t(19;22)(q13;q12) Translocation leading to the novel fusion gene EWSR1-ZNF444 in soft tissue myoepithelial carcinoma

Genome to phenome Association for Pork Belly Parameters Elucidates Three Regulation Distinctions: Adipogenesis, muscle formation, and their transcription factors

Genome to phenome analysis is necessary in livestock areas because of its various and complex phenotypes. Pork belly is a favorable part of meat worldwide, including East Asia. A previous study has suggested that the three key transcription factors (ZNF444, NFYA and PPARG) affecting pork belly traits include total volume, the volume of total fat and muscle, and component muscles of the corresponding slice. However, other transcription factor genes affecting each slice other than pork belly component traits still needed to be identified. Thus, we aimed to analyze pork belly components at the genome to phenome level for identifying key transcription factor genes and their co-associated networks. The range of node numbers against each component trait via the association weight matrix was from 598 to 3020. Premised on the result, an in silico functional approach was performed. Each co-association network enriched three key transcription factors in adipogenesis and skeletal muscle proliferation, mesoderm development, metabolism, and gene transcription. The three key transcription factors and their related genes may be useful in comprehending their effect of pork belly construction.

Update on Sinonasal Tract Malignancies: Advances in Diagnostic Modalities

CONTEXT.—

Sinonasal tract malignancies are rare cancers with frequent morphologic overlap. Given the similar histologic profiles seen in many of these entities, they often present a diagnostic challenge to the practicing pathologist.

OBJECTIVE.—

To provide a streamlined algorithm using histologic clues, immunohistochemical profiles, and molecular assays to aid in diagnosis of these lesions.

DATA SOURCES.—

Sources were the World Health Organization Tumor Classification, literature review, and institutional experience.

CONCLUSIONS.—

Although many sinonasal tract malignancies show similar histology, distinct immunohistochemical and molecular profiles can help parse out differences, thereby facilitating diagnosis for the pathologist.

Myoepithelial Tumors of Bone With EWSR1::PBX3 Fusion: A Spectrum From Benign to Malignant

The EWSR1::PBX3 fusion gene, commonly associated with cutaneous syncytial myoepitheliomas, is also found in myoepithelial tumors (METs) of bone and soft tissue. These tumors typically demonstrate benign histology and favorable outcomes. This study examines 6 previously unreported intraosseous METs harboring the EWSR1::PBX3 fusion, focusing on their histopathologic characteristics, immunophenotype, clinical and radiographic profiles, and patient outcomes. The cohort comprised 5 men and 1 woman, aged 25 to 65 years (median age: 31 years), with tumors located in the proximal tibia (3 cases), distal radius (2 cases), and ilium (1 case) and sizes between 3.2 and 12.2 cm (median size: 3.9 cm). Imaging showed osteolytic lesions with varying degrees of cortical involvement and soft tissue extension in 3 cases. Histologically, 4 tumors showed mainly uniform oval-to-spindled cells in syncytial or fascicular arrangements within a collagenous matrix, displaying either bland nuclear features or mild atypia, and low to slightly elevated mitotic activity (≤1 per 10 high-power fields in 3 cases and 6 per 10 high-power fields in 1), classifying them as benign or atypical METs. In contrast, 2 tumors exhibited pronounced nuclear atypia with ovoid, spindled, epithelioid and round cells, hyperchromatic nuclei, inconspicuous nucleoli, increased N/C ratios, high mitotic rates (17 and 19 per 10 high-power fields), and extensive necrosis. Both tumors behaved aggressively-one patient underwent amputation after neoadjuvant chemotherapy and radiation, and the other died within 7 months with the disease still present. Immunohistochemically, the tumors consistently expressed epithelial membrane antigen and S100 but lacked keratin (AE1/AE3) expression. Our study demonstrated that bone METs with EWSR1::PBX3 fusions encompass a histologic continuum from benign to malignant, with benign/atypical METs mirroring their cutaneous analogs in morphology, and malignant variants distinguished by heterogeneous cytologic and architectural features, pronounced nuclear atypia, and high mitotic rates.

SMARCB1/INI1-deficient epithelioid and myxoid neoplasms in paratesticular region: Expanding the clinicopathologic and molecular spectrum

SMARCB1/INI1-deficient soft tissue tumors with epithelioid and myxoid features are diverse and mainly include soft tissue myoepithelial tumor, extraskeletal myxoid chondrosarcoma, and the recently described myoepithelioma-like tumor of the vulvar region and myxoepithelioid tumor with chordoid features. Because of their overlapping features, the accurate diagnosis and classification of these tumors are often challenging. Herein, we report two unique cases of SMARCB1/INI1-deficient soft tissue neoplasm with epithelioid and myxoid features occurring in male paratesticular region. The first case was a 52-year-old man presented with an intermittent painful left paratesticular mass for 1 year. The second case was a 41-year-old man presented with a painless paratesticular mass on the right side for 3 months. Both patients underwent an orchiectomy. After 6 and 26 months of follow-up, both were alive with no evidence of recurrence or metastasis. In both cases, the tumor was relatively well-demarcated and showed monomorphic round to epithelioid cells arranged in a nested, trabecular, reticular, and corded pattern, setting in a myxohyalinized and vascularized matrix. The tumor cells showed relatively uniform round nuclei with vesicular chromatin and variably prominent nucleoli. No rhabdoid cells were identified. Mitoses numbered 3 and 2 per 10 high-power fields. Tumor necrosis or lymphovascular invasion was absent. Immunohistochemically, both tumors expressed epithelial membrane antigen (focal), calponin (focal), and CD99. SMARCB1/INI1 expression was deficient in both cases. In addition, case 1 diffusely expressed pan-cytokeratin, and case 2 diffusely expressed CD34 and synaptophysin. Molecular genetically, case 1 showed SMARCB1 homozygous deletion as detected by fluorescence in-situ hybridization (FISH), and case 2 demonstrated SMARCB1 copy number deletions by next-generation sequencing and SMARCB1 monoallelic deletion by FISH. Both cases lacked EWSR1 rearrangements by FISH. The overall clinicopathologic profiles of the two cases made it difficult to classify them as one of the established categories of SMARCB1/INI1-deficient mesenchymal tumors. Our study further expands the clinicopathologic and molecular spectrum of SMARCB1/INI1-deficient epithelioid and myxoid neoplasms and highlights the challenges to diagnose these tumors.

Detection of salivary gland and sinonasal fusions by a next-generation sequencing based, ligation-dependent, multiplex RT-PCR assay

AIMS

The discovery of tumour type-specific gene fusion oncogenes in benign and malignant salivary gland and sinonasal (SGSN) tumours has significantly increased our knowledge about their molecular pathology and classification.

