrane trafficking, cell cycle control, and gene transcription. Cumulative recent evidence supports important roles for these proteins in the maintenance of genomic stability. Indeed, DNA damage response (DDR) and repair mechanisms are some of the prime biological processes that underlie several disease phenotypes, including genetic disorders, cancer, senescence, and premature aging. Many reports guided by different experimental approaches and molecular hypotheses have demonstrated that, to some extent, direct modulation of Rho GTPase activity, their downstream effectors, or actin cytoskeleton regulation contribute to these cellular events. Although much attention has been paid to this family in the context of canonical actin cytoskeleton remodeling, here we provide a contextualized review of the interplay between Rho GTPase signaling pathways and the DDR and DNA repair signaling components. Interesting questions yet to be addressed relate to the spatiotemporal dynamics of this collective response and whether it correlates with different subcellular pools of Rho GTPases. We highlight the direct and indirect targets, some of which still lack experimental validation data, likely associated with Rho GTPase activation that provides compelling evidence for further investigation in DNA damage-associated events and with potential therapeutic applications in translational medicine.

Recent Advances in the Diagnosis and Pathogenesis of Neurofibromatosis Type 1 (NF1)-associated Peripheral Nervous System Neoplasms

The diagnosis of a neurofibroma or a malignant peripheral nerve sheath tumor (MPNST) often raises the question of whether the patient has the genetic disorder neurofibromatosis type 1 (NF1) as well as how this will impact the patient's outcome, what their risk is for developing additional neoplasms and whether treatment options differ for NF1-associated and sporadic peripheral nerve sheath tumors. Establishing a diagnosis of NF1 is challenging as this disorder has numerous neoplastic and non-neoplastic manifestations which are variably present in individual patients. Further, other genetic diseases affecting the Ras signaling cascade (RASopathies) mimic many of the clinical features of NF1. Here, we review the clinical manifestations of NF1 and compare and contrast them with those of the RASopathies. We also consider current approaches to genetic testing for germline NF1 mutations. We then focus on NF1-associated neurofibromas, considering first the complicated clinical behavior and pathology of these neoplasms and then discussing our current understanding of the genomic abnormalities that drive their pathogenesis, including the mutations encountered in atypical neurofibromas. As several neurofibroma subtypes are capable of undergoing malignant transformation to become MPNSTs, we compare and contrast patient outcomes in sporadic, NF1-associated and radiation-induced MPNSTs, and review the challenging pathology of these lesions. The mutations involved in neurofibroma-MPNST progression, including the recent identification of mutations affecting epigenetic regulators, are then considered. Finally, we explore how our current understanding of neurofibroma and MPNST pathogenesis is informing the design of new therapies for these neoplasms.

Comprehensive establishment and characterization of orthoxenograft mouse models of malignant peripheral nerve sheath tumors for personalized medicine

Malignant peripheral nerve sheath tumors (MPNSTs) are soft-tissue sarcomas that can arise either sporadically or in association with neurofibromatosis type 1 (NF1). These aggressive malignancies confer poor survival, with no effective therapy available. We present the generation and characterization of five distinct MPNST orthoxenograft models for preclinical testing and personalized medicine. Four of the models are patient-derived tumor xenografts (PDTX), two independent MPNSTs from the same NF1 patient and two from different sporadic patients. The fifth model is an orthoxenograft derived from an NF1-related MPNST cell line. All MPNST orthoxenografts were generated by tumor implantation, or cell line injection, next to the sciatic nerve of nude mice, and were perpetuated by 7–10 mouse-to-mouse passages. The models reliably recapitulate the histopathological properties of their parental primary tumors. They also mimic distal dissemination properties in mice. Human stroma was rapidly lost after MPNST engraftment and replaced by murine stroma, which facilitated genomic tumor characterization. Compatible with an origin in a catastrophic event and subsequent genome stabilization, MPNST contained highly altered genomes that remained remarkably stable in orthoxenograft establishment and along passages. Mutational frequency and type of somatic point mutations were highly variable among the different MPNSTs modeled, but very consistent when comparing primary tumors with matched orthoxenografts generated. Unsupervised cluster analysis and principal component analysis (PCA) using an MPNST expression signature of ~1,000 genes grouped together all primary tumor–orthoxenograft pairs. Our work points to differences in the engraftment process of primary tumors compared with the engraftment of established cell lines. Following standardization and extensive characterization and validation, the orthoxenograft models were used for initial preclinical drug testing. Sorafenib (a BRAF inhibitor), in combination with doxorubicin or rapamycin, was found to be the most effective treatment for reducing MPNST growth. The development of genomically well-characterized preclinical models for MPNST allowed the evaluation of novel therapeutic strategies for personalized medicine.

The Challenge of Cancer Genomics in Rare Nervous System Neoplasms: Malignant Peripheral Nerve Sheath Tumors as a Paradigm for Cross-Species Comparative Oncogenomics

Comprehensive genomic analyses of common nervous system cancers provide new insights into their pathogenesis, diagnosis, and treatment. Although analogous studies of rare nervous system tumors are needed, there are major barriers to performing such studies. Cross-species comparative oncogenomics, identifying driver mutations in mouse cancer models and validating them in human tumors, is a promising alternative. Although still in its infancy, this approach is being applied to malignant peripheral nerve sheath tumors (MPNSTs), rare Schwann cell-derived malignancies that occur sporadically, after radiotherapy, and in neurofibromatosis type 1. Studies of human neurofibromatosis type 1-associated tumors suggest that NF1 tumor suppressor loss in Schwann cells triggers cell-autonomous and intercellular changes, resulting in development of benign neurofibromas; subsequent neurofibroma-MPNST progression is caused by aberrant growth factor signaling and mutations affecting the p16(INK4A)-cyclin D1-CDK4-Rb and p19(ARF)-Mdm2-p53 cell cycle pathways. Mice with Nf1, Trp53, and/or Cdkn2a mutations that overexpress the Schwann cell mitogen neuregulin-1 or overexpress the epidermal growth factor receptor validate observations in human tumors and, to various degrees, model human tumorigenesis. Genomic analyses of MPNSTs arising in neuregulin-1 and epidermal growth factor receptor-overexpressing mice and forward genetic screens with Sleeping Beauty transposons implicate additional signaling cascades in MPNST pathogenesis. These studies confirm the utility of mouse models for MPNST driver gene discovery and provide new insights into the complexity of MPNST pathogenesis.

