Myoepithelial carcinoma of soft tissue in children: an aggressive neoplasm analyzed in a series of 29 cases

(125)I interstitial brachytherapy for the treatment of myoepithelial carcinoma of the oral and maxillofacial region

PURPOSE

This study evaluated the treatment of myoepithelial carcinoma (MC) of the oral and maxillofacial region with radioactive iodine ((125)I) seed implantation.

METHODS AND MATERIALS

Twenty-seven patients with MC in the oral and maxillofacial region were treated with (125)I seed implantation between March 2006 and October 2012. Thirteen of the 27 patients (8/8 patients with primary disease and 5/19 patients with recurrent disease) were treated on an adjuvant setting after resections, and the other 14 patients were treated by brachytherapy after a recurrence precluding a surgical resection for salvage. The sites of the MC were the parotid for 18 patients, oral cavity for 2 patients, and base of skull for 7 patients. Recurrence-free survival (RFS), overall survival (OS) rates, and side effects were retrospectively reviewed.

RESULTS

Patients were followed for 6-105 months (median 37 months). The 3- and 5-year RFS rates were 51.9% and 46.1%, respectively. The 3- and 5-year OS rates were 68.6% and 51.5%, respectively. The OS and RFS were significantly better among the 8 patients treated upfront in comparison with the 19 patients treated for salvage at relapse. The OS was worst for the 7 patients with base of skull region disease. No severe complications were observed during followup.

CONCLUSIONS

This study showed (125)I brachytherapy is a feasible and effective modality for the treatment of MC. These findings should be interpreted cautiously due to the small number of patients and the relatively short followup.

Epithelioid Sarcoma: Diagnostic Features and Genetics

Epithelioid sarcoma (ES) is a rare, aggressive soft-tissue neoplasm of uncertain differentiation, characterized by nodular aggregates of epithelioid cells, which are immunoreactive to cytokeratins (CKs) and epithelial membrane antigen, and often for CD34. It has a propensity for multifocal disease at presentation, local recurrence, and regional metastasis. These are aggressive neoplasms with particularly poor prognosis after regional or distant metastatic disease, for which surgical resection is still the mainstay of treatment, and options for patients with metastatic disease remain undefined. There are 2 distinct variants: classic ES, which typically presents as a subcutaneous or deep dermal mass in the distal extremities of young adults and comprises nodular distributions of relatively uniform epithelioid cells with central necrosis, and the proximal variant, which has a predilection for proximal limbs and limb girdles and the midline of the trunk, which is composed of sheets of larger, more atypical cells with variable rhabdoid morphology. Both classic and proximal-type ESs are associated with the loss of SMARCB1/INI1 protein expression, but appear otherwise molecularly relatively heterogeneous. We review classic and proximal-type ES, discussing morphology, immunohistochemical and genetic findings, the differential diagnosis, and the future potential for targeted therapies.

Recently described neoplasms of the sinonasal tract

Surgical pathology of the sinonasal region (i.e., nasal cavity and the paranasal sinuses) is notoriously difficult, due in part to the remarkable diversity of neoplasms that may be encountered in this area. In addition, a number of neoplasms have been only recently described in the sinonasal tract, further compounding the difficulty for pathologists who are not yet familiar with them. This manuscript will review the clinicopathologic features of some of the recently described sinonasal tumor types: NUT midline carcinoma, HPV-related carcinoma with adenoid cystic-like features, SMARCB1 (INI-1) deficient sinonasal carcinoma, biphenotypic sinonasal sarcoma, and adamantinoma-like Ewing family tumor.

Ossifying fibromyxoid tumor: morphology, genetics, and differential diagnosis

Ossifying fibromyxoid tumor (OFMT) is a soft tissue neoplasm of uncertain differentiation and intermediate (rarely metastasizing) biologic potential, with typical morphologic features, of an encapsulated, lobulated tumor comprising uniform polygonal cells within fibromyxoid stroma, which is surrounded by or contains metaplastic bone, classically as a peripheral rim of lamellar bone. Ossifying fibromyxoid tumor can arise at almost any site, although most frequently occurs within the extremities and trunk. Although most behave in a benign fashion, tumors can rarely show atypical or malignant features. It is now established that OFMTs represent translocation-associated tumors, with up to 85% associated with recurrent gene rearrangements, mostly involving the PHF1 gene (including in typical, atypical, and malignant neoplasms), with EP400-PHF1 in approximately 40% of tumors, and ZC3H7B-BCOR, MEAF6-PHF1, and EPC1-PHF1 fusions also described. Correct diagnosis is clinically important to ensure correct treatment and prognostication, both to avoid overdiagnosing OFMT as a malignant neoplasm such as osteosarcoma and also because of the propensity for aggressive behavior in a small number of OFMT. We review OFMT, with emphasis on the morphologic spectrum, recent molecular genetic findings, and the differential diagnosis.

Primary Intracranial Myoepithelial Neoplasm

Myoepithelial neoplasms were originally described in the salivary glands but their spectrum has been expanding with reports in other locations, including soft tissue. Intracranial cases are exceptionally rare outside the sellar region where they are assumed to be arising from Rathke pouch rests. Two cases of pediatric intracranial myoepithelial neoplasm in the interhemispheric fissure and the right cerebral hemisphere are reported here. Imaging studies suggest that the second case was associated with cerebrospinal fluid dissemination. Both cases showed typical variation in morphology and immunophenotype between more epithelioid and more mesenchymal features. The differential diagnosis at this particular anatomic location includes meningioma, which can show some overlap in immunophenotype since both tumors express EMA as well as GLUT1. One case was positive for EWSR1 rearrangement by fluorescence in situ hybridization. One patient is disease free at last follow-up while the other succumbed to the disease within days illustrating the clinical spectrum of these tumors.

A Rare Pediatric Example of Subcutaneous Extraskeletal Osteosarcoma: A Case Report and Review of the Morphologic Differential Diagnosis

Primary extraskeletal osteosarcoma is an exceedingly rare malignant neoplasm that accounts for approximately 1% of soft tissue sarcomas and most often occurs in the deep soft tissues of adults. Extraskeletal osteosarcoma is characterized by the production of osteoid, bone, and/or chondroid matrix. The diagnosis of extraskeletal osteosarcoma requires careful radiologic and clinical correlation to ensure that the patient does not have an underlying bone primary. This is a case report of primary subcutaneous extraskeletal osteosarcoma arising in the thigh of a 15-year-old girl with a complex karyotype, and the morphologic differential diagnosis is reviewed.