METHODS AND RESULTS

We developed a new targeted multiplexed next-generation sequencing (NGS)-based method that utilizes ligation dependent reverse-transcriptase polymerase chain reaction (LD-RT-PCR) to detect oncogenic fusion transcripts involving 116 genes, leading to 96 gene fusions known to be recurrently rearranged in these tumours. In all, 180 SGSN tumours (formalin-fixed, paraffin-embedded samples, 141 specimens and 39 core needle biopsies) from the REFCORpath (French network for rare head and neck cancers) with previously identified fusion genes by fluorescent in situ hybridisation (FISH), RT-PCR, or molecular immunohistochemistry were selected to test its specificity and sensitivity and validate its diagnostic use. Tested tumours encompassed 14 major tumours types, including secretory carcinoma, mucoepidermoid carcinoma, adenoid cystic carcinoma, salivary gland intraductal carcinoma, clear cell carcinoma, pleomorphic adenoma, adamantinoma-like Ewing Sarcoma, EWSR1::COLCA2 sinonasal sarcoma, DEK::AFF2 sinonasal carcinoma, and biphenotypic sinonasal sarcoma. In-frame fusion transcripts were detected in 97.8% of cases (176/180). Gene fusion assay results correlated with conventional techniques (immunohistochemistry [IHC], FISH, and RT-PCR) in 176/180 tumours (97.8%).

CONCLUSION

This targeted multiplexed NGS-based LD-RT-PCR method is a robust, highly sensitive method for the detection of recurrent gene fusions from routine clinical SGSN tumours. It can be easily customized to cover new fusions. These results are promising for implementing an integrated NGS system to rapidly detect genetic aberrations, facilitating accurate, genomics-based diagnoses, and accelerate time to precision therapies in SGSN tumours.

EWSR1 rearranged primary renal myoepithelial carcinoma: a diagnostic conundrum

Primary renal myoepithelial carcinoma is an exceedingly rare neoplasm with an aggressive phenotype and Ewing sarcoma breakpoint region 1 (EWSR1) rearrangement in a small fraction of cases. In addition to its rarity, the diagnosis can be challenging for the pathologist due to morphologic heterogeneity, particularly on the biopsy specimen. At times, immunohistochemistry may be indecisive; therefore, molecular studies should be undertaken for clinching the diagnosis. We aim to illustrate a case of primary myoepithelial carcinoma of the kidney with EWSR1-rearrangement in a 67-year-old male patient who presented with right supraclavicular mass, which was clinically diagnosed as carcinoma of an unknown primary. An elaborate immunohistochemical work-up aided by fluorescent in-situ hybridization allowed us to reach a conclusive diagnosis. This unusual case report advocates that one should be aware of the histological mimickers and begin with broad differential diagnoses alongside sporadic ones and then narrow them down with appropriate ancillary studies.

Top 10 Basaloid Neoplasms of the Sinonasal Tract

BACKGROUND

Basaloid neoplasms of the sinonasal tract represent a significant group of tumors with histological overlap but often with different etiologies (i.e., viral, genetics), clinical management, and prognostic significance.

METHODS

Review.

RESULTS

"Basaloid" generally refers to cells with coarse chromatin in round nuclei and sparse cytoplasm, resembling cells of epithelial basal layers or imparting an "immature" appearance. Tumors with this characteristic in the sinonasal tract are represented by a spectrum of benign to high-grade malignant neoplasms, such as adenoid cystic carcinoma, NUT carcinoma, sinonasal undifferentiated carcinoma, SWI/SNF complex-deficient carcinomas, and adamantinoma-like Ewing sarcoma.

CONCLUSION

In some instances, histology alone may be sufficient for diagnosis. However, limited biopsy material or fine-needle aspiration specimens may be particularly challenging. Therefore, often other diagnostic procedures, including a combination of histology, immunohistochemistry (IHC), DNA and RNA testing, and molecular genetics are necessary to establish an accurate diagnosis.

Whole-genome characterization of myoepithelial carcinomas of the soft tissue

Myoepithelial carcinomas (MECs) of soft tissue are rare and aggressive tumors affecting young adults and children, but their molecular landscape has not been comprehensively explored through genome sequencing. Here, we present the whole-exome sequencing (WES), whole-genome sequencing (WGS), and RNA sequencing findings of two MECs. Patients 1 and 2 (P1, P2), both male, were diagnosed at 27 and 37 yr of age, respectively, with shoulder (P1) and inguinal (P2) soft tissue tumors. Both patients developed metastatic disease, and P2 died of disease. P1 tumor showed a rhabdoid cytomorphology and a complete loss of INI1 (SMARCB1) expression, associated with a homozygous SMARCB1 deletion. The tumor from P2 showed a clear cell/small cell morphology, retained INI1 expression and strong S100 positivity. By WES and WGS, tumors from both patients displayed low tumor mutation burdens, and no targetable alterations in cancer genes were detected. P2's tumor harbored an EWSR1::KLF15 rearrangement, whereas the tumor from P1 showed a novel ASCC2::GGNBP2 fusion. WGS evidenced a complex genomic event involving mainly Chromosomes 17 and 22 in the tumor from P1, which was consistent with chromoplexy. These findings are consistent with previous reports of EWSR1 rearrangements (50% of cases) in MECs and provide a genetic basis for the loss of SMARCB1 protein expression observed through immunohistochemistry in 10% of 40% of MEC cases. The lack of additional driver mutations in these tumors supports the hypothesis that these alterations are the key molecular events in MEC evolution. Furthermore, the presence of complex structural variant patterns, invisible to WES, highlights the novel biological insights that can be gained through the application of WGS to rare cancers.

Undifferentiated and dedifferentiated soft tissue neoplasms: Immunohistochemical surrogates for differential diagnosis

Undifferentiated soft tissue sarcomas (USTS) are described in the current World Health Organization Classification of Soft Tissue and Bone Tumours as those showing no identifiable line of differentiation when analyzed by presently available technologies. This is a markedly heterogeneous group, and the diagnosis of USTS remains one of exclusion. USTS can be divided into four morphologic subgroups: pleomorphic, spindle cell, round cell and epithelioid undifferentiated sarcomas, with this combined group accounting for up to 20% of all soft tissue sarcomas. As molecular advances enable the stratification of emerging genetic subsets within USTS, particularly within undifferentiated round cell sarcomas, other groups, particularly the category of undifferentiated pleomorphic sarcomas (UPS), still remain difficult to substratify and represent heterogeneous collections of neoplasms often representing the common morphologic endpoints of a variety of malignant tumors of various (mesenchymal and non-mesenchymal) lineages. However, recent molecular developments have also enabled the identification and correct classification of many tumors from various lines of differentiation that would previously have been bracketed under 'UPS'. This includes pleomorphic neoplasms and dedifferentiated neoplasms (the latter typically manifesting with an undifferentiated pleomorphic morphology) of mesenchymal (e.g. solitary fibrous tumor and gastrointestinal stromal tumor) and non-mesenchymal (e.g. melanoma and carcinoma) origin. The precise categorization of 'pleomorphic' or 'undifferentiated' neoplasms is critical for prognostication, as, for example, dedifferentiated liposarcoma typically behaves less aggressively than other pleomorphic sarcomas, and for management, including the potential for targeted therapies based on underlying recurrent molecular features. In this review we focus on undifferentiated and dedifferentiated pleomorphic and spindle cell neoplasms, summarizing their key genetic, morphologic and immunophenotypic features in the routine diagnostic setting, and the use of immunohistochemistry in their principal differential diagnosis, and highlight new developments and entities in the group of undifferentiated and dedifferentiated soft tissue sarcomas.