Trp53 haploinsufficiency modifies EGFR-driven peripheral nerve sheath tumorigenesis

Malignant peripheral nerve sheath tumors (MPNSTs) are genetically diverse, aggressive sarcomas that occur sporadically or in association with neurofibromatosis type 1 syndrome. Reduced TP53 gene expression and amplification/overexpression of the epidermal growth factor receptor (EGFR) gene occur in MPNST formation. We focused on determining the cooperativity between reduced TP53 expression and EGFR overexpression for Schwann cell transformation in vitro (immortalized human Schwann cells) and MPNST formation in vivo (transgenic mice). Human gene copy number alteration data, microarray expression data, and TMA analysis indicate that TP53 haploinsufficiency and increased EGFR expression co-occur in human MPNST samples. Concurrent modulation of EGFR and TP53 expression in HSC1λ cells significantly increased proliferation and anchorage-independent growth in vitro. Transgenic mice heterozygous for a Trp53-null allele and overexpressing EGFR in Schwann cells had a significant increase in neurofibroma and grade 3 PNST (MPNST) formation compared with single transgenic controls. Histological analysis of tumors identified a significant increase in pAkt expression in grade 3 PNSTs compared with neurofibromas. Array comparative genome hybridization analysis of grade 3 PNSTs identified recurrent focal regions of chromosomal gains with significant enrichment in genes involved in extracellular signal-regulated kinase 5 signaling. Collectively, altered p53 expression cooperates with overexpression of EGFR in Schwann cells to enhance in vitro oncogenic properties and tumorigenesis and progression in vivo.

Forward genetic screen for malignant peripheral nerve sheath tumor formation identifies new genes and pathways driving tumorigenesis

Malignant peripheral nerve sheath tumors (MPNSTs) are sarcomas of Schwann cell-lineage origin that occur sporadically or in association with the inherited syndrome, Neurofibromatosis Type 1. To identify genetic drivers of MPNST development, we utilized the Sleeping Beauty (SB) transposon-based somatic mutagenesis system in mice with somatic loss of tumor protein p53 (Trp53) function and/or overexpression of epidermal growth factor receptor (EGFR). Common insertion site (CIS) analysis of 269 neurofibromas and 106 MPNSTs identified 695 and 87 sites with a statistically significant number of recurrent transposon insertions, respectively. Comparison to human data sets revealed novel and known driver genes for MPNST formation at these sites. Pairwise co-occurrence analysis of CIS-associated genes identified many cooperating mutations that are enriched for in Wnt/CTNNB1, PI3K/Akt/mTor, and growth factor receptor signaling pathways. Lastly, we identified several novel proto-oncogenes including forkhead box R2 (Foxr2), which we functionally validated as a proto-oncogene involved in MPNST maintenance.

Transgenic mice overexpressing neuregulin-1 model neurofibroma-malignant peripheral nerve sheath tumor progression and implicate specific chromosomal copy number variations in tumorigenesis

Patients with neurofibromatosis type 1 (NF1) develop benign plexiform neurofibromas that frequently progress to become malignant peripheral nerve sheath tumors (MPNSTs). A genetically engineered mouse model that accurately models plexiform neurofibroma-MPNST progression in humans would facilitate identification of somatic mutations driving this process. We previously reported that transgenic mice overexpressing the growth factor neuregulin-1 in Schwann cells (P(0)-GGFβ3 mice) develop MPNSTs. To determine whether P(0)-GGFβ3 mice accurately model human neurofibroma-MPNST progression, cohorts of these animals were monitored through death and were necropsied; 94% developed multiple neurofibromas, with 70% carrying smaller numbers of MPNSTs. Nascent MPNSTs were identified within neurofibromas, suggesting that these sarcomas arise from neurofibromas. Although neurofibromin expression was maintained, P(0)-GGFβ3 MPNSTs exhibited Ras hyperactivation, as in human NF1-associated MPNSTs. P(0)-GGFβ3 MPNSTs also exhibited abnormalities in the p16(INK4A)-cyclin D/CDK4-Rb and p19(ARF)-Mdm-p53 pathways, analogous to their human counterparts. Array comparative genomic hybridization (CGH) demonstrated reproducible chromosomal alterations in P(0)-GGFβ3 MPNST cells (including universal chromosome 11 gains) and focal gains and losses affecting 39 neoplasia-associated genes (including Pten, Tpd52, Myc, Gli1, Xiap, and Bbc3/PUMA). Array comparative genomic hybridization also identified recurrent focal copy number variations affecting genes not previously linked to neurofibroma or MPNST pathogenesis. We conclude that P(0)-GGFβ3 mice represent a robust model of neurofibroma-MPNST progression useful for identifying novel genes driving neurofibroma and MPNST pathogenesis.

Genomic changes in chromosomes 10, 16, and X in malignant peripheral nerve sheath tumors identify a high-risk patient group

PURPOSE

The purpose of this study was to identify genetic aberrations contributing to clinical aggressiveness of malignant peripheral nerve sheath tumors (MPNSTs).

PATIENTS AND METHODS

Samples from 48 MPNSTs and 10 neurofibromas were collected from 51 patients with (n = 31) or without (n = 20) neurofibromatosis type 1 (NF1). Genome-wide DNA copy number changes were assessed by chromosomal and array-based comparative genomic hybridization (CGH) and examined for prognostic significance. For a subset of 20 samples, RNA microarray data were integrated with the genome data to identify potential target genes.

RESULTS

Forty-four (92%) MPNSTs displayed DNA copy number changes (median, 18 changes per tumor; range, 2 to 35 changes). Known frequent chromosomal gains at chromosome arms 8q (69%), 17q (67%), and 7p (52%) and losses from 9p (50%), 11q (48%), and 17p (44%) were confirmed. Additionally, gains at 16p or losses from 10q or Xq identified a high-risk group with only 11% 10-year disease-specific survival (P = .00005). Multivariate analyses including NF1 status, tumor location, size, grade, sex, complete remission, and initial metastatic status showed that the genomic high-risk group was the most significant predictor of poor survival. Several genes whose expression was affected by the DNA copy number aberrations were identified.

CONCLUSION

The presence of specific genetic aberrations was strongly associated with poor survival independent of known clinical risk factors. Conversely, within the total patient cohort with 34% 10-year disease-specific survival, a low-risk group was identified: without changes at chromosomes 10q, 16p, or Xq in their MPNSTs, the patients had 74% 10-year survival.

How does the Schwann cell lineage form tumors in NF1?

