Angiomatoid fibrous histiocytoma (AFH) is a rare mesenchymal neoplasm of borderline malignancy (locally recurring, rarely metastasizing), most often involving the limbs, trunk, and head/neck. Rarely, AFH may involve unusual locations. Herein, we characterize the clinicopathologic features of 26 AFH of the distal extremities, including acral sites. The tumors occurred in 19 females and 7 males ranging in age from 12 to 76 years (median, 23 years). Tumors involved the upper (n = 19) and lower (n = 6) distal extremity; one affected an unspecified digital site. Twenty-two cases occurred in acral locations (hands and feet). Subsets of cases showed the following morphologic features: multinodular architecture (26/26), lymphoid cuffs (23/26), prominent stromal myxoid change (11/25), angiomatoid features (9/26), and cytologic pleomorphism (8/26). The average mitotic count was 1/10 HPF; 3 cases showed brisk mitotic activity (> 10 mitoses/10 HPF). Immunohistochemistry revealed variable expression of desmin (16/25), EMA (14/21) and ALK (5/8). Molecular testing revealed EWSR1 rearrangements in 17/18 cases (94%). Among 12 tumors with known fusion partners, the fusions partner was CREB1 in 6 cases (50%), CREM in 4 tumors (33%), ATF1 in one tumor (8%) and PBX3 (8%) in another tumor. Prominent myxoid features were noted in 75% CREM versus 33% of CREB1 versus 0% of ATF1-fused tumors. AFH occurring in distal extremity/acral locations have a predilection for females, upper extremity locations, frequent unusual (solid, non-angiomatoid and myxoid) morphology and higher frequency of CREM over ATF1 fusions. Awareness of the morphologic spectrum of these rare neoplasms is essential for correct classification.

• Keywords
• Clear cell sarcoma, Genetic landscape, Mimics, Precision medicine, Profiling, Targeted next generation sequencing,
• MeSH
• Child MeSH
• Adult MeSH
• Oncogene Proteins, Fusion genetics   MeSH
• Genotype MeSH
• In Situ Hybridization, Fluorescence MeSH
• Extremities pathology   MeSH
• Middle Aged MeSH
• Humans MeSH
• Histiocytoma, Malignant Fibrous * genetics   pathology   MeSH
• Adolescent MeSH
• Young Adult MeSH
• Biomarkers, Tumor genetics   analysis   MeSH
• Soft Tissue Neoplasms * pathology   genetics   MeSH
• RNA-Binding Protein EWS genetics   MeSH
• Aged MeSH
• Check Tag
• Child MeSH
• Adult MeSH
• Middle Aged MeSH
• Humans MeSH
• Adolescent MeSH
• Young Adult MeSH
• Male MeSH
• Aged MeSH
• Female MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• EWSR1 protein, human MeSH Browser
• Oncogene Proteins, Fusion MeSH
• Biomarkers, Tumor MeSH
• RNA-Binding Protein EWS MeSH

RNA metabolism plays an essential role in the development of both oocytes and embryos. Their dependence on stored maternal transcripts is due to a long period of silenced transcription in which the oocyte undergoes meiotic maturation and fertilization. Although maternal RNAs are unusually stable, they should be replaced by "zygotic" transcripts during the transition from oocyte to zygote. Analysis of ncRNA and mRNA distribution in the oocyte can provide clues to the fate of RNA in the single-cell environment.Our work focuses on the visualization of the subcellular distribution of specific RNAs in mammalian oocytes and early embryos. The localization of many RNAs in the oocyte and embryo is still not fully understood. In this chapter, we describe an optimized protocol for RNAscope, a type of RNA fluorescence in situ hybridization (RNA FISH), which is a valuable technique for exploring mammalian oocytes and embryos. The method is based on a specific probe design strategy that enables signal amplification together with simultaneous background suppression. Additionally, it is suitable for quantitative spatio-temporal analysis of specific RNA transcripts. RNAscope, a simple and a reliable protocol, contributes to advancing our understanding of RNA biology in the context of germ cell development.

