Cloning and characterization of the Ewing's sarcoma and peripheral neuroepithelioma t(11;22) translocation breakpoints

Transcriptional regulation of IGF-I receptor gene expression by novel isoforms of the EWS-WT1 fusion protein

The EWS family of genes is involved in numerous chromosomal translocations that are characteristic of a variety of sarcomas. A recently described member of this group is desmoplastic small round cell tumor (DSRCT), which is characterized by a recurrent t(11;22)(p13;q12) translocation that fuses the 5' exons of the EWS gene to the 3' exons of the WT1 gene. The originally described chimera comprises exons 1-7 of EWS and exons 8-10 of WT1. We have previously reported that the WT1 protein represses the expression of the IGF-I receptor gene, whereas the EWS(1-7)-WT1(8-10) fusion protein activates IGF-I receptor gene expression. It has recently become apparent that EWS-WT1 chimeras produced in DSCRT are heterogeneous as a result of fusions of different regions of the EWS gene to the WT1 gene. We have recently characterized additional EWS-WT1 translocations that involve the juxtaposition of EWS exons 7 or 8 to WT1 exon 8, and an EWS-WT1 chimera that lacks EWS exon 6. The chimeric transcription factors encoded by these various translocations differ in their DNA-binding characteristics and their ability to transactivate the IGF-I receptor promoter. These data suggest that the molecular pathology of DSRCT is more complex than previously appreciated, and that this diversity may provide the foundation for predictive genotype-phenotype correlations in the future.

Primary Ewing's sarcoma/primitive neuroectodermal tumor of the kidney: a clinicopathologic and immunohistochemical analysis of 11 cases

Ewing's sarcoma/primitive neuroectodermal tumor (ES/PNET) is an extraordinarily rare primary tumor in the kidney and can be mistaken for a variety of other round cell tumors, including blastema-predominant Wilms' tumor (WT). Approximately 90% of ES/PNET have a specific t(11;22), which results in a chimeric EWS-FLI-1 protein. Immunohistochemistry for the carboxy-terminus of FLI-1 is sensitive and highly specific for the diagnosis of ES/PNET. WT-1, the WT-associated tumor suppressor gene, is overexpressed in WT but not in ES/PNET. No study has examined FLI-1 or WT-1 expression in renal ES/PNET. The clinicopathologic features of 11 renal ES/PNET were studied along with immunohistochemistry for cytokeratin, desmin, CD99, FLI-1, and WT-1. WT were also immunostained for CD99 (5 cases), FLI-1 (10 cases), and WT-1 (9 cases). The patients (6 men, 5 women) ranged from 18 to 49 years of age (mean, 34 yr). The mean tumor size was 11.8 +/- 3.8 cm (mean +/- standard deviation). Presenting symptoms included abdominal/flank pain and/or hematuria. Grossly, all tumors showed necrosis and hemorrhage, and 4 had cystic change. Microscopically, all tumors showed vaguely lobular growth, primitive round cells, and variable rosette formation. Epithelial, myogenous, or cartilaginous differentiation was not seen. Immunohistochemical results on the renal ES/PNET were cytokeratin (2/8 focal), desmin (0/9), CD99 (8/8), FLI-1 (5/8), and WT-1 (0/8). In comparison, the WT only rarely expressed CD99 (1/5) and did not express FLI-1 (0/10), but were usually WT-1-positive (7/9). Follow-up on 8 cases (mean, 28 mo; range, 6-64 mo) showed 4 lung and pleural metastases, 1 bone metastasis, liver metastasis, 2 local recurrences, and 5 deaths from disease (median time to death, 16.8 mo). No case had distant metastatic disease at presentation. Adjuvant therapy included chemotherapy (8 cases), radiation (3 cases), and bone marrow transplantation (1 case). Our study affirms a unique proclivity of renal ES/PNET for young adults and that it is a highly aggressive neoplasm, with rapid death in many cases, usually after the development of treatment-resistant lung metastases. These tumors must be distinguished from blastema-predominant WT and other primitive renal tumors that require different therapy. FLI-1 and WT-1 immunohistochemistry may be valuable in this differential diagnosis, given the known immunophenotypic overlap between ES/PNET and blastema-predominant WT with regard to CD99, cytokeratin, and desmin. The accurate distinction between these two entities has clear prognostic and therapeutic implications.

Intraarticular synovial sarcoma confirmed by SYT-SSX fusion transcript

A case of intraarticular synovial sarcoma arising in the knee verified by detection of the tumor-specific SYT-SSX fusion transcript is described. Although it is extremely rare, synovial sarcoma may occur entirely within a joint space. The molecular assay for detecting a tumor-specific chimeric gene is a valuable tool for diagnosis of soft tissue sarcoma, especially for diagnostically difficult cases and tumors in unusual locations.

Adamantinoma-like Ewing's sarcoma and Ewing's-like adamantinoma. The t(11; 22), t(21; 22) status

Adamantinoma of the long bones and Ewing's sarcoma are two malignant tumours between which, at first sight, there seems to be no morphological and clinical relationship. Both tumours, however, are known to express cytokeratins. Adamantinoma is a tumour of true epithelial nature, predominantly expressing cytokeratins 14 and 19. Ewing's sarcoma, believed to be from neuroectodermal origin, like other mesenchymal tumours, can aberrantly express cytokeratin 8 and 18. In the literature there are some reports of tumours showing clinical and/or morphological overlap between adamantinoma and Ewing's sarcoma, suggesting a possible relationship. These studies are mostly based on the epithelioid configuration of these lesions and their cytokeratin expression on immunohistochemistry. This raises the question of whether there is occasionally a morphological similarity between adamantinoma and Ewing's sarcoma, or whether there is a common genetic background. The Ewing's sarcoma/primitive peripheral neuroectodermal tumour (PNET) family is characterized in 90-95% of cases by a t(11; 22) and in 5-10% of cases by t(21; 22). In the few reports in the literature on cytogenetic investigations on adamantinoma, these translocations were never found using classical karyotyping. This study investigated the putative presence of t(11; 22) and t(21; 22) in 14 cases of adamantinoma by RT-PCR. These translocations were not found in any of these cases. The results support the view that these tumours are genetically and clinically distinct, but may eventually show overlapping morphological and immunohistochemical features.