Neurofibromas are benign tumors of peripheral nerve that occur sporadically or in patients with the autosomal dominant tumor predisposition syndrome neurofibromatosis type 1 (NF1). Multiple neurofibroma subtypes exist which differ in their site of occurrence, their association with NF1, and their tendency to undergo transformation to become malignant peripheral nerve sheath tumors (MPNSTs), the most common malignancy associated with NF1. Most NF1 patients carry a constitutional mutation of the NF1 tumor suppressor gene. Neurofibromas develop in these patients when an unknown cell type in the Schwann cell lineage loses its remaining functional NF1 gene and initiates a complex series of interactions with other cell types; these interactions may be influenced by aberrant expression of growth factors and growth factor receptors and the action of modifier genes. Cells within certain neurofibroma subtypes subsequently accumulate additional mutations affecting the p19(ARF)-MDM2-TP53 and p16INK4A-Rb signaling cascades, mutations of other as yet unidentified genes, and amplification of growth factor receptor genes, resulting in their transformation into MPNSTs. These observations have been validated using a variety of transgenic and knockout mouse models that recapitulate neurofibroma and MPNST pathogenesis. A new generation of mouse models is also providing important new insights into the identity of the cell type in the Schwann cell lineage that gives rise to neurofibromas. Our improving understanding of the mechanisms underlying the pathogenesis of neurofibromas and MPNSTs raises intriguing new questions about the origin and pathogenesis of these neoplasms and establishes models for the development of new therapies targeting these neoplasms.

Identification of p53 as a strong predictor of survival for patients with malignant peripheral nerve sheath tumors

The purpose of this study was to identify new prognostic biomarkers with clinical impact in malignant peripheral nerve sheath tumor (MPNST), a highly aggressive malignancy for which no consensus therapy exists besides surgery. We have used tissue microarrays (TMAs) to assess in situ expression of 14 cell-cycle-regulating proteins in 64 well-characterized MPNST patients: 36 sporadic and 28 with neurofibromatosis type 1 (NF1). We developed a new software application for evaluation and logistics of the TMA images and performed a literature survey of cell cycle proteins in MPNST. For NF1-associated patients, there was a clear association between nuclear expression of p53 and poor survival (p = 0.004). Among the other proteins analyzed, we also found significant associations between survival and clinical variables, but none were as strong as that for p53. For the total series of MPNSTs, p53 was shown to be an independent predictor of survival, and patients without remission, with tumor size larger than 8 cm, and with positive p53 expression had a 60 times greater risk of dying within the first 5 years compared with the remaining patients (p = 0.000002). This is the most comprehensive study of in situ protein expression in MPNST so far, and expressed p53 was found to be a strong surrogate marker for outcome. Patients in complete remission with a primary p53-positive MPNST diagnosis may be considered in a high-risk subgroup and candidates for adjuvant treatment.

DNA copy number changes in high-grade malignant peripheral nerve sheath tumors by array CGH

Background

Malignant peripheral nerve sheath tumors (MPNSTs) are rare and highly aggressive soft tissue tumors showing complex chromosomal aberrations. In order to identify recurrent chromosomal regions of gain and loss, and thereby novel gene targets of potential importance for MPNST development and/or progression, we have analyzed DNA copy number changes in seven high-grade MPNSTs using microarray-based comparative genomic hybridization (array CGH).

Results

Considerable more gains than losses were observed, and the most frequent minimal recurrent regions of gain included 1q24.1-q24.2, 1q24.3-q25.1, 8p23.1-p12, 9q34.11-q34.13 and 17q23.2-q25.3, all gained in five of seven samples. The 17q23.2-q25.3 region was gained in all five patients with poor outcome and not in the two patients with disease-free survival. cDNA microarray analysis and quantitative real-time reverse transcription PCR were used to investigate expression of genes located within these regions. The gene lysyl oxidase-like 2 (LOXL2) was identified as a candidate target for the 8p23.1-p12 gain. Within 17q, the genes topoisomerase II-α (TOP2A), ets variant gene 4 (E1A enhancer binding protein, E1AF) (ETV4) and baculoviral IAP repeat-containing 5 (survivin) (BIRC5) showed increased expression in all samples compared to two benign tumors. Increased expression of these genes has previously been associated with poor survival in other malignancies, and for TOP2A, in MPNSTs as well. In addition, we have analyzed the expression of five micro RNAs located within the 17q23.2-q25.3 region, but none of them showed high expression levels compared to the benign tumors.

Conclusion

Our study shows the potential of using DNA copy number changes obtained by array CGH to predict the prognosis of MPNST patients. Although no clear correlations between the expression level and patient outcome were observed, the genes TOP2A, ETV4 and BIRC5 are interesting candidate targets for the 17q gain associated with poor survival.

Imatinib mesylate inhibits cell invasion of malignant peripheral nerve sheath tumor induced by platelet-derived growth factor-BB

Malignant peripheral nerve sheath tumor (MPNST) is rare, highly aggressive, resistant to radiochemotherapy, and associated with poor prognosis. Basic research to develop new treatment regimes is critically needed. This study was designed to identify motogenic factor(s) involved in MPNST cell invasion and inhibitor(s) of such invasive activity. We profiled the invasion-inducing activities of eight motogenic growth factors on two human MPNST cell lines, FU-SFT8611 and 9817, using in vitro Matrigel invasion assays. Platelet-derived growth factor-BB (PDGF-BB) was identified as the most effective MPNST cell invasion-inducing factor. Epidermal growth factor (EGF) and hepatocyte growth factor (HGF) also stimulated invasion in one MPNST cell line. Expressions of PDGF-BB and EGF receptors (PDGFR-beta and EGFR) mRNAs were detected more frequently and their proteins were expressed at higher levels in MPNST tissues than benign peripheral nerve sheath tumors (schwannomas and neurofibromas). In both MPNST cell lines, PDGF-BB induced tyrosine phosphorylation of PDGFR-beta but not of PDGFR-alpha, and specific PDGFR-beta inhibition by small interfering RNA to the receptor inhibited PDGF-BB-stimulated MPNST cell invasion, suggesting the predominant role of PDGFR-beta. Inhibition of PDGFR-beta phosphorylation by pretreatment with herbimycin A and imatinib mesylate effectively suppressed basement membrane invasion and cell growth in vitro. No mutations were present in exons 12 and 18 of PDGFR-beta in both MPNST cell lines and 10 human MPNST tissues examined. Our results indicated that PDGF-BB enhanced the invasive activity of MPNST cells through PDGFR phosphorylation and that imatinib inhibited such activity. The results provide the ground for further assessment of the therapeutic potential of imatinib in suppressing the invasion and growth of MPNST.