Myoepithelioma-like Tumors of the Vulvar Region: A Distinctive Group of SMARCB1-deficient Neoplasms

We describe 9 tumors that resemble soft tissue myoepitheliomas but possess certain traits that do not fit perfectly into this category. These tumors, herein referred to as "myoepithelioma-like tumors of the vulvar region," occurred in the subcutis of the vulva and surrounding regions of adult women aged 24 to 65 years. Histologically, the tumors measured 2 to 7.7 cm and were well circumscribed, focally encapsulated, and lobulated. Tumor cells had an epithelioid to spindled shape, with fine amphophilic cytoplasm, and uniform nuclei with vesicular chromatin and nucleoli. The tumor stroma was relatively hypervascular, and comprised a mixture of myxoid and nonmyxoid components. Myxoid areas accounted for <5% to 95% of the tumor volume, wherein cells proliferated singly or in a loosely cohesive manner. In nonmyxoid areas, tumors cells grew in diffuse sheets or storiform arrangements. Immunohistochemically, all tested tumors were positive for vimentin, epithelial membrane antigen, and estrogen receptor; most tumors expressed actin. All tumors were negative for S100 protein, glial fibrillary acidic protein, and CD34. Cytokeratin expression was absent in all but 2 tumors, which showed rare positivity. SMARCB1 expression was deficient in all cases. EWSR1, FUS, and NR4A3 rearrangements were absent. All tumors were treated through surgery. Although 3 tumors regrew or recurred after intralesional excision, all 9 patients were alive without metastases at a mean follow-up of 66 months. Myoepithelioma-like tumors of the vulvar region constitute a distinct group of tumors, although future research is required to determine whether they are an unusual subtype of soft tissue myoepitheliomas or a separate disease.

Myoepithelial Tumors: An Update

Primary myoepithelial neoplasms of soft tissue are uncommon, and have been increasingly characterized by clinicopathologic and genetic means. Tumors are classified as mixed tumor/chondroid syringoma, myoepithelioma, and myoepithelial carcinoma, and they share morphologic, immunophenotypic, and genetic features with their salivary gland counterparts. However, soft tissue myoepithelial tumors are classified as malignant based on the presence of cytologic atypia, in contrast to the criterion of invasive growth in salivary gland sites. This review discusses the clinicopathologic and morphologic characteristics, distinct variants, and currently known genetic alterations of myoepithelial neoplasms of soft tissue, skin, and bone.

Cutaneous epithelioid malignant peripheral nerve sheath tumour: a clinicopathological analysis of 11 cases

AIMS

Epithelioid malignant peripheral nerve sheath tumour (E-MPNST) is a distinctive variant of malignant peripheral nerve sheath tumour characterized by the predominance of epithelioid cells, diffuse S100 positivity and infrequent association with neurofibromatosis type 1. The aim of this study was to further delineate clinicopathological features of cutaneous E-MPNST, correlate them with disease outcome and discuss differential diagnosis.

METHODS AND RESULTS

We analysed 11 cutaneous E-MPNSTs (six males, five females, median age 49 years, median size 1.6 cm). Tumours showed a predilection for lower extremities (45%) and trunk (45%), followed by upper extremity (9%). Follow-up was available for nine of 11 patients (range 24-100 months, median 52 months). Four patients had an uneventful clinical course (44%), two developed local recurrence(s) (22%) and three died due to disseminated disease (33%). No histological parameters were found to predict local recurrence(s), development of distant metastases or disease outcome, including size, percentage of epithelioid component, number of mitoses per 10 high-power fields, degree of nuclear atypia or site of occurrence (dermis, dermis/subcutis, subcutis) (P > 0.05). Immunohistochemically, all tumours were diffusely S100-positive, with a subset displaying loss of integrase interactor 1 (INI1) expression (50%).

CONCLUSIONS

Cutaneous E-MPNST has the potential to pursue an aggressive clinical course, associated with wide dissemination and unfavourable disease outcome.

Salivary gland myoepithelial carcinoma

Salivary gland myoepithelial carcinoma (MC) or malignant myoepithelioma is a rare entity. MC usually presents as a slow-growing painless mass arising in the parotid gland, but may involve other salivary glands. This tumour may be particularly locally aggressive, but its clinical and biological features are not yet fully understood. MC may arise from pre-existing benign lesions, such as pleomorphic adenomas or benign myoepitheliomas, or may arise de novo. It usually affects patients over 50 years old, with no gender preference. Because it is often asymptomatic, the presentation and diagnosis can be delayed by months, even years. The current WHO classification considers MC to be an intermediate- to high-grade malignancy. Other published data suggest it is likely to be a high-grade neoplasm, consistent with its aggressive behaviour. Its epidemiology, histopathological features, immunohistochemical profile, clinical behaviour and optimal management are not well understood. Following review of the current literature we aim to address these.

Epithelioid malignant peripheral nerve sheath tumor: clinicopathologic analysis of 63 cases

Epithelioid malignant peripheral nerve sheath tumor (EMPNST) is rare and differs from conventional malignant peripheral nerve sheath tumor by showing diffuse S-100 protein positivity, infrequent association with NF1, and occasional origin in a schwannoma. Loss of INI1 expression is seen in a subset of tumors. The purpose of this study was to further define clinicopathologic features and outcome data in a large series of EMPNST. Sixty-three cases were identified in consultation files. The patient group consisted of 33 men and 30 women; the median age was 44 years (range, 6 to 80 y). One patient was reported to have NF1. One patient had 3 seemingly separate primary EMPNSTs during his 12-year clinical course. The median tumor size was 3.0 cm (range, 0.4 to 20 cm), and tumors were located most frequently on the lower extremity (30/63; 48%) and trunk (16/63; 25%). Most tumors were superficial (5 dermal, 38 subcutaneous); 15 were subfascial, and 5 were visceral. Microscopically, tumors comprised a relatively uniform but clearly atypical population of epithelioid cells. The majority of tumors demonstrated a multilobular growth pattern, with lobules and nests surrounded by myxoid and/or fibrous stroma. Tumor cells were round, polygonal, or ovoid and had round vesicular nuclei and abundant amphophilic to palely eosinophilic cytoplasm. Focal spindled morphology was seen in one third of cases. Most tumors (55/63; 87%) showed marked cytologic atypia with irregular vesicular nuclei and prominent nucleoli. Mitotic rate ranged from 1 to 46/10 HPF (median, 5/10 HPF); atypical mitotic figures were seen in 7 cases. Necrosis was present in 17 tumors. Twelve tumors were associated with a nerve. Nine tumors arose in a schwannoma (6 conventional type, 3 epithelioid) and 1 in a neurofibroma (in the NF1 patient). All tumors expressed S-100 protein, and the majority showed strong and diffuse staining (87%; 55/63). There was no expression of the melanocytic markers Mart-1/Melan-A (0/58), HMB-45 (0/57), and MiTF (0/9). Other immunohistochemical results included variable staining for GFAP (24/40; 60%) and EMA (4/29; 14%), whereas keratin was consistently negative (0/33). INI1 expression was lost in 67% of tumors examined (35/52). Most tumors were treated by surgical resection; 13 also received chemotherapy and/or radiation. Follow-up data were available for 31 cases and ranged in duration from 3 months to 20 years (median, 36 mo). Twenty-two patients have no evidence of disease at the time of follow-up. Nine patients developed local recurrence, 3 of whom were reported to be disease-free at the time of latest follow-up (44 mo, 19 y, and 20 y). Five patients developed distant metastases, and 4 patients died of disease (including 2 with unresectable recurrent tumors). Recurrence, metastasis, and disease-related death were observed independent of anatomic site or depth. In summary, EMPNST is a morphologically distinct variant that most commonly affects adults on the lower extremity or trunk, although a wide age range and site distribution are seen. Most tumors arise in superficial soft tissue, are diffusely S-100 positive, and two thirds show INI1 loss. On the basis of available follow-up information there is a comparatively low risk for recurrence and metastasis, irrespective of tumor depth.

Malignant epithelioid peripheral nerve sheath tumor with prominent reticular/microcystic pattern in a child: a low-grade neoplasm with 18-years follow-up

Malignant peripheral nerve sheath tumors (MPNSTs) constitute <2% of soft tissue neoplasms in children and display a wide histologic spectrum including low-grade and epithelioid variants, although most are high-grade spindle cell sarcomas. Here, we describe an unusual case of a large retroperitoneal epithelioid MPNST diagnosed in a 7-year-old girl without family history or clinical features of neurofibromatosis type 1. The patient was treated by repeated surgical interventions, polychemotherapy, autologous stem cell transplantation, and irradiation therapy. Over the years, she developed multiple disseminated abdominal recurrences but is currently alive with very slowly progressing disseminated intra-abdominal disease 18 years from initial diagnosis. Histologically, the tumor was composed of medium-sized polygonal and ovoid-to-spindled cells set within a copious myxoid matrix with a prominent reticular and microcystic pattern reminiscent of the recently described reticular/microcystic schwannoma. Immunohistochemistry revealed strong and diffuse expression of S100, CD56, CD57, collagen IV, and neuron-specific enolase, with negativity for perineurial cell markers (claudin-1, epithelial membrane antigen, and glucose transporter-1) and other lineage-specific mesenchymal and epithelial antigens. This unusual variant of low-grade MPNST must be differentiated from a variety of other entities, in particular benign perineurioma, myxoid neurofibroma, and benign reticular/microcystic schwannoma. Confinement of the recurrent disease to the abdominal cavity emphasizes the necessity of primary curative wide excision of this highly recurring but nonmetastasizing low-grade neoplasm.

An update on the application of newly described immunohistochemical markers in soft tissue pathology

CONTEXT

During the last 5 to 10 years, significant progress has been made in the molecular characterization of soft tissue tumors, predominantly with the identification of recurrent translocations or amplification of certain genes in different tumor types. Alongside this, translational efforts have identified many novel and diagnostically useful immunohistochemical markers for many of these tumor types.

OBJECTIVE

This article reviews a select group of recently described immunohistochemical markers of particular use in the evaluation of mesenchymal neoplasms; the underlying biology of the protein product, practical utility, and limitations of each marker are discussed in detail.

DATA SOURCES

Literature review, authors' research data, and personal practice experience serve as sources.

CONCLUSIONS

There are many diagnostically useful immunohistochemical markers to help confirm the diagnosis of many different soft tissue tumor types, some of which have reduced the need for additional, and more costly, studies, such as fluorescence in situ hybridization. However, no one marker is 100% specific for a given tumor, and knowledge of potential pitfalls and overlap in patterns of staining among other tumor types is crucial to ensure the appropriate application of these markers in clinical practice.

Myoepithelial carcinoma of the stomach: A diagnostic pitfall

Myoepithelioma/myoepithelial carcinomas are not commonly found in soft tissues and are especially rare at visceral sites. This report describes a case of a rare low-grade myoepithelial carcinoma of the stomach. A 61-year-old female patient presented with postprandial abdominal discomfort. Endoscopy revealed a 1.1 cm submucosal lesion. Local excision was performed after malignancy was confirmed by biopsy. The resection margin is free of tumor and she received no adjuvant therapy. The tumor was characterized by multinodular growth with biphasic epithelioid and spindle components. Infiltrative margin and nuclear pleomorphism are seen. Tumor cells were positive for both epithelial and myoepithelial markers. Evidence of epithelial differentiation was confirmed by electron microscopy. No EWSR1 rearrangement was detected. The final diagnosis was low-grade myoepithelial gastric carcinoma. The patient is currently well, and no evidence of recurrence or metastasis was found after ten-month of follow-up. Myoepithelial carcinoma should be considered in the differential diagnosis of a biphasic gastric tumor.

Myoepithelial neoplasms of soft tissue: an updated review of the clinicopathologic, immunophenotypic, and genetic features

Myoepithelial tumors in skin and soft tissue are uncommon but have been increasingly characterized over the past decade. Men and women are equally affected across all age groups and lesions arise most frequently on the extremities and limb girdles. Approximately 20 % of cases occur in pediatric patients, in whom they are frequently malignant. Similar to their salivary gland counterparts, myoepithelial tumors of soft tissue demonstrate heterogeneous morphologic and immunophenotypic features. Tumors are classified as mixed tumor/chondroid syringoma, myoepithelioma, and myoepithelial carcinoma; in soft tissue, tumors having at least moderate cytologic atypia are classified as malignant. Mixed tumor and myoepithelioma show a benign clinical course, with recurrence in up to 20 % (typically secondary to incomplete excision), and do not metastasize. In contrast, myoepithelial carcinoma shows more aggressive behavior with recurrence and metastasis in up to 40-50 % of cases. The majority of myoepithelial neoplasms typically coexpress epithelial antigens (cytokeratin and/or EMA) and S-100 protein; GFAP and p63 are frequently positive and a subset of malignant neoplasms lose INI1 expression. Up to 45 % of myoepitheliomas and myoepithelial carcinomas harbor EWSR1 gene rearrangements, unlike mixed tumor/chondroid syringoma which is characterized by PLAG1 gene rearrangement. While mixed tumor/chondroid syringoma are likely related to primary salivary myoepithelial tumors, soft tissue myoepithelioma and myoepithelial carcinoma appear to be pathologically distinct neoplasms.