EWSR1-The Most Common Rearranged Gene in Soft Tissue Lesions, Which Also Occurs in Different Bone Lesions: An Updated Review

EWSR1 belongs to the FET family of RNA-binding proteins including also Fused in Sarcoma (FUS), and TATA-box binding protein Associated Factor 15 (TAF15). As consequence of the multifunctional role of EWSR1 leading to a high frequency of transcription of the chromosomal region where the gene is located, EWSR1 is exposed to aberrations such as rearrangements. Consecutive binding to other genes leads to chimeric proteins inducing oncogenesis. The other TET family members are homologous. With the advent of widely used modern molecular techniques during the last decades, it has become obvious that EWSR1 is involved in the development of diverse benign and malignant tumors with mesenchymal, neuroectodermal, and epithelial/myoepithelial features. As oncogenic transformation mediated by EWSR1-fusion proteins leads to such diverse tumor types, there must be a selection on the multipotent stem cell level. In this review, we will focus on the wide variety of soft tissue and bone entities, including benign and malignant lesions, harboring EWSR1 rearrangement. Fusion gene analysis is the diagnostic gold standard in most of these tumors. We present clinicopathologic, immunohistochemical, and molecular features and discuss differential diagnoses.

EWSR1-ATF1 Fusion in a Myoepithelial Carcinoma of Soft Tissue With Small Round Cell Morphology: A Potential Diagnostic Pitfall

Myoepithelial tumors of soft tissue are rare mesenchymal neoplasms that overlap with their salivary gland and skin counterparts at both the histopathologic and molecular levels. EWSR1 gene rearrangements with various fusion partners represent a common genetic event in myoepithelial tumors of soft tissue, whether benign or malignant, and may prove useful as a diagnostic tool in difficult cases. However, the number of diagnostic entities with EWSR1 gene rearrangements has grown considerably in recent years, and there is significant morphologic and immunophenotypic overlap amongst this group, underscoring the importance of fusion testing to detect fusion partners that are characteristic of discrete diagnostic entities. Herein, we report a malignant myoepithelial tumor of soft tissue/myoepithelial carcinoma with an undifferentiated round cell morphology arising in a pediatric patient with a EWSR1-ATF1 gene fusion.

Molecular Profiling of Clear Cell Myoepithelial Carcinoma of Salivary Glands With EWSR1 Rearrangement Identifies Frequent PLAG1 Gene Fusions But No EWSR1 Fusion Transcripts

Myoepithelial carcinoma of salivary glands is an underrecognized and challenging entity with a broad morphologic spectrum, including an EWSR1-rearranged clear cell variant. Myoepithelial carcinoma is generally aggressive with largely unknown genetic features. A retrospective review of Salivary Gland Tumor Registry in Pilsen searching for the key words "clear cell myoepithelial carcinoma," "hyalinizing clear cell," and "clear cell malignant myoepithelioma" yielded 94 clear cell myoepithelial carcinomas (CCMCs) for molecular analysis of EWSR1 rearrangement using fluorescence in situ hybridization (FISH). Tumors positive for EWSR1 gene rearrangement were tested by next-generation sequencing (NGS) using fusion-detecting panels. NGS results were confirmed by reverse-transcription polymerase chain reaction or by FISH. Twenty-six tumors originally diagnosed as CCMC (26/94, 27.6%) revealed split signals for EWSR1 by FISH. Six of these tumors (6/26, 23%) displayed amplification of the EWSR1 locus. Fifteen cases were analyzable by NGS, whereas 9 were not, and tissue was not available in 2 cases. None of the CCMCs with EWSR1 rearrangements detected by FISH had an EWSR1 fusion transcript. Fusion transcripts were detected in 6 cases (6/15, 40%), including LIFR-PLAG1 and CTNNB1-PLAG1, in 2 cases each, and CHCHD7-PLAG1 and EWSR1-ATF1 fusions were identified in 1 case each. Seven cases, including those with PLAG1 fusion, were positive for PLAG1 rearrangement by FISH, with notable exception of CHCHD7-PLAG1, which is an inversion not detectable by FISH. One single case with EWSR1-ATF1 fusion in NGS showed ATF1 gene rearrangement by FISH and was reclassified as clear cell carcinoma (CCC). In addition, another 4 cases revealed ATF1 rearrangement by FISH and were reclassified as CCC as well. Moreover, 12/68 (17%) CCMCs with intact EWSR1 gene were selected randomly and analyzed by NGS. PLAG1 fusions were found in 5 cases (5/12, 41.6%) with LIFR (2 cases), FGFR1 (2 cases), and CTNNB1 (1 case) as partner genes. Overall, PLAG1 gene rearrangements were detected in 10/38 (26%) tested cases. None of the tumors had SMARCB1 loss by immunohistochemistry as a possible explanation for the EWSR1 abnormalities in FISH. Novel findings in our NGS study suggest that EWSR1-FISH positive CCMC is a gene fusion-driven disease with frequent oncogenic PLAG1 fusions, including LIFR-PLAG1 and CTNNB1-PLAG1 in most cases. Productive EWSR1 fusions are found only in a minority of EWSR1-ATF1-rearranged cases, which were in part reclassifiable as CCCs. Detectable EWSR1-FISH abnormality in CCMCs without gene fusion perhaps represents a passenger mutation with minor or no oncologic effect.

Update on SWI/SNF-related gynecologic mesenchymal neoplasms: SMARCA4-deficient uterine sarcoma and SMARCB1-deficient vulvar neoplasms

Our knowledge regarding the role of genes encoding the chromatin remodeling switch/sucrose non-fermenting (SWI/SNF) complex in the initiation and progression of gynecologic malignancies continues to evolve. This review focuses on gynecologic tumors in which the sole or primary genetic alteration is in SMARCA4 or SMARCB1, two members of the SWI/SNF chromatin remodeling complex. In this review, we present a brief overview of the classical example of such tumors, ovarian small cell carcinoma of hypercalcemic type, and then a detailed review and update of SMARCB1-deficient and SMARCA4-deficient tumors of the uterus and vulva.

