Extraosseous Ewing's sarcoma versus primitive rhabdomyosarcoma: diagnostic criteria and clinical correlation

Electron Microscopy in an Oncologic Institution. Diagnostic Usefulness in Surgical Pathology

A retrospective survey of all electron microscopic (EM) examinations of surgical pathology specimens obtained at the Istituto Nazionale Tumori of Milan over a 5-year period (1981-1985) was carried out. During this time a total of 259 cases were examined: for 97 (38%) electron microscopy provided a substantial diagnostic contribution, whereas in 151 (58%) it confirmed the previous light microscopic diagnosis. In our experience, EM was most useful for diagnosing selected cases of cutaneous malignant melanoma predominantly metastatic, rhabdomyosarcoma, neuroblastoma and poorly differentiated neuroepithelial tumors and less helpful in the further analysis of cases of malignant mesothelioma, Ewing's sarcoma, leiomyosarcoma and fibrohistiocytic malignancies. In cases of well-differentiated neuroepithelial tumors, such as carcinoids, EM data was essentially confirmatory of (immuno)-histochemical findings.

Ewing sarcoma/peripheral primitive neuroectodermal tumor and related tumors

Ewing sarcoma/peripheral primitive neuroectodermal tumor (EWS/pPNET) and other tumors with EWS gene rearrangements encompass a malignant and intermediate neoplasm with a broad anatomic distribution and a wide age range but a predilection for soft tissue in children, adolescents, and young adults. The overlapping histologic, immunohistochemical and cytogenetic and molecular genetic features create diagnostic challenges despite significant clinical and prognostic differences. Ewing sarcoma is the 3rd most common sarcoma in children and adolescents, and desmoplastic small round cell tumor is a rare neoplasm that occurs more often in older children, adolescents, and young adults. Pathologic examination is complemented by immunohistochemistry, cytogenetics, and molecular genetics. This article reviews the clinicopathologic features of EWS/pPNET and desmoplastic small round cell tumor in the spectrum of tumors with EWS gene rearrangements. Other tumors with different histopathologic features and an EWS gene rearrangement are discussed elsewhere in this volume.

Pathobiologic markers of the ewing sarcoma family of tumors: state of the art and prediction of behaviour

Over the past three decades, the outcome of Ewing sarcoma family tumor (ESFT) patients who are nonmetastatic at presentation has improved considerably. The prognosis of patients with metastatic disease at the time of diagnosis and recurrence after therapy remains dismal. Drug-resistant disease at diagnosis or at relapse remains a major cause of mortality among patients diagnosed with ESFT. In order to improve the outcome for patients with potential relapse, there is an urgent need to find reliable markers that either predict tumor behaviour at diagnosis or identify therapeutic molecular targets at the time of recurrence. An improved understanding of the cell of origin and the molecular pathways that regulate tumorigenicity in ESFT should aid us in the search for novel therapies for ESFT. The purpose of this paper is thus to outline current concepts of sarcomagenesis in ESFT and to discuss ESFT patterns of differentiation and molecular markers that might affect prognosis or direct future therapeutic development.

Primary Extraskeletal Ewing Sarcoma of the Thoracic Spinal Epidural Space: A Case Report

Cases of extraskeletal Ewing sarcoma (EES) originating primarily within the spinal epidural space, are very rare and have a very poor prognosis. There is no standard therapy for this disease.

We report the case of a 23-year-old man presenting with symptoms of back pain and numbness of both legs for 10 days. Imaging studies revealed a dorsal soft-tissue, extradural mass at the T8–9 vertebral level. The patient underwent a laminectomy and complete excision of the tumor. The EES diagnosis was confirmed by histologic analysis including immunohistochemistry and by presence of the EWS-ERG due to the t (21: 22) (q22: q12) chromosomal translocation by a reverse transcriptase-polymerase chain reaction (RT-PCR). This is the first report of spinal epidural EES with presence of the EWS-ERG fusion transcript. Post-operatively, the patient received aggressive adjuvant chemotherapy and radiotherapy.