Novel FUS-KLF17 and EWSR1-KLF17 fusions in myoepithelial tumors

Myoepithelial (ME) tumors of soft tissue and bone display a heterogeneous histologic spectrum and in about half of the cases harbor EWSR1 gene rearrangements. Despite rare case reports, the prevalence of fused in sarcoma (FUS) gene abnormalities and its related fusion partners remains undetermined among ME tumors. Therefore, we screened 66 EWSR1-negative ME tumors for FUS abnormalities by fluorescence in situ hybridization (FISH). In an index FUS-rearranged case, 3'-rapid amplification of cDNA ends (RACE) was applied to identify the fusion partner. Results were further confirmed by reverse transcription-PCR, followed by FISH screening the entire cohort of FUS-rearranged and EWSR1-positive ME lesions lacking a known fusion partner. The correlation between genotype and clinicopathological features was also investigated. As a result, six (9%) FUS-rearranged cases were identified, spanning divergent age groups, tumor locations, and morphologic features. A novel FUS-KLF17 fusion was identified by 3'-RACE in an 11-year-old girl with a foot lesion associated with locoregional metastases. Three additional cases with FUS-KLF17 fusions were identified and one KLF17 rearrangement (6.3%) was found among the 16 EWSR1-positive cases tested. The KLF17-related ME tumors affected younger patients and often exhibited trabecular growth in a myxohyaline stroma, but this genotype did not correlate with a malignant phenotype. In conclusion, a small subset of ME tumors harbor FUS rearrangements, two thirds of them being associated with KLF17 fusion. FUS FISH analysis is recommended in EWSR1-negative lesions in which a ME diagnosis is suspected. KLF17 is also a rare gene fusion partner to EWSR1-rearranged ME tumors.

Contemporary diagnostics: sarcoma pathology update

Sarcoma diagnosis continues to evolve as new information is discovered. Certain tumors have been downgraded (dermal leiomyosarcoma) and an atypical category designed for others. Recently entities include myxoinflammatory fibroblastic sarcoma, myoepithelioma, and pseudomyogenic hemangioendothelioma. The terms malignant fibrous histiocytoma and hemangiopericytoma are outdated. New immunostains (STAT6, SOX10, ERG) add diagnostic specificity, and new risk assessment models are described for sarcomas where grading and staging has failed to provide adequate prognosis.

Rhabdoid tumor predisposition syndrome

Rhabdoid tumors (RT), or malignant rhabdoid tumors, are among the most aggressive and lethal forms of human cancer. They can arise in any location in the body but are most commonly observed in the brain, where they are called atypical teratoid/rhabdoid tumors (AT/RT), and in the kidneys, where they are called rhabdoid tumors of the kidney. The vast majority of rhabdoid tumors present with a loss of function in the SMARCB1 gene, also known as INI1, BAF47, and hSNF5, a core member of the SWI/SNF chromatin-remodeling complex. Recently, mutations in a 2nd locus of the SWI/SNF complex, the SMARCA4 gene, also known as BRG1, were found in rhabdoid tumors with retention of SMARCB1 expression. Familial cases may occur in a condition known as rhabdoid tumor predisposition syndrome (RTPS). In RTPS, germline inactivation of 1 allele of a gene occurs. When the mutation occurs in the SMARCB1 gene, the syndrome is called RTPS1, and when the mutation occurs in the SMARCA4 gene it is called RTPS2. Children presenting with RTPS tend to develop tumors at a younger age, but the impact that germline mutation has on survival remains unclear. Adults who carry the mutation tend to develop multiple schwannomas. The diagnosis of RTPS should be considered in patients with RT, especially if they have multiple primary tumors, and/or in individuals with a family history of RT. Because germline mutations result in an increased risk of carriers developing RT, genetic counseling for families with this condition is recommended.

Myoepithelial tumor of soft tissue: histology and genetics of an evolving entity

Myoepithelial neoplasms represent a heterogeneous group of tumors of which classification is incomplete and evolving. Those of the soft tissues often form genetically distinct subgroups that differ from those arising within salivary glands. Soft-tissue myoepithelial tumors (including mixed tumors that show true glandular or ductal differentiation) exhibit a spectrum of different morphologic patterns, making them difficult to distinguish from a variety of other neoplasms. They have been increasingly shown to harbor genetic fusions involving EWSR1 and partner genes that are not seen in the well-characterized tumor classes involving EWSR1 translocations. We review the spectrum of soft-tissue myoepithelial tumors, discussing recent immunohistochemical and genetic findings and the differential diagnosis.

Differential SALL4 immunoexpression in malignant rhabdoid tumours and epithelioid sarcomas

AIMS

Malignant rhabdoid tumours (MRTs) and epithelioid sarcomas (ESs) are distinctive malignant neoplasms with characteristic clinicopathological features. However, these two tumour types share some phenotypic features, such as epithelioid/rhabdoid cytology, expression of epithelial markers, and immunohistochemical loss of INI1. The distinction can be problematic in atypical clinical settings, and ancillary diagnostic tools are needed. The expression of CD34 is widely cited as favouring the diagnosis of ES, but no formal comparative study has been performed in the post-INI1 era. Here, we evaluated the utility of SALL4 for differentiating MRTs from ESs, and compared its performance with that of CD34.

METHODS AND RESULTS

Fifteen MRTs and 36 ESs were retrieved. All MRTs and ESs lacked INI1 reactivity, except for one MRT that lacked BRG1. A representative slide from each case was stained using antibodies against SALL4 and CD34. Ten (67%) of the 15 MRTs expressed SALL4. In contrast, only one (3%) of the 36 ESs expressed SALL4. CD34 staining was observed in nine (60%) of the MRTs and 29 (81%) of the ESs.