NDRG1-PLAG1 and TRPS1-PLAG1 Fusion Genes in Chondroid Syringoma

BACKGROUND/AIM

Chondroid syringoma is a rare benign tumor emanating from sweat glands. Although rearrangements of the pleomorphic adenoma gene 1 (PLAG1) have been reported in such tumors, information on PLAG1 fusion genes is very limited.

MATERIALS AND METHODS

Cytogenetic, fluorescence in situ hybridization, RNA sequencing, array comparative genomic hybridization, reverse transcription polymerase chain reaction, and Sanger sequencing analyses were performed on two chondroid syringoma cases.

RESULTS

Both tumors had structural rearrangements of chromosome 8. An NDRG1-PLAG1 transcript was found in the first tumor in which exon 3 of PLAG1 was fused with exon 1 of NDRG1. A TRPS1-PLAG1 chimeric transcript was detected in the second chondroid syringoma in which exon 2 or exon 3 of PLAG1 was fused with exon 1 of TRPS1.

CONCLUSION

The NDRG1-PLAG1 and TRPS1-PLAG1 resemble other PLAG1 fusion genes inasmuch as the expression of PLAG1 comes under the control of the NDRG1 or TRPS1 promoter.

Myoepithelioma of soft tissue and bone, and myoepithelioma-like tumors of the vulvar region: Clinicopathological study of 15 cases by PLAG1 immunohistochemistry

We demonstrated the clinicopathological findings of 13 myoepitheliomas of soft tissue and bone (MESTBs) and two myoepithelioma-like tumors of the vulvar region (MELTVRs), focusing on the association between nuclear atypia and clinical course, and the utility of immunohistochemistry (IHC) of pleomorphic adenoma gene 1 (PLAG1) for the pathological diagnosis of these tumors. Of the 13 MESTBs, eight, one and four cases exhibited mild, moderate and severe nuclear atypia, respectively. Two cases with venous invasion showed severe nuclear atypia and both died of advanced disease. Two MELTVR cases showed moderate nuclear atypia and had no evidence of disease after surgery. On IHC, 12 of 13 (92.3%) MESTBs showed PLAG1 immunoreactivity and none of the MELTVRs expressed PLAG1. In addition, MELTVRs showed loss of INI1 expression. In contrast, all MESTBs retained INI1 expression. Fluorescence in situ hybridization detected EWSR1, FUS and PLAG1 rearrangement in 5 (38.5%), 0 (0%) and 2 (15.4%) of the 13 MESTBs, respectively. No EWSR1, FUS and PLAG1 rearrangement were observed in the METLVRs. In conclusion, MESTBs with both severe nuclear atypia and venous invasion would be indicative of malignant potential. PLAG1 might be a useful IHC marker in MESTB diagnosis.

SWI/SNF complex-deficient soft tissue neoplasms: An update

The SWItch Sucrose Non-Fermentable (SWI/SNF) chromatin remodeling complex is a large multi-subunit protein assembly that orchestrates chromatin compaction and accessibility for gene transcription in an ATP-dependent manner. As a key epigenetic regulator, the SWI/SNF complex coordinates gene expression, cell proliferation and differentiation, and its biologic functions, in part, antagonize the polycomb repressive complex 2. The mammalian SWI/SNF complex consists of 15 subunits encoded by 29 genes, some of which are recurrently mutated in human cancers, in the germline or sporadic setting. Most SWI/SNF-deficient tumors share common "rhabdoid" cytomorphology. SMARCB1 (INI1) is the subunit most frequently inactivated in soft tissue neoplasms. Specifically, SMARCB1 deficiency is observed as the genetic hallmark in virtually all malignant rhabdoid tumors, and most cases of epithelioid sarcoma and poorly differentiated chordoma. In addition, subsets of myoepithelial carcinoma (10-40%), extraskeletal myxoid chondrosarcoma (20%), epithelioid schwannoma (40%), and epithelioid malignant peripheral nerve sheath tumor (70%) demonstrate SMARCB1 loss. The gene encoding the SS18 subunit is involved in the SS18-SSX rearrangement, which is pathognomonic of synovial sarcoma and indirectly inactivates SMARCB1. Finally, undifferentiated SMARCA4-deficient thoracic sarcomas are defined by SMARCA4 subunit inactivation, leading to SMARCA4 and SMARCA2 loss. Rarely, inactivation of alternate but biologically equivalent key regulators can substitute for canonical subunit deficiency, such as SMARCA4 inactivation in cases of SMARCB1-retained epithelioid sarcoma. This review briefly highlights SWI/SNF complex biologic functions and its roles in human cancer and provides a detailed update on recent advances in soft tissue neoplasms with canonical SWI/SNF complex deficiency, correlating morphologic, genomic, and immunohistochemical findings.

Pulmonary Myoepithelial Tumors With Exuberant Reactive Pneumocytes: Proposed Reclassification of So-called Pneumocytic Adenomyoepithelioma

Pneumocytic adenomyoepithelioma (PAM) was first described in 2007 and was included in the 2015 World Health Organization Classification of lung tumors as a variant of epithelial-myoepithelial tumor. This rare pulmonary neoplasm was reported to show both myoepithelial and duct-like components, with the latter exhibiting pneumocytic differentiation with TTF-1 expression. We present an index case and 6 additional retrospectively identified cases of pulmonary tumors with prototypical features of PAM. However, with additional clinicoradiologic, histologic, immunohistochemical and cytogenetic data, we were able to reclassify them as myoepithelial neoplasms-both primary and metastatic-with entrapped exuberantly hyperplastic alveolar structures lined by TTF-1 pneumocytes. We reviewed the available literature related to PAM and myoepithelial tumors. Our cases suggest that the entity referred to as PAM represents interstitial growth of myoepithelial neoplasms enticing marked proliferation of entrapped pneumocytes rather than a distinct biphasic neoplasm with pneumocytic differentiation.

Cutaneous Syncytial Myoepithelioma Is Characterized by Recurrent EWSR1-PBX3 Fusions

Cutaneous syncytial myoepithelioma (CSM) is a rare but distinctive benign variant in the family of myoepithelial neoplasms of skin and soft tissue. CSM has unique morphologic and immunohistochemical features, characterized by intradermal syncytial growth of spindled, ovoid, and histiocytoid cells and consistent staining for S-100 protein and EMA, and differs from other myoepithelial tumors by showing only infrequent keratin staining. Rearrangement of the EWSR1 gene is now known to occur in up to half of all skin and soft tissue myoepithelial tumors, with a wide family of documented fusion partners. In 2013, we reported frequent (80%) EWSR1 rearrangements in CSM, but were unable to identify the fusion partner using available studies at that time. After recent identification of an index case of CSM harboring an EWSR1-PBX3 fusion, we used a combination of targeted RNA sequencing and fluorescence in situ hybridization (FISH) studies to investigate the genetic features of a cohort of CSM. An EWSR1-PBX3 fusion was identified in all 13 cases successfully tested. RNA sequencing was successful in 8/13 cases, all of which were found to have identical breakpoints fusing exon 8 of EWSR1 to exon 5 of PBX3. FISH confirmed both EWSR1 and PBX3 rearrangements in 9/9 cases tested, which included 4 confirmed to have EWSR1-PBX3 fusion by RNA-Seq, 3 cases that failed RNA-Seq, and 2 cases examined by FISH alone. Two cases failed RNA sequencing but had no additional tissue remaining for FISH studies. Our findings demonstrate that EWSR1-PBX3 fusions occur in most (and possibly all) cases of CSM.

ZSCAN16 promotes proliferation, migration and invasion of bladder cancer via regulating NF-kB, AKT, mTOR, P38 and other genes

BACKGROUND

As one of the most common genitourinary malignancies worldwide, bladder cancer affects about 3.4 million people globally, with 430,000 new cases a year since 2015. Despite the advances in bladder cancer diagnosis and therapy, there has been little progress in the patients' overall survival in nearly 30 years. Therefore, investigating novel molecular therapeutic targets is required to gain insight into the tumorigenesis of bladder cancer, which ultimately may be used to develop more effective therapeutic strategies.

METHODS

Herein, we used gene knockdown in vitro and in vivo to unveil the unknown roles of ZSCAN16 in bladder cancer. Afterward, to decipher the unknown regulatory role of ZSCAN16 in tumor progression, we verified that a bunch of genes including NF-κB, AKT, mTOR, and P38 were the key downstream regulators of ZSCAN16 by western blot and rescue experiments.

RESULTS

We found high expression of ZSCAN16 transcripts in bladder cancer cells and tumor samples from the TCGA database and tissue microarray bank, demonstrated in correlation with poor prognosis for bladder cancer patients. The in vitro experiments indicated that the silencing of ZSCAN16 by shRNA lentivirus promoted apoptosis and inhibited proliferation, colony formation, as well as migration and invasion in T24 cells. By investigating the signaling pathways, we proved ZSCAN16 play a novel role as oncogenic gene in bladder cancer by regulating NF-κB, AKT, mTOR, P38 and other genes. Furthermore, the in vivo experiments identified that ZSCAN16 knockdown retarded the tumor growth in nude mice.

CONCLUSIONS

In summary, these findings revealed that ZSCAN16 is a potential novel oncogene in the development and progression of bladder cancer. This study will shed light on developing novel therapeutic targets in the future treatment of bladder cancer.

Fusion of the Genes PHF1 and TFE3 in Malignant Chondroid Syringoma

BACKGROUND/AIM

Malignant chondroid syringoma is a rare tumor of unknown pathogenesis.

MATERIALS AND METHODS

Genetic analyses were performed on a malignant chondroid syringoma.

RESULTS

G-banding analysis of short-term cultured tumor cells yielded the karyotype 46,Y,t(X;6)(p11;p21)[15]/46,XY[2]. RNA sequencing detected an in-frame fusion of PHF1 from 6p21 with TFE3 from Xp11, verified by RT-PCR and Sanger sequencing. Genomic PCR showed that the PHF1-TFE3 junction was identical to the fusion found by RNA sequencing and RT-PCR.

CONCLUSION

Malignant chondroid syringoma is genetically related to tumors with PHF1 rearrangements such as low-grade endometrial sarcoma and ossifying fibromyxoid tumor, but also with tumors having TFE3 rearrangements such as renal cell carcinoma, alveolar soft part sarcoma, PEComa, and epithelioid hemangioendothelioma. Further investigations on malignant chondroid syringomas are needed in order to determine whether genetic heterogeneity exists among them and the clinical impact of the PHF1-TFE3 fusion.

Soft Tissue Special Issue: Myoepithelial Neoplasms of Soft Tissue: An Updated Review with Emphasis on Diagnostic Considerations in the Head and Neck

Primary myoepithelial neoplasms of soft tissue have been shown to be related to their salivary gland counterparts, with which they often share morphologic, immunophenotypic, and molecular genetic features, such as the presence of PLAG1 rearrangement in both soft tissue mixed tumor and salivary pleomorphic adenoma. However, important distinctions remain between soft tissue and salivary myoepithelial neoplasms, namely differing criteria for malignancy. This review provides an overview of the current understanding of the clinicopathologic and molecular features of soft tissue myoepithelial neoplasms, including discussion of the similarities and differences between soft tissue and salivary counterparts and relevant diagnostic issues specific to head and neck pathology practice.

Myoepithelioma-like tumor of the vulvar region: a case report in China and review of the literature

Background

Myoepithelioma-like tumor of the vulvar region (MELTVR) is a recently described mesenchymal neoplasm which typically arising in vulvar regions of adult women.

Case presentation

Here we report a case of a 65-year-old woman who presented with a 6-year history of subcutaneous mass in the vulvar region. The mass had recently increased in size continuously. Histologically, the tumor cells had an epithelioid to spindled shape. Epithelioid tumor cells proliferated singly or in a loosely cohesive manner with myxoid areas, while spindled tumor cells grew in diffuse sheets or storiform arrangements mainly in nonmyxoid areas. Immunohistochemically, the tumor cells were positive for vimentin, epithelial membrane antigen, calponin, and were partially mild to moderate positive for estrogen receptor, but completely negative for S100 protein, glial fibrillary acidic protein, CD34, desmin, SMA and cytokeratin. INI1/SMARCB1 expression was deficient. EWSR1 and FUS genes were intact tested by fluorescence in situ hybridization analysis. Based on these findings, we diagnose this case as MELTVR. The patient remained relapse-free after the lesion was widely excised during 8 months follow-up.

Conclusions

This disease should be included in the differential diagnostic list of vulvar tumors with epithelioid to spindled morphology. Recognition of its histopathological features and immunohistochemical reactivity will help to understand the tumor better.

Primary cutaneous biphasic sarcomatoid basal cell carcinoma with myoepithelial carcinoma differentiation: A new variant

Isolated cases of basal cell carcinoma (BCC) with partial myoepithelial component have been described. However, myoepithelial differentiation has not been described in sarcomatoid basal cell carcinomas, which usually show features resembling osteosarcoma, chondrosarcoma, or leiomyosarcoma. We report a case of an 87-year-old man with a forehead lesion that histologically showed a minor component of conventional nodular BCC in transition with a major biphasic sarcomatoid growth composed of invasive spindle-cell and epithelial-like components, the latter with a reticular pattern and scattered ductal structures. Both components showed cytological atypia and high mitotic rate (26/10HPF), with atypical mitotic figures. BER-EP4 immunostaining was exclusively found in the nodular BCC component whereas the sarcomatoid component revealed immunostaining for α-smooth muscle actin (SMA), muscle-specific actin (MSA), calponin, and p63 in both epithelial-like and spindle-cell populations. Focal immunoreactivity was observed in the epithelial component for S100 and glial fibrillary acidic protein (GFAP). Furthermore, EWSR1-PBX1 gene fusion was also detected. This is to our knowledge, the first fully documented case of biphasic sarcomatoid BCC with myoepithelial carcinoma differentiation.