Identification of a novel amplicon at distal 17q containing theBIRC5/SURVIVINgene in malignant peripheral nerve sheath tumours

Previous studies have suggested that amplification of genes, notably the TOP2A gene, on chromosome arm 17q may be important for the development of malignant peripheral nerve sheath tumour (MPNST). In order to study the frequency, distribution, and chromosomal organization of rearrangements at 17q, interphase and metaphase fluorescence in situ hybridization (FISH) were used to evaluate copy number changes at 17q in 28 MPNSTs. Increased copy numbers were seen for the ERBB2 and TOP2A genes in eight and nine cases, respectively, supporting a potential role for these two genes in MPNST tumourigenesis. Net gain of distal 17q material was observed in 16 of the 28 MPNSTs, with high-level gain in three cases, and was associated with poor outcome. Among the 26 patients for whom follow-up data were available, gain of distal 17q was present in 11 of 12 tumours that had metastasized, compared with 4 of 14 of those that had not metastasized. Detailed FISH mapping analysis of metaphase spreads identified a 2 Mb commonly gained/amplified region at 17q25. Among the genes mapping to this region, BIRC5, which encodes the baculoviral IAP repeat-containing protein 5/survivin protein, is a strong candidate target gene for amplification, as it has been previously shown to be overexpressed in neurofibromatosis type 1-associated MPNST. Three other genes that co-amplified with BIRC5 represent other potential candidate genes: PTDSR involved in apoptosis; SEPT9 overexpressed in human malignant brain tumours; and SOCS3 involved in cell survival and differentiation of neurons.

Loss of p16 (INK4A) expression is associated with allelic imbalance/loss of heterozygosity of chromosome 9p21 in microdissected malignant peripheral nerve sheath tumors

The p16 is a tumor suppressor gene on the short arm of chromosome 9p21. The product of the p16 acts as a negative cell cycle regulator by inhibiting G1 cyclin-dependent kinases that phosphorylate the retinoblastoma protein. This study was designed to assess the frequency of genetic loss of 9p21 and to determine the role of p16 the pathogenesis of sporadic and neurofibromatosis 1 (NF1)-associated malignant peripheral nerve sheath tumors (MPNSTs). The authors examined 15 cases for p16 protein expression and 10 cases for allelic imbalance (AI)/loss of heterozygosity (LOH) of chromosome 9p. DNA was microdissected from normal and neoplastic tissues. AI/LOH analysis was performed using six microsatellite markers on the 9p region. On immunohistochemical analysis 80% of cases showed abnormal expression of p16. Similarly, 8 of 10 cases revealed genetic loss with at least one microsatellite marker. The most frequent deletion was that within the coding sequence. Of p16 at me D9S974 locus. These findings emphasize the role of loss of p16 in the development of both sporadic and NF1-associated MPNSTs.

Chromosomal aberrations and microsatellite instability of malignant peripheral nerve sheath tumors: a study of 10 tumors from nine patients

Malignant peripheral nerve sheath tumor (MPNST) is an uncommon soft tissue neoplasm with a poor prognosis, occurring sporadically or associated with neurofibromatosis type 1 (NF1); however, the histogenesis of MPNST remains unclear, especially in sporadic tumors. There are two major forms of genomic instability in human cancer: chromosomal instability (CIN) and microsatellite instability (MSI). An inverse relationship has recently been demonstrated between CIN and MSI in colorectal cancers. CIN and MSI are suggested to be individual pathways, which are involved in the pathogenesis and which may lead to specific clinical and pathological characteristics. To elucidate the chromosomal aberration as a consequence of CIN and MSI status of MPNST, we karyotyped 10 MPNSTs from nine patients, and examined the MSI of seven microsatellite markers using high-resolution fluorescence microsatellite analysis; 2 out of 10 cases (20%) had normal karyotypes, and 8 out of 10 cases (80%) revealed structural and numerical chromosomal aberrations. Three of the 10 cases (30%) showed near triploidy. The most frequent aberration was -22 (40%), followed by +2, +14, -13, -17, and -18 (30% each). An MSI-low status was observed in 30% of cases; the remaining cases showed microsatellite stability. These findings suggest that chromosomal aberration as a consequence of CIN has a greater role in the pathogenesis of MPNST than does that due to MSI.

An imprinted locus epistatically influences Nstr1 and Nstr2 to control resistance to nerve sheath tumors in a neurofibromatosis type 1 mouse model

Cancer is a complex disease in which cells acquire many genetic and epigenetic alterations. We have examined how three types of alterations, mutations in tumor suppressor genes, changes in an imprinted locus, and polymorphic loci, interact to affect tumor susceptibility in a mouse model of neurofibromatosis type 1 (NF1). Mutations in tumor suppressor genes such as TP53 and in oncogenes such as KRAS have major effects on tumorigenesis due to the central roles of these genes in cell proliferation and cell survival. Imprinted genes expressed from only one parental chromosome affect tumorigenesis if their monoallelic expression is lost or duplicated. Because imprinted loci are within regions deleted or amplified in cancer, the parental origin of genomic rearrangements could affect tumorigenesis. Gene polymorphisms can vary tumor incidence by affecting rate-limiting steps in tumorigenesis within tumor cells or surrounding stroma. In our mouse model of NF1, the incidence of tumors mutant for the tumor suppressor genes Nf1 and Trp53 is strongly modified by a linked imprinted locus acting epistatically on two unlinked polymorphic loci, Nstr1 and Nstr2. This interaction of an imprinted locus and polymorphic susceptibility loci has profound implications for human mapping studies where the parental contribution of alleles is often unknown.

Molecular cytogenetic analysis in the study of brain tumors: findings and applications

Classic cytogenetics has evolved from black and white to technicolor images of chromosomes as a result of advances in fluorescence in situ hybridization (FISH) techniques, and is now called molecular cytogenetics. Improvements in the quality and diversity of probes suitable for FISH, coupled with advances in computerized image analysis, now permit the genome or tissue of interest to be analyzed in detail on a glass slide. It is evident that the growing list of options for cytogenetic analysis has improved the understanding of chromosomal changes in disease initiation, progression, and response to treatment. The contributions of classic and molecular cytogenetics to the study of brain tumors have provided scientists and clinicians alike with new avenues for investigation. In this review the authors summarize the contributions of molecular cytogenetics to the study of brain tumors, encompassing the findings of classic cytogenetics, interphase- and metaphase-based FISH studies, spectral karyotyping, and metaphase- and array-based comparative genomic hybridization. In addition, this review also details the role of molecular cytogenetic techniques in other aspects of understanding the pathogenesis of brain tumors, including xenograft, cancer stem cell, and telomere length studies.

Therapy-induced malignant neoplasms in Nf1 mutant mice

Therapy-induced cancers are a severe complication of genotoxic therapies. We used heterozygous Nf1 mutant mice as a sensitized genetic background to investigate tumor induction by radiation (RAD) and cyclophosphamide (CY). Mutagen-exposed Nf1(+/-) mice developed secondary cancers that are common in humans, including myeloid malignancies, sarcomas, and breast cancers. RAD cooperated strongly with heterozygous Nf1 inactivation in tumorigenesis. Most of the solid tumors showed loss of the wild-type Nf1 allele but retained two Trp53 alleles. Comparative genomic hybridization demonstrated distinct patterns of copy number aberrations in sarcomas and breast cancers from Nf1 mutant mice, and tumor cell lines showed deregulated Ras signaling. Nf1(+/-) mice provide a tractable model for investigating the pathogenesis of common mutagen-induced cancers and for testing preventive strategies.