CONCLUSIONS

Despite moderate sensitivity, SALL4 expression may aid in distinguishing MRTs from ESs. CD34 was found to have questionable utility in making such distinctions.

Synovial sarcoma: defining features and diagnostic evolution

Synovial sarcoma (SS) is a malignant mesenchymal neoplasm with variable epithelial differentiation, with a propensity to occur in young adults and which can arise at almost any site. It is generally viewed and treated as a high-grade sarcoma. As one of the first sarcomas to be defined by the presence of a specific chromosomal translocation leading to the production of the SS18-SSX fusion oncogene, it is perhaps the archetypal "translocation-associated sarcoma," and its translocation remains unique to this tumor type. Synovial sarcoma has a variety of morphologic patterns, but its chief forms are the classic biphasic pattern, of glandular or solid epithelial structures with monomorphic spindle cells and the monophasic pattern, of fascicles of spindle cells with only immunohistochemical or ultrastructural evidence of epithelial differentiation. However, there is significant morphologic heterogeneity and overlap with a variety of other neoplasms, which can cause diagnostic challenge, particularly as the immunoprofile is varied, SS18-SSX is not detected in 100% of SSs, and they may occur at unusual sites. Correct diagnosis is clinically important, due to the relative chemosensitivity of SS in relation to other sarcomas, for prognostication and because of the potential for treatment with specific targeted therapies in the near future. We review SS, with emphasis on the diagnostic spectrum, recent immunohistochemical and genetic findings, and the differential diagnosis.

SMARCB1 (INI-1)-deficient carcinomas of the sinonasal tract

SMARCB1 (INI-1) is a tumor-suppressor gene located on chromosome 22q11.2. Its gene product is ubiquitously expressed in nuclei of all normal tissues. SMARCB1 gene inactivation has been implicated in the pathogenesis of a diverse group of malignant neoplasms that tend to share "rhabdoid" cytomorphology. This group of SMARCB1-deficient tumors is now further expanded by a subset of carcinomas arising in the sinonasal tract. SMARCB1 immunostaining was performed on 142 sinonasal carcinomas. Tumors that showed loss of expression were further characterized for SMARCB1 deletions by fluorescence in situ hybridization. Nine of 142 (6%) primary sinonasal carcinomas showed loss of SMARCB1 expression by immunohistochemistry. Five patients were women, and patients ranged in age from 33 to 78 years (mean 59 y). The SMARCB1-deficient tumors were characterized by nests, sheets, and cords of cells without any histologic evidence of specific (eg, squamous or glandular) differentiation. The tumors comprised varying proportions of basaloid and rhabdoid cells. The SMARCB1-deficient carcinomas had been diagnosed as nonkeratinizing squamous cell carcinomas (n=3), sinonasal undifferentiated carcinomas (n=2), myoepithelial carcinoma (n=2), nonintestinal adenocarcinoma (n=1), and carcinoma, not otherwise specified (n=1). Fluorescence in situ hybridization analysis revealed SMARCB1 deletions in 6 of 8 (75%) carcinomas. The SMARCB1-deficient carcinomas did not harbor human papillomavirus or NUT-1 alterations. Six patients presented with T4 disease, 5 patients developed local recurrences and/or distant metastases, and 4 died of their disease. Inactivation of the SMARCB1 tumor-suppressor gene appears to be involved in the pathogenesis of a subset of sinonasal carcinomas, further expanding the family of SMARCB1-deficient neoplasms and further delineating a bewildering group of poorly/undifferentiated, aggressive carcinomas arising at this site. The ability to detect SMARCB1 loss by immunohistochemistry, particularly when dealing with poorly differentiated carcinomas with basaloid or rhabdoid features, should facilitate a more comprehensive understanding of these sinonasal carcinomas including clinical behavior and response to targeted therapies.

EWSR1-PBX3: a novel gene fusion in myoepithelial tumors

The genetics of myoepithelial tumors (ME) of soft tissue and bone have recently been investigated, with EWSR1-related gene fusions being seen in approximately half of the tumors. The fusion partners of EWSR1 so far described include POU5F1, PBX1, ZNF444 and, in a rare case, ATF1. We investigated by RNA sequencing an index case of EWSR1-rearranged ME of the tibia, lacking a known fusion partner, and identified a novel EWSR1-PBX3 fusion. The fusion was further validated by reverse transcriptase polymerase chain reaction and fluorescence in situ hybridization (FISH). To evaluate if this is a recurrent event, an additional cohort of 22 EWSR1-rearranged ME cases lacking a fusion partner were screened by FISH for abnormalities in PBX3 gene. Thus, two additional cases were identified showing an EWSR1-PBX3 gene fusion. One of them was also intraosseous involving the ankle, while the other occurred in the soft tissue of the index finger. The morphology of the EWSR1-PBX3 fusion positive cases showed similar findings, with nests or sheets of epithelioid to spindle cells in a partially myxoid to collagenous matrix. All three cases showed expression of S100 and EMA by immunohistochemistry. In summary, we report a novel EWSR1-PBX3 gene fusion in a small subset of ME, thereby expanding the spectrum of EWSR1-related gene fusions seen in these tumors. This gene fusion seems to occur preferentially in skeletal ME, with two of the three study cases occurring in intraosseous locations.

Challenging epithelioid mesenchymal neoplasms: mimics and traps

Epithelioid mesenchymal malignancies represent a major diagnostic challenge. Epithelioid morphology can be observed in a variety of soft tissue neoplasms, however there exist specific subtypes in which an epithelioid apperance constitutes the most distinctive morphological feature. Moving from epithelioid sarcoma of Enzinger (the prototype of sarcoma with epithelioid morphology), this review will focus on the most relevant entities: namely epithelioid haemangioendothelioma and angiosarcoma, pseudomyogenic haemangioendothelioma, epithelioid malignant peripheral nerve sheath tumour, epithelioid sclerosing fibrosarcoma, epithelioid pleomorphic liposarcoma, alveolar soft part sarcoma, and undifferentiated soft tissue sarcoma with epithelioid morphology. Differential diagnoses and major pitfalls will be discussed in detail.