• Keywords
• Embryo, Oocyte, RNA FISH, Single-molecule imaging, mRNA,
• MeSH
• Embryo, Mammalian * metabolism   MeSH
• In Situ Hybridization, Fluorescence * methods   MeSH
• RNA, Messenger genetics   MeSH
• Mice MeSH
• Oocytes * metabolism   MeSH
• RNA * genetics   metabolism   MeSH
• Animals MeSH
• Check Tag
• Mice MeSH
• Female MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• RNA, Messenger MeSH
• RNA * MeSH

This investigation describes the clinicoradiologic, pathologic, and molecular features of a unique soft tissue tumor characterized by a peripheral shell of bone and composed of bland myoid spindle and epithelioid cells that are keratin-positive. Our study cohort consists of 6 men and 6 women, with a mean age of 32 years. The tumors arose in the extremities (n = 9) and proximal limb girdle (n = 3) and were equally distributed between deep and superficial soft tissues. Patients reported dull painless masses of several months to >10 years duration (mean: 2.9 years). Imaging demonstrated a complete or partial peripheral shell of bone that could extend centrally, and the tumor's mean size was 5.7 cm. Histologically, the tumors were composed of uniform, eosinophilic myoid spindled cells growing in sheets and intersecting fascicles, surrounded by mature lamellar and/or woven bone. Also present was an admixed component of intermediate-sized epithelioid cells with eosinophilic cytoplasm. Mitotic activity was consistently low. Immunohistochemistry showed strong multifocal staining for keratins, and 50% (5/10) showed focal staining for S100; however, all were negative for SMA, desmin, SOX10, ERG, and CD34. Genetic analysis by multiple targeted RNA sequencing panels was negative (n = 10); however, whole transcriptome sequencing (n = 8) revealed a recurrent and novel in-frame SRSF7::NFATC3 fusion in 4 tumors. Dual fluorescence in situ hybridization probes for SRSF7::NFATC3 successfully confirmed this fusion and identified a fifth case, which had not undergone whole transcriptome sequencing but was negative by a targeted RNA fusion panel. Methylation profiling (n = 8) demonstrated a shared epigenetic profile distinct from other entities. Clinical follow-up (n = 11) showed no evidence of recurrence after primary excision with a mean of 41.6 months. In summary, we describe a novel soft tissue tumor designated "ossifying spindled and epithelioid tumor" as a descriptive histologic term that also emphasizes its close radiologic mimic, ossifying fibromyxoid tumor. All cases have behaved in a benign fashion without recurrence following simple excision. Awareness of this entity is important, so that it can be distinguished from other neoplasms that have more aggressive biological potential.

• Keywords
• SRSF7::NFATC3, myositis ossificans, ossifying fibromyxoid tumor, ossifying spindled and epithelioid tumor, radiology, soft tissue tumor,
• Publication type
• Journal Article MeSH

Sclerosing mucoepidermoid carcinoma (SMEC) of the salivary glands is a rare variant of low-grade mucoepidermoid carcinoma with scanty cellular atypia characterized by marked fibrosis/sclerosis and a rich inflammatory infiltrate. Herein, we report 25 unpublished cases of SMEC, two of them with prominent eosinophilia (2/25; 8%) and three with abundant IgG4-positive plasma cells (3/25; 12%). In our series of salivary SMEC, molecular analysis using fluorescence in situ hybridization (FISH) and/or next-generation sequencing (NGS) provided evidence of MAML2 gene rearrangement in 18 cases of the 21 analyzable cases tested (86%), while this gene locus was intact in 3 cases (14%). This study focuses on the diagnostic criteria of salivary SMEC given its challenge of abundant collagenous stroma, minimal residual neoplastic areas, and inconspicuous mucous cells. Follow-up data of our cases indicate that salivary SMECs have favorable outcomes. Molecular analysis for MAML2 gene rearrangement suggests that SMECs of salivary glands represent a rare variant of conventional low-grade MECs of salivary glands. In contrast, SMECs of the thyroid gland are genetically distinct from salivary-type thyroid MECs.

• Keywords
• MAML2 rearrangement, IgG4, Keloid-like stromal fibrosis, SMEC, Salivary gland, Sclerosing mucoepidermoid carcinoma, Sclerosis, Tissue eosinophilia,
• MeSH
• DNA-Binding Proteins genetics   MeSