Identification of CD56 and CD57 by flow cytometry in Ewing’s sarcoma or primitive neuroectodermal tumor

 CD56 and CD57 are commonly considered as natural killer and neuroectodermal markers, but their expression has been identified in a wide spectrum of neoplasms including some cases of Ewing’s sarcoma (ES) and primitive neuroectodermal tumor (PNET). We report two cases of small, round blue cell tumor (SRBCT), in which flow cytometry immunophenotyping (FCI) detected strong expression of CD56 and CD57 (one case). Immunohistochemical staining with Leu-19 and Leu-7 confirmed the FI results. Although CD56 and CD57 expression is consistent with ES/PNET, it can be potentially misleading if results of FCI are interpreted in the absence of other findings. These cases suggest the utility of FCI in undifferentiated SRBCT. The literature on CD56 and CD57 expression in ES/PNET is reviewed and discussed. Received: 5 January 1998 / Accepted: 19 February 1998     

Histological heterogeneity of Ewing’s sarcoma/PNET: an immunohistochemical analysis of 415 genetically confirmed cases with clinical support

Ewing’s sarcoma (ES)/peripheral neuroectodermal tumor (PNET) are malignant neoplasms affecting children and young adults. We performed a study to typify the histological diversity and evaluate antibodies that may offer diagnostic/prognostic support. In total, 415 cases of genetically confirmed paraffin-embedded ES/PNET were analyzed on whole sections and in tissue microarrays. This study confirms the structural heterogeneity of ES/PNET, distinguishing three major subtypes: conventional ES (280 cases); PNET (53 cases); and atypical ES/PNET (80), including large cells, vascular-like patterns, spindle pattern, and adamantinoma-like configuration. All cases presented positivity for at least three of the four tested antibodies (CD99, FLI1, HNK1, and CAV1). CAV1 appeared as a diagnostic immunomarker of ES/PNET being positive in CD99-negative cases. Hence, the immunohistochemical analysis confirmed the diagnostic value of all four antibodies, which together cover more than 99% of the tumors, independently of the histological variety. The univariate analysis for survival revealed atypical ES as the only histological parameter apparently associated with less favorable clinical outcome, particularly in the subgroup of patients treated with surgery. In conclusion, the diagnosis of atypical ES is a challenge for the pathologist and needs support from molecular techniques to perform an optimal differential diagnosis with other small round cell tumors.     

Diagnostic utility of MIC-2 immunocytochemical staining in the differential diagnosis of small blue cell tumors

Ewing's sarcoma (ES) and peripheral neuroectodermal tumor (PNET) are considered in the differential diagnosis of small round blue cell tumors of infancy and childhood which includes neuroblastoma, rhabdomyosarcoma and malignant lymphoma. Fine-needle aspiration diagnosis of these neoplasms can be particularly difficult when the neoplasms are composed of poorly differentiated cells or fail to produce a stroma. MIC-2 is a highly sensitive and specific marker for the PNET/ES group of neoplasms and has been studied extensively in surgical pathology. Other small blue cell neoplasms including rhabdomyosarcoma, blastemal Wilm's tumor, and lymphoblastic lymphoma have also shown positivity, but the staining reactions are usually weak and focal. The utility of this marker in the differential of small blue cell neoplasms in cytologic material has not been examined. Twenty cases of small blue cell neoplasms obtained by fine-needle aspiration (FNA) were studied. MIC-2 antibody was applied retrospectively to formalin-fixed cell block material and destained alcohol-fixed and air-dried cytologic preparations. These cases include primitive neuroectodermal tumor (five cases), Ewing's sarcoma (two cases), neuroblastoma (four cases), Wilms's tumor (four cases), lymphoblastic lymphoma (two cases), and small-cell carcinoma (three cases). The cases were judged positive when the majority of the cells showed cytoplasmic staining. Diffuse cytoplasmic staining was observed in all seven cases of PNET/ES. Staining could be seen on the destained air-dried smears (three cases), fixed smears (two cases), or the cell block material (two cases). None of the other 13 small blue cell neoplasms showed positive staining. We conclude that MIC-2 is a sensitive and specific marker for the PNET/ES group of neoplasms in specimens from formalin-fixed cell block, air-dried, and alcohol-fixed cytologic material and is useful in the differential diagnosis of small blue cell tumors. Diagn. Cytopathol. 1998;19:410–416. © 1998 Wiley-Liss, Inc.     

Immunophenotypic analysis of anaplastic large cell lymphoma by flow cytometry

We studied the antigen expression profiles of 19 anaplastic large cell lymphoma (ALCL) cases by multiparameter flow cytometry. The neoplastic cells expressed CD45, HLA-DR, and CD30 in all cases. At least 1 T cell-associated antigen was expressed in each case (CD2, 12/17 [71%]; CD4, 12/19 [63%]; CD3, 6/19 [32%]; CD7, 6/19 [32%]; CD5, 5/19 [26%]; CD8, 4/19 [21%]). CD25 was expressed in 14 (88%) of 16 cases. CD13 was expressed unexpectedly in 8 (47%) of 17 cases. One CD13+ ALCL also was positive for CD33 and 2 others for CD15, CD19, CD20, CD22, CD14, and CD36 were not expressed. Anaplastic lymphoma kinase protein was detected in about 33% (3/9) of ALCLs examined by flow cytometric immunophenotyping (FCI); expression was validated by immunohistochemical analysis. Of 19 ALCL cases, 12 were diagnosed solely based on FCI findings in conjunction with morphologic evaluation of body fluid (1 case), fine-needle aspirate (3 cases), or excisional biopsy specimen (8 cases). The diagnoses of the remaining 7 cases were suggested strongly by FCI and confirmed by immunohistochemical analysis. FCI is useful to aid in diagnosis of ALCL, particularly along with fine-needle aspiration evaluation. ALCL with aberrant expression of myeloid antigens should not be mistaken for extramedullary myeloid tumor.     

Is preoperative cytologic diagnosis of epithelioid sarcoma possible?

Epithelioid sarcoma (ES) is a rare malignant neoplasm of the soft tissues with a predilection for distal extremities of young adults. A "proximal" variant was recently described. The preoperative fine-needle aspiration cytology (FNAC) differential diagnosis with necrotizing granuloma, carcinoma, melanoma, and other neoplasms with epithelioid morphology can be difficult and few cases have been described in the literature. The authors present the preoperative FNAC findings of 10 aspirates of ES, corresponding to seven patients (four men and three women, ages 13-72 years). The cytologic features were compared with histologic features as well as with the FNA patterns of other neoplasms with epithelioid morphology that may be included in the differential diagnosis. Cytologic smears showed tumor cells with an epithelioid to spindle cell morphology, dispersed and in loose clusters in close relation with a fibrillar hyaline material. The cells showed moderate anisocariosis, a vast well-defined, often dense cytoplasm with immunoexpression of vimentin, cytokeratin, and CD 34. When the FNA cytologic features described above are accompanied by the adequate clinical setting and are supported by immunocytochemistry, an accurate preoperative cytologic diagnosis of ES is possible.     

Lineage-specific identification of nonhematopoietic neoplasms by flow cytometry

To extend flow cytometry (FC) to the diagnosis of nonhematopoietic neoplasms, we have developed new flow cytometric assays to identify expression of cytokeratin, epithelial cell adhesion molecule (EpCAM)/epithelial glycoprotein-2, myogenin, and CD99. To validate these assays, we correlated the flow cytometric results with the histologic and immunohistochemical results on paraffin-embedded tissue in a series of 21 cases, including 17 carcinomas, 1 atypical carcinoid, 2 rhabdomyosarcomas, and 1 Ewing sarcoma/primitive neuroectodermal tumor (ES/PNET). Six of 7 assayed carcinomas and the carcinoid were positive for cytoplasmic cytokeratin by the flow cytometric assay. EpCAM was expressed by 11 of 12 carcinomas that were assayed by FC. Both rhabdomyosarcomas expressed myogenin by FC, and the ES/PNET case expressed CD99. Interestingly, the blast-associated antigen CD90 was expressed uniformly on the ES/PNET case and on subsets of cells in the rhabdomyosarcoma and carcinoma cases. Potential applications of the flow cytometric assay to nonhematopoietic neoplasms will include evaluating samples with limited material, monitoring disease persistence and recurrence in patients with previous diagnoses, and making rapid diagnoses in urgent cases.     