Divergent differentiation in malignant soft tissue neoplasms: the paradigm of liposarcoma and malignant peripheral nerve sheath tumor

In tumors clonality does not always translate into morphologic uniformity. While most sarcomas exhibit only one line of histologic differentiation, a minority may display a strikingly diverse phenotype in addition to the main lineage. This phenomenon not only presents a diagnostic problem but also raises questions about the commitment of tumor cells toward a specific phenotype. Among sarcomas, malignant peripheral nerve sheath tumor (MPNST) and dedifferentiated liposarcoma are two entities in which divergent differentiation is a relatively frequent event. Diagnostically it is crucial to recognize the "primary" sarcoma in such tumors correctly and distinguish it from the "secondary" divergent elements. The presence of the latter could be the first morphologic clue to a specific sarcoma type. Even though it may be difficult to explain the pathogenesis of divergent differentiation, divergence still illustrates that the phenotype of a tumor cell is not set in stone but can be modulated or switched by a number of factors.

Expression patterns of cell cycle components in sporadic and neurofibromatosis type 1-related malignant peripheral nerve sheath tumors

The molecular biology underlying the development of highly malignant peripheral nerve sheath tumors (MPNSTs) remains mostly unknown. In the present study, the expression pattern of 10 selected cell cycle components is investigated in a series of 15 MPNSTs from patients with (n = 9) or without (n = 5) neurofibromatosis type 1 (NF1). Thirteen tumors did not express the cyclin-dependent kinase inhibitor, p16(INK4A), an observation that was related to homozygote gene deletions in three tumors, heterozygote deletions in five, and gross gene rearrangements in five. The absence of protein expression in the tumors with one seemingly intact allele was not caused by promoter hypermethylation of p16(INK4A) or p14(ARF). All tumor samples expressed normal sized RB1, cyclin D3, CDK2, CDK4, p21(CIP1), and p27(KlP1) proteins, and only a single tumor showed an aberrant protein band for one of these proteins, p21(CIP1). Cyclin D1 was absent in four tumors; all except one tumor showed expression of TP53 protein, and three of nine MPNSTs had expression of normal-sized MDM2. In conclusion, this study shows that the vast majority of MPNSTs had gross rearrangements of the p16(INK4A) gene, explaining the absence of the encoded protein in the same tumors. The level of expression was equally distributed between the familial (NF1) and sporadic cases, although it should be noted that the 2 cases with p16(INK4A) expression were sporadic. The data imply that the complete absence of p16(INK4A) is sufficient for activation of the cell cycle in most MPNSTs; thus, it is not necessary for tumor proliferation to further stimulate the cycle through alteration of other central components.

Tumor suppressor mutations and growth factor signaling in the pathogenesis of NF1-associated peripheral nerve sheath tumors. I. The role of tumor suppressor mutations

Patients with neurofibromatosis type 1 (NF1), a common autosomal dominant tumor predisposition syndrome, develop benign cutaneous, intraneural, and plexiform neurofibromas and malignant peripheral nerve sheath tumors (MPNSTs), an aggressive form of Schwann cell neoplasm that frequently arises from plexiform neurofibromas. Impressive advances have been made in defining the molecular mechanisms responsible for neurofibroma and MPNST tumorigenesis, including the identification of key tumor suppressor gene mutations, an improved understanding of the functions of these tumor suppressors, and the production of transgenic mouse models in which tumor suppressor gene mutations predispose animals to the development of neurofibromas and MPNSTs. It has also become apparent that dysregulated growth factor signaling cooperates with tumor suppressor mutations to promote neurofibroma and MPNST tumorigenesis. In Part I of this two-part review, we consider findings demonstrating that Schwann cells are the primary neoplastic cell type in neurofibromas and MPNSTs and that specific tumor suppressor gene mutations promote the development of these tumors. In Part II, which will be published in a later issue, we will review evidence indicating that inappropriate growth factor signaling contributes to this process by stimulating the proliferation, survival, and migration of Schwann cells whose regulatory mechanisms have been crippled by a loss of tumor suppressor function.

Malignant peripheral nerve sheath tumor with rhabdomyoblastic differentiation (malignant triton tumor) with balanced t(7;9)(q11.2;p24) and unbalanced translocation der(16)t(1;16)(q23;q13)

Malignant peripheral nerve sheath tumors (MPNST) with skeletal muscle differentiation are termed malignant triton tumors. A case of malignant triton tumor arising in a patient without signs of neurofibromatosis with two consistent chromosomal abnormalities is described. The first was of a balanced translocation between the long arm of chromosome 7 and the short arm of chromosome 9. The second was an unbalanced rearrangement between chromosomes 1 and 16, leading to partial trisomy for the long arm of chromosome 1 and partial monosomy for the long arm of chromosome 16. Review of previous reports on chromosomal abnormalities in malignant triton tumors revealed consistent abnormalities involving chromosome 1, regardless of the presence or absence of neurofibromatosis. This finding may relate to the observed poor prognostic outcome in this type of sarcoma. Also unique to our case is the translocation involving 7q and 9p, both regions may play a role in MPNST.

Clonal chromosome abnormalities in a plexiform cellular schwannoma

Cellular schwannomas are uncommon tumors of Schwann cells that can rarely have a plexiform architecture. Cellular schwannomas can be confused with low-grade malignant peripheral nerve sheath tumors (MPNST) but have been noted to have a benign clinical course. There are few published cytogenetic analyses of cellular schwannomas and, to our knowledge, there are no reports of the plexiform variant of cellular schwannoma to date. Cellular schwannomas are reported to have cytogenetic changes similar to those seen in benign schwannomas with near-diploid karyotypes having simple numerical changes often involving chromosomes 22, 7, and the sex chromosomes. MPNST are markedly different, with extensive genetic heterogeneity and complex karyotypes. We report clonal numerical changes in a cellular schwannoma with plexiform architecture: 47,XY,+17 and 48,XY,+17,+18. These findings add to the karyotypic spectrum of peripheral nerve sheath tumors.

Topoisomerase-II alpha is upregulated in malignant peripheral nerve sheath tumors and associated with clinical outcome

PURPOSE

To identify target genes of clinical significance for patients with malignant peripheral-nerve sheath tumor (MPNST), an aggressive cancer for which no consensus therapy exists.

MATERIALS AND METHODS

Biopsies and clinical data from 51 patients with MPNST were included in this study. Based on our previous research implicating chromosome arm 17q amplification in MPNST, we performed gene expression analyses of 14 MPNSTs using chromosome 17-specific cDNA microarrays. Copy numbers of selected gene probes and centromere probes were then determined by interphase fluorescence in situ hybridization in 16 MPNSTs. Finally, we generated a tissue microarray containing 79 samples from 44 MPNSTs, on which in situ protein expressions of candidate genes were examined and related to clinical end points.

