Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Neuroectodermal Tumors, Primitive, Peripheral”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 181 records · Page 10Linked to original sources
PubMed2000

Expression of protein gene product 9.5 and tyrosine hydroxylase in childhood small round cell tumors.

Small round cell tumors of childhood can be histologically ambiguous, can require tumor markers for an accurate diagnosis, and include neuroblastoma, peripheral primitive neuroectodermal tumor (pPNET), Ewing's sarcoma (ES), lymphoma, and rhabdomyosarcoma. Because the cell type of origin for ES remains controversial, characterizing gene expression in ES can provide diagnostic markers and lead to better understanding of tumor biology. We studied RNA expression of the neuronal genes protein gene product 9.5 (PGP 9.5) and tyrosine hydroxylase (TH) by Northern analysis in cell lines and tissue from small round cell tumors. PGP 9.5 showed strong expression in 17 of 17 neuroblastoma cell lines, 9 of 9 pPNET cell lines, and 11 of 11 ES cell lines. PGP 9.5 was weakly expressed in 1 of 1 alveolar rhabdomyosarcoma cell lines but not in 1 of 1 embryonal rhabdomyosarcomas, and weak expression was seen in 1 of 7 leukemia cell lines. In tumor tissue, all 12 neuroblastomas expressed PGP 9.5, as did all 7 pPNET and all 7 ES. PGP 9.5 was very weakly expressed in 6 of 9 rhabdomyosarcomas and 1 of 9 lymphomas. TH was expressed only in neuroblastomas, and no TH expression was seen in cell lines or tissue from other tumors. As high expression of PGP 9.5 was only found in neural tumors; PGP 9.5 expression by ES provides further evidence for a neural origin of this tumor, whereas TH expression is highly specific for neuroblastomas. PGP 9.5 expression should allow sensitive detection of minimal residual disease for ES and pPNET using reverse transcription-PCR, and the variability in TH and PGP 9.5 expression levels in neuroblastomas indicates that expression of both genes should be used for monitoring minimal residual disease by reverse transcription-PCR.

Adolescent↗
PubMed2003

Induction of tenascin-C by tumor-specific EWS-ETS fusion genes.

Ewing sarcoma (ES) and peripheral primitive neuroectodermal tumors (PNETs) are associated with a chromosomal translocation resulting in a fusion of the amino-terminus of EWS with the DNA-binding domain of an ETS transcription factor (most commonly FLI1 or ERG). Although previous reports suggested that these chimera proteins would act as aberrant transcription factors, their downstream targets have not been fully elucidated. To identify downstream targets of these EWS-ETS fusion proteins, we introduced EWS-ETS fusion constructs into a human fibrosarcoma cell line, HT-1080, by retroviral transduction. Here we report that Tenascin-C (TNC) is induced to a significantly higher level in cells expressing EWS-ETSs than in cells expressing normal ETSs. Furthermore, through use of an antisense cDNA expression vector we show that expression of endogenous TNC mRNA and protein were reduced coordinately with attenuation of EWS-FLI1 fusion protein expression. A chromatin immunoprecipitation assay showed direct interaction between the TNC promoter and the EWS-FLI1 fusion protein in vivo. In addition, a luciferase reporter assay revealed that EWS-ETSs upregulated the TNC gene through four ETS binding sites in the TNC promoter. High levels of TNC expression were observed in a subset of ES cell lines (3 of 6) and primary tumors (4 of 6). Together with previous studies showing that TNC expression is involved in the invasive and malignant phenotype of several tumor types, our data suggest that the oncogenic effect of EWS-ETS may be mediated in part by upregulating of TNC expression.

DNA, Antisense↗
PubMed1996

Olfactory neuroblastoma and other round cell lesions of the sinonasal region.

