Spontaneous expression of the CIC::DUX4 fusion oncoprotein from a conditional allele potently drives sarcoma formation in genetically engineered mice.

CIC::DUX4 sarcoma (CDS) is a rare but highly aggressive undifferentiated small round cell sarcoma driven by a fusion between the tumor suppressor Capicua (CIC) and DUX4. Currently, there are no effective treatments and efforts to identify and translate better therapies are limited by the scarcity of patient tumor samples and cell lines. To address this limitation, we generated three genetically engineered mouse models of CDS (Ch7CDS, Ai9CDS, and TOPCDS). Remarkably, chimeric mice from all three conditional models developed spontaneous soft tissue tumors and disseminated disease in the absence of Cre-recombinase. The penetrance of spontaneous (Cre-independent) tumor formation was complete irrespective of bi-allelic Cic function and the distance between adjacent loxP sites. Characterization of soft tissue and presumed metastatic tumors showed that they consistently expressed the CIC::DUX4 fusion protein and many downstream markers of the disease credentialing the models as CDS. In addition, tumor-derived cell lines were generated and ChIP-seq was preformed to map fusion-gene specific binding using an N-terminal HA epitope tag. These datasets, along with paired H3K27ac ChIP-sequencing maps, validate CIC::DUX4 as a neomorphic transcriptional activator. Moreover, they are consistent with a model where ETS family transcription factors are cooperative and redundant drivers of the core regulatory circuitry in CDS.

Unusual Neuroendocrine Differentiation in a Small Round Cell Angiosarcoma: A Potential Histologic Mimicker of Superficial Ewing Sarcoma.

Neuroendocrine differentiation or aberrant expression of neuroendocrine markers is very uncommon in angiosarcomas (AS) and creates a challenging differential diagnosis with other superficial or soft tissue tumors. Herein, we report a new case of superficial AS presenting as a tumor lesion on the little finger of the right hand of a 52-year-old man. The tumor displayed CD56, chromogranin-A, and synaptophysin immunoreactivity. Tumor cells were positive for vascular markers (CD31, FLI1, ERG, D2-40, VE-cadherin, VEGR1,2, and 3), CD99, and EMA, but were negative for S100, CK (AE1/AE3), CK20, polyomavirus, and myogenic (desmin and myogenin) and melanocyte markers (melan-A and HMB45). Ki67 immunostains indicated high proliferative activity (>50%). The whole-body computed tomography did not reveal distant disease. The initial assessment considered several tumor subtypes as possible histological diagnoses, including Ewing sarcoma, Ewing-like sarcoma, Merkel cell carcinoma, and undifferentiated "small round cell sarcoma". Fluorescence in situ hybridization analysis was negative for EWSR1 translocation and molecular analysis failed to detect any EWSR1, CIC, SYT or BCOR rearrangement. As a follow-up investigation, we tested 17 cutaneous/superficial AS for neuroendocrine markers; however, only one of these showed focal CD56 and synaptophysin expression. In conclusion, the present findings indicate that neuroendocrine differentiation is a very infrequent feature in AS. We report an AS of the finger with an uncommon histological appearance and immunohistochemical profile: predominant round cell tumor proliferation and neuroendocrine differentiation. Pathologists should be aware of these potential histological and immunohistochemical pitfalls in AS.

Clinicopathologic Diversity of Undifferentiated Sarcoma With BCOR-CCNB3 Fusion: Analysis of 11 Cases With a Reappraisal of the Utility of Immunohistochemistry for BCOR and CCNB3.