WHO classification of soft tissue tumours: an update based on the 2013 (4th) edition

The fourth edition of the World Health Organization (WHO) Classification of Tumours of Soft Tissue and Bone was published in February 2013, and serves to provide an updated classification scheme and reproducible diagnostic criteria for pathologists. Given the relative rarity of soft tissue tumours and the rapid rate of immunohistochemical and genetic/molecular developments (not infrequently facilitating recognition of new tumour entities), this updated text edited by a consensus group is important for both practising pathologists and oncologists. The 2013 WHO classification includes several changes in soft tissue tumour classification, including several new entities (e.g., pseudomyogenic haemangioendothelioma, haemosiderotic fibrolipomatous tumour, and acral fibromyxoma), three newly included sections for gastrointestinal stromal tumours, nerve sheath tumours, and undifferentiated/unclassified soft tissue tumours, respectively, various 'reclassified' tumours, and a plethora of new genetic and molecular data for established tumour types that facilitate better definition and are useful as diagnostic tools. This article briefly outlines these updates based on the 2013 WHO classification of soft tissue tumours.

Myoepithelial carcinoma treatment in children: a report from the TREP project

BACKGROUND

Myoepithelial carcinoma (MC) of soft tissues is an aggressive tumor that rarely affects children, for whom no established treatment protocols exist. As part of the TREP (Tumori Rari in Età Pediatrica) project - an Italian network dedicated to children and adolescents with very rare tumors - we present a series of patients with MC, who were treated homogeneously and achieved a satisfactory outcome.

PROCEDURE

From 2005 to 2012, seven patients (age 0.5-9.2 years) with a diagnosis of MC were registered in the TREP study. After one patient treated with ifosfamide, cisplatin, and etoposide showed tumor shrinkage and experienced long-term disease remission, all subsequent patients were treated with the same chemotherapy regimen. All patients also received radiotherapy.

RESULTS

Initial surgical management involved a biopsy in three cases and tumor resection in 4. Response to initial chemotherapy was evaluable in four patients: two had a partial remission, one a minor response and one stable disease. Four patients received external-beam radiotherapy and three had brachytherapy. Overall, six patients are alive in first complete remission with a median follow-up of 2.5 years (0.9-5.1 years).

CONCLUSIONS

Though our experience is limited to a small number of patients, our treatment strategy for patients with MC is appears clinically useful and demonstrates how cooperation within the TREP project has enabled enough data to be collected to propose treatment recommendations for pediatric patients with this very rare tumor.

Myoepithelioma of the Orbital Apex and Middle Cranial Fossa: Case Report and Review of the Literature

Myoepitheliomas are rare tumours that originate from glandular tissues such as the parotid or salivary glands, and less commonly from soft tissues of the head, neck, and other parts of the body. Intraorbital myoepitheliomas generally arise from the lacrimal gland. Intracranial myoepitheliomas are rare. We report a myoepithelioma of the orbital apex that did not originate from the lacrimal gland. It extended to the middle cranial fossa from the orbital apex and involved the dura and adjacent bone. A diagnostic biopsy via a lateral orbitotomy preceded resection. We review the natural course and histopathology of myoepithelial neoplasms, the surgical nuances of approaching an orbital apex tumour with maximal functional preservation, and the optimal management practices of these rare lesions.

Recently characterized soft tissue tumors that bring biologic insight

Previously unrecognized but clinicopathologically (and often molecularly) distinct types of soft tissue tumor continue to be characterized, allowing wider recognition, more consistent application of diagnostic criteria, more reliable prediction of tumor behavior and enhancement of existing classification schemes. Examples of such 'entities' that have become much better understood over the past decade or so include deep 'benign' fibrous histiocytoma, hemosiderotic fibrolipomatous tumor, PEComa, spindle cell liposarcoma, myoepithelial tumors of soft tissue and spindle cell/sclerosing rhabdomyosarcoma. These tumor types, as well as the insights which they have engendered, are briefly reviewed here.

Prognostic value of MIB-1, p53, epidermal growth factor receptor, and INI1 in childhood chordomas

BACKGROUND

Chordomas are slow-growing tumors and most commonly involve the sacrum and clivus. Multiple recurrences are frequent. Childhood chordomas are rare and often show exceptionally aggressive behavior, resulting in short survival and a high incidence of metastatic spread.

OBJECTIVE

This study examined the histologic features and immunohistochemical profile of pediatric chordomas and compared them with their adult counterparts.

METHODS

Nine pediatric and 13 adult cases were included in the study. Childhood chordomas were classified into conventional, atypical, and poorly differentiated types. Immunohistochemistry was performed for cytokeratin, epithelial membrane antigen, vimentin, S100, brachyury, p53, INI1, epidermal growth factor receptor (EGFR), and CD117. Cytogenetic analyses were performed in a subset of tumors for SMARCB1/INI1 locus on 22q chromosome by fluorescent in situ hybridization (FISH) and analysis of the SMARCB1/INI1 gene sequence.

RESULTS

All tumors showed expression of cytokeratin, epithelial membrane antigen, S100, vimentin, brachyury, and EGFR. Atypical morphology, p53 expression, higher MIB-1 labelling index (LI), and INI1 loss were more frequently seen in pediatric chordomas as compared with adults. None of the tumors showed CD117 expression. No point mutation in the SMARCB1/INI1 gene was noted in the tumors examined; however, 4 pediatric and 1 adult chordoma showed loss of this locus on FISH analysis.

CONCLUSIONS

A subset of pediatric chordomas with atypical histomorphologic features needs to be identified, as they behave in an aggressive manner and require adjuvant therapy. Pediatric chordomas more frequently show p53 expression, INI1 loss, and higher MIB-1 LI as compared with adults, whereas EGFR expression is common to both.

Imprint cytology of soft tissue myoepithelioma: a case study

Soft tissue myoepithelioma is a rare neoplasm composed of myoepithelial cells. Here, we describe the cytologic features of soft tissue myoepithelioma arising on the right forearm in an 18-year-old man. The excised tumor (3.0×1.8×1.5 cm) was well-demarcated, yellow-gray, soft, and myxoid. The cytologic smears showed round to spindle, epithelioid, and plasmacytoid cells in the myxoid background. The nuclei were uniform, round to ovoid, with finely distributed chromatin and eosinophilic or pale cytoplasm. The tumor cells demonstrated immunoreactivity for cytokeratin (AE1/AE3), epithelial membrane antigen, S100 protein, and glial fibrillary acidic protein. Electron microscopy showed intermediate filaments, desmosomes, and basal lamina.