Sixty-nine round cell lesions of the sinonasal region (22 olfactory neuroblastomas [ONBs], 17 malignant lymphomas, nine Ewing's sarcomas [ES], nine rhabdomyosarcomas, three sinonasal undifferentiated carcinomas, five malignant melanomas, and four pituitary adenomas) were studied in an attempt to define the differential diagnostic capabilities of antibody to MIC2 and bcl-2 in paraffin-embedded tissue in the distinction of these lesions. In addition, antibody to p53 was applied in each case to define the incidence of p53 positivity among these various tumor types. Each of the ES cases was MIC2 positive; each of the other cases was MIC2 negative. Positivity for bcl-2 was confined to two cases, one of them a malignant lymphoma (85% of cells positive) and one an ONB (5% of cells positive). Small numbers of scattered p53-positive cells appeared in the majority of cases studied, without regard for the specific tumor type; only a single case, a malignant lymphoma, showed a majority (approximately 90%) of p53-positive cells. These results indicate that the MIC2 antibody is a useful method by which to distinguish ES from a variety of other round cell lesions that may be encountered in the sinonasal region. The practical applications of antibody to bcl-2 and p53 seem to be much more limited; by contrast, neither bcl-2 positive cells nor abundant p53 cells identified by immunohistochemical analysis seemed to be frequent findings in any of the tumor types studied. Although ONBs have been included with the peripheral primitive neuroectodermal tumors for classification purposes, these tumors diverge from the ES/primitive neuroectodermal tumor family in that they do not seem to share either the MIC2 positivity or the t(11;22) chromosomal translocation that typify the ES/primitive neuroectodermal tumor family of lesions. Although bcl-2 positivity has been associated with a light microscopic finding of an unfavorable histologic pattern in retroperitoneal neuroblastomas, it does not seem that bcl-2 positivity in ONB will select for a clinically distinctive subset of patients.

12E7 Antigen↗
PubMed1996

Vla and alpha 6 beta 4 integrin expression in neuroendocrine carcinomas of the skin (their xenografts on nude mice and a corresponding primary culture).

Immunohistological expression of VLA1-5 and alpha 6 beta 4 integrins have been studied in 21 cases of primary neuroendocrine carcinomas of the skin (NECS), three xenografts on nude mice and one NECS cell culture. The phenotypic properties of NECS cells were largely maintained in NECS grafted on athymic nude-mice and in the corresponding cell line. Our results indicate that alpha 1 beta 1 and to a lesser extent alpha 3 beta 1, alpha 5 beta 1 are the main integrins expressed in NECS. In addition, VLA2, 4 and alpha 6 beta 4 are heterogeneously expressed in the same group of tumors and very sparsely present. These data suggest that like neuroblastoma and primitive peripheral neuroectodermal tumor (pPNET) the absence or the heterogeneous distribution of such integrins is correlated with the aggressive behaviour of NECS although long-term follow-up was not available for our cases. On the other hand, the alpha 1 expression could be regarded as a novel marker for differential diagnosis between NECS (alpha 1+) and pPNET (alpha 1-). The alpha 1 beta 1, alpha 2 beta 1, alpha 3 beta 1, alpha 5 beta 1 heterodimers in the 21 NECS studied showed an uniform pericellular staining of both the peripheral cells and central cells of the tumor islands. The predominant expression of alpha 1 beta 1 is consistent with the hypothesis of a primitive epithelial totipotential origin in NECS.

Animals↗
PubMed2002

Immunohistochemical staining for KIT (CD117) in soft tissue sarcomas is very limited in distribution.

We performed immunohistochemical analysis for KIT in 365 soft tissue sarcomas. Most tumors evaluated were completely negative for KIT, including all cases of leiomyosarcoma, rhabdomyosarcoma, myxofibrosarcoma, liposarcoma, solitary fibrous tumor, synovial sarcoma, dermatofibrosarcoma protuberans, schwannoma, malignant peripheral nerve sheath tumor, clear cell sarcoma, low-grade endometrial stromal sarcoma, and follicular dendritic cell sarcoma. Tumors showing occasional immunoreactivity for KIT included extraskeletal myxoid chondrosarcoma (2/20), Ewing sarcoma/malignant primitive peripheral neuroectodermal tumor (4/20), melanotic schwannoma (3/5), metastatic melanoma (4/20), and angiosarcoma (5/20). In most cases, staining for KIT was focal. Rare tumor cells showing KIT positivity were identified in a small number of other tumors. This study demonstrates very limited expression of KIT in soft tissue tumors other than gastrointestinal stromal tumors and underscores the discriminatory value of KIT immunohistochemical analysis for differential diagnosis. As some of these findings differ markedly from previous reports, it is evident again that variations in immunohistochemical technique can lead to major discrepancies in positive staining. Since treatment eligibility for selective tyrosine kinase inhibitors such as STI571 hinges on positive immunostaining, standardization and reproducibility of meaningful results are critically important.

Chondrosarcoma↗
PubMed1999

Primitive neuroectodermal tumor of the orbit in an adult. A case report and literature review.