Undifferentiated sarcoma harboring the BCOR-CCNB3 fusion is characterized by its predilection to affect skeletons of adolescent males, cellular small round/spindle cell morphology, and CCNB3 immunoreactivity. We analyzed 11 cases of BCOR-CCNB3 sarcoma, 10 of which were identified in a reverse transcription-polymerase chain reaction-based screen of 85 patient samples recorded in our database as unclassified small round or spindle cell sarcomas. BCOR rearrangements were confirmed by fluorescence in situ hybridization in 8 tumors. All patients were males aged between 6 and 31 years. In addition to 5 tumors in soft tissue and 4 in the axial or appendicular skeletons, which are typical locations, a tumor was located in the paranasal sinus and another in the lung. Microscopically, the tumors comprised proliferating atypical spindle and/or small round cells with diverse morphologic features such as small concentric whorls, myxoid stroma, a hemangiopericytomatous appearance, and/or hyalinized collagen resembling a solitary fibrous tumor, and angiomatous or slit-like spaces containing extravasated erythrocytes. Tumor cells were immunoreactive to CCNB3 (9/11), BCOR (10/10), TLE1 (6/10), bcl-2 (9/11), CD99 (8/10), CD56 (8/10), c-kit (4/10), and cyclin D1 (10/10). In an immunohistochemical analysis of an additional 412 small round or spindle cell tumors, CCNB3 was detected in 6 (1.5%) and BCOR in 18 (4.4%). Our analysis highlights the varying clinicopathologic features of this tumor, which partially overlap with other small round or spindle cell tumors, including solitary fibrous tumor and vascular tumors. Because CCNB3 and BCOR immunohistochemistry lacks adequate sensitivity and specificity, a molecular genetic approach remains essential for diagnosis.

Primary undifferentiated small round cell sarcoma of the deep abdominal wall with a novel variant of t(10;19) CIC-DUX4 gene fusion.

We experienced a 38-year-old Japanese male with t(10;19) CIC-DUX4 -positive undifferentiated small round cell sarcoma in the deep abdominal wall. Three months before his first visit to our hospital, he noticed a mass in his right abdominal wall. Computed tomography on admission revealed a solid abdominal tumor 70×53mm in size and multiple small tumors in both lungs. The biopsy of the abdominal tumor revealed undifferentiated small round cell sarcoma, suggestive of Ewing sarcoma. Under the clinical diagnosis of Ewing-like sarcoma of the abdominal wall with multiple lung metastases, several cycles of ICE (ifosfamide, carboplatin and etoposide) therapy were performed. After the chemotherapy, the lung metastases disappeared, while the primary lesion rapidly grew. Additional VDC (vincristine, doxorubicin and cyclophosphamide) therapy was carried out without apparent effect. Although the surgical removal of the primary lesion was done, peritoneal dissemination and a huge metastatic liver tumor appeared thereafter. The patient died of disease progression two months after the surgery. The total clinical course was approximately one year, showing that the tumor was extremely aggressive. The tumor cells of the surgical specimen were positive for CD99, WT1, calretinin, INI1, ERG and Fli1 by immunohistochemistry. Fusion gene analyses using the frozen surgical material revealed negativity for EWSR1-Fli1, EWSR1-ERG and t(4;19) CIC-DUX4 fusions, but positivity for t(10;19) CIC-DUX4 fusion. Thus, we made a final pathological diagnosis of t(10;19) CIC-DUX4-positive undifferentiated small round cell sarcoma. To our knowledge, this is the 13th case of t(10;19) CIC-DUX4 undifferentiated small round cell sarcoma with precise clinicopathological information. Especially in our case, two types of t(10;19) CIC-DUX4 fusion transcripts were observed, both of which are in-frame and novel.

A novel CIC-FOXO4 gene fusion in undifferentiated small round cell sarcoma: a genetically distinct variant of Ewing-like sarcoma.

Differential diagnosis of small round cell sarcomas (SRCSs) grouped under the Ewing sarcoma family of tumors (ESFT) can be a challenging situation for pathologists. Recent studies have revealed that some groups of Ewing-like sarcoma show typical ESFT morphology but lack any EWSR1-ETS gene fusions. Here we identified a novel gene fusion, CIC-FOXO4, in a case of Ewing-like sarcoma with a t(X;19)(q13;q13.3) translocation. The patient was a 63-year-old man who had an asymptomatic, 30-mm, well-demarcated, intramuscular mass in his right posterior neck, and imaging findings suggested a diagnosis of high-grade sarcoma. He was treated with complete resection and subsequent radiotherapy and chemotherapy. He was alive without local recurrence or distant metastasis 6 months after the operation. Histologic examination revealed SRCS with abundant desmoplastic fibrous stroma suggesting a desmoplastic small round cell tumor. Immunohistochemical analysis showed weak to moderate and partial staining for MIC2 (CD99) and WT1, respectively. High-throughput transcriptome sequencing revealed a gene fusion, and the genomic rearrangement between the CIC and FOXO4 genes was identified by fluorescence in situ hybridization. Aside from the desmoplastic stroma, the CIC-FOXO4 fusion sarcoma showed morphologic and immunohistochemical similarity to ESFT and Ewing-like sarcomas, including the recently described CIC-DUX4 fusion sarcoma. Although clinicopathologic analysis with additional cases is necessary, we conclude that CIC-FOXO4 fusion sarcoma is a new type of Ewing-like sarcoma that has a specific genetic signature. These findings have important implications for the differential diagnosis of SRCS.