Cutaneous syncytial myoepithelioma: clinicopathologic characterization in a series of 38 cases

Cutaneous myoepithelial tumors demonstrate heterogenous morphologic and immunophenotypic features. We previously described, in brief, 7 cases of cutaneous myoepithelioma showing solid syncytial growth of ovoid, spindled, or histiocytoid cells. We now present the clinicopathologic features in a series of 38 cases of this distinctive syncytial variant, which were diagnosed between 1997 and 2012 (mostly seen in consultation). There were 27 men and 11 women, with a median age of 39 years (range, 2 mo to 74 y). Primary anatomic sites were the upper extremity (11, including 2 on the hand), upper limb girdle (3), lower extremity (14; 3 on the foot), back (6), face (2), chest (1), and buttock (1); the typical presentation was as either a polypoid or papular lesion. Tumors were well circumscribed and centered in the dermis and ranged in size from 0.3 to 2.7 cm (median 0.8 cm). Microscopically all tumors showed a solid sheet-like growth of uniformly sized ovoid to spindled or histiocytoid cells with palely eosinophilic syncytial cytoplasm. Nuclei were vesicular with fine chromatin and small or inconspicuous nucleoli and exhibited minimal to no atypia. Mitoses ranged from 0 to 4 per 10 HPF; 28 tumors showed no mitoses. Necrosis and lymphovascular invasion were consistently absent. Adipocytic metaplasia, appearing as superficial fat entrapped within the tumor, was seen in 12 cases. Chondro-osseous differentiation was seen in 1 tumor. All tumors examined were diffusely positive for EMA, and the majority showed diffuse staining for S-100 protein (5 showing focal staining). Keratin staining was focal in 1 of 33 tumors and seen in rare cells in 3 other cases. There was also positivity for GFAP (14/33), SMA (9/13), and p63 (6/11). Most lesions were treated by local excision. The majority of tumors tested (14/17; 82%) were positive by fluorescence in situ hybridization for EWSR1 gene rearrangement; testing for potential fusion partners (PBX1, ZNF444, POU5F1, DUX4, ATF1, CREB1, NR4A3, DDIT3, and NFATc2) was negative in all EWSR1-rearranged tumors. No FUS gene rearrangement was detected in 2 tumors lacking EWSR1 rearrangement. Follow-up information is available for 21 patients (mean follow-up 15 mo). One patient with a positive deep margin developed a local recurrence 51 months after initial biopsy. All other patients with available follow-up information, including 11 who had positive deep margins, are alive with no evidence of disease and no reported metastases. In summary, cutaneous syncytial myoepithelioma is a morphologically distinct variant that more frequently affects men, occurs over a wide age range, and usually presents on the extremities. Tumors are positive for S-100 protein and EMA, and, unlike most myoepithelial neoplasms, keratin staining is infrequent. EWSR1 gene rearrangement is present in nearly all tumors tested and likely involves a novel fusion partner. Prior reports describe some risk of recurrence and metastasis for cutaneous myoepithelial tumors; however, the syncytial variant appears to behave in a benign manner and only rarely recurs locally.

Epithelioid sarcoma is associated with a high percentage of SMARCB1 deletions

SMARCB1 gene alterations were first described in highly malignant rhabdoid tumors of the kidney, brain (atypical teratoid/rhabdoid tumor) and soft tissue. An increasing number of tumors have now shown loss of SMARCB1 protein expression by immunohistochemistry, including the majority of epithelioid sarcomas. However, investigations of SMARCB1 gene alterations in epithelioid sarcoma have produced conflicting results. The aim of this study was to evaluate SMARCB1 status using Sanger sequencing of the coding region and multiplex ligation-dependent probe amplification, a rapid and sensitive method for detecting intragenic deletions and duplications, which has not been used in previous studies. Twenty-one epithelioid sarcomas of both classical and proximal type were selected for SMARCB1 gene testing and SMARCB1 immunohistochemistry. Nineteen of 21 (90%) epithelioid sarcomas were SMARCB1 negative by immunohistochemistry. Twelve of the 19 (63%) had adequate DNA recovery for evaluation. Ten of 12 (83%) tumors showed homozygous deletions of the gene. Two cases showed heterozygous deletions and polymorphisms, but no sequence mutations. These results confirm the high frequency of SMARCB1 deletions in epithelioid sarcoma and show that multiplex ligation-dependent probe amplification is a reliable method for detection of deletions in these cases, which can be performed on formalin-fixed, paraffin-embedded tissue. Given the high percentage of SMARCB1 alterations in epithelioid sarcoma, these findings argue against using SMARCB1 gene deletion as a tool in distinguishing them from malignant rhabdoid tumors.

Cutaneous neoplasms showing EWSR1 rearrangement

Rearrangements of the EWSR1 gene are found in an increasing number of human neoplasms, including several tumors that can involve the skin: Ewing sarcoma/primitive neuroectodermal tumor, angiomatoid (malignant) fibrous histiocytoma, myoepithelioma of soft tissue, and clear cell sarcoma. Although these tumors share this common genetic link, they have very different clinical features, morphology, immunophenotype, and sometimes fusion gene partners; these will be the subjects of this review.

Primary juxtacortical myoepithelioma/mixed tumor of the bone: a report of 3 cases with clinicopathologic, immunohistochemical, ultrastructural, and molecular characterization

We describe the clinicopathological, immunohistochemical, and molecular features of 3 primary juxtacortical myoepithelioma/mixed tumor of bone. The patients were 2 males (13 and 23 years of age) and a 15-year-old female. The juxtacortical lesions were all located in the femur, and were surgically removed, 2 with wide margins and one with marginal margins. This latter tumor recurred locally 18 months later. The 3 patients were free of disease at 6 to 17 months follow-up. Histologically, all lesions showed a prominent multinodular architecture, and were formed by epithelioid and stellate elements, organized in solid sheets, or embedded in myxoid or chondroid matrix. Areas of osteoid formation were also observed. One tumor had the appearance of classical mixed tumor, showing aspects of duct formation and focal squamous differentiation. Immunohistochemically, all cases were positive for cytokeratins, epithelial membrane antigen, and S100 protein. The expression of other myoepithelial markers, including p63, glial fibrillary acid protein and calponin was more limited. No rearrangement of Ewing sarcoma region 1 (EWSR1) and fused in sarcoma (FUS) genes was observed by fluorescent in situ hybridization. To our knowledge, this is the first report of primary myoepitheliomas of bone arising at juxtacortical sites. These lesions must be distinguished from other benign and malignant bone and cartilage-forming surface tumors, including periosteal chondroma and chondrosarcoma, juxtacortical chondromyxoid fibroma, and periosteal and paraosteal osteosarcoma. The clinicoradiologic presentation and their histological and immunohistochemical features are distinctive enough to allow the separation from these entities.