Myoepithelioma of bone: ultrastructural, immunohistochemical and molecular study of three cases

Primary intraosseous myoepithelial tumors are rare neoplasms with only a handful of cases described in the medical literature. To date, intraosseous variant of benign myoepithelioma, due to its rarity, has not been studied ultrastructurally, and only one case of a malignant intraosseous myoepithelioma has been described. Three cases were retrieved from the files at the Massachusetts General Hospital (MGH). A diagnosis of benign myoepithelioma was made in case 1 and malignant epithelioma in cases 2 and 3. Ultrastructurally, intermediate filaments (without dense bodies) were found in each case with an abundance in case 1 and lesser amounts in cases 2 and 3. Surprisingly, cell junctions were not identified in case 1. However, they were found occasionally as intermediate junctions in case 2 and were easily identified as desmosome like junctions in case 3. The nucleus was irregular in the neoplastic cells of benign myoepithelioma which contrasted with cases 2 and 3 where the nuclei were oval yet had visible nucleoli. Herein, we add three new cases, including two new cases of malignant myoepithelioma. We also provide the first ultrastructural description of benign myoepithelioma of bone.

Clinical, pathological, and genomic features of EWSR1-PATZ1 fusion sarcoma

Molecular diagnostics of sarcoma subtypes commonly involve the identification of characteristic oncogenic fusions. EWSR1-PATZ1 is a rare fusion partnering in sarcoma, with few cases reported in the literature. In the current study, a series of 11 cases of EWSR1-PATZ1 fusion positive malignancies are described. EWSR1-PATZ1-related sarcomas occur across a wide age range and have a strong predilection for chest wall primary site. Secondary driver mutations in cell-cycle genes, and in particular CDKN2A (71%), are common in EWSR1-PATZ1 sarcomas in this series. In a subset of cases, an extended clinical and histopathological review was performed, as was confirmation and characterization of the fusion breakpoint revealing a novel intronic pseudoexon sequence insertion. Unified by a shared gene fusion, EWSR1-PATZ1 sarcomas otherwise appear to exhibit divergent morphology, a polyphenotypic immunoprofile, and variable clinical behavior posing challenges for precise classification.

Mesenchymal Tumors with EWSR1 Gene Rearrangements

Among the various genes that can be rearranged in soft tissue neoplasms associated with nonrandom chromosomal translocations, EWSR1 is the most frequent one to partner with other genes to generate recurrent fusion genes. This leads to a spectrum of clinically and pathologically diverse mesenchymal and nonmesenchymal neoplasms, variably manifesting as small round cell, spindle cell, clear cell or adipocytic tumors, or tumors with distinctive myxoid stroma. This review summarizes the growing list of mesenchymal neoplasms that are associated with EWSR1 gene rearrangements.

Primary Epithelioid Sarcoma of the Zygomatic Bone

Primary epithelioid sarcoma (ES) of bone is extremely rare with only 2 reported cases in the English literature. A previously healthy 18-year-old man presented with a 6-month history of right facial numbness and tingling and right eye diplopia. A computerized tomography scan revealed an ill-defined mass with dense osseous matrix centered in the right zygomatic bone. An outside biopsy was read as osteosarcoma. The resection specimen revealed large epithelioid and spindle cells embedded in a prominent hyalinized matrix with focal metaplastic bone formation. The tumor cells were strongly and diffusely positive for AE1/AE3 and epithelial membrane antigen, but a definitive diagnosis of ES was not immediately reached due to the presence of dense hyalinized matrix and weak expression of SAT2B by tumor cells. Deficient INI1 protein expression by immunohistochemistry and homozygous loss of the SMARCB1 gene by chromosomal microarray analysis ultimately justified this tumor's designation as ES.

EWSR1-NFATC2 and FUS-NFATC2 Gene Fusion-Associated Mesenchymal Tumors: Clinicopathologic Correlation and Literature Review

The spectrum of mesenchymal tumors associated with rearrangements of the EWSR1 gene has been growing in recent years due to progress in molecular detection techniques. Originally identified as the gene involved in the pathogenesis of Ewing sarcoma, the EWSR1 gene is now known to be rearranged in diverse clinical and histopathological entities. The NFATC2 gene is one of the many translocation partners of EWSR1 in gene fusions in a morphologically typical, albeit rare, subgroup of mesenchymal tumors. Little is known about the clinical characteristics of tumors containing NFATC2 gene rearrangements since most of the few reports published describe molecular rather than clinical aspects. In the current study, we report three patients with tumors carrying the EWSR1-NFATC2 gene translocation, including one rare primary tumor of soft tissues. Another patient with a benign-appearing bone tumor with a unique FUS-NFATC2 gene translocation is described. In various mesenchymal tumors (e.g., myxoid/round cell liposarcoma, low-grade fibromyxoid sarcoma, or angiomatoid fibrous histiocytoma), the FUS gene, as a member of the TET family, may be alternatively rearranged instead of the EWSR1 gene without any noticeable influence on the microscopical appearance or clinical outcome. This fact seems not to apply to mesenchymal tumors with the involvement of the NFATC2 gene because both in our experience and according to the extensive literature review, they have different properties on the morphological and molecular level. Both ESWSR1-NFATC2 and FUS-NFATC2 fusion-carrying tumors do not show microscopical or clinical features of Ewing sarcoma.

Prognostication in Mesenchymal Tumors: Can We Improve?

Prognostication in mesenchymal tumors can be challenging. They exhibit diverse, and sometimes overlapping, histologic features that are not always predictive of their true behavior. This article highlights examples of both traditional and emerging sarcoma biomarkers.

Primary Myoepithelial Carcinoma of the Conjunctiva

A 38-year-old female, otherwise fit and well, presented with a mass on her left medial bulbar conjunctiva that had been enlarging for several months. Examinations showed a fixed pinkish tumour, 9 mm in maximum extent, spanning from the plica to the medial limbus. The tumour was removed in toto. Histology revealed it to be a biphasic tumour composed of lobules and infiltrative cords within a sclerotic matrix. The cells were spindle-shaped to epithelioid, with nuclear atypia and occasional mitotic figures. The tumour was positive for smooth muscle actin, beta-catenin, and vimentin. All other markers of myoepithelial differentiation and cytokeratins were negative. Genetic analysis showed no evidence of EWSR1 or PLAG1 rearrangements. The light microscopic features and immunohistochemistry strongly supported a tumour with myoepithelial differentiation. The cellular atypia, mitotic activity, and infiltrative edges all pointed to myoepithelial carcinoma. Body imaging/screening showed no evidence of tumour elsewhere, supporting that the tumour was a primary of the conjunctiva. This is the first report of a myoepithelial tumour of the conjunctiva. The patient remains recurrence-free after 3 years of follow-up.