At 63 months after surgery, the patient is without clinical or radiological evidence of recurrent or metastatic disease.

Early discovery of EES and a complete resection followed by the aggressive treatment with radiation and chemotherapy may improve disease-free and overall survival.

Rhabdomyosarcomas in adults and children: an update

CONTEXT

Rhabdomyosarcomas comprise a relatively common diagnostic entity among childhood cancers and a relatively rare one among adult tumors. They may possess a variety of histologies that generally differ among age groups. These lesions appear to be separate biologic entities as well as morphologic categories, with embryonal tumors having genetic lesions related to loss of heterozygosity and aberrant parental imprinting, alveolar tumors containing genetic fusions between PAX and forkhead genes, and pleomorphic tumors showing an accumulation of genetic lesions similar to other adult high-grade sarcomas.

OBJECTIVE

To present guidelines for diagnosis of rhabdomyosarcoma and recent finding concerning the biology and classification of these lesions.

DATA SOURCES

Review of recent and older published literature and distillation of the authors' experience.

CONCLUSIONS

Infants and young children tend to have embryonal rhabdomyosarcomas, adolescents and young adults tend to have alveolar rhabdomyosarcomas, and older adults tend to have pleomorphic rhabdomyosarcomas, although there is some overlap. Newer rare entities, including spindle cell rhabdomyosarcoma and sclerosing rhabdomyosarcoma, have been described in children and adults. Fusion-positive tumors have a distinct molecular signature with downstream activation of a number of myogenic and tumorigenic factors. Genetic testing may be successfully used for diagnosis and may guide therapy in future clinical trials. Differential diagnosis has become simpler than in previous years, because of use of myogenic factors in immunohistochemistry, but classification based solely on histologic features remains challenging.

Primary spinal epidural extraosseous Ewing's sarcoma: report of five cases and literature review

Ewing's sarcoma is the most common malignant bone tumour occurring in children and adolescents and exists in two different clinicopathological entities: osseous Ewing's sarcoma (OES) and extraosseous Ewing's sarcoma (EES). Five cases of primary epidural EES are described, which presented with non-specific symptoms leading to a long diagnostic delay. The median age at diagnosis was 22 years (range 13-36 years). The median diagnostic delay was 3 months. All patients had one or more neurological deficits. All underwent surgical exploration with a laminectomy and partial resection followed by adjuvant radiotherapy to a dose of 46-50 Gy and chemotherapy with VAC (vincristine, adriamycin and cyclophosphamide) alternating with ICE (ifosphamide, cisplatin and etoposide) for at least six cycles. The mean follow-up period is 21.2 months (range 11-32 months). Four of the five patients achieved a complete remission and are disease free at the time of writing this report. Two patients have a residual neurological deficit--both having presented with long history of neurological deficit. Primary spinal epidural EES should be suspected whenever young patients present with back pain and/or radicular pain, have abnormal neurology and an extradural mass is demonstrated on MRI. Surgical excision followed by adjuvant radiotherapy (50 Gy) and combination chemotherapy (VAC alternating with ICE) achieved local and systemic control in these patients. A greater number of patients and longer follow up are required to evolve a generally accepted treatment policy for this aggressive but potentially curable malignancy.

Ewing's sarcoma/primitive neuroectodermal tumor of the ureter: a case report and review of the literature

Extraosseous Ewing's sarcoma/primitive neuroectodermal tumor (ES/PNET) is a rare soft tissue tumor of childhood usually found in the extremities. The authors present the case of a 17-year-old girl who presented with right flank pain and hematuria and during operation was found to have a right ureteral mass. The histopathologic, immunohistochemical, ultrastructural, and cytogenetic characteristics of the excised mass were consistent with extraosseous ES/PNET. This is the first known reported case of extraosseous ES/ PNET of the ureter. The pathologic features and clinical management of this case, as well as a review of the literature, are presented.