OBJECTIVE: The authors describe the salient clinical, radiologic, and histopathologic features of an orbital primitive neuroectodermal tumor in a 28-year-old man. This is an extremely rare tumor of the orbit, previously reported exclusively in children. DESIGN: Case report. INTERVENTION: Excisional biopsy of the tumor en bloc was performed. MAIN OUTCOME MEASURES: Histopathologic examination was performed by standard techniques and immunohistochemical stains on formaldehyde-fixed, paraffin-embedded tumor tissues. RESULTS: Histologic examination of the sections of the tumor showed small, blue, round cells with occasional Homer-Wright rosette formations. The tumor cells stained positively with neuron-specific enolase and vimentin. CONCLUSIONS: This newly recognized, highly unusual peripheral primitive neuroectodermal tumor should be considered in the differential diagnosis of hypercellular, small, round cell tumor of the orbit in adults.

Adult↗
PubMed1999

Neuroectodermal differentiation in Ewing's sarcoma family of tumors does not predict tumor behavior.

The observation that neuroectodermal differentiation imparts a worse prognosis to the Ewing family of tumors has been suggested by some studies and refuted by others. To assess whether the diagnosis of Ewing's sarcoma versus peripheral primitive neuroectodermal tumor (PNET) affects prognosis, we analyzed tumors from 63 analogously treated pediatric and young adult patients from the National Cancer Institute and St Jude Children's Research Hospital and retrospectively compared the results with clinical outcomes. The tumors were assessed using standard light microscopy and immunohistochemical stains for neuron-specific enolase, CD57, S100 protein, neurofilament protein, and synaptophysin with or without antigen retrieval. Ultrastructural evaluation was also performed in 39 tumors. Classification was performed using Kiel criteria as well as a modified classification. Kaplan-Meier analyses, with Mantel-Haenzel evaluation of the significance of the differences, were performed separately for localized or metastatic tumors. Using the Kiel classification on a subset of 60 cases, 39 tumors qualified as PNET and 21 as Ewing's sarcoma. Using the modified classification on a subset of 61 cases, 14 were classified as PNET, 21 as atypical Ewing's sarcoma, and 26 as Ewing's sarcoma. The addition of electron microscopy to the diagnostic armamentarium significantly increased the likelihood of identifying PNET. No significant differences in event-free or overall survival were seen using either the modified or Kiel classification, regardless of the ancillary diagnostic techniques employed. In this exploratory analysis, neuroectodermal differentiation did not play a role in clinical outcome. Confirmation of this finding will require a larger, separate study of similarly treated patients, and it may not apply to older patients.

Adolescent↗
PubMedDate not supplied

Intra-abdominal polyphenotypic tumor.

The presence of t(11;22)(q24;q12) is often considered diagnostic of Ewing sarcoma and peripheral primitive neuroectodermal tumor (pPNET). We report a case of a polyphenotypic tumor that possessed this translocation as detected by reverse transcriptase polymerase chain reaction (RT-PCR). This tumor was positive for vimentin, desmin, low-molecular-weight keratin, neuron-specific enolase, S-100 protein, and CD57 by immunohistochemistry. Of note, the tumor was negative for MIC2. The tumor had double-minute chromosomes with > 100 copies of the MDM2 gene. Thus, the presence of the t(11;22)(q24;q12) translocation should not be considered diagnostic of Ewing sarcoma and pPNET in the absence of supporting histologic evidence such as positive staining for MIC2. The presence of this translocation in Ewing sarcoma and pPNET has been taken as evidence that these two tumors are related. Rather than extending this relationship to include some polyphenotypic tumors, other tumors may acquire this genetic change during tumor progression. Treatment regimens for tumors may be better based on phenotype rather than genotype when these two profiles are seemingly in conflict.

Abdominal Neoplasms↗
PubMed1994

Primitive neuroectodermal tumor of the orbit.

A 10-year-old girl developed a lump in the lateral aspect of the right eyebrow over a 3-week period. Computed tomography and magnetic resonance imaging revealed a soft-tissue mass in the superolateral aspect of the right orbit associated with zygo-maticofrontal bone erosion and hyperostosis. An incisional biopsy specimen was studied using light microscopy, immunohistochemical staining, and electron microscopy, resulting in a diagnosis of peripheral primitive neuroectodermal tumor. The results of an extensive evaluation for systemic involvement were negative. The patient was subsequently treated with chemotherapy and radiation therapy. Primary primitive neuroectodermal tumor of the orbit is rare. The differential diagnosis and the diagnostic features of this entity are discussed herein.