Applications of Ancillary Testing in the Cytologic Diagnosis of Soft Tissue Neoplasms

Soft tissue neoplasms are diagnostically challenging, although many advances in ancillary testing now enable accurate classification of fine-needle aspiration biopsies by detection of characteristic immunophenotypes (including protein correlates of molecular alterations) and molecular features. Although there are many useful diagnostic immunohistochemical markers and molecular assays, their diagnostic utility relies on correlation with clinical and morphologic features, judicious application, and appropriate interpretation because no single test is perfectly sensitive or specific. This review discusses applications of ancillary testing for commonly encountered soft tissue neoplasms in cytopathologic practice in the context of a pattern-based approach.

EWSR1-NFATC2 gene fusion in a soft tissue tumor with epithelioid round cell morphology and abundant stroma: a case report and review of the literature

Mesenchymal round cell tumors are a diverse group of neoplasms defined by primitive, often high-grade cytomorphology. The most common molecular alterations detected in these tumors are gene rearrangements involving EWSR1 to one of many fusion partners. Rare EWSR1-NFATC2 gene rearrangements, corresponding to a t(20;22) gene translocation, have been described in mesenchymal tumors with clear round cell morphology and a predilection for the skeleton. We present a case of a tumor harboring the EWSR1-NFATC2 gene fusion arising in the subcutaneous tissue of a young woman. The tumor exhibited corded and trabecular architecture of epithelioid cells within abundant myxoid and fibrous stroma. The cells showed strong immunoreactivity for NKX2.2, variable CD99, keratin, and epithelial membrane antigen, but were negative for S100 and myoepithelial markers. Importantly, similar to previously reported cases, the clinical course was more indolent than that of Ewing sarcoma. This case highlights the distinctive clinicopathological characteristics of EWSR1-NFATC2 gene fusion-associated neoplasms that distinguish them from Ewing sarcoma.

Case Reports in Oncological Medicine Myoepithelioma: A New Rearrangement Involving the LPP Locus in a Case of Multiple Bone and Soft Tissue Lesions

We report a case of multiple myoepithelioma with synchronous bone and soft tissue tumors, associated with a new genomic alteration of the LPP locus. The lesions occurred in the foot by presenting one lump in the plantar soft tissue, and three lesions were detected in the calcaneus and in the navicular bone. All tumors showed the double immunophenotype of epithelial markers and S100 protein expression. No rearrangement of the EWSR1 and FUS loci was detected as reported in myoepitheliomas. However, molecular karyotyping detected an unbalanced rearrangement of the LPP locus, not involving the HMGA2 locus, which is the most frequent translocation partner observed in benign mesenchymal tumors such as lipomas (of soft tissue as well as parosteal) and pulmonary chondroid hamartoma.

Malignant Ewing-Like Neoplasm With an EWSR1-KLF15 Fusion: At the Crossroads of a Myoepithelial Carcinoma and a Ewing-Like Sarcoma. A Case Report With Treatment Options

We present a case of a malignant Ewing-like neoplasm of the parotid gland in a 20-year-old woman with an EWSR1-KLF15 gene fusion that presented with pulmonary metastasis. Despite the fact that the tumor was essentially immunohistochemically negative for keratins, p63, and p40, we interpret this neoplasm as an unusual form of a high-grade myoepithelial carcinoma based on its focal plasmacytoid cytology, chondromyxoid matrix, SOX10, S100 protein, and calponin expression, and the knowledge that the EWSR1-KLF15 gene fusion has, to date, only been identified in 2 tumors, both myoepithelial carcinomas of the kidney. We also present a cytogenetic analysis of this unusual tumor. This "Ewing-like myoepithelial carcinoma" initially did not respond to 2 cycles of ifosfamide and etoposide alternated with a cycle of cytoxan, adriamycin, and vincristine, a standard regimen for Ewing sarcoma. Subsequent oral pazopanib therapy did result in a reduction of the patient's pulmonary and nodal disease.

A rare large cutaneous chondroid syringoma involving a toe: A case report

RATIONALE

Chondroid syringoma (CS) occurs mostly on the face and neck, and rarely occurs in the toe. Malignant CS is invasive, grows quickly, and has a high recurrence rate. The presence of a bilobed CS in 1 toe has never been reported in the literature.

PATIENT CONCERNS

A 72-year-old male patient presented with a mass in a third toe of his right foot. The mass had slowly grown in 2 years. He felt mild pain and the mass occupied most of the tip of the toe.

DIAGNOSES

Radiographs showed a large soft-tissue mass in the third toe of his right foot without any bone destruction. Ultrasonogram showed 2 partly fused hypoechoic masses within the lesion. The mass was therefore diagnosed as a benign CS.

INTERVENTIONS

We amputated the toe with the mass under local anesthesia. The postoperative pathohistological examinations confirmed that the lesion was a bipartite CS exhibiting active cellular proliferation.

OUTCOMES

Two years after surgery, there was no tumor recurrence.

LESSONS

CS can also present as multiple adjacent masses. Complete surgical resection and long-term follow-up are essential.

Cytologic diagnosis of round cell sarcomas in the era of ancillary testing: an updated review

Round cell sarcomas constitute a large proportion of "small round blue cell tumors," which encompass a broad differential diagnosis and can be difficult to distinguish on cytomorphologic grounds alone. Numerous pathogenetic insights and advances in ancillary testing in soft tissue pathology over the last several decades have made accurate classification of soft tissue neoplasms increasingly feasible. Immunohistochemistry and genetic/molecular testing can now be performed on all cytologic preparations, including unstained smears, needle rinses, cell blocks, and liquid-based preparations, and this has greatly increased our diagnostic abilities. Nevertheless, there remain numerous diagnostic challenges, including variable sensitivity and specificity of available immunohistochemical markers, overlapping immunophenotypes between entities, and "promiscuity" of genetic alterations such as EWSR1 rearrangements, present in a multitude of tumor types. Herein we provide a review on the cytologic, immunohistochemical, and genetic features of the more frequently encountered round cell sarcomas, as well as recently described entities, with an emphasis on diagnostic pitfalls and judicious use of ancillary studies.