Fine-needle aspiration cytology of extraskeletal Ewing's sarcoma

Extraskeletal Ewing's sarcoma (EES) is a round-cell malignancy that manifests most commonly in the paravertebral and intercostal regions. It occurs predominantly in adolescents and young adults, between the ages of 10 and 30 yr, and follows an aggressive course with a high recurrence rate. Distant metastasis is also common. The tumor is often confused with other round, small-cell neoplasms, including primitive neuroectodermal tumor, neuroblastoma, embryonal rhabdomyosarcoma, and lymphoma. This report pertains to a fine-needle aspiration cytologic diagnosis of EES, supported by clinicopathologic and fine structural correlations in a 56-yr-old man who presented with a rapidly growing, massive, right groin mass. The smears showed a diffuse cellular population of malignant round cells composed of two types: one group of larger cell exhibiting a thin-rim, pale cytoplasm, less hyperchromatic nuclei, nucleoli, and diffusely dispersed chromatinic nuclear details; and the second group of smaller and darker cells with highly hyperchromatic and almost smudged nuclei. These are chief cells and dark cells, respectively. Special studies revealed significant intracytoplasmic glycogen and positive vimentin and HBA-71 immunostaining. Cytogenetic findings of chromosomal 11;22 translocation is also supportive of the diagnosis of EES.

Orbital rhabdomyosarcomas and related tumors in childhood: relationship of morphology to prognosis--an Intergroup Rhabdomyosarcoma study

Children and adolescents who develop rhabdomyosarcoma (RMS) and related sarcomas in the orbit and treated on Intergroup Rhabdomyosarcoma protocols have had an extremely high cure rate. This study evaluates the possible relationship between their tumor morphologic subtypes and this high cure rate. The histology of tumors was re-reviewed from 229 of the 264 patients with tumors of the orbit, conjunctiva, and eyelids treated on Intergroup Rhabdomyosarcoma Studies (IRS I, II, III, and IV pilot protocols, and followed through July, 1992. Immunohistochemistry was applied in selected cases. Clinical correlations were done on all 264 cases including both the re-reviewed cases and those reviewed only by the IRS Pathology committee. The 5-year survival rate of 24 children with alveolar RMS was 74% (p < .001). All five infants diagnosed to have an alveolar RMS died before the age of one. Two hundred and twenty-one patients (84%) had embryonal RMS. About three-fourths of the re-reviewed embryonal RMS tumors showed only minimal rhabdomyoblastic differentiation. Thirty-one had a spindle cell RMS, two were anaplastic variants. The 5-year survival rate for patients with embryonal RMS subtypes combined was 94%, and 97% for the 144 patients with poorly differentiated embryonal RMS. In contrast, 90 of 432 IRS II patients treated for poorly differentiated embryonal RMS located in extraocular sites had a 66% survival estimate.

Appraisal of the comparative utility of immunohistochemistry and electron microscopy in the diagnosis of childhood round cell tumors

To provide an objective assessment of the comparative utility of fluorescence- and peroxidase-based immunohistochemistry and electron microscopy, an observer blinded study was conducted under realistic study conditions utilizing a large sampling of poorly differentiated pediatric round cell tumors. Working independently, using a single ancillary technique of particular expertise, each of three investigators attempted to render a specific diagnosis with regard to 50 diagnostically challenging tumors. The results were compared against the subsequent "file diagnosis" established by consensus with all relevant information made available. A grading scheme was applied wherein points were awarded based on the accuracy and confidence of diagnosis. A comparative efficiency rating, expressed as a percentage, was formulated by dividing the number of points awarded each technique by the total number of points theoretically available. Electron microscopy proved superior overall, with an efficiency rating of 89%. Immunoperoxidase and immunofluorescence studies yielded efficiency ratings of 71 and 61%, respectively. Used in combination, the techniques achieved an efficiency rating of 95%. Application of these ancillary techniques resulted in a revision of the provisional diagnosis in 11 of 50 cases, and left only two cases without a firm specific diagnosis.

Patterns of differentiation in extraosseous Ewing's sarcoma cells. An in vitro study

BACKGROUND

In vitro, tissue culture-associated differentiation assays have facilitated the identification of multiple tumor-cell types.