PNET-like features of synovial sarcoma of the lung: a pitfall in the cytologic diagnosis of soft-tissue tumors

Fine-needle aspiration (FNA) cytology of soft-tissue tumors is evolving. As more experience is gained, we are becoming aware of potential pitfalls. We describe 2 cases of synovial sarcoma of the lung, primary and metastatic, in patients who had FNA biopsy performed on a lung mass. The cytologic smears showed extremely cellular groups of malignant small round cells, intersected by small blood vessels, with numerous loose single cells, in a background of macrophages and mature lymphocytes. The tumors displayed monomorphic cells forming rosettes and displaying occasional mitoses. A diagnosis of neuroendocrine tumor/primitive neuroepithelial tumor (PNET) was suspected. Furthermore, this suspicion was supported by immunohistochemical stains, which showed positivity for a neuroendocrine marker, Leu 7 (case 1), and for a neural marker, CD 99 (O 13 or HBA 71) (both cases); and negativity for cytokeratins (case 1). The resection specimen of case 1 had mostly tightly packed small round cells, with occasional rosettes, similar to the FNA biopsy, and focal areas composed of spindle cells, organized in a focal fibrosarcoma-like and hemangiopericytoma-like pattern. A balanced translocation between chromosomes X and 18, demonstrated by both karyotyping and fluorescent in situ hybridization (FISH), enabled us to make a diagnosis of synovial sarcoma, which was histologically classified as poorly differentiated. Case 2 was a metastatic biphasic synovial sarcoma of the arm, with a prominent epithelial component. Synovial sarcoma, when composed mainly of small round cells on cytologic smears, is a great mimicker of neuroendocrine/PNET tumors, with light microscopic and immunohistochemical overlap. Awareness of this potential pitfall may aid in preventing a misdiagnosis. Its recognition is of major concern, especially for the poorly differentiated variant, because it is associated with a worse prognosis.     

Small-cell variant of synovial sarcoma: fine-needle aspiration with ancillary features and potential diagnostic pitfalls

We report a small-cell variant of synovial sarcoma examined by fine-needle aspiration (FNA) biopsy. The patient is a 23-yr-old female who had a synovial sarcoma involving the left infratemporal region, diagnosed at 7 yr of age, followed by a metastatic lesion involving the lung and chest wall 16 yr later. The chest wall metastases was sampled by FNA biopsy. The aspirate consisted of numerous, small, round cells with very high nuclear-to-cytoplasmic ratios. The cytomorphologic features could potentially be confused with other pediatric small round cell tumors. Ancillary studies demonstrated positive staining of the neoplastic cells for cytokeratin, epithelial membrane antigen (EMA), and CD99. The differential diagnosis of other small round cell tumors that may be mistaken for the small-cell variant of synovial sarcoma are presented. We believe that this is the first FNA report detailing the cytologic and ancillary features of the small-cell variant of synovial sarcoma.     

CD99 reactivity in mesenchymal chondrosarcoma

CD99 reactivity has been reported to be a sensitive and specific marker for Ewing's sarcoma (ES) and primitive neuroectodermal tumor (PNET). However, within the group of “small round blue cell tumors,” the specificity has not been extensively examined. We investigated the immunoreactivity of mesenchymal chondrosarcoma to CD99 using the 013 antibody and found reactivity in 11 of 11 (100%) of cases, specifically in the “small round blue cell” component. All cases showed strong reactivity involving more than 50% of the small round blue cells with a distinct membrane pattern of staining. Staining was either absent or focal and weak in cartilaginous areas. We conclude that mesenchymal chondrosarcoma cannot be distinguished from ES/PNET on the basis of CD99 immunoreactivity.     

Fine-needle aspiration biopsy of metastatic Ewing's sarcoma with MIC2 (CD99) immunocytochemistry

The use of fine-needle aspiration biopsy (FNAB) has been infrequently described as a diagnostic modality for Ewing's sarcoma (ES) patient follow-up and management. The purpose of this study is to examine the use and accuracy of FNAB combined with MIC2 immunocytochemistry for evaluating metastases in patients with ES. Records from Saint Louis University Health Sciences Center and Indiana University Medical Centers identified patients with known ES who had undergone FNAB for evaluation of potential metastases. Immunocytochemical analysis for MIC2 (CD99) was performed retrospectively on cell blocks and direct aspirate smears. FNABs from nine patients were procured either percutaneously or under radiologic guidance and in all cases a definitive cytologic diagnosis of metastatic ES was rendered. Aspirates were cellular with many single discohesive small round cells and occasional loosely cohesive clusters. The nuclei were round with a fine chromatin pattern and small nucleoli. The cytoplasm was scanty and the nuclear-cytoplasmic ratio was high. Six of six cases showed strongly positive immunocytochemical labeling for MIC2. Immunocytochemistry with MIC2 in FNAB aspirate smears can provide supportive evidence of ES in patients with known disease. Diagn. Cytopathol. 1998;19:382–384. © 1998 Wiley-Liss, Inc.     