RESULTS

Among several deregulated genes found by cDNA microarray analyses, topoisomerase II alpha (TOP2A) was the most overexpressed gene in MPNSTs compared with benign neurofibromas. Excess copies of the TOP2A were also seen at the DNA level in 10 of 16 cases, and high expression of the TOP2A protein was seen in 83% of the tumors on the tissue microarray. The TOP2A-expressing tumors were associated with poor cancer-specific survival and presence of metastases.

CONCLUSION

We have identified TOP2A as a target gene in MPNST, using a focused gene expression profiling followed by a DNA copy number evaluation and clinical validation of the encoded protein using a tissue microarray. This study is the first to suggest that TOP2A expression may be a predictive factor for adverse outcome in MPNST.

Cytogenetic characterization of three malignant peripheral nerve sheath tumors

Malignant peripheral nerve sheath tumors (MPNST) are soft tissue sarcomas occurring frequently in patients with neurofibromatosis 1. We present three fully karyotyped cases of MPNST revealing aberrant near-triploid karyotypes. In all three cases we found deletions of chromosome arms or chromosomes 1p, 10q, 9, and 15, as well as gain of chromosome 7 in two NF1-associated cases and gain of chromosome 8 in an NF1-associated and a sporadic case. The chromosomal region of the NF1 gene was cytogenetically unchanged in all cases, whereas two MPNST cases showed losses of the region 22q harboring the locus of the NF2 gene.

Evidence for involvement of a tumor suppressor gene on 1p in malignant peripheral nerve sheath tumors

Malignant peripheral nerve sheath tumors (MPNST) are rare soft-tissue malignancies. The genetic basis of these tumors is still poorly understood. Cytogenetic analyses predominantly revealed complex karyotypes, precluding the identification of recurrent chromosomal changes. We report loss of 1p material in a near-diploid karyotype with few or no additional structural chromosome changes in two sporadic cases of MPNST, indicating an important role of 1p loss in MPNST development. In one of these two tumors, a distal 1p deletion (1p31.2 approximately pter) was detected suggesting involvement of a tumor suppressor gene located within this distal region of 1p. Further evidence for recurrent 1p loss in MPNST was obtained by interphase fluorescence in situ hybridization, which showed loss of 1p material in 3 out of 13 tumors. These findings together with data from the literature suggest that loss of a tumor suppressor gene located within distal 1p is implicated in the pathogenesis of MPNST.

Differential NF1, p16, and EGFR patterns by interphase cytogenetics (FISH) in malignant peripheral nerve sheath tumor (MPNST) and morphologically similar spindle cell neoplasms

Malignant peripheral nerve sheath tumors (MPNSTs) are diagnostically challenging neoplasms for which sensitive and specific immunohistochemical markers are lacking. Although limited to date, previous studies have suggested that NF1 (17q), NF2 (22q), p16 (9p), and EGFR (7p) alterations may be involved in MPNST tumorigenesis. To determine whether specific genetic changes differentiate between MPNST and morphologically similar neoplasms, we assessed these chromosomal regions in 22 MPNSTs (9 NF1-associated, 13 sporadic), 13 plexiform neurofibromas, 5 cellular schwannomas, 8 synovial sarcomas, 6 fibrosarcomas, and 13 hemangiopericytomas by 2-color FISH. NF1 deletions, often in the form of monosomy 17, were found in MPNSTs (76%). neurofibromas (31%), hemangiopericytomas (17%), and fibrosarcomas (17%), but not in synovial sarcomas or cellular schwannomas. NF1 losses were encountered more frequently in MPNSTs versus other sarcomas (p < 0.001), as were p16 homozygous deletions (45% vs 0%; p < 0.001), EGFR amplifications (26% vs 0%; p = 0.006), and polysomies for either chromosomes 7 (53% vs 12%; p = 0.003) or 22 (50% vs 4%; p < 0.001). Hemizygous or homozygous p16 deletions were detected in 75% of MPNSTs, but not in benign nerve sheath tumors (p < 0.001). Thus, FISH analysis identifies relatively specific genetic patterns that may be useful in selected cases, for which the differential diagnosis includes low- or high-grade MPNST.

Ossifying fibromyxoid tumor of soft parts. Cytogenetic findings

Ossifying fibromyxoid tumor (OFMT) of soft parts is a recently described, rare but morphologically distinctive soft tissue tumor. The histogenesis of this lesion remains uncertain, although several immunohistochemical and ultrastructural features suggest that it is an unusual neural tumor, possibly of Schwann cell origin. We report here a case of a malignant variant of OFMT that occurred in the foot of a 52-year-old man. The karyotype of a pulmonary metastasis exhibited the following complex numeric and structural aberrations:72 approximately 74,XXY,-5,+6,+del(8)(p21),del(9)(p22),+10,der(11)t(3;11)(p21;p15),del(12) (q13),der(13)t(5;13)(q13;q34),+18,+19,+20,-22 [cp10]. A kidney metastasis exhibited the following karyotypic abnormalities: 46,XY,add(3)(p11),+der(3)t(3;?;11)(3qter-->3p11::?::11q13-->11qter), -5,del(8)(p21),add(9)(q22),del(9)(p22),der(11)t(3;11)(p21;p15),del(12)(q13),+der(13)t(5;13) (q13;q34),-22. To our knowledge, this is the first reported case of OFMT in which clonal chromosomal aberrations have been shown.

Cytogenetic characterization of six malignant peripheral nerve sheath tumors: comparison of karyotyping and comparative genomic hybridization

We analysed six malignant peripheral nerve sheath tumors (MPNSTs) from four patients using metaphase preparations and compared the results with those obtained by using comparative genomic hybridization (CGH). All six tumors showed structural and numerical chromosomal aberrations, mostly of chromosomes 1, 5, 7-10, 14-17, 19, 21, and 22. The number of chromosomes per tumor cell ranged from 42 to 104. We could not find a recurrent specific pattern of structural changes after comparing the MPNSTs of different patients. However, aberrations of different tumors from the same patient were nearly identical. In the four patients, we found a total of 117 breakpoints, mostly in 21q11.2 (seven times), in 8q11.2 and 14q10 (six times each), in 5q11.2 and 15q26 (four times each), in 8p11.2, 10q11.2, 16q22, 19q13.3, and 22q10 (three times each). In three MPNSTs, double minute chromosomes (dmin) we detected with metaphase investigations and high-level amplifications by using CGH, respectively. C-MYC gene amplification and loss of the P53 gene could be ruled out by locus-specific probes for the common gain of 8q and for losses of 17p. When comparing the CGH results with those of karyotyping an overlap in the most frequent gains in 7q, 8q, 15q, and 17q was observed. However, we found more frequent losses in 19q in the metaphase investigations.