METHODS

We have investigated the capability of differentiation of three extraosseous Ewing's sarcoma cell lines toward a neural and muscular direction by in vitro stimulation with dibutyryl cyclic adenosine-monophosphate (db cAMP) and 5-azacytidine, respectively.

RESULTS

Elongation of cytoplasmic processes and increase of neural markers chromogranin, S-100 protein, and glial fibrillary acidic protein were observed after db cAMP treatment of these lines and neurosecretory granules as well as myelin figures were demonstrated ultrastructurally. These results support the existence of several pathways of neural differentiation in vitro--neuroblastic, Schwannian, and central glial--in stages of maturation more advanced than those previously reported in Ewing's sarcoma of bone. The cell lines showed no definitive myoblastic differentiation after 5-azacytidine treatment.

CONCLUSIONS

These data suggest that these three extraosseous Ewing's sarcoma cell lines configurate a heterogeneous group of tumors with respect to capability of differentiation into the neural lineage, arrested at more advanced stages of neural crest development than Ewing's sarcoma of bone and without capability of myoblastic differentiation with 5-azacytidine.

Small cell osteosarcoma of bone: an immunohistochemical study with differential diagnostic considerations

Seventy-nine cases of small round cell tumors involving bone were studied in an attempt to learn whether the immunohistochemical features of the lesions might allow distinction of small cell osteosarcoma from other potential differential diagnostic considerations, including Ewing's sarcoma, atypical Ewing's sarcoma, primitive neuroectodermal tumor, mesenchymal chondrosarcoma, lymphoma, and the Askin tumor. The tissues studied were all formalin-fixed, decalcified, paraffin sections from patients between the ages of 16 and 48 years. With one exception (a small cell osteosarcoma), none of the lesions was cytokeratin positive. Moreover, none of the lesions was epithelial membrane antigen, desmin, factor VIII-related antigen, synaptophysin, or Leu-M1 positive. Accordingly, strong positivity for these antibodies in a majority of tumor cells should prompt inclusion of tumor types other than those listed above in the differential diagnosis. Vimentin positivity was seen in a majority of the tumors studied irrespective of histologic type. Scattered tumor cells (< 25%) showed positivity with antibodies to muscle-specific actin and smooth muscle actin in several of the different tumor types studied. No lesions other than lymphoma were leukocyte-common antigen (LCA) positive; all but two lymphomas were LCA positive, while all but one lymphoma were L26 positive. One (lymphoblastic) lymphoma was LCA and L26 negative. S-100, neuron-specific enolase, and Leu-7 did not prove to be specific for "neural-associated" tumors, but rather appeared in some small cell osteosarcomas, Ewing's sarcomas, atypical Ewing's sarcomas, primitive neuroectodermal tumors, mesenchymal chondrosarcomas, lymphomas, and Askin tumors. Antibody to cell surface antigen HBA71 was positive in three Ewing's sarcomas (two typical and one atypical) and negative in small cell osteosarcoma (three cases), mesenchymal chondrosarcoma (two cases), and lymphoma (one case). While some guidance may be derived from analysis of immunohistochemical staining patterns in a given lesion, the results reported in the present study do not suggest that routine immunohistochemistry alone will permit distinction of these small cell tumors of bone from one another. The value of immunohistochemical studies appears to lie particularly in the use of antibodies to LCA and S-100 protein to distinguish lymphoma and mesenchymal chondrosarcoma, and perhaps antibody to HBA71 to distinguish neural family lesions (such as Ewing's sarcoma), from other small cell tumors, such as small cell osteosarcoma.

Ultrastructural characterization of poorly differentiated rhabdomyosarcomas

Twenty-five rhabdomyosarcomas, histopathologically and immunocytochemically classified as embryonal (12 cases), alveolar (11 cases), and pleomorphic (two cases), were studied by routine and immunogold electron microscopy, to identify, in poorly differentiated cells, reproducible markers useful for diagnostic purposes. Rhabdomyoblasts with rudimentary sarcomeres were observed in 12 cases (48%). Large cells (named oval cells) with an oval shape and an eccentric nucleus, like rhabdomyoblasts but lacking organized myofilaments, were observed in 20 cases (80%). By immunogold electron microscopy, performed on four of 25 cases, both oval cells and rhabdomyoblasts showed abundant intermediate filaments positive for desmin. Oval cells may be used as markers of poorly differentiated rhabdomyosarcomas.