Fine-needle aspiration of subacute granulomatous thyroiditis (De Quervain's thyroiditis): A clinico-cytologic review of 36 cases

Although subacute granulomatous thyroiditis (SGT) is usually diagnosed clinically, there are other thyroid conditions that must be ruled out. This task is achieved by means of fine-needle aspiration (FNA). In retrospect, the clinical and cytologic findings seen in 36 SGT cases are reassessed with a view to deciding which findings are most reliable for reaching a confident cytologic diagnosis. These are: the simultaneous presence in the same aspirate of the following cells: 1) follicular cells with intravacuolar granules and/or plump transformed follicular cells; 2) epithelioid granulomas; 3) multinucleated giant cells; 4) an acute and chronic inflammatory dirty background; 5) the absence of the following cells: fire-flare cells, hypertrophic follicular cells, oncocytic cells, and transformed lymphocytes. The absence of one or more of these requirements does not exclude SGT but does increase the number of thyroid conditions that come into the differential diagnosis. In these cases, it is essential to review clinical data carefully and to submit the patient to a close clinical and FNA follow-up. Diagn. Cytopathol. 16:214–220, 1997. © 1997 Wiley-Liss, Inc.     

Collision tumor of primary merkel cell carcinoma and chronic lymphocytic leukemia/small lymphocytic lymphoma,diagnosed on ultrasound‐guided fine‐needle aspiration biopsy: A unique case report and review of literature

We report an extremely rare case of skin collision tumor between primary Merkel cell carcinoma (MCC) and chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL) first diagnosed on ultrasound‐guided fine‐needle aspiration biopsy (US‐FNA). A 95‐year‐old female with a history of CLL presented with a slow growing left malar mass was referred to our clinic for US‐FNA. US scan showed a well‐defined subcutaneous mass (2.78 cm) with complex echogenicity. On‐site assessment showed a cellular aspiration which was interpreted as small blue round cell tumor. On further examination, smears and cell block showed dimorphic populations of relatively larger cells with neuroendocrine features and smaller lymphoid cells. Immunocytochemical studies of cell block sections revealed that the larger cells were positive for CD56, Chromogranin, Synaptophysin, CK8/18, CK20 (dot‐like pattern); and the smaller cells were positive for CD45. Flow cytometric analysis showed a majority of CD16/CD56 positive cells, 17% of monoclonal B‐cells, and 14% of reactive T cells. The immunophenotype of the monoclonal B cells were of CLL/SLL. The diagnosis of a collision tumor composed of primary MCC and CLL/SLL was confirmed. Surgical resection of the mass one month later concurred with the FNA cytological diagnosis. The fact that surgical specimen displayed a solid tumor with both CLL/SLL and MCC components ruled out the possibility that the FNA merely had MCC with peripheral leukemic blood contaminant. No additional MCC lesion was found in the patient, which ruled out the possibility of metastatic MCC to a lymphomatous lymph node. Diagn. Cytopathol. 2015;43:66–71. © 2014 Wiley Periodicals, Inc.     

Detection of a subset of CD30+ anaplastic large cell lymphoma by interphase fluorescence in situ hybridization