Child↗
PubMed1996

Detection of the EWS/WT1 gene fusion by reverse transcriptase-polymerase chain reaction in the diagnosis of intra-abdominal desmoplastic small round cell tumor.

We report two cases of intra-abdominal desmoplastic small round cell tumor with characteristic clinical, histological, immunohistochemical, and ultrastructural features. Fusion of the EWS gene on chromosome 22 and the WT1 gene on chromosome 11, resulting from the chromosomal translocation t(11;22)(p13;q12), was detected by reverse transcriptase polymerase chain reaction (RT-PCR) in both cases. This translocation has been previously reported in this type of tumor using either cytogenetic or molecular biological techniques. Tumor tissue from both cases revealed no chimeric fusion transcripts characteristic of the Ewing sarcoma family of peripheral primitive neuroectodermal tumors or of alveolar rhabdomyosarcoma, two tumors in the differential diagnosis of intra-abdominal desmoplastic small round cell tumor. This report demonstrates the utility of molecular studies as an adjunct in the diagnosis of this rare and aggressive tumor.

Abdominal Neoplasms↗
PubMed1988

Pathologic features of extraosseous Ewing's sarcoma: a report from the Intergroup Rhabdomyosarcoma Study.

Eighty-four cases of extraosseous Ewing's sarcoma (EOE) were found during the pathology review of the Intergroup Rhabdomyosarcoma Study I and II. Patients commonly presented during or after adolescence with the most common primary sites including the trunk, extremities, and retroperitoneum. Males were slightly more affected. Histologic sections of 74 tumors in the pathology repository were re-reviewed with attention to rosette formation (positive in 18 cases) and glycogen deposition (++ in 21, + in 36, +/- in 11, and - in 2 of 70 cases examined). Fourteen tumors (7 with rosettes and 7 without) were selected for immunohistochemical and ultrastructural studies, and 13 showed single or multiple neural markers (neuron-specific enolase in 8, S-100 protein in 6, and neurosecretory-type granules in 9). These possible cases of neural EOE could be divided into three subgroups: tumor with bidirectional neuroblastic and schwannian differentiation (5 cases), tumor with monodirectional neuroblastic differentiation (7 cases), and tumor with monodirectional schwannian differentiation (1 case). EOE with a neural nature may be categorized into a spectrum of peripheral primitive neuroectodermal tumors. Clinical, histopathologic, and biologic differences between this disease and conventional sympathetic neuroblastoma are discussed.

Child↗
PubMed1996

Cytogenetics and tissue culture of small round cell tumors of bone and soft tissue.

The variety of tumor-specific cytogenetic and genetic alterations among small round cell tumors (Ewing family of tumors, rhabdomyosarcoma, neuroblastoma, and lymphoma) increases the possibility of genotypic diagnosis of them. In Ewing's sarcoma and related peripheral primitive neuroectodermal tumors, a (11;22)(q24;q12) translocation is associated with hybrid transcripts of the EWS gene with the FLIl gene. In alveolar rhabdomyosarcoma, a (2;13)(q35;qt4) translocation is associated with a chimeric gene between PAX3 and FKHR. Specific genetic alterations of the short arm of chromosome 1 and amplification of the MYCN gene are diagnostically useful in neuroblastomas as the immunoglobulin or T-cell receptor gene rearrangements and chromosome translocations in lymphomas. Thus, cytogenetics and genetics provide an essential adjunct to diagnostic surgical pathology in the case of small round cell tumors, which often present substantial diagnostic challenges. Likewise, in vitro culture studies represent another approach in determining histogenetic origin, novel genes, novel mechanisms of gene dysregulation, and the biological characteristics of small round cell tumors.

Bone Neoplasms↗
PubMed2003

Primitive neuroectodermal tumors, embryonal tumors, and other small cell and poorly differentiated malignant neoplasms of the central and peripheral nervous systems.