Undifferentiated small round cell sarcoma with t(4;19)(q35;q13.1) CIC-DUX4 fusion: a novel highly aggressive soft tissue tumor with distinctive histopathology.

A subset of small round cell sarcomas remains difficult to classify. Among these, a rare tumor harboring a t(4;19)(q35;q13.1) with CIC-DUX4 fusion has been described. The aim of this study is to better understand its clinicopathologic features. Four cases of CIC-DUX4 sarcoma, all arising in adults (3 women, 1 man, aged 20 to 43 y), were identified using conventional cytogenetic, reverse transcription polymerase chain reaction (RT-PCR) and fluorescence in situ hybridization (FISH) methods. All 4 tumors demonstrated CIC-DUX4 fusion transcript by both RT-PCR and FISH and CIC rearrangement by FISH. Cytogenetic results from 2 tumors showed t(4;19)(q35;q13.1) occurring as part of a simple karyotype in 1 tumor and as part of a complex karyotype in the other, the latter from a postchemotherapy specimen. Both tumors harbored trisomy 8 and lacked any other known sarcoma-associated translocation. No EWS or SYT rearrangements were detected by RT-PCR or FISH. The tumors had small round cell morphology with a distinctive constellation of histologic features including extensive geographic necrosis, mild nuclear pleomorphism with coarse chromatin and prominent nucleoli, clear cell areas, and focal myxoid matrix. Only focal staining for CD99 was present in each tumor. Two had very focal cytokeratin staining. All tumors were negative for desmin, myogenin, TLE-1, and S100 protein, whereas nuclear INI-1 staining was retained. The tumors were highly aggressive, and all patients died of disseminated disease within 16.8 months. CIC-DUX4 sarcoma represents a novel translocation-associated sarcoma with distinctive histopathologic features and rapid disease progression.

Small cell extraskeletal osteosarcoma.

Extraskeletal osteosarcoma is a rare malignant mesenchymal neoplasm that accounts for <4% of all osteosarcomas and approximately 1.2% of all soft tissue sarcomas. Among the extraskeletal osteosarcomas, the small cell type is extremely rare. This article describes a 31-year-old man who had small cell extraskeletal osteosarcoma arising from the semimembranosus muscle. An incisional biopsy was performed and the histopathological findings showed many small cells and osteoid formation. The results were reported as a malignant small round cell tumor, consistent with an extraskeletal Ewing's sarcoma or primitive neuroectodermal tumor. Immunohistochemically, the tumor showed reactivity with antibodies against CD99 and neuron-specific enolase, but not with antibodies against S100 protein, CD138, alpha smooth muscle actin, chromogranin, Ki-67, leukocyte common antigen, epithelial membrane antigen, CD30, or desmin. The patient refused neoadjuvant chemotherapy. One week after an open biopsy, a wide marginal resection was performed. The final diagnosis was small cell extraskeletal osteosarcoma. Adjuvant chemotherapy was performed using doxorubicin, ifosfamide, and cisplatin together with a total of 60 Gy of radiation therapy. At 2-year follow-up, the functional Enneking score of the operated lower extremity was 28 points. We performed chest computed tomography, magnetic resonance imaging, and positron emission tomography-computed tomography. There were no regional recurrence and distant metastasis. Presently the patient is disease free.

Desmoplastic small round cell tumor: a clinical, pathological, and immunohistochemical study of 18 Chinese cases.