Immunohistochemical detection of EWS and FLI-1 proteinss in Ewing sarcoma and primitive neuroectodermal tumors: comparative analysis with CD99 (MIC-2) expression

The molecular analysis of the t(11;22) rearrangement involving EWS/FLI-1 genes is likely to be of diagnostic value in Ewing sarcoma (ES) and primitive neuroectodermal tumors (PNET). The objective of the current study was to analyze the immunohistochemical expression of the EWS and FLI-1 proteins in a group of small round-cell tumors (SRCT) to determine their specificity and relevance in their differential diagnosis. Forty-eight cases-10 conventional ES, 4 large-cell ES, 5 PNET, 9 neuroblastomas (NB), 6 undifferentiated synovial sarcomas (SS), 5 rhabdomyosarcomas (RB), 5 non-Hodgkin lymphomas (NHL), 1 round-cell liposarcoma, and 3 mesenchymal chondrosarcomas-were analyzed. Immunocytochemistry was performed on paraffin sections after the LSAB method and antigen retrieval using ethylenediaminetetraacetic acid buffer (pH 6). Primary antibodies included FLI-1 (C-19), EWS (N-18), EWS (C-19), and CD99 (MIC-2). As expected, CD-99 expression was found in 100% of ES/PNET cases, in 2 cases of RB, 2 SS, and 1 NHL. FLI-1 protein was observed as nuclear staining in 16 cases of ES/PNET (84%) and in 4 cases of NHL, 2 NB, and 3 SS. Normal endothelial cells and lymphocytes also were positive. EWS expression (both proteins N-18 and C-19) was detected not only in 95% of ES/PNET cases but also in more than 50% of cases from the other tumoral types (4 of 9 and 7 of 9 NB, 5 of 6 and 6 of 6 SS, 3 of 5 and 5 of 5 RB, and 2 of 5 and 3 of 5 NHL, respectively). Whereas EWS expression does not appear specific for ES/PNET, analysis of FLI-1 expression together with CD-99 is a powerful marker for ES/PNET and important factors in the differential diagnosis of SRCT.

Ewing's sarcoma/primitive neuroectodermal tumor of the chest wall

Ewing's sarcoma/primitive neuroectodermal tumor is the most common tumor of the chest wall in children and adolescents. It is extremely malignant with a high frequency of both metastatic spread and of local recurrence. Cure requires intensive therapy to control both distant and local disease. Surgery and high-dose radiotherapy can achieve equivalent local control; however, radiation is associated with the additional morbidities of second malignancy and a significant adverse impact on both cardiac and pulmonary function. The optimal therapeutic sequence is initial biopsy followed by induction chemotherapy with subsequent resection of the primary tumor. This approach will achieve the lowest incidence of tumor present at the margins of resection and, hence, need for postoperative radiotherapy. The chest wall is a rare site for tumors in children and adolescents. In a series reported from St Jude's Children's Research Hospital, chest wall tumors constituted only 1.8% of the solid childhood tumors. They are primarily mesenchymal in origin and the Ewing's sarcoma/primitive neuroectodermal tumors (PNET) predominate. This report concentrates on the later tumors. They are recognized to be extremely malignant, and cure in those who present with metastatic disease is very difficult to achieve. Recent advances in our understanding of their cytogenetic basis and optimal treatment are presented.

Expression of Fli-1, a nuclear transcription factor, distinguishes vascular neoplasms from potential mimics

Fli-1 protein, a member of the ETS family of DNAbinding transcription factors, is involved in cellular proliferation and tumorigenesis. Approximately 90% of Ewing's sarcoma/primitive neuroectodermal tumors (ES/PNET) have a specific translocation, t(11;22)(q24;q12), which results in fusion of EWS to Fli-1, and production of an EWS-Fli-1 fusion protein. We have recently shown that immunohistochemistry for the carboxy terminal of Fli-1 protein is sensitive and highly specific for the diagnosis of ES/PNET. In our earlier study we noted that among normal tissues only endothelial cells and small lymphocytes expressed Fli-1. Fli-1 expression in vascular neoplasms has not been previously studied. Formalin-fixed paraffin-embedded tissue from 54 vascular tumors and 75 nonvascular tumors were immunostained for Fli-1 (1:120, Sc 356, Santa Cruz Biotechnology, Santa Cruz, CA), after steam heat-induced epitope retrieval. Only cases with >10% of cells showing nuclear staining were accepted as positive. Cases without positive internal controls (endothelium and small lymphocytes) were not scored. Positive internal controls were present in 122 of 129 cases (95%). One vascular tumor (Kaposi's sarcoma) and 7 nonvascular tumors (2 epithelioid sarcomas and 5 carcinomas) without internal controls were not scored. Fli-1 was expressed by 50 of 53 vascular tumors scored (94%), including 20 of 22 angiosarcomas, 11 of 12 hemangioendotheliomas, 7 of 7 hemangiomas, and 12 of 12 Kaposi's sarcomas. In contrast, Fli-1 expression was absent in the 68 nonvascular tumors scored (0 of 68), including 16 sarcomas, 7 melanomas, and 45 carcinomas. The results of this study strongly suggest a role for Fli-1 as a novel marker of both benign and malignant vascular tumors. The sensitivity (94%) and specificity (100%) of Fli-1 with regards to the cases evaluated in this study equal or exceed those of the established vascular markers, CD31, CD34, and von Willebrand factor. As the first nuclear, rather than cytoplasmic or membranous marker of endothelium, Fli-1 immunostaining also generally lacks cytoplasmic staining artifacts that are the result of endogenous peroxidases or biotin.

Translocation (10;11;22)(p14;q24;q12) characterized by fluorescence in situ hybridization in a case of Ewing's tumor

It is well recognized that the identification by classic cytogenetics of t(11;22)(q24;q12) is a useful aid in the accurate diagnosis of Ewing's sarcoma and related tumors. This translocation induces the EWS/FLI-1 fusion transcript, which can be detected by reverse transcription-polymerase chain reaction. Recent studies have also used fluorescence in situ hybridization (FISH) to demonstrate the translocation. The authors coupled classic cytogenetics and FISH on tumor cells from the original specimen, the local recurrence, and the pulmonary metastasis as well as from the xenografted tumors in a case of extraosseous Ewing's sarcoma. FISH analysis not only confirmed the cytogenetic results but also allowed the identification of a tumor-specific chromosome change, consistent with a complex translocation, t(10;11;22), as well as revealed other chromosomal rearrangements on both metaphases and interphase nuclei of each material. In addition this technique served to identify, in the interphase nuclei of the original tumor, the clone that became dominant, from the cytogenetic point of view, in the lung metastasis and in the nude mice xenografted tumors. Current results indicate that the use of FISH on metaphases and interphase nuclei is an easy and reliable approach to complement or even to substitute classic cytogenetic studies for the detection of specific chromosomal rearrangements, especially for determining complex translocations and for describing tumoral clones with different cytogenetic markers.