DNA copy number amplifications in sarcomas with homogeneously staining regions and double minutes

To identify DNA amplifications in sarcomas, comparative genomic hybridization was performed on 27 cases that were likely to display high-level DNA copy number gains. In all cases, chromosome banding analysis had revealed homogeneously staining regions or double minutes, i.e., cytogenetic signs of gene amplification. In most cases, gains predominated over losses. Low-level amplifications (ratio 1.3:1.5) were seen in 20 cases. High-level amplifications (ratio >1.5) exceeded the frequencies seen in published, unselected sarcomas of similar histotypes and were detected in 16 tumors: 4/4 osteosarcomas, 5/8 malignant fibrous histiocytomas, 3/7 leiomyosarcomas, 1/2 myosarcomas, 0/1 liposarcoma, 0/1 rhabdomyosarcoma, 1/1 pleomorphic sarcoma, 0/1 myxofibrosarcoma, 1/1 malignant mesenchymona, and 1/1 malignant schwannoma, with two to four chromosomal regions involved in nine tumors. Recurrent amplifications involved 1p33-p32, 5p15-p14, 7pter-p12, 7q21-qter, 8q21.3-qter, 11q22-q23, 16p13.2-p12, 19q12-q13.1, 20q11.2-qter, and 22q12-q13. Most of the recurrent gains/amplifications we detected have been reported in sarcomas previously. A novel gain/amplification was seen at 2q14.3-q21 in five cases of four sarcoma types. The disparate pattern of amplified sequences, the poor correspondence between the localization of low- and high-level amplifications, and the chromosomal position of homogeneously staining regions suggest the involvement of many genes in the amplifications and that the genes rarely maintain their native position in these tumors.

Small GTPase Rac1: structure, localization, and expression of the human gene

Rac1 is a member of the Rho family of small GTPases involved in signal transduction pathways that control proliferation, adhesion, and migration of cells during embryonic development and invasiveness of tumor cells. Here we present the complete structure of the human RAC1 gene and characterize its expression. The gene comprises 7 exons over a length of 29 kb and is localized to chromosome 7p22. The GC-rich gene promoter shows characteristics of a housekeeping gene and Northern blot studies revealed ubiquitous expression of two rac1 transcripts, 1.2 and 2.5 kb in size. The two transcripts are expressed in tissue-specific ratios, reflecting competition between two alternative polyadenylation sites. The RAC1 but not RAC2 gene contains an additional exon 3b that is included by alternative splicing into the variant Rac1b, a constitutively active mutant which induces the formation of lamellipodia in fibroblasts. These data indicate that the RAC1 gene encodes two signaling GTPases. The gene structure reported here will enable studies on the regulation of RAC1 expression during tumorigenesis and development.

Loss of 14q and 22q in gastrointestinal stromal tumors (pacemaker cell tumors)

Gastrointestinal stromal tumors (GISTs), also referred to as "gastrointestinal pacemaker cell tumors (GIPACT)" are mesenchymal neoplasms that are phenotypically similar to the interstitial cells of Cajal (ICC). Cytogenetic studies of this entity are rare and molecular cytogenetic studies utilizing chromosome-specific probes are nonexistent. In the current study, cytogenetic and molecular cytogenetic analysis of 12 histologically and immunohistochemically confirmed GISTs revealed loss of a whole chromosome 14 or region(s) of 14q in 8 tumors evaluated (67%) and loss of a whole chromosome 22 or region(s) of 22q in 8 (67%) patients. Loss of 14q and 22q were observed in histologically benign and malignant GISTs. Structural rearrangements of chromosome 1 were observed in 2 malignant GISTs. These findings indicate that loss of 14q and 22q are nonrandom, early events in GIST tumorigenesis and suggest that tumor suppressor genes responsible for the development of this neoplasm may be located on these chromosomal arms.

Comparative cytogenetic study of spindle cell and pleomorphic leiomyosarcomas of soft tissues: a report from the CHAMP Study Group

Leiomyosarcomas (LMS) of soft tissues frequently show complex karyotypic changes, and no specific aberration has been identified. The aim of this study was to search for recurrent chromosome aberrations in soft tissue LMSs and to correlate these, if present, with morphological and clinical parameters. From a series of soft tissue sarcomas thoroughly reexamined cytogenetically and histopathologically, 45 LMSs were retrieved; 35 were classified microscopically as spindle cell, 3 as epithelioid, and 7 as pleomorphic. Clonal chromosome changes were present in 14, 3, and 3 cases, respectively. This series was combined with 11 previously published, karyotypically abnormal pleomorphic LMSs for cytogenetic-clinico-histopathological correlations. The breakpoints were widely scattered, with no predilection of any of the recurrent breakpoints and losses to any of the morphologic subtypes. Combining numerical and unbalanced structural changes, the most frequently lost segments were 3p21-p23 (11 cases), 8p21-pter, 13q12-q13, 13q32-qter (10 cases each), 1q42-qter, 2p15-pter, 18p11 (9 cases each), 1p36, 11q23-qter (8 cases each), and 10q23-qter (7 cases). The most frequent gain was 1q12-q31 (6 cases). There was a greater frequency of losses in 1p and 8p and a lower frequency of losses in 10q and 13q in tumors that had metastasized than in localized tumors. We conclude that LMSs with clonal abnormalities display highly complex karyotypic changes and extensive heterogeneity. No significant correlation exists between these changes and age and sex of the patients, or with depth of tumor, topography, microscopic subtype, or tumor grade. Losses in 1p36 and 8p21-pter may be associated with increased risk of metastases. Comparison of our findings in soft tissue LMS with those previously reported in LMS in other locations suggest that the karyotypic profile is more dependent on site of origin than on microscopic features.

Cytogenetic characterization of peripheral nerve sheath tumours: a report of the CHAMP study group

The findings of characteristic, sometimes pathognomonic, chromosome aberrations in several types of soft tissue tumours have not only added to our understanding of the mechanisms behind the genesis of these tumours, but have also revealed the importance of cytogenetic analysis as a diagnostic tool. For many soft tissue tumours, including peripheral nerve sheath tumours, the number of analysed cases is, however, still very low, precluding evaluations of the clinical or biological significance of different chromosomal patterns. As part of an ongoing project aiming at identifying clinical-histopathological-cytogenetic correlations among soft tissue tumours, a series of 46 benign, the vast majority of which were located in the extremities, and 20 malignant peripheral nerve sheath tumours (BPNSTs and MPNSTs, respectively) that had been successfully analysed by chromosome banding techniques were evaluated with regard to clinical, morphological, and cytogenetic features. Clonal chromosome aberrations were found in 20 BPNSTs, with abnormal karyotypes being significantly more frequent among Schwannomas than among neurofibromas. Recurrent aberrations, all of which were confined to the Schwannoma subtypes, included loss of 22q material, loss of a sex chromosome, and trisomy 7. The results show that the cytogenetic features of Schwannomas are not dependent on the site of origin. The MPNSTs, all of which had clonal chromosome aberrations, displayed complex karyotypes with numerous structural and numerical changes, except in two cases showing +7 and -22, respectively, as the sole changes. None of the recurrent imbalances was restricted to either NF1-associated or sporadic MPNST, nor was any of the imbalances significantly associated with clinical outcome. The presence of a triploid or tetraploid clone was, however, associated with grade 3 tumours and a poor prognosis. The cytogenetic findings in peripheral nerve sheath tumours show that the karyotype is a good discriminator between BPNSTs and MPNSTs, and that the pattern of aberrations among the latter may add prognostic information.