Desmoplastic small round cell tumor (DSRCT) was first reported in 1989. Generally, DSRCT is considered to be an aggressive malignant neoplasm that mainly occurs in the abdominal cavity and has been often seen in adolescents and young male adults. In the present study, a total of 18 cases of DSRCT reported in China between October 1998 and June 2006, including one case treated by the authors, were reviewed and analyzed. Among them, 14 had tumors in the abdominal cavity; the other four cases had tumors in the left fossa orbitalis, the root of the tongue, the soft tissue behind the left eyeball, and the abdominal wall (umbilicus). Overall, the 1-year, 3-year, and 5-year survival rates were 52.36%, 27.92%, and 27.92%, respectively. The survival rate of DSRCT patients is disappointing; however, the survival of patients who had resection of the tumor or received comprehensive clinical treatment is satisfactory.

Binarization of microarray data on the basis of a mixture model.

Although gathered as continuous data, expression measurements from gene microarrays may be quantized before downstream analysis and modeling. This is especially true for modeling gene prediction and genetic regulatory networks. Coarse quantization results in lower computational requirements, lower data requirements for model inference, and easier conceptualization. This paper proposes a mixture model for binarization. For each gene, the model, composed of a sum of two distributions, is fit to expression data for that gene, and data points are binarized according to the model. The mixture model is based on the assumption of multiplicative up-regulation. The proposed method is compared with mean and median binarization by comparing classification performance based on the binary data from the different methods. Classification is performed for simulated data generated from a microarray model studied previously and for cancer data arising from two studies involving hereditary breast cancer and small, round blue-cell tumors of childhood.

Occult lymph node metastasis from desmoplastic small round cell tumor diagnosed by fine needle aspiration cytology. A case report.

BACKGROUND: Desmoplastic small round cell tumor (DSRCT) is a rare but well-defined neoplasm generally forming in the abdominal or pelvic cavity of young males and has distinct clinical, immunohistochemical and molecular features. Cytologic features of DSRCT have been described on fine needle aspiration of primary tumors. An occult lymph node metastasis of DSRCT diagnosed through the cytologic features, a basic immunocytochemical panel and DNA ploidy evaluation on cytospins obtained by fine needle aspiration is reported. CASE: Aspiration cytology was performed on an inguinal lymph node from a 20-year-old male. A Diff-Quik-stained smear showed mature lymphocytes and groups of undifferentiated, small cells with scanty cytoplasm, dense and coarse chromatin, and small nucleoli. Basic immunocytochemical stains showed negativity for leukocyte-common antigen and neuron-specific enolase and positivity for cytokeratin cocktail (Cam 5.2), vimentin and desmin, the last with characteristic paranuclear dotlike positivity. DNA ploidy evaluation showed an aneuploid histogram with a low 5c exceeding rate. CONCLUSION: Cytologic and immunocytochemical features suggest the diagnosis of DSRCT on fine needle aspiration cytology samples even in cases of a metastatic, unknown primary tumor. Because of the tumor's aggressiveness, a rapid and accurate diagnosis is required.

Electron microscopy and other ancillary techniques in the diagnosis of small round cell tumors.

The current study disusses a new approach to the group of small round cell tumors (SRCTs) independently of their primary anatomical location. We perform this analysis supported mainly by morphological means and particularly with the help of immunohistochemistry and electron microscopy; the last of which continues to play a decisive role in their differential diagnosis. The microscopical similarity of many of these tumors often makes the diagnosis in routine histology extremely difficult, due to the varying degree of heterogeneity present, and may have important therapeutic and prognostic implications. Thus a correct final diagnosis is mandatory for the clinic. Within the group of tumors that express a dominant or occasional small round cell pattern "SRCT" (neoplasms of the Central Nervous System excluded) are included: Ewing's sarcoma and peripheral neuroectodermal tumor (Es/pPNET) comprising its varieties, neuroblastoma, desmoplastic small round cell tumor, rhabdomyosarcoma, alveolar, solid and embryonal, small cell osteosarcoma, chondrosarcoma, myxoid and mesenchymal, round cell and myxoid liposarcoma, synovial sarcoma (monophasic undiffentiated), primitive malignant peripheral nerve sheath tumor (malignant small cell schwannoma), malignant non-Hogdkin lymphoma, Merkel cell tumor of the skin (small cell carcinoma including neuroendocrine carcinoma). This study discusses in each case not only the histology, supported by immunohistochemistry, but also the main ultrastructural characteristics. We are conscious that in some cases further cytogenetic or molecular biology support may be necessary, when considering the limits of morphology today. Thus, short references on molecular genetics, complementing the structural findings, are given.