Primary primitive neuroectodermal tumor of the kidney

Primitive neuroectodermal tumor (PNET) is a small round cell sarcoma that mainly develops in the central nervous system and soft tissues of childhood; however recently, primary occurrence of this tumor in the kidney has been reported. We experienced one case of PNET primarily arose in the kidney without metastasis. The patient was a 28-year-old man whose chief complaint was abdominal pain, especially on exercise. On computed tomography scan and magnetic resonance imaging, a solid lesion was found in the left kidney, and a left nephrectomy was performed based on the diagnosis of a tumor in the left kidney. The tumor was within the parenchyma of lower end of left kidney protruding into the abdominal cavity. Histologically, diffuse proliferation of primitive small round cells with rosette formation was found. Immunohistochemically, MIC2 gene product, neuron-specific enolase and S-100 protein were positive. No metastasis to the regional lymph nodes was found. From these observations, the tumor was diagnosed as PNET primarily arising in the left kidney. Although chromosome analysis was not performed, EWS-FLI1 chimera gene was identified by reverse transcriptase-polymerase chain reaction on the freshly frozen specimen and fluorescence in situ hybridization on paraffin sections.

Immunohistochemical detection of FLI-1 protein expression: a study of 132 round cell tumors with emphasis on CD99-positive mimics of Ewing's sarcoma/primitive neuroectodermal tumor

The histologic and immunohistochemical differentiation of Ewing' s sarcoma/primitive neuroectodermal tumor (ES/PNET) from other small, blue, round cell tumors may be difficult. Despite initial promise, CD99 (MIC2) has not proven to be a specific marker. Approximately 90% of ES/PNET have a specific t(11; 22)(q24;q12) that results in fusion of the EWS and FLI-1 genes, and overexpression of FLI-1 protein. A recent study has shown immunohistochemical FLI-1 expression in five of seven of the ES/PNET cases tested. We evaluated FLI-1 expression in 132 well-characterized small, blue, round cell tumors. All tumors were immunostained for FLI-1 (1:40, Sc 356 polyclonal, Santa Cruz Biotechnology) using steam heat for epitope retrieval. Only nuclear staining was accepted as positive. Endothelial cells were strongly positive in all cases and served as an internal control. In many cases, a subset of lymphocytes also stained positive. No staining was seen in any other normal tissue. FLI-1 expression was seen in 29 of 41 (71%) ES/PNET, 7 of 8 (88%) lymphoblastic lymphomas, 0 of 8 poorly differentiated synovial sarcomas (PDSS), 0 of 32 rhabdomyosarcoma (RMS), 0 of 30 neuroblastomas, 0 of 8 esthesioneuroblastomas, 0 of 3 Wilms' tumors, 0 of 1 mesenchymal chondrosarcoma, and in 1 of 1 desmoplastic round cell tumor. This last case was known to have an EWS/WT-1 fusion. Although the EWS/FLI-1 fusion gene is specific for ES/PNET, FLI-1 protein expression is not. Significantly, the great majority of lymphoblastic lymphomas (also CD99-positive) are strongly FLI-1-positive. Immunohistochemical detection of FLI-1 may be valuable in confirming the diagnosis of ES/ PNET in cases in which molecular genetic evaluation is not feasible. FLI-1 protein expression is also helpful in distinguishing ES/PNET from other tumors that may be CD99-positive, such as PDSS and RMS. It is not surprising that some ES/ PNET are FLI-1-negative, because not all ES/PNET have the classic EWS/FLI-1, and some cases of ES/PNET may produce either low levels of protein or idiotypically different protein.

Fluorescence in situ hybridization determination of 22q12-q13 deletion in two intracerebral ependymomas

The sole cytogenetic abnormalities encountered in two childhood anaplastic intracerebral ependymomas were an isodicentric chromosome 22 in one case and an unbalanced chromosome 22 translocation associated with a partial deletion in the other. Fluorescence in situ hybridization analysis showed that the common 22q arm loss did not involve the rhabdoid region but included the EWS and NF2 loci. These results, in conjunction with data in the literature, suggest that the most frequently recurrent genomic loss in ependymomas does not involve the proximal 22q11.2 chromosome region but is localized distally to the hSNF5/INI1 locus. A tumor-suppressor gene, independent of the NF2 gene, which seems to be exclusively involved in intramedullary spinal cord ependymomas, might be implicated in the genesis of these intracranial tumors.

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.

Ewing sarcoma family of tumors

The Ewing sarcoma family of tumors (ESFT) shares a common neural histogenesis, tumor genetics, and a fascinating biology, all of which hold the promise of identifying new therapeutic targets. The genetic hallmark of ESFT is the presence of the t(11;22)(q24;q12), which creates the EWS/FLI1 fusion gene and results in the expression of a chimeric protein. This article reviews much of the important work that has been reported over the past year regarding the biology and therapy of ESFT. Major studies include the observation that the early region (E1A) of human adenovirus type 5 is directly linked to and may initiate production of the EWS/FLI1 fusion transcript in normal human fibroblasts and keratinocytes. In addition, there is new information regarding the function of EWS/FLI1 and downstream signals by which it acts. New clinical information continues to support the addition of ifosfamide to standard chemotherapy regimens and help further refine prognostic features, including biologic features that may someday allow better risk stratification and therapy design.