Many different types of small cell, embryonal, and poorly differentiated neoplasms originate within the central and peripheral nervous systems. Because appropriate treatment is based on a correct diagnosis, the surgical pathologist must be familiar both with basic characteristics of each of the numerous entities as well as the spectrum of morphologic features that each may display. The nosology and nomenclature of these tumors have a rich and varied history. One basic distinction is between primitive neuroectodermal tumors of the central nervous system (cPNETs) and primitive neuroectodermal tumors of the peripheral nervous system (pPNETs), which are clinicopathologically and genetically distinct. Among the cPNETs are medulloblastoma, pineoblastoma, cerebral neuroblastoma, ependymoblastoma, medulloepithelioma, primary rhabdomyosarcoma, and atypical teratoid/rhabdoid tumor, whereas the pPNETs comprise the more differentiated end of a spectrum of neoplasms that include skeletal and extraskeletal Ewing's sarcoma.

Central Nervous System Neoplasms↗
PubMed1995

The MIC2 antibody 013. Practical application for the study of thymic epithelial tumors.

The lymphocytes that accompany thymomas express an immature T-cell phenotype, as usually demonstrated by CD1 or TdT immunoreactivity. Even when thymomas metastasize or occur in ectopic sites, the infiltrating T lymphocytes show this unique immature phenotype, contrasting with thymic and nonthymic carcinomas, in which the infiltrating T lymphocytes typically show a mature phenotype (CD1 and TdT negative). Therefore, the presence of an immature T-cell population in an epithelial tumor strongly supports a diagnosis of thymoma. The availability of an antibody that consistently marks immature T-cells in routine paraffin sections would be of great help in the study of thymic tumors. In this report, we describe the use of MIC2 antibody (013), which has been widely used for the diagnosis of Ewing's sarcomas and peripheral primitive neuroectodermal tumors because it intensely stains thymocytes. Immunohistochemical staining was performed on paraffin sections of normal/hyperplastic thymus (18 cases), thymoma (62 cases), thymic carcinoma (nine cases), tumors showing borderline features between thymoma and thymic carcinoma (three cases), and ectopic hamartomatous thymoma (two cases). T-cell and B-cell antibodies were also applied to aid in the interpretation. In the normal thymus, almost all lymphocytes in the cortex stained with 013, whereas fewer than 5% of those in the medulla were 013 positive. In thymomas, including the three ectopic thymomas and the single case of metastatic thymoma, most lymphocytes were 013 positive, except the spindle-cell foci (medullary thymoma or medullary component of mixed thymoma), in which the percentage of 013-positive lymphocytes was lower (5-30%). Within the pale foci of "medullary differentiation" and the perivascular spaces of lymphocyte-rich thymomas, few lymphocytes showed 013 positivity, indicating that the T lymphocytes in these areas were more mature. None of the thymic carcinomas harbored 013-positive lymphocytes. Among the three cases of borderline thymoma/thymic carcinoma, only one harbored 013-positive lymphocytes. The 013-positive lymphocytes were not seen in the ectopic hamartomatous thymomas. In normal lymph nodes and nonthymic carcinomas studied as controls, there were no or at most small numbers of isolated 013-positive lymphocytes. We conclude that interpreted in the proper context, MIC2 antibody can serve as a useful marker of immature T-cells and thus help in the confirmation of a diagnosis of thymoma in small biopsy specimens, ectopic thymoma, or metastatic thymoma; in the distinction between invasive thymoma and thymic carcinoma; and in the classification of thymomas.

12E7 Antigen↗
PubMedDate not supplied

[Autologous peripheral stem cell transplantation in children].

19 children between 3 and 23 years underwent 79 leukapheres for collection of blood stem cells. In children suffering from acute lymphoblastic leukemia (ALL), Non Hodgkin's Lymphoma (NHL) and Ewing's Sarcoma (ES) we collected 6.87 x 10(4) CFU-GM/kg (range 2,65-21.7), if collections were started with the first platelet rise. In children with peripheral primitive neuroectodermal tumors (PNET) and neuroblastoma (NBL) we gained only 1.20 x 10(4) CFU-GM/kg (range 0.09-2.24). 17 children received high dose chemoradiotherapy and peripheral stem cell +/- bone marrow rescue. 9 suffered from solid tumors, 8 from hematopoietic malignancies. 9 were transfused with peripheral stem cells only, 8 received bone marrow in addition. Time to reach 0.5 x 10(9)/l granulocytes was very short-median 31 days (12-65), in 4 children receiving more than 5 x 10(4) CFU-GM/kg 12 to 13 days, only. On January 31st, 1989 6/17 children are alive in complete remission after a median observation time of 14.5 months (3-26) after autologous stem cell transfusion, one child is alive in "no remission", 7 died with relapse, 3 died because of infections (2 x aspergillosis, 1 x pseudomonas septicemia). The collection of blood derived stem cells by leukaphereses was well tolerated even in very small children and easily repeatable. With optimal timing high stem cell numbers were obtainable, resulting in a very short duration of posttransplant granulocytopenia.