T/null-cell anaplastic large cell lymphoma (ALCL) is a morphologically and clinically heterogeneous group of non-Hodgkin's lymphoma; to date several morphologic variants have been described on histologic specimens. However, the cytologic features of these variants in the fine-needle aspiration (FNA) specimens have not been well evaluated. The t(2;5)(p23;q35) has been identified in a subset of T/null-ALCL and is known to be associated with a favorable prognosis. We reviewed the cytomorphologic characteristics in 24 FNA specimens of ALCL. In all cases, the diagnosis was confirmed on histologic specimens, and immunohistochemical studies for anaplastic lymphoma kinase (ALK) protein expression were performed on the aspirates. The presence of ALK breakpoints were evaluated in nine cases, using a DNA break-apart probe on chromosome 2 covering the ALK gene by fluorescence in situ hybridization (FISH) techniques. Two hundred cells per case were examined. The results were expressed as the percentage of cells containing more than two signals of chromosome 2 to the total number of cells counted. FNA sites included lymph nodes (20), lung (2), breast (1), and soft tissue (1). The median age of the patients was 56 yr (range, 17-75 yr). Twenty cases had systemic involvement; in four cases, skin was the primary site with secondary involvement of the lymph nodes. All cases were CD30(+) by immunohistochemistry; 20 were of T-cell phenotype and 4 were null cell type. The cytologic evaluation revealed typical anaplastic morphology (common type) with many "hallmark cells" in 16 (67%) cases. Other morphologic variants identified were small cell pattern in five cases, monomorphic pattern in two cases, and lymphohistiocytic pattern in one case. FISH studies showed that six (66.7%) of nine cases had at least two signals of chromosome 2, consistent with ALK breakpoints. With careful cytomorphologic evaluation in conjunction with appropriate immunohistochemical studies, a diagnosis of ALCL can be confidently made in the FNA specimens in the cellular aspirates and its morphologic variants also can be recognized. Furthermore, the FNA specimen is suitable in detecting ALK breakpoints by FISH study, permitting rapid identification of a subset of patients with ALCL, who may have a favorable prognosis. Using a commercially available probe, detection of ALK breakpoints in the FNA specimens is simple and can be a useful diagnostic adjunct in cases where distinction from other lymphomas or lymphoid lesions is morphologically difficult.     

Fine‐needle aspiration cytology of Merkel cell carcinoma—A review of 69 cases

This study reviewed the clinical presentation, cytologic findings, and the immunophenotype of 69 Merkel cell carcinoma (MCC) cases sampled by fine‐needle aspiration (FNA). Demographic and clinical data, the cytology findings, and results of ancillary testing were reviewed. Median patient age was 78 years (37?104) with a 1:1.8 female to male ratio. The most common FNA sites sampled included lymph nodes in the neck, the axillary region, the inguinal region and the parotid gland. Most patients had a history of MCC (68%) and/or non‐MCC malignancy (70%). The common cytologic pattern was a cellular smear with malignant cells arranged in a dispersed pattern with variable numbers of disorganized groups of cells. Cytoplasm was scant or absent and nuclei showed mild to moderate anisokaryosis, stippled chromatin, inconspicuous nucleoli, and nuclear molding. Numerous apoptotic bodies were often present. Cell block samples (28 cases) were usually positive for cytokeratins in a perinuclear dot pattern, including 88% of cases with CK20 positivity. CD56 was the most sensitive (95%) neuroendocrine marker on cell blocks and was also positive with flow cytometry in nine cases tested. MCC is most commonly seen in FNA specimens from the head and neck of elderly patients, often with a history of previous skin lesions. Occasional cases present in younger patients and some may be mistaken for other round blue cell tumors, such as lymphoma. CD 56 may be a useful marker in cell block preparations and in flow cytometric analysis of MCC. Diagn. Cytopathol. 2014;42:924–928. © 2014 Wiley Periodicals, Inc.     

Cytodiagnosis of primary lymphoma of bone on fine-needle aspiration cytology specimens: review of 25 cases

Diagnosis of nodal lymphomas on fine-needle aspiration (FNA) cytologic specimens has been well established. However, cytodiagnosis of primary lymphoma of bone has not been well documented because of its rarity. We undertook a retrospective study of 25 cases of FNA cytologic specimens of primary lymphoma of bone. The slides were available for review in 20 cases; each case was evaluated with 15 cytologic features in conjunction with immunophenotyping and available surgical materials. Three diagnostic categories were assigned, including nondiagnostic (4/16%), suspicious (3/12%), and malignant (18/72%). Among the 18 malignant lymphoma, all were diagnosed on the basis of cytologic materials together with immunocytochemistry, except that two cases also relied on the cell blocks. The nondiagnostic and suspicious cases were subsequently confirmed to be malignant lymphoma on the surgical core biopsies. Of the 25 cases, 23 cases were large B-cell lymphoma, one follicular lymphoma large cell type, and one small lymphocytic lymphoma. False-positive or false-negative cases were not present in this study series. In conclusion, the vast majority of primary lymphoma of bone can be accurately diagnosed and classified on FNA cytologic specimens in conjunction with immunocytochemistry. The nondiagnostic and suspicious categories can be further reduced or eliminated by improving FNA techniques or by recommendation of surgical core biopsies together with other techniques such as flow cytometry and molecular analysis.     