Ewing's family of tumors involving structures related to the central nervous system: a review

This review consolidates information gleaned from several case reports and larger series on Ewing's sarcoma family of tumors (EFT) involving structures related to and found in the central nervous system (CNS). These tumors involve the skull, the spinal column, adjacent soft tissues, the meninges, and the brain. We have separated the cases by skull region and spinal column level, and we discuss the attendant differences in prognosis following treatment by neurosurgery, radiation, and chemotherapy. Light and electron microscopic features can be used to differentiate EFT from other small round blue cell tumors that involve the CNS (central primitive neuroectodermal tumor, lymphoma, etc.). Recent molecular and genetic findings in EFT provide new diagnostic methods. We conclude that EFT involving the CNS and adjacent structures is not so rare as previously stated and that the prognosis is more favorable, as a rule, than for the more common examples arising in the long bones and pelvis.

A Practical Approach to the Differential Diagnosis of Small Round Cell Tumors of Infancy Using Recent Scientific and Technical Advances

Scientific and technical advances have direct impact on the day to day practice of surgical pathology. Pathologists must learn to use new findings to improve diagnostic classification and add clinically useful information in a fiscally responsible manner. The undifferentiated tumors of young people (historically referred to as small round cell tumors of infancy) are a useful example of how new information has become an important part of routine practice. This article describes a practical approach to the differential diagnosis of small round cell tumors using immunophenotypic and genetic analysis as an aid to increase confidence and diagnostic accuracy. Int J Surg Pathol 8(2):87-97, 2000

Primary vulvar and vaginal extraosseous Ewing's sarcoma/peripheral neuroectodermal tumor: diagnostic confirmation with CD99 immunostaining and reverse transcriptase-polymerase chain reaction

Two cases of extraosseous Ewing's sarcoma/peripheral neuroectodermal tumor arising in unusual, superficial sites are reported. One tumor involved the vaginal wall of a 35-year-old woman, and the other neoplasm arose in the dermis of the vulva in a 28-year-old woman. The tumors showed characteristic microscopic features of Ewing's sarcoma/peripheral neuroectodermal tumor with nodular monotonous proliferations of undifferentiated, small, round, hyperchromatic cells with a low mitotic index. Rare rosette-like formations were apparent only in the vulvar neoplasm. The tumors displayed intense immunoreactivity in a membranous pattern for CD99, the cell surface glycoprotein encoded by the MIC2 gene. Genetically, the tumors expressed the EWS/FLI-1 chimeric transcript, derived from the t(11;22)(q24;q12) chromosomal translocation. Both patients had localized disease treated with wide local excision; one received postoperative chemotherapy, and the other received chemotherapy and radiotherapy. To date, 18 and 19 months after diagnosis, neither patient has had clinical evidence of local recurrence or metastasis. To our knowledge, these are the first reported cases of vaginal and vulvar Ewing's sarcoma/peripheral neuroectodermal tumor, confirmed with molecular genetic analysis, in the English literature.

Molecular biology of the Ewing's sarcoma/primitive neuroectodermal tumor family

Ewing's sarcoma (ES) and primitive neuroectodermal tumor (PNET) are members of a tumor family consistently associated with chromosomal translocation and functional fusion of the EWS gene to any of several structurally related transcription factor genes. Similar gene fusion events occur in other mesenchymal and hematopoietic tumors and are tumor-specific. The resulting novel transcription factor-like chimeric proteins are believed to contribute to tumor biology by aberrant regulation of gene expression altering critical controls of cell proliferation and differentiation. These tumor-specific molecular rearrangements are useful for primary diagnosis, may provide prognostic information, and present potential therapeutic targets. The recent advances in our understanding of the molecular biology of ES and PNET represent a paradigm for the application of the basic biology of neoplasia to clinical management of patients.

Molecular detection of low-level disease in patients with cancer

The accurate detection of low-level disease in patients with cancer is essential to improve the staging of disease and consequently to define appropriate treatment strategies. Most methods currently used for staging are based on imaging studies and histological and immunocytochemical analysis of tissues such as bone marrow aspirates, or antibody assays for marker proteins secreted into the circulation. These methods have limited sensitivity. However, assays for nucleic acid-based markers may be valuable tools for the sensitive detection, assessment, and monitoring of disease status in asymptomatic cancer patients. Application of these methods may allow the early detection of cancer, when the tumour burden is smaller and the disease potentially more curable. The last decade has seen the application of polymerase chain reaction (PCR)-based methods to the detection of tumour in a wide variety of compartments, including peripheral blood, bone marrow, lymph nodes, urine, sputum, faeces, pancreatic juice, and more recently plasma. Molecular detection of disease by PCR has targeted DNA and RNA markers, including mutations, microsatellites, and tissue-specific gene expression. It is likely that these molecular methods will provide important clinical information, though their current clinical utility remains unclear. The current status of nucleic acid-based assays for the detection and assessment of disease status in the management of patients with solid tumours is reviewed.

Esthesioneuroblastoma is not a member of the primitive peripheral neuroectodermal tumour-Ewing's group

Esthesioneuroblastoma (ENB) is a rare, site-specific, locally aggressive neuronal malignancy so far thought to belong to primitive peripheral neuroectodermal tumour-Ewing's tumour (pPNETs-ETs). Its anatomical location, in addition to morphologic, immunophenotypic and ultrastructural features, suggests its origin in the neuronal or neuroendocrine cells of the olfactory epithelium. However, the cytogenetic and molecular data currently available appear controversial on the presence of the typical translocation t(11;22)(q24;q12) and of trisomy 8, chromosomal changes that characterize the tumours belonging to the pPNETs-ETs. Herein we have analysed five ENB tumour specimens for trisomy 8 by fluorescence in situ hybridization (FISH), for the presence of EWS gene rearrangements by FISH, reverse transcription polymerase chain reaction and Southern blot analyses, as well as for the expression of the Ewing sarcoma-associated MIC2 antigen by immunohistochemistry. Neither EWS/FLI-I, EWS/ERG and EWS/FEV fusion genes nor MIC2 expression were found in any tumour, whereas trisomy 8 was found in one case only. Moreover, DNA from three cases analysed by Southern blot did not show EWS gene rearrangements. Our results support the evidence that ENB is not a member of the pPNETs-ETs.