Retroperitoneal extraosseous Ewing's sarcoma with renal involvement: US and MRI findings

A case of retroperitoneal extraosseous Ewing's sarcoma (EES) with renal involvement, which simulated an exophytic renal mass, is reported. EES is a rare soft tissue tumor that can occur anywhere in the soft tissues, but is seen most commonly in the extremities. Although EES is histologically similar to osseous Ewing's sarcoma, it is usually found in older patients. EES should be included in the differential diagnosis of soft tissue tumors, especially in the second and third decade of life.

Primary Ewing's sarcoma of the skull: follow-up with bone scanning

The authors report and discuss an extremely rare case of primary Ewing's sarcoma originating in the flat bones of the skull. The case was followed up by serial bone scanning during the postoperative period. A subclinical recurrence was detected as a focus at the original site 2.5 years after the first operation. Following a second operation and adjuvant chemotherapy the patient is still asymptomatic.

Malignant peripheral neuroectodermal tumor and its necessary distinction from Ewing's sarcoma. A report from the Kiel Pediatric Tumor Registry

A new classification scheme is proposed for the differential diagnosis of Ewing's sarcoma and malignant peripheral neuroectodermal tumor (MPNT) based on conventional light microscopic and immunohistochemical findings. The presence of Homer-Wright rosettes and/or the expression of at least two neural markers is diagnostic of MPNT Ewing's sarcoma. Ewing's sarcoma was diagnosed in cases lacking Homer-Wright rosettes and expressing no neural marker or only one in immunohistochemistry. Using this "new" approach considerable differences were found between both tumor types. Although most MPNT were located in the thoracopulmonary region, Ewing's sarcoma was located predominantly in the pelvis and extremities. The mean age of MPNT patients was greater than that of Ewing's sarcoma patients. Most importantly, however, was a statistically significant difference in prognosis: disease-free survival in Ewing's sarcoma patients at 7.5 years follow-up was 60% compared with 45% MPNT patients (P = 0.026). The detection of HNK-1 in MPNT indicated a more aggressive biologic behavior, and the expression of protein S-100 appeared to be correlated with a more favorable clinical course.

Primary spinal epidural extraosseous Ewing's sarcoma

The case of a 7-year-old boy with a spinal epidural extraosseous Ewing's sarcoma (EES) is presented. He is in complete remission without neurologic deficit 40 months after diagnosis. Another 15 cases were found in the literature and are discussed together with this patient. Twelve of them were male patients. The mean age of the patients was 17.5 years (range, 4 to 47). Symptoms included back pain and/or radicular pain (100%), paresis of one or both legs (83%), sensory disturbances, and bladder and bowel dysfunction. The mean diagnostic delay was 5.8 months. Each patient underwent laminectomy; complete resection of the tumor was impossible in more than 50% of the cases. Most patients received radiation therapy and/or chemotherapy. Four patients suffered from local recurrence, eight from metastases. Ten (63%) patients died, 1 to 48 months (mean, 16) after diagnosis. The differential diagnosis is discussed, including disk herniation and several benign and malignant tumors.

Immunohistochemical study of childhood rhabdomyosarcomas and related neoplasms. Results of an Intergroup Rhabdomyosarcoma study project