Malignant transformation of neurofibromas in neurofibromatosis 1 is associated with CDKN2A/p16 inactivation

Patients with neurofibromatosis 1 (NF1) are predisposed to develop multiple neurofibromas (NFs) and are at risk for transformation of NFs to malignant peripheral nerve sheath tumors (MPNSTs). Little is known, however, about the biological events involved in the malignant transformation of NFs. We examined the CDKN2A/p16 gene and p16 protein in NFs and MPNSTs from patients with NF1. On immunohistochemical analysis, all NFs expressed p16 protein. The MPNSTs, however, were essentially immunonegative for p16, with striking transitions in cases that contained both benign and malignant elements. None of the benign tumors had CDKN2A/p16 deletions, whereas three of six MPNSTs appeared to have homozygous CDKN2A/p16 deletions. Methylation analysis and mutation analysis of CDKN2A/p16 in MPNSTs did not reveal any abnormalities. These results show that malignant transformation of NF is associated with loss of p16 expression, which is often secondary to homozygous deletion of the CDKN2A/p16 gene. The findings suggest that CDKN2A/p16 inactivation occurs during the malignant transformation of NFs in NF1 patients and raises the possibility that p16 immunohistochemistry may provide ancillary information in the distinction of NF from MPNST.

Computer-assisted cytogenetic analysis of 51 malignant peripheral-nerve-sheath tumors: sporadic vs. neurofibromatosis-type-1-associated malignant schwannomas

Cytogenetic studies in small groups of patients with malignant peripheral-nerve-sheath tumors (MPNST) revealed complex karyotypes with no consistent changes. A computer-assisted cytogenetic analysis using a cytogenetic database was performed to determine recurrent cytogenetic alterations in 51 MPNSTs (44 from the literature and 7 new cases) and to allow direct cytogenetic comparison between NF-1-associated and sporadic MPNSTs. Significant loss (p < 0.05) was observed in the chromosomal regions 9p2, 11p1, 11q2 and 18p1. Also, loss in 1p3, 9p1, 11q1, 12q2, 17p1, 18q1-q2, 19p1, 22q1, X and Y was detected. Gain of chromosomal material was found in chromosome 7, especially 7q1 (p < 0.05). Most involved breakpoints were: 1p13, 1q21, 7p22, 9p11, 17p11, 17q11, 22q11. Cytogenetic differences between NF-1-associated and sporadic MPNSTs included a relative loss of chromosomal material in NF-1-associated MPNSTs in 1p3, 4p1 and 21p1-q2 and a relative gain in 15p1-q1. Differences in breakpoints between the NF-1 associated and the sporadic MPNST group were observed in 1p21-22 (28% of NF-1 vs. 0% of sporadic MPNSTs), 1p32-34 (17% vs. 0%), 8p11-12 (7% vs. 27%) and 17q10-12 (24% vs. 7%). This approach, in which the cytogenetic results of various reports are combined, shows that losses in 9p2 and gains in 7q1 could be of oncogenetic importance in MPNSTs. Loss of 17q1, on which the NF-1 gene has been located (17q11.2), is not a common cytogenetic finding in NF-1-associated MPNSTs. The observed differences between NF-1-associated and sporadic MPNSTs might reflect different oncogenetic pathways.

Diagnostic and prognostic implications of the unfolding molecular biology of bone and soft tissue tumours

Sarcomas account for approximately 1-2% of human malignant disease and are relatively uncommon. Histopathological study of these mesenchymal tumours at light microscopic and ultrastructural level may not always provide an unambiguous diagnosis. It has become apparent with the identification of increasing numbers of tumour specific genetic alterations that (cyto) genetic evaluation could become a very helpful adjunct to histopathological assessment in reaching a correct diagnosis. Thus, once the different tumour types can be accurately identified and classified, more meaningful clinical trials can be initiated to evaluate and select optimal methods of management. In addition, an increasing awareness and understanding of the molecular changes associated with, and the genetic variability in, the various tumour groups is beginning to provide important new information about clinical progression and prognosis.

Correlation between clinicopathological features and karyotype in spindle cell sarcomas. A report of 130 cases from the CHAMP study group

Soft-tissue tumors have proved to be a fruitful area for the identification of reproducible cytogenetic aberrations, especially among pediatric round-cell sarcomas and lipomatous tumors. Thus far, however, data regarding sarcomas of monomorphic spindle cell type have been limited and somewhat disappointing, with the notable exception of synovial sarcoma. As part of an ongoing international collaborative study, 130 karyotyped spindle-cell sarcomas were reviewed and classified histologically, without knowledge of the clinical and karyotypic data, with the aim of identifying objective correlations between morphology, karyotype, and clinical parameters. Clonal chromosomal abnormalities were identified in 82 cases studied (63%), but only in the group of synovial sarcomas was there clear correlation between the cytogenetic findings, in the form of a consistent t(X;18)(p11;q11), and morphology. Among leiomyosarcomas (41 cases) and malignant peripheral nerve sheath tumors (MPNSTs; 27 cases) as well as in individual examples of rarer entities, there was a general tendency for karyotypic complexity associated with frequent loss or rearrangement of chromosome arms 1p, 10p, 11q, 12q, 17p, and 22q. Rearrangements of 17q (the region of the NF1 gene) were seen in 9/27 (33%) of MPNSTs. Among nine cases of solitary fibrous tumor (in which previous cytogenetic data are very limited) no consistent aberrations were identified. We conclude that, with the exception of synovial sarcoma, most spindle-cell sarcomas share with pleomorphic sarcomas the tendency for karyotypic complexity. There was no indication (in most of these lesions) that detectable cytogenetic aberrations could either facilitate their diagnosis or help to determine prognosis. There is a clear need to further study and understand the significance of multiple chromosomal abnormalities in this group of mesenchymal neoplasms with the particular goal of determining their role in the process of tumor development.