Use of tumor-specific gene expression for the differential diagnosis of neuroblastoma from other pediatric small round-cell malignancies

The differential diagnosis of neuroblastoma from other small round-cell tumors of childhood, although clinically of great importance, is sometimes difficult due to the almost indistinguishable appearance of such tumors by conventional microscopy. Because neuroblastomas are characterized by the synthesis of catecholamines, we investigated the possibility that expression of genes involved in this pathway could serve as a molecular marker for this disease. A reverse transcriptase polymerase chain reaction assay was used to analyze expression of tyrosine hydroxylase and dopa decarboxylase in 84 pediatric malignancies including 55 neuroblastomas, 6 Ewing's sarcomas/primitive neuroectodermal tumors, 7 lymphomas, 6 leukemias, 2 rhabdomyosarcomas, 6 osteosarcomas, and 2 phaeochromocytomas. Of the 55 neuroblastoma samples analyzed, 54 expressed clearly detectable levels of both genes. The one sample that did not express either of the genes was rediagnosed both clinically and by molecular genetic analysis as a Ewing's sarcoma. Of the 29 non-neuroblastoma tumor samples examined, the only tumor samples that expressed clearly detectable levels of both tyrosine hydroxylase and dopa decarboxylase were phaeochromocytomas. Like neuroblastomas, these tumors are characterized by high levels of catecholamines. These findings suggest that expression of genes involved in catecholamine biosynthesis may be useful for differentiating neuroblastoma from other small round-cell tumors of childhood.

Prognostic impact of deletions at 1p36 and numerical aberrations in Ewing tumors

Ewing's sarcoma, peripheral primitive neuroectodermal tumors, and Askin tumors are referred to as Ewing tumors (ETs), and are characterized by high MIC2 expression and a t(11;22)(q24;q12) or other rearrangements involving 22q12. In addition to these constant aberrations, facultative numerical and structural aberrations have been reported: gains of chromosomes 8 and 12, the unbalanced translocation t(1;16), and deletions at the short arm of chromosome 1. To evaluate the frequency and to study the biological impact of these facultative aberrations, we analyzed tumor specimens from 58 ET patients by classical cytogenetics and/or in situ hybridization techniques and compared these data with clinical parameters. Gains of chromosomes 8 and 12 were detected in 55% (32/58) and 24% (14/58) of the cases, respectively. Loss of chromosome 16 or der (16)t(1;16) chromosomes were found in 20% (10/51); deletions at 1p36 were observed in 18% (9/51) of the cases evaluated. The presence of these aberrations did not correlate with age and sex of the patients, with the location of the primary tumor or with the extent of disease at diagnosis by chi-square analysis and Fisher's exact test. Patients with tumors harboring gains of chromosome 8 showed a slightly better clinical outcome (n = 14/30, P = 0.17), whereas gains of chromosome 12 did not influence the clinical outcome (n = 7/30, P = 0.63). However, Kaplan and Meier analysis revealed that deletions at the short arm of chromosome 1 were associated with an unfavorable outcome in patients with localized disease (n = 6/22; P = 0.004).

Documentation of EWS gene rearrangements by fluorescence in-situ hybridization (FISH) in frozen sections of Ewing's sarcoma-peripheral primitive neuroectodermal tumor

Prompt and accurate diagnosis of small round cell tumors warrants ancillary studies. Recently, two-color fluorescence in-situ hybridization (FISH) using probes for specific gene rearrangements has gained wide acceptance. EWS gene rearrangements, present in essentially 100% of Ewing's Sarcoma/peripheral primitive neuroectodermal tumor, were evaluated by FISH on frozen sections (FS) of tumor biopsies from 10 patients, plus a negative control, and in seven other malignant neoplasms of childhood. 4mu FS were hybridized overnight, using a single EWS gene-specific probe spanning the EWS breakpoint. We identified EWS rearrangements in 8 of 10 cases (80%) of Ewing's Sarcoma/pPNET. There are no known false positives in diploid or near-diploid tumors, or in any of the non-EWS tumors tested; the uncommon false negative can be confirmed by RT-PCR. Hyperdiploid cases with multiple copies of chromosome 22 may be better evaluated by two-color FISH. This is the first use on FS biopsy material of a single probe for EWS, capable of detecting all known EWS rearrangements, in ES and other tumors. Utilization of this ancillary technique on FS for ES/pPNET and other tumors with distinctive chromosomal translocation is highly specific, reliable, expeditious (24-36 hours) and cost-effective.

Adamantinoma-like Ewing's sarcoma: genomic confirmation, phenotypic drift

Ewing's sarcoma, a highly malignant neoplasm, is characterized by an 11;22 translocation [t(11;22) (q24;q12)], resulting in the fusion of genes FLII and EWS. Adamantinoma of extragnathic bones, a low-grade malignant neoplasm with epithelial features, is not typically considered in the differential diagnosis of Ewing's sarcoma. In this study, three osseous Ewing's sarcomas with histological, immunohistochemical, or ultrastructural epithelial features were subjected to reverse transcription-polymerase chain reaction and sequencing studies for the Ewing's sarcoma molecular rearrangement. (Two of the three cases were originally described as adamantinomas or nontypical Ewing's sarcoma before the availability of genetic characterization.) In addition, traditional cytogenetic analysis and a unique combined interphase molecular cytogenetic/ immunocytochemical approach with bicolor 11;22 translocation breakpoint flanking probes (cosmids) and pancytokeratin antibodies were performed on one neoplasm. At(11;22) (q24;q12) was found in one neoplasm and a type II EWS/FLI-1 fusion transcript was detected in all three neoplasms. The combined genetic/immunocytochemical approach revealed the presence of the 11 ;22 translocation in the nuclei of cytokeratin immunoreactive cells. These genotypic and phenotypic findings delineate a novel Ewing's sarcoma histologic variant, "adamantinoma-like Ewing's sarcoma."