The authors assessed a panel of immunohistochemical stains against 109 pediatric solid tumors, primarily rhabdomyosarcomas, under the auspices of the Intergroup Rhabdomyosarcoma Study. Fresh tumor tissue received from participating organizations was divided into portions that were either frozen or fixed in formalin, alcohol, or B5. Immunostaining was performed by the avidin-biotin complex method using monoclonal antibodies to desmin, neurofilaments, vimentin, cytokeratin, and leukocyte common antigen on cryostat sections. Tissue was also embedded in paraffin and stained with antimuscle-specific actin (MSA) and polyclonal antibodies to desmin, creatine kinase M subunit (CKM), myoglobin, and neuron-specific enolase (NSE). Antidesmin staining of cryostat sections was the most sensitive indicator of rhabdomyosarcoma (58 of 62 specimens positive). Results with this reagent in alcohol-fixed and formalin-fixed tissue were similar (46 of 56 positive versus 43 of 56 positive, respectively) and comparable with results with anti-MSA in formalin-fixed tissue (43 of 55 positive). However, the proportion of cells stained by antidesmin was higher in alcohol-fixed tissue than in formalin-fixed tissue. Staining with antimyoglobin and anti-CKM was much less satisfactory, with positivity rates of 17 of 37 and 11 of 57, respectively, in formalin-fixed rhabdomyosarcomas. Immunostaining of muscle markers revealed evidence of myogenesis in six undifferentiated sarcomas and in two sarcomas with inadequate histologic study on hematoxylin-eosin-stained sections. However, positivity was also noticed in samples of fibromatosis, Wilms' tumor, ectomesenchyoma, peripheral primitive neuroectodermal tumor, renal rhabdoid tumor, myositis ossificans, malignant fibrous histiocytoma, and embryonal sarcoma of the liver. The authors conclude that combined use of antidesmin and anti-MSA enhances the diagnosis of childhood sarcomas, especially when employed with other techniques such as electron microscopic study.

Soft tissue Ewing's sarcoma. Characterization in established cultures and xenografts with evidence of a neuroectodermic phenotype

This study characterizes the histogenesis of soft tissue Ewing's sarcoma (StEs) based upon an analysis of three tumors. Long-term cultured cell lines and nude mice xenografts were established from original neoplasms or from their metastases. Histologically they revealed a small round cell pattern without signs of differentiation. Several ultrastructural features of neural type were found; the same were also seen on culture cell lines. Moreover, immunohistochemical study for neural markers revealed the presence of HNK-1, NSE, LIRC-LON 36, S-100 protein, glial fibrillary acidic protein, neurofilaments (70 kilodaltons), and chromogranin; some of these markers were present only in the transplants. Cytokeratin was also seen. The translocation t(11;22)(q24;q12) was found in all three neoplasms together with other chromosomal abnormalities. N-myc RNA gave negative results whereas c-myc RNA was expressed. Therefore it may be postulated that StEs displays neuroectodermal features somewhat similar to those seen in peripheral neuroepithelioma as well as in atypical Ewing's sarcoma of bone.

Comparative phenotypes in rhabdomyosarcomas and developing skeletal muscle

The morphological and immunohistochemical phenotypes of 51 rhabdomyosarcomas from young people have been described and contrasted with phenotypes in developing skeletal muscle from 20 fetuses and neonates. The tumours express markers in a cumulative and consistent sequence--vimentin, desmin, fast myosin, myoglobin--which evolves pari passu with morphological differentiation and follows the same pattern found in normal myogenesis. Changes in immunohistochemical phenotype are documented in residual and recurrent tumours excised after chemotherapy. The presumptive rhabdomyoblastic nature of some primitive tumours, marking with vimentin alone, is discussed.

Extraosseous Ewing's sarcoma. A study of 42 cases

Fifty patients at the Mayo Clinic (Rochester, MN) from 1935 to 1985 met the histologic criteria for extraosseous Ewing's sarcoma. Forty-two had soft tissue primaries without bony involvement and formed the basis for this retrospective study of the clinical behavior and management of extraosseous Ewing's sarcoma. There were 19 male and 23 female patients (mean age, 22 years). Metastases were documented in 30 of the patients, six at the time of presentation and 24 occurring up to 11 years later, most commonly to lungs or bone. Three patients were lost to follow-up. Sixteen of 35 patients (46%) had local recurrence. Overall survival was 15 of 39 (38.5%) at 5 years. Decreased survival was noted with pelvic tumors, incomplete resections, and presence of metastatic disease, whereas increased survival was associated with wide surgical resection with negative microscopic margins, adjuvant local radiation therapy, and presentation since 1970 (48% 5-year survival compared with 28% before 1970).