FNA biopsy of small round cell tumors of childhood: Cytomorphologic features and the role of ancillary studies

Pediatric tumors which are conventionally considered to be small round cell tumors (SRCTs) include the prototypical neuroblas-toma as well as rhabdomyosarcoma (RMS), Ewing's sarcoma (ES), malignant lymphoma, and primitive neuroectodermal tumor (PNET). Other malignancies may be considered in the differential diagnosis such as small-cell osteogenic sarcoma, un-differentiated (anaplastic) hepatoblastoma, granulocytic sarcoma, blastemal type Wilms' tumor, and desmoplastic small-cell tumor of the peritoneum. The cytomorphologic features of conventional SRCTs is presented as well as the utility of ancillary studies performed on the aspirated material in making a specific and correct diagnosis. The role of the immediate cytologic assessment of the aspirate is stress, since this is a critical step in formulating an initial diagnostic impression that should prompt the need for additional material for pertinent ancillary studies. Although challenging, FNA cytology of SRCTs of childhood can be diagnostic in the majority of cases, allowing specific therapy to be given to patients with unresectable SRCTs without a tissue biopsy as well as documenting recurrent and/or metastatic disease. © 1994 Wiley-Liss, Inc.     

Fine‐needle aspiration findings of a rare hematopoietic neoplasm presenting as obstructive jaundice

A 51‐year‐old female who presented with obstructive jaundice was found to have masses in the pancreatic head and tail as well as suspicious liver and periaortic masses on imaging. Aspiration cytology of the pancreatic tail mass showed abundant large single cells with vacuolated eosinophilic cytoplasm, marked nuclear pleomorphism, large bizarre irregular nuclei, binucleation, and prominent nucleoli. Numerous cells also showed intracytoplasmic black to brown pigmentation. A cell block was obtained and extensive immunohistochemical staining was performed. S‐100, HMB‐45, Sox10, pancytokeratin, CK7, RCC antigen, synaptophysin, HepPar 1, inhibin, CD45, CD21, and CD123 were negative, making melanoma, epithelial malignancies, lymphoma, follicular dendritic and plasmacytoid dendritic cell neoplasms less likely. CD4 and CD56 showed partial positivity, and CD68, CD163, and CD14 were positive, supporting the diagnosis of histiocytic sarcoma. Surgical specimens and immunohistochemistry confirmed the cytologic findings. Histiocytic sarcoma is a rare aggressive malignancy of histiocytic origin with most cases presenting in adults in extranodal sites, most commonly the intestinal tract. Few cases are reported in the literature, presenting diagnostic challenges for cytopathologists when seen on fine‐needle aspiration. We present the first reported case of histiocytic sarcoma presenting as a pancreatic mass, diagnosed by endoscopic ultrasound guided fine‐needle aspiration (EUS‐FNA). This entity is rarely described on cytology and arose in a location in which EUS‐FNA is the diagnostic modality of choice. This case study highlights that cytopathologists should be aware of histiocytic sarcoma occurring in extranodal locations accessible by EUS‐FNA and be familiar with the cytomorphologic appearance.     

Primitive neuroectodermal tumor of the breast: immunohistochemistry and fluorescence in situ hybridization

A case of primitive neuroectodermal tumor (PNET) that developed as a breast lump in a 47-year-old Japanese woman is reported. After fine-needle aspiration (FNA) cytology, a mastectomy was performed. The surgical specimen was a well-circumscribed tumor, 21 x 18 x 18 mm, localized in the breast. The tumor cells were small and round with scant cytoplasm, and proliferated in sheets or solid nests. No intraductal carcinoma component was present. The tumor cells were immunohistochemically positive for neural cell adhesion molecule (CD56), neuron-specific enolase and synaptophysin, and they showed membranous immunoreactivity for the MIC2 protein (CD99). Fluorescence in situ hybridization (FISH) indicated a rearrangement of the EWS region on chromosome 22, which is highly specific for Ewing's sarcoma and PNET, which are referred to as the Ewing's sarcoma family of tumors (EFT). No other lesions suggestive of the primary site of this tumor, such as bone, soft tissue, or other organs were detected. The patient has been disease free for 6 months after surgery followed by chemoradiation therapy. FISH is extremely useful for accurate diagnosis of EFT, especially in cases of unusual locations.