Regulatory role of mevalonate and N-linked glycosylation in proliferation and expression of the EWS/FLI-1 fusion protein in Ewing's sarcoma cells

The Ewing's sarcoma cell line RD-ES, which carries the EWS/FLI-1 fusion gene, responded to the 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor lovastatin with growth arrest. Replenishment of mevalonate (MVA) to the arrested cells restored cell growth. However, if tunicamycin (TM), which is an inhibitor of N-linked glycosylation, was present together with MVA the cells remained arrested, indicating that N-linked glycosylation is of importance for growth of Ewing's sarcoma cells. Inhibition of the biosynthesis of EWS/FLI-1 fusion protein by treatment with antisense oligonucleotides also led to growth arrest, suggesting that this protein is of importance for cell growth. We investigated whether MVA synthesis and N-linked glycosylation could be involved in regulation of the expression of the EWS/FLI-1 fusion protein, which in fact contains four potential sites for N-linked glycosylation. We found that inhibition of both HMG-CoA reductase and N-linked glycosylation drastically decreased the expression of the fusion protein, which mainly appears in the cell nuclei. There was no significant difference in the inhibitory effect on the fusion protein between the cytoplasm and the cell nuclei, indicating that the transport of the fusion protein to the cell nucleus is not affected. The fusion protein did not exhibit any gel electrophoretic mobility shift after treatment of the cells with lovastatin or TM, and it did not incorporate [3H]glucosamine. Therefore we can conclude that the fusion protein is not a glycoprotein. The decreased expression of the fusion protein following lovastatin or TM treatment was found to be due to a lowered stability of de novo-synthesized fusion protein. The down-regulation of the fusion protein was correlated to growth arrest. Furthermore, the kinetics between the expression of EWS/FLI-1 fusion protein and the initiation of DNA synthesis in MVA-stimulated cells were similar. Taken together, our data suggest that the regulatory role of N-linked glycosylation in the expression of the EWS/FLI-1 fusion protein is important for growth of Ewing's sarcoma cells. Possible mechanisms underlying TM-induced decrease in EWS/FLI-1 expression may involve the breaking of growth factor receptor pathways.

Sensitive detection of rare Ewing's sarcoma cells in peripheral blood by reverse transcriptase polymerase chain reaction

Disseminated disease is very important in the clinical assessment of pediatric sarcomas. Several reports suggest that reverse transcriptase polymerase chain reaction (RT-PCR) holds great promise in the early staging of cancer patients in general. However, the complexities of these protocols hamper adequate standardization, and their application as routine diagnostic tools has been difficult. The aim of this study is to assess the actual minimal number of tumor cells that may be detected by RT-PCR in a blood sample. Specific tumor cell dilutions from a Ewing's sarcoma cell line reconstituted in peripheral blood from healthy individuals were "ficolled" and submitted to RNA extraction for cDNA preparation and PCR amplification of the t(11-22) (q24;q12) fusion transcript. After PCR amplification, we were able to detect the EWS/FI-1 chimeric gene product at a dilution of 10 tumor cells per 1 or 2 mL of blood. Our simple method supports a role for routine clinical use of RT-PCR in the detection of circulating Ewing's sarcoma cells.

A novel EWS-ERG rearrangement generating two hybrid mRNAs in a peripheral primitive neuroectodermal tumour (pPNET) with a t(15;22) translocation

The occurrence of a t(15;22) translocation in a peripheral primitive neuroectodermal tumour (pPNET) has been previously reported. Molecular examination revealed the presence in tumour mRNA of two hybrid transcripts containing the 5' portion of the EWS gene fused to the 3' portion of the ERG gene. Sequence analyses indicated that both aberrant mRNAs most likely originated from the same rearrangement, which produced different hybrid isoforms due to the presence of an alternatively spliced exon in the ERG gene. To the authors' knowledge, this is the first report of the detection of two hybrid EWS-ERG mRNAs within the same tumour.

Desmoplastic small round cell tumor: RT-PCR analysis and immunohistochemical detection of the Wilm's tumor gene WT1

Desmoplastic small round cell tumor is an aggressive neoplasm first described in 1991. Recently, a reciprocal translocation t(11;22)(p13;q12) has been characterized by conventional cytogenetic studies and molecular analysis. This translocation involves the Ewing's sarcoma gene on chromosome 22 and the Wilms' tumor gene WT1 on chromosome 11. The chimeric transcript corresponding to the fusion gene could be detected by the reverse transcriptase-polymerase chain reaction (RT-PCR). Using an anti-WT1 antibody, the WT1 part of the putative chimeric protein could be recognized by immunohistochemistry. We describe two well-characterized cases of intraabdominal desmoplastic small round cell tumor in two male patients aged 14 and 28 with both RT-PCR analysis and immunostaining for WT1. In this report, we insist on the necessity to increase the RT-PCR analysis in DSRCT in order to obtain a precise differential diagnosis. In addition, WT1 immunostaining may serve as a useful diagnostic marker for DSRCT.

Chromosome translocation based on illegitimate recombination in human tumors

Recurrent chromosome translocations in nonhematological tumors are restricted to specific subtypes, and their mechanism is currently unknown. Analysis of the sequence data of 113 interchromosomal junctions derived from 77 Ewing's tumors carrying the characteristic t(11;22) translocation indicate that, in this tumor, translocations are initiated independently on each chromosome in regions that lack site specific recombination signal. Local sequence duplications, deletions, and, most importantly, inversions that are diagnostic of DNA hairpin formation indicate that, at the breakpoint, single-stranded DNA ends are processed individually before interchromosomal joining. Taken together, these observations suggest that chromosome translocations in Ewing's tumors are mediated through a genuine illegitimate recombination mechanism.

Molecular genetics in the diagnosis and prognosis of solid pediatric tumors

The field of molecular genetics continues to see an ever increasing number of applications to pediatric tumor analysis. Studies in pediatric tumors have identified novel genes and other genetic changes, a large number of which reflect one of the following mechanisms: (1) activation of proto-oncogenes; (2) loss of tumor suppressor genes; or (3) creation of novel fusion proteins. At least one of these mechanisms is operational in each of the following pediatric tumors: neuroblastoma, Ewing sarcoma and peripheral primitive neuroectodermal tumor (pPNET), intra-abdominal desmoplastic small-cell tumor, rhabdomyosarcoma, synovial sarcoma, and Wilms tumor. Out of this research has come not only an increased understanding of oncogenesis but also, for each of the tumors listed above, diagnostic and/or prognostic markers that can be used by the pathologist and oncologist to improve overall patient management.

Melanotic neuroectodermal tumor of infancy: a molecular genetic study

Melanotic neuroectodermal tumor of infancy is a rare but well-recognized entity in pediatric pathology. However, the relationship of this tumor to other pediatric small cell tumors with neuroectodermal features (such as neuroblastoma, Ewing sarcoma/peripheral primitive neuroectodermal tumor, and desmoplastic small round cell tumor) is undetermined. Molecular genetic studies of melanotic neuroectodermal tumor of infancy have not been reported. We studied three typical cases of melanotic neuroectodermal tumor of infancy in an attempt to link this tumor to other small cell tumors with well-characterized molecular genetic changes. Tests performed included: detection of MYCN gene amplification and deletion of 1p (all 3 cases), and presence of the t(11;22)(q24;q12) and the t(11;22)(p13;q12) translocations (2 of 3 cases). None of these tests yielded positive results. Thus, there is no genetic basis at present to link melanotic neuroectodermal tumor of infancy to neuroblastoma, Ewing sarcoma/peripheral primitive neuroectodermal tumor, or desmoplastic small round cell tumor.