Synovial sarcoma mimicking desmoplastic small round-cell tumor: critical role for molecular diagnosis.

BACKGROUND: The identification of recently described nonrandom chromosomal defects specific for various small round-cell and spindle-cell sarcomas can eliminate diagnostic uncertainty arising from the clinical and histopathologic overlap of soft tissue neoplasms. METHODS: A 26-year-old man presented with bulky abdominal-pelvic disease. Immunohistochemical and molecular studies on tumor were performed. Treatment was instituted using cycles of high-dose cyclophosphamide (4,200 mg/m2) with doxorubicin (75 mg/m2). RESULTS: Clinical findings pointed to desmoplastic small round-cell tumor. The tumor was histologically undifferentiated and immunoreactive for vimentin but negative for other markers. Reverse transcriptase-polymerase chain reaction revealed the SYT/SSX2 fusion transcript of the synovial sarcoma t(X;18) chromosomal rearrangement. The high-dose chemotherapy, plus surgery, achieved a complete remission, but recurrent disease emerged 13 months from diagnosis. CONCLUSIONS: This clinically unique case of synovial sarcoma highlights how the use of now readily available molecular techniques will allow more accurate appraisals of the incidence and anatomic distribution of soft tissue neoplasms-information that bears upon pathogenesis and treatment. This case confirms the utility of high-dose alkylator-based therapy for synovial sarcoma. It also demonstrates that with nonlocalized solid tumors, the eradication of minimal residual disease remains an elusive goal. One alternative involves immunologic attack against markers derived from tumor-specific chromosomal defects such as those found in our patient.

Ca125 and neuron-specific enolase (NSE) as tumour markers for intra-abdominal desmoplastic small round-cell tumours.

Seven consecutive patients with intra-abdominal desmoplastic small round-cell tumours were screened at presentation for carcinoembryonic antigen (CEA), Ca19-9, Ca15-3, Ca125, alpha-fetoprotein (AFP), human chorionic gonadotrophin (hCG) and neuron-specific enolase (NSE). Initially elevated tumour markers were used to monitor therapy and follow-up. Tumour marker assays were all in the normal range, with the exception of Ca125 and NSE. The Ca125 level was initially high in six of the seven patients (86%) with a median value of 200 U ml-1 and a range of 22-735 U ml-1. The NSE value was elevated before therapy in three of the five patients (60%) for whom assay results were available, with a median of 19 ng ml-1 and a range of 6.8-37.5 ng ml-1 . Ca1 25 normalized in five out of six cases and NSE always normalized during chemotherapy, but neither of these two tumour markers correlated specifically with response, as only one patient experienced a partial response, five tumour stabilization and the remaining patient tumour progression. At progression, Ca125 was again elevated in two out of four cases several weeks before clinical relapse and NSE in only one out of three cases. Ca125 and NSE are frequently raised in the serum of patients with intra-abdominal desmoplastic small round-cell tumours before therapy, but are not reliable monitors of the course of the disease. However, normalization is frequently associated with an improvement of symptoms or a moderate clinical response.

Biphasic intra-abdominal desmoplastic small cell tumor in a patient with proximal spinal muscular atrophy.

A case is reported of intra-abdominal desmoplastic small cell tumor (IDSCT) with biphasic histologic features in a patient with proximal spinal muscular atrophy. The tumor was composed of small epithelial cell nests with spindle cell sarcomatous areas. Both areas were surrounded by a desmoplastic stroma. Immunohistochemical studies revealed reactivity for low molecular weight cytokeratin, epithelial membrane antigen, vimentin, desmin and Leu-7 in both areas. Electron microscopic examination demonstrated paranuclear aggregates of intermediate filaments, zonula adherens and basement membrane-like material in the epithelial cells, while spindle cells in the tumor had fewer intracytoplasmic organelles. However, intermediate or transitional forms of both types of tumor cells were frequently observed. Although IDSCT are known to express multi-phenotypes immunohistochemically, attention should be paid to the broad spectrum of cell morphology in these tumors.