Adolescent↗
PubMed1990

Soft tissue tumors in first year of life: a report of 190 cases.

A comprehensive review of soft tissue tumors in children and adolescents disclosed the presence of 190 neoplasms in 183 patients, which were diagnosed in infants between birth and 12 months of age; these infants represented approximately 20% of our entire pediatric soft tissue tumor series. In excess of 75% of cases were pathologically benign with the hemangioendothelioma, lymphangioma, and fibromatosis-myofibromatosis constituting the majority of cases in this category. Fibrous histiocytoma and lipoblastoma were the other two benign entities. Congenital-infantile fibrosarcoma was considered a borderline tumor because of its infrequently manifested potential for metastasis; none of the 13 cases in the present study behaved in a malignant fashion. Embryonal rhabdomyosarcoma and peripheral primitive neuroectodermal tumor were the two principal types (17 of 27 cases) of malignant soft tissue tumors. In contrast to soft tissue tumors in the first two decades, those in the first year of life were more often benign despite their cellularity and presence of mitotic activity. Fibroblastic-myofibroblastic tumors were more frequent in this young age group, whereas neurogenic and myogenic tumors were relatively more common in children older than 1 year of age. The trunk and head and neck region were the preferred topographic sites rather than the extremities, which was the case in children beyond the first year of life.

Female↗
PubMed2005

Cytokeratin-positive meningeal peripheral PNET/Ewing's sarcoma of the cervical spinal cord: diagnostic value of genetic analysis.

Peripheral primitive neuroectodermal tumor (PNET)/Ewing's sarcoma (ES) of the central nervous system is extremely rare and should be differentiated from central PNET and other small blue round cell tumors. We describe a case of a meningeal peripheral PNET/ES of the spinal cord in an 11-year-old boy. Immunohistochemically, the small blue round cell tumor showed expression of epithelial markers and of CD99, thus posing an important differential diagnostic problem with a poorly differentiated synovial sarcoma. Fluorescence in situ hybridization revealed rearrangement of the EWS gene, as seen in peripheral PNET/ES. Peripheral PNET/ES does occur in the central nervous system, but its diagnosis can be extremely difficult on morphologic and immunohistochemical grounds alone. Genetic analysis plays a key role in its distinction from other small blue round cell tumors.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1998

Monoclonal antibody NB84 in the differential diagnosis of neuroblastoma and other small round cell tumors.

Two hundred fifty-five well-characterized formaldehyde-fixed and paraffin-embedded small round cell tumors mainly from children and young adults including 105 neuroblastomas were immunohistochemically analyzed with the NB84 monoclonal antibody raised to neuroblastoma cells. Most of the undifferentiated neuroblastomas (21 of 22) and all 83 differentiated neuroblastomas reacted with NB84, but none of these tumors were CD99 positive. Compared with synaptophysin, NB84 was more sensitive, although less specific, in the identification of neuroblastoma in formaldehyde-fixed tissue. In addition to neuroblastoma, skeletal and extraskeletal Ewing's sarcoma and medulloblastoma showed NB84 reactivity in approximately 20% of cases, and 50% of desmoplastic small round cell tumors showed positive cells, usually in smaller numbers than the neuroblastomas. The NB84 reactivity was seen slightly more commonly in morphologically defined (rosette-positive) cases of peripheral primitive neuroectodermal tumors than in Ewing's sarcoma. However, the NB84 positivity did not correlate with the expression of other neural markers (neurofilament proteins, CD57, and synaptophysin) in these tumors. All other small round cell tumors including rhabdomyosarcomas, Wilms' tumors, and lymphomas were NB84 negative. In the case of NB84-positive tumors other than neuroblastoma, their specific reactivity for other markers was useful (Ewing's sarcoma CD99 positive, desmoplastic small round cell tumor desmin and keratin positive). The NB84 monoclonal antibody is a useful reagent to separate neuroblastoma from other small round cell tumors. In problem cases it is best used in a panel together with other markers that address the significant differential diagnostic alternatives.

Adolescent↗