Askin tumor and acute myeloid leukemia in a patient with constitutional partial Y disomy

We report the case of a young adult male carrying a constitutional unbalanced t(Y;13)(q11-12;p13) leading to a partial Y disomy, and presenting successively, in a 39-month interval, with an Askin tumor and a t(8;21) acute myeloid leukemia. The origin of the two neoplasias in this patient is discussed.

Molecular diagnosis of Ewing tumors: improved detection of EWS-FLI-1 and EWS-ERG chimeric transcripts and rapid determination of exon combinations

Most Ewing tumors (ET), including Ewing sarcomas, peripheral primitive neuroectodermal tumors (PNET), and Askin's tumors, can be defined according to the specific chromosomal translocations t(11;22)(q24;q12) (EWS-FLI-1) or t(21;22)(q21;q12) (EWS-ERG). Detection of the chimeric RNA transcripts by reverse transcriptase-polymerase chain reaction (RT-PCR) has greatly facilitated the diagnosis of ET. Because of variable chromosomal breakpoint locations, however, the EWS gene fusions with FLI-1 and ERG genes are highly heterogenous, resulting in different sizes of the amplification products. To improve the diagnostic usefulness of the RT-PCR assay, we have developed an assay to detect chimeric mRNA transcripts by nested RT-PCR, followed by digestion of the PCR fragments with three different restriction endonucleases. This allows confirmation of the specificity of the PCR product and provides a rapid method to determine the combination of exons present in a transcript. In the 12 Ewing tumors tested, five different exon combinations were detected. In nine repeat biopsies of four patients, the case-specific translocation remained unchanged. One additional central PNET had no ET-specific translocation. In conclusion, the suggested combination of RT-PCR and restriction analysis of the PCR products allows a rapid and specific determination of ET-specific translocations.

Renal primitive neuroectodermal tumor: a morphologic, cytogenetic, and molecular analysis with the establishment of two cultured cell lines

We report two patients with renal primitive neuroectodermal tumor (PNET) in whom the diagnosis was established by both a cytogenetic and a molecular analysis. Histologically, both renal tumors were composed of uniform immature round cells with a positive immunoreactivity for O13 (p30/32 MIC2). The cytogenetic analysis with in situ hybridization (chromosome painting) demonstrated reciprocal translocation t(11;22)(q24;q12) specific to PNET in the cultured cells derived from each tumor. The reverse transcriptase-polymerase chain reaction (RT-PCR) in both tumors demonstrated EWS/ FLI-1 fusion transcripts, representing the molecular equivalent of t(11;22). A Southern blot analysis also confirmed EWS gene rearrangement in both renal tumors. In addition, the authors also established two new cell lines (designated as FU-RPNT-1 and FU-RPNT-2) from renal PNETs. When transplanted into athymic mice, FU-RPNT-1 and FU-RPNT-2 reproduced and maintained the morphologic and molecular characteristics of the original tumors. In conclusion, the detection of t(11;22) and EWS/FLI-1 fusion transcripts is considered to provide a novel adjunctive method for diagnosing renal PNET. These newly established cell lines thus may be used to investigate the biologic behavior related to renal PNETs.

Cytogenetic aberrations and DNA ploidy in soft tissue sarcoma. A Southwest Oncology Group Study

We performed cytogenetic analysis and determined DNA content by flow cytometry (FCM) on freshly disaggregated tumor biopsies from 45 patients with soft tissue sarcomas (STS). Cytogenetically aberrant clones characterized 30 (67%) tumors, with the remaining 15 yielding normal karyotypes with or without nonclonal aberrations. No tumors with multiple unrelated clones were observed. Among the 30 tumors with clonally abnormal karyotypes, 21 (70%) had near-diploid stemlines, six were near-triploid and three were near-tetraploid. Ten of the clonally aberrant tumors contained nonrandom chromosomal translocations characteristic of histologic subtypes. Overrepresentation of chromosomes 7 and 8 were common numerical aberrations. Structural aberrations most often involved chromosomes 1, 7, 9, 12, and 14. Clustering of breaks in 9p resulting in partial loss of the short arm was frequent. Unstable aberrations including rings, dicentrics, large markers, small numbers of double minutes, and telomeric associations were seen in nine tumors. With FCM, 27 (60%) tumors had aneuploid DNA content and 18 (40%) were DNA diploid. Of those 18 DNA diploid tumors, 11 showed clonal karyotypic aberrations. In addition, apparent discrepancies between the results of the cytogenetics and FCM with respect to ploidy pattern were seen in 13 samples; 11 had DNA content in the peritriploid to peritetraploid range but the corresponding karyotype was normal or near-diploid. When the findings of the cytogenetics and DNA content analyses were combined, an abnormal cell population by one or both methods was detected in 38 (84%) tumors. The concurrent application of standard cytogenetics and DNA ploidy by FCM provide complementary information confirming a high incidence of genetic alterations in STS.

Multiple chromosomal mechanisms generate an EWS/FLI1 or an EWS/ERG fusion gene in Ewing tumors

The t(11;22)(q24;q12) translocation is found in about 85% of Ewing tumors and leads in all cases to an EWS/FLI1 fusion gene. In a few instances, complex translocations, involving chromosomes 11, 22 and a third chromosome or other variant translocations not involving chromosome 11 also have been reported. These rearrangements generate an active fusion gene between the EWS gene and either the human FLI1 gene or other members of the ETS gene family: the ERG gene localized in band 21q22.2, the ETV1 gene localized in band 7p22, or the E1AF gene localized in band 17q12. Using fluorescence in situ hybridization (FISH) on interphase nuclei or metaphases, we report here the characterization of particular karyotypes in Ewing tumors, namely a complex t(2;11;22) translocation, a variant t(12;22) translocation, and one Ewing tumor without specific rearrangements but with an EWS/ERG fusion gene demonstrated by molecular analysis. These molecular cytogenetic methods allowed us (1) to precisely localize the genomic breakpoints within-EWSR1 and EWSR2 and to identify the chromosome carrying the fusion gene; (2) to determine the nature of events generating the fusion genes; (3) to demonstrate that some variant translocations represent masked complex translocations; and (4) to show that the generation of an EWS/ERG fusion gene cannot be obtained through a simple balanced translocation.