Neoadjuvant radiation therapy for the management of myoepithelial carcinoma of the upper extremity

Myoepithelial tumors of the soft tissue are a rare tumor displaying myoepithelial elements and lacking obvious ductal differentiation. The rarity of these precludes any evidence-based consensus regarding optimal management. Nevertheless, the current approach to these lesions begins with amputation or complete excision. The efficacy of neoadjuvant or adjuvant radiation therapy or chemotherapy has not been established. Here, we present the first report to the authors' knowledge of neoadjuvant radiation therapy for the treatment of this rare soft tissue neoplasm and review the management and outcomes of published cases of myoepithelial carcinoma. A patient with a soft tissue myoepithelial carcinoma that declined both amputation and chemotherapy was treated with neoadjuvant radiation therapy and wide surgical excision followed by a brachytherapy boost to the resected tumor bed. Neoadjuvant radiation therapy resulted in an excellent response with extensive treatment-related changes consisting predominantly of fibrosis, hyalinization and hemorrhage and only 10% residual viable myoepithelial carcinoma present in the surgical specimen.

Myoepithelial Carcinoma of the Paracecal Mesentery: Aggressive Behavior of a Rare Neoplasm at an Unusual Anatomic Site

Myoepithelial tumors of the soft tissues represent a rare group of neoplasms that vary in their clinical behavior, pathologic features and genetics. They are histopathologically typified by a myoepithelial immunohistochemical phenotype, of expression of one or more epithelial markers, S100 protein and smooth muscle actin. Because of their rarity and occurrence over a wide age range and at a variety of anatomic sites, they can be difficult to diagnose due to the lack of familiarity by physicians, which is compounded by their spectrum of histologic features and morphologic overlap with several other neoplasms. Recent genetic insights have aided classification, and it is increasingly understood that soft tissue myoepithelial neoplasms can be stratified into two distinct morphologic and genetic subgroups. We describe a case of a 44-year-old man who was diagnosed with a primary myoepithelial neoplasm of the paracecal mesentery, which showed aggressive local recurrence after four years. The tumor was composed of cords of ovoid cells within chondromyxoid stroma, and displayed a characteristic pancytokeratin, S100 protein and smooth muscle actin-positive myoepithelial immunoprofile. Primary myoepithelioma has not been previously described at this site, and this case highlights this varied family of tumors, emphasizes the need to consider myoepithelial tumor in the differential diagnoses of carcinoma variants occurring in the bowel or mesentery, and also adds to the number of reported myoepithelial neoplasms showing markedly aggressive behavior.

Refinements in Sarcoma Classification in the Current 2013 World Health Organization Classification of Tumours of Soft Tissue and Bone

The fourth edition of the World Health Organization (WHO) Classification of Tumours of Soft Tissue and Bone was published in February 2013. The 2013 WHO volume provides an updated classification scheme and reproducible diagnostic criteria, which are based on recent clinicopathologic studies and genetic and molecular data that facilitated refined definition of established tumor types, recognition of novel entities, and the development of novel diagnostic markers. This article reviews updates and changes in the classification of bone and soft tissue tumors from the 2002 volume.

Expanding the Spectrum of Renal Tumors in Children: Primary Renal Myoepithelial Carcinomas With a Novel EWSR1-KLF15 Fusion

We report the first 2 examples of primary renal myoepithelial carcinoma (MEC), both occurring in children. Both tumors had the unique morphologic features, immunophenotype, and EWSR1 gene rearrangements supporting the diagnosis. In keeping with the previous observations of an aggressive behavior in pediatric MEC, both cases presented with advanced local stage and distant metastases at the time of diagnosis. The EWSR1 translocation partner was identified as the Kruppel-like factor 15 (KLF15) gene in both tumors, and the novel EWSR1-KLF15 gene fusion transcripts were verified using reverse transcription polymerase chain reaction and Sanger dideoxy sequencing. So far, a role for KLF15 in carcinogenesis has not been established, in contrast to other members of the Kruppel-like family of transcription factors, and no rearrangements involving this gene have been documented to our knowledge. These findings expand the spectrum of pediatric renal tumors to include MEC. The characterization of novel EWSR1-KLF15 fusion transcripts carries important diagnostic implications, as well as clues to understand the pathogenesis of these neoplasms.

Thoracic Myoepithelial Tumors: A Pathologic and Molecular Study of 8 Cases With Review of the Literature

Thoracic myoepithelial tumors (MTs) are a rare group of tumors showing predominant or exclusive myoepithelial differentiation. They are poorly characterized from both a morphologic and genetic standpoint, in particular features that separate benign from malignant behavior. We examined the histologic and immunohistochemical features of 8 primary thoracic MTs and performed fluorescence in situ hybridization for EWSR1, FUS, PLAG1, and HMGA2, as well as several partner genes. Half (4/8) of the MTs occurred in large airways, and 3 had infiltrative borders. All cases showed immunoreactivity for epithelial markers, in conjunction with S100 protein or myogenic markers. MTs showed morphologic characteristics analogous to MTs at other sites, with no tumors having ductal differentiation. Necrosis and/or lymphovascular invasion was present in 5 cases, with mitotic activity ranging from 0 to 6 mitoses/2 mm² (mean 1). Metastases occurred in 2 cases, and no patients died of disease. Gene rearrangements were identified in half of the cases, with EWSR1-PBX1, EWSR1-ZNF444, and FUS-KLF17 fusions identified in 1 case each and 1 case having EWSR1 rearrangement with no partner identified. No cases were found to have HMGA2 or PLAG1 abnormalities. Compared with fusion-negative tumors, fusion-positive tumors tended to occur in patients who were younger (50 vs. 58 y), female (1:3 vs. 3:1 male:female ratio), and demonstrated predominantly spindle and clear cell morphology. Using a combined data set of our case series with 16 cases from the literature, poor prognosis was significantly correlated with metastases (P=0.003), necrosis (P=0.027), and ≥5 mitoses/2 mm²/10 high-power field (P=0.005). In summary, we identify a subset of thoracic MTs harboring rearrangements in EWSR1 or FUS, and our data suggest that necrosis and increased mitotic activity correlate with aggressive clinical behavior.

Soft Tissue Myoepithelial Carcinoma Metastatic to the Cecum: Highlighting an Unusual Metastatic Pattern and the Need for Diagnostic Awareness

Myoepithelial neoplasms of the soft tissues are a rare, heterogeneous group of tumors for which classification continues to evolve. While well defined within salivary glands, they can also arise in viscera and soft tissues, where diagnosis is challenging due to the lack of clinical and pathological familiarity. We present the case of a 36 year old man with myoepithelial carcinoma arising as a primary tumor within the soft tissues of the neck, which metastasized to the cecum, causing intussusception. This spindle cell neoplasm showed the classic S100 protein, smooth muscle actin and pancytokeratin-positive immunoprofile. Metastasis of myoepithelial carcinoma to the cecum has not been previously described, and coupled with the spindle cell morphology, may cause significant diagnostic difficulty in the absence of clinical familiarity, particularly as there is morphologic overlap with spindle cell neoplasms arising more commonly in gastrointestinal sites, including gastrointestinal stromal tumor, leiomyosarcoma and sarcomatoid carcinoma.