Recurrent intrapulmonary malignant small cell tumor of the thoracopulmonary region with metastasis to the oral cavity: review of literature and case report.

Malignant small cell tumor of the thoracopulmonary region (MSCT) was first described in 1979 and has been referred to as the Askin tumor. This malignant neoplasm is a member of the peripheral primitive neuroectodermal tumor (PPNET) family and typically involves the periosteum, soft tissue, and extrapulmonary tissue of the thoracic wall. MSCT may also involve the lung parenchyma by local extension or may arise de novo in peripheral lung tissue. Local recurrence, abdominal involvement by tumor extravasation across the diaphragm, and skeletal metastatic disease are relatively common. However, metastasis to the head and neck region and in particular to the oral cavity is extremely rare. We present a recurrent intrapulmonary MSCT with metastasis to the oral cavity in an adolescent Hispanic boy, and review the literature regarding this member of the PPNET family. Differentiation from neuroblastoma may be made based on immunoreactivity for beta 2 microglobulin and HBA71 and lack of immunoreactivity for chromogranin in PPNET and MSCT. Ultrastructural features commonly seen in MSCT and PPNET are round to ovoid tumor cells with occasional cytoplasmic processes with relatively few pleomorphic dense core granules. These tumors lack the gangliocytic and Schwann cell differentiation that is characteristic of neuroblastoma. MSCT and PPNET have a common reciprocal cytogenetic translocation [t(11;22)q(24;q12)], which is shared with Ewing's sarcoma. Prognosis in MSCT is quite dismal, with a 2-year survival of 38% and a 6-year survival of only 14%.

Round cell sarcomas of possible myelomonocytic origin localized at the lip of aged dogs.

Four round cell tumors, situated at the lip of dogs older than 4 years of age, which could not be further classified, were examined light and electron microscopically, immunocytochemically and in part functionally and cytochemically. Immunocytochemically they were positive for vimentin, but negative for cytokeratin, desmin, neurofilament, synaptophysin, S-100 protein, neuron specific enolase, lysozyme, IgG and a pan-T-cell marker. Cell lines were established from two malignant neoplasms. In vitro, neoplastic cells had morphological, functional and cytochemical properties of myelomonocytic cells. A tumor cell-specific polyclonal rabbit antiserum reacted immunocytochemically positive with primary and recurrent tumors and metastases of the original and the three other round cell tumors. Immunoblotting demonstrated a main band with approximately 65-75 kDa. All four tumors were present in aged dogs and metastasized. They most likely represent a distinct group of malignant tumors among the canine round cell tumors.

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.

Small round and spindle cell sarcoma with neuronal differentiation and oncocyte-like features of the thoracic wall: a case report with histological, immunohistochemical and ultrastructural examinations.

A case of small round and spindle cell sarcoma with neuronal differentiation and oncocyte-like features is presented. The tumor was encountered in a 32 year old Japanese woman with an initial presentation of palpable tumor in the left lateral region of the thorax. The resected tumor was a partially well encapsulated whitish medullary one and consisted of small round and spindle tumor cells, together with so-called rhabdoid cells in the small round cell area. Although pseudorosettes were often observed, true rosette formation could not be detected anywhere. Ultrastructurally, despite a histologic variety of tumor cells, most tumor cells possessed numerous mitochondria, some of which occasionally contained abnormal filamentous or crystalloid structures. Various amounts of microfilaments were present in most tumor cells and microtubules were present in a few. A minority of small round cells possessed a small number of neurosecretory granules, especially in short cytoplasmic processes. A positive immunoreaction for neuron specific enolase was found by immunohistochemical examination in several small round tumor cells and for neurofilaments in lesser numbers. Despite the lack of S-100 protein, MB2 was detected in both small round and spindle cells. On the basis of these findings, the tumor of the present case corresponds to malignant peripheral nerve sheath tumor with neuronal differentiation and oncocytic features.