Fusion genes resulting from alternative chromosomal translocations are overexpressed by gene-specific mechanisms in alveolar rhabdomyosarcoma

Chromosomal translocations identified in hematopoietic and solid tumors result in deregulated expression of protooncogenes or creation of chimeric proteins with tumorigenic potential. In the pediatric solid tumor alveolar rhabdomyosarcoma, a consistent t(2;13)(q35;q14) or variant t(1;13)(p36;q14) translocation generates PAX3-FKHR or PAX7-FKHR fusion proteins, respectively. In this report, we demonstrate that in addition to functional alterations these translocations are associated with fusion product overexpression. Furthermore, PAX3-FKHR and PAX7-FKHR overexpression occurs by distinct mechanisms. Transcription of PAX3-FKHR is increased relative to wild-type PAX3 by a copy number-independent process. In contrast, PAX7-FKHR overexpression results from fusion gene amplification. Thus, gene-specific mechanisms were selected to overexpress PAX3-FKHR and PAX7-FKHR in alveolar rhabdomyosarcoma, presumably due to differences in regulation between the wild-type loci. We postulate that these overexpression mechanisms ensure a critical level of gene product for the oncogenic effects of these fusions.

LINE-I element insertion at the t(11;22) translocation breakpoint of a desmoplastic small round cell tumor

A t(11;22)(p13;p12) chromosomal translocation, juxtaposing the Wilms' tumor (WT1) and Ewing's sarcoma (EWS) genes, is the cytogenetic hallmark of desmoplastic small round cell tumor (DSRCT), a primitive multiphenotypic sarcoma arising in serosal tissues. Chimeric transcripts generated by this rearrangement encode an aberrant transcription factor that fuses the 5' region of EWS with a 3' WT1 segment. We describe the insertion of a LINE-I DNA mobile genetic element at the genomic breakpoint of a DSRCT chromosomal translocation. A 480 bp heterologous DNA segment with homology to the LINE-I DNA consensus sequence was located between EWS intron 8 and WT1 exon 8 in the productively rearranged allele. Sequence homology corresponded to the LINE-I ORF-2, which encodes a protein with reverse-transcriptase activity. The heterologous inserted fragment was not evident in the germline of normal tissue from the patient, suggesting that transposition occurred in somatic cells, possibly during the process of chromosomal rearrangement. This case represents the first example of LINE-I DNA transposition at the fusion site of a tumor-associated chromosomal rearrangement.

EWS-FLI1 fusion transcripts identified in patients with typical neuroblastoma

The t(11.22)(q24.q12) results in expression of a chimeric RNA product, EWS-FLI1. This RNA product is expressed in over 85% of tumours belonging to the Ewing's family, and is increasingly used as a definitive characteristic of these tumours. In this study, we evaluated reverse transcriptase-polymerase chain (RT-PCR) for EWS-FLI1 fusion transcripts in 18 neurally derived small round cell tumours. These included six Ewing's family tumours and 12 neuroblastomas. EWS-FLI1 fusion transcripts were identified in all six Ewing's tumours, but also in two of the 12 neuroblastomas. One neuroblastoma contained the classic type 1 fusion transcript, and the second a type 1 transcript containing a 66 bp (base pair) insert that was not derived from the EWS or FLI1 gene. The presence of EWS-FLI1 fusion products in RNA extracted from primary neuroblastoma suggests the identification of EWS-FLI1 fusion transcripts is not pathognomonic for tumours of the Ewing's family. The clinical significance of these fusion transcripts in neuroblastoma is not known.

Musculoskeletal oncology--advances in cytogenetics and molecular genetics and their clinical implications

Although musculoskeletal malignancies comprise a small group of cancers, a vast number of histological subtypes have been identified attesting to the heterogeneity of this class of tumours and the growing interest in their development. The mode of management for both bone and soft tissue sarcomas has been examined extensively and treatment guidelines have been proposed. Despite the intensive study and multidisciplinary treatment, a substantial proportion of tumours remain recalcitrant to therapy and recur locally and systemically. Improved methods of characterising these tumours may help in understanding their biology. Cytogenetic and molecular genetic techniques allow a subcellular dissection of these malignancies which may aid the identification of mechanisms that are important in tumorigenesis. Already candidate genes have been isolated which may play an important role in the deregulation of proliferation and or the adoption of a malignant phenotype, features which are fundamental in tumour development. By studying the molecular biology and cytogenetics of tumours it may be possible to improve diagnostic and prognostic accuracy thereby minimising over and under treatment.

Chromosomal rearrangement t(11;22) in extraskeletal Ewing's sarcoma and primitive neuroectodermal tumour analysed by fluorescence in situ hybridization using paraffin-embedded tissue

The clonal chromosomal rearrangement t(11;22) has been reported by karyotypic analysis to be specific for Ewing's sarcoma of bone and soft tissue origin as well as primitive neuroectodermal tumour. In this report, immunohistological analysis of MIC 2 expression and fluorescence in situ hybridization (FISH) were performed using paraffin-embedded tissues. We examined t(11;22) in the nuclei isolated from two Ewing's sarcomas, four primitive neuroectodermal tumours, and three neuroblastomas, which served as negative controls by FISH with an alpha-satellite DNA probe for chromosome 11, a chromosome 22 marker probe, and whole chromosome painting probes for both chromosomes 11 and 22. Both cases of Ewing's sarcoma and the four primitive neuroectodermal tumour specimens were immunoreactive for MIC 2. Both Ewing's sarcomas and three of the four primitive neuroectodermal tumours contained the tumour-specific t(11;22), but the three neuroblastomas did not show this translocation. Based on the cytogenetic results and on the immunohistological investigation of MIC 2 expression, Ewing's sarcoma is suggested to be related closely to primitive neuroectodermal tumour. FISH is a useful aid in determining the tumour type of Ewing's sarcoma and putative related tumours.