Metastatic parotid myoepithelial carcinoma in a 7-year-old boy

Myoepithelial carcinoma is a rare malignancy of the parotid gland that is usually seen in adults. We report the first case in children of myoepithelial carcinoma of the parotid gland with massive invasion of the facial nerve and metastasis to cervical lymph nodes. Due to its rarity, the treatment and the clinical course of this tumor are not well defined yet. We performed a total parotidectomy, a modified neck dissection, and a postoperative radiotherapy in 7-year-old boy. Sparing of the facial nerve was impossible; it was sacrificed and grafted with a sural nerve. Histopathology confirmed the diagnosis of a parotid gland carcinoma and immunohistochemical markers showed that the tumor cells express cytokeratin, epithelial membrane antigen, cytokeratin 7, smooth muscle actin, P63, CEA, and S100. This pattern of immunostaining is consistent with the diagnosis of myoepithelial carcinoma. On the postoperative tenth month he presented with a pulmonary and lumbar vertebra metastasis.

Soft tissue tumors of uncertain origin

Many soft tissue tumors of childhood lack obvious differentiation toward a defined mesenchymal tissue type or have a phenotype that does not correspond to any defined normal tissue. These challenging tumors are currently regarded as neoplasms of uncertain differentiation. Nonetheless, there have been great strides in the understanding of their pathologic and genetic features and biologic underpinnings. The application of new genetic information to the pathologic diagnosis among this group of tumors is an emerging area in diagnostic pediatric pathology. This article reviews the clinicopathologic features of tumors of uncertain and/or miscellaneous origin, with an emphasis on the unique aspects of these neoplasms in children and adolescents, use of diagnostic adjuncts, and differential diagnosis.

NR4A3 rearrangement reliably distinguishes between the clinicopathologically overlapping entities myoepithelial carcinoma of soft tissue and cellular extraskeletal myxoid chondrosarcoma

Myoepithelial carcinoma of soft tissue (MEC) and cellular extraskeletal myxoid chondrosarcoma (cEMC) share striking similarities. In this paper, we compare ten MECs with five cEMCs. MEC patients had an equal gender distribution. The age range was 15–76 years (mean, 42 years). Tumours were located on extremities, pelvic girdle, vulva and neck. Follow-up, available for nine patients, ranged from 4 to 85 months (mean, 35 months). Five patients were alive without evidence of disease, two were alive with disease and two died 8 months after the initial diagnosis. cEMCs were from three males and two females with an age range of 37–82 years (mean, 57 years); they presented in extremities, shoulder and paravertebral/cervical. Follow-up, available for four patients, ranged from 6 to 220 months (mean, 61 months). All patients were alive, two with recurrences and/or metastases and two without evidence of disease. Morphologically, the distinction between these two entities was difficult since all cases exhibited features typically seen in myoepithelial tumours. Immunohistochemically, MECs expressed pan-keratin (80 %), epithelial membrane antigen (EMA; 57 %), S100 (50 %), alpha-smooth muscle actin (ASMA; 75 %), calponin (67 %) and p63 (25 %). S100 and EMA were expressed in 40 % of cEMC cases respectively with additional immunoreactivity for p63, ASMA and glial fibrillary acidic protein in one case. Pan-keratin was negative in all neoplasms. NR4A3 rearrangement was present in four of four cEMCs and in none of the MECs. In contrast, three of nine (33 %) MECs and four of five (80 %) cEMCs showed an EWSR1 rearrangement. In summary, MECs and cEMCs share clinical, morphological, immunohistochemical and genetic characteristics. The pathognomic rearrangement of NR4A3 is a useful diagnostic feature in identifying cEMCs.

The prognostic significance of p63 and Ki-67 expression in myoepithelial carcinoma

Background

Myoepithelial carcinoma is a rare tumour. The clinical and biological behaviours of these tumours are variable. Although many factors have been evaluated as potential prognostic indicators, including clinical stage, site and size of the tumour, high proliferative activity, extensive invasion into the surrounding tissue, perineural permeation, the abnormal presence of nuclear DNA content, and marked cellular pleomorphism, there are no definite histological features that clearly correlate with their behaviour. Thus, conclusions regarding prognostic factors and ideal treatment may emerge as the number of investigated myoepithelial carcinoma cases accumulate.

Methods

Using immunohistochemistry, expression levels of p63 and Ki-67 were determined in 16 myoepithelial carcinoma samples and correlated with clinicopathological characteristics and patient prognosis.

Results

p63 expression was detected in six of the myoepithelial carcinoma tissues (37.5%) and Ki-67 was detected in five (31.3%). In addition, p63 and Ki-67 expression levels were associated with myoepithelial carcinoma recurrence and metastasis. All six patients with p63-positive expression died due to disease or cardiovascular disease (mean survival time = 50.5 months), and p63 expression was statistically significant with respect to survival (P = 0.01). Four patients with Ki-67-positive expression died due to disease or cardiovascular disease (mean survival time = 44.0 months); however, there was no statistically significant difference between Ki-67 expression and survival (P = 0.24).

Conclusions

Recurrence and metastasis in myoepithelial carcinomas are more frequent in p63-positive and Ki-67-positive EMCs, and poor prognosis is associated with overexpression of p63.

Metastasis of soft-tissue myoepithelial carcinoma to clivus

The differential diagnosis for masses involving the clivus is broad. The authors present a case of myoepithelial carcinoma metastatic to the clivus, a lesion that has not been reported to their knowledge. This 14-year-old girl with a history of myoepithelial carcinoma originating in the soft tissues of the left hip and metastatic to the lung presented with left lateral gaze palsy. Imaging demonstrated a 3 × 3-cm osteolytic mass in the clivus. Microscopic transsphenoidal resection with endoscopic assistance was performed. Pathological findings were consistent with the previously diagnosed myoepithelial carcinoma. Within 4 weeks postoperatively and 2 weeks into a chemotherapeutic regimen, the tumor exhibited progression. Radiation therapy was started and growth of the tumor was halted. Myoepithelial carcinoma should be included in the differential diagnosis for clival masses, especially in patients with previously diagnosed myoepithelial carcinoma. The primary management of this tumor should be with chemotherapy and radiation, with surgery serving only for decompression.

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.