Alveolar rhabdomyosarcoma metastatic to the ovary. A report of two cases and a discussion of the differential diagnosis of small cell malignant tumors of the ovary

Two young women with alveolar rhabdomyosarcoma metastatic to the ovary are reported. In each case, the ovarian involvement was detected within a few weeks of the discovery of a soft tissue mass by the patient. Symptoms attributable to the ovarian tumor dominated the initial clinical picture in one case. In the other case, the soft tissue mass was not appreciated by the treating physicians until after the diagnosis of rhabdomyosarcoma had been established by examination of the ovarian tumor. The ovarian tumor was unilateral in one case and bilateral in the other. One primary site was the right foot and the other primary site was the left forearm. These cases illustrate that metastatic alveolar rhabdomyosarcoma rarely enters into the differential diagnosis of a small cell malignant tumor of the ovary. Both patients experienced progression of their disease and died, despite aggressive chemotherapy, within 1 year of presentation.

Rhabdomyosarcoma in children: a histological and immunohistochemical study of 59 cases

Recent studies have suggested that rhabdomyosarcoma can be divided into favourable and unfavourable histology groups. Those subtypes comprising the unfavourable histology group are alveolar, monomorphous round cell and anaplastic rhabdomyosarcoma, with a favourable histology group of embryonal rhabdomyosarcomas. An immunohistological study was undertaken on 59 childhood rhabdomyosarcomas, using antisera to keratin, S100 protein, vimentin, desmin, myoglobin, and troponin T. Our results suggest that desmin is the single most useful antibody in the diagnosis of rhabdomyosarcoma and was expressed in all our cases. The expression of troponin T in the majority of embryonal rhabdomyosarcomas but not in the other histological types has prognostic implications.

Undifferentiated small round-cell tumors of childhood: the immunocytochemical demonstration of myogenic differentiation in fine-needle aspirates

The recognition of myogenic differentiation is not always possible using routine light or electron microscopic techniques. In this article, we describe our experience with two small round-cell neoplasms occurring in young children, each of which exhibited an undifferentiated light microscopic appearance. In both cases, myogenic features were revealed by immunocytochemical methods applied to fine-needle aspiration (FNA) biopsies. Each was immunoreactive for desmin and vimentin and failed to react with antibodies to leukocyte-common antigen. Moreover, formalin-fixed tissue sections of one case were negative for cytokeratin and epithelial membrane antigen. Sporadic reactivity for neuron-specific enolase and Leu-7 antigen was observed in occasional cells in FNA specimens, but synaptophysin was not identified. The rapidity of the method and the reliability of the immunocytochemical findings, when compared with routine cytologic evaluation, emphasize the diagnostic utility of immunocytochemical analysis when FNAs of pediatric soft-tissue tumors are obtained.

Peripheral neuroectodermal sarcoma of soft tissue (peripheral neuroepithelioma): a pathologic study of ten cases with differential diagnosis regarding other small, round-cell sarcomas

Peripheral neuroepithelioma of soft tissue belongs to the group of peripheral neuroectodermal tumors (PNETs), but because of its clinical, biological, and morphological characteristics, it differs from other small, round-cell sarcomas that appear in children (neuroblastoma) or in the thoracopulmonary region (Askin's tumor) and bone (peripheral neuroectodermal sarcoma of bone). We report ten new cases of such PNET variety, based on their histologic, immunohistochemical, and electron microscopic findings. In all of these cases, the clinicopathologic correlations demonstrated high malignancy, with an ominous outcome in nine cases. The mean age of the patients was 32.6 years and there was a clear male predominance (eight men, two women). Histologically, the presence of Homer-Wright rosettes is mandatory for diagnosis, being complemented with positive immunohistochemistry for several neural immunomarkers using paraffin-embedded material. Neuron-specific enolase, E-36, HNK-1, and chromogranin neural markers proved to be positive in a high number of cases, but other markers (S-100 protein, synapto-physin, GFA protein, and neurofilaments [70 kilodalton]) were absent. Electron microscopy confirmed the presence of neural structures, both by scanning and transmission electron microscopy.

Characterization of pyruvate kinase from human rhabdomyosarcoma in relation to immunohistochemical and morphological criteria

We have compared the pyruvate kinase (PK) isoenzyme pattern of three rhabdomyosarcomas with foetal skeletal muscle tissue of 19 and 23 weeks of gestation, together with adult muscle in relation to immunohistochemical and morphological criteria. In foetal tissue of 19 weeks of gestation a focal immunopositivity for desmin and myoglobin was observed, whereas in tissue of 23 weeks an overall positivity for these proteins was present. Two of the three neoplasms were poorly differentiated and of the alveolar subtype. They were desmin immunoreactive. Some large spindle-shaped cells expressed myoglobin. The third one was more differentiated in microscopic characteristics and all cells showed immunoreactivity for desmin and myoglobin. In the foetal tissues five forms of pyruvate kinase isoenzymes were present with K2M2 as the predominant form. In adult muscle tissue only M4 was present. The tumors were characterized by a profound shift to the K-type, whereas the M4-type was not expressed at all. A difference in isoenzyme composition of pyruvate kinase was found between the morphologically less differentiated tumors and the more differentiated tumor; in the latter more M-subunits were expressed.

Two new cases of primary peripheral neuroepithelioma of soft tissue with translocation t(11;22)(q24;q12)

A direct cytogenetic analysis was performed on tumor samples obtained from two patients with clinical and histopathologic diagnosis of primary peripheral neuroepithelioma. Both tumors presented the translocation t(11;22)(q24;q12). These results confirm those previously obtained by other authors and suggest a common histogenetic origin for this tumor with Ewing's sarcoma and Askin's tumor, in which the same translocation has been described.

Cellular junctions in a spectrum of human malignant tumors

Cellular junctions in tumors are often considered a hallmark of epithelial differentiation. However, junctions are also seen in tumors having a different differentiation. This observation prompted us to study cellular junctions in malignant nonepithelial tumors. We found a variety of cellular junctions in such tumors, although the majority were poorly formed. This observation is of importance for diagnostic purposes. We have also tried to clarify the nomenclature of cellular junctions as applied in tumor diagnosis by proposing a systematic categorization of terms in everyday use by pathologists and by referring more extensively to the term paired subplasmalemmal densities (PSD) for non-well-formed junctions.

Small round blue cell sarcoma of bone mimicking atypical Ewing's sarcoma with neuroectodermal features. An analysis of five cases with immunohistochemical and electron microscopic support

Ewing's sarcoma (ES) of bone may occasionally display rosette-like textures mimicking Homer-Wright ones, as seen in neuroectodermic neoplasms (neuroblastoma, peripheral neuroepithelioma). Of a group of 39 cases of ES, reviewed with electron microscopic study, the authors have isolated five atypical ES, which histologically also possessed neuroectodermic traces. These tumors were composed of small round blue cells with rosette-like figures and cytoplasmic glycogen. The immunohistochemical analysis showed positivity for neuron-specific enolase (NSE) as well as for HNK-1 (leu-7) monoclonal antibody. Electron microscopic examination confirmed the tumor cell as being of small round type, with a dense chromatine pattern and the presence of isolated dendritic processes, as well as synaptic-like buttons; intermediate filaments, neurotubuli, and dense-core neurosecretory granules also were seen. Moreover, in two cases basement-like condensations surrounded some cells. Scanning electron microscopic study in one case confirmed the presence of rosette-like figures and cell elongations with short dendritic projections of the cytoplasm. Clinically and radiologically these cases showed features similar to ES of bone; one case, located in the chest wall, had a local relapse after treatment, with the histologic features of a pleomorphic neuroblastoma. The authors conclude that these tumors resemble closely immature neuroepithelioma of soft tissue but, being primary to bone, are superimposable on those described as "neuroectodermal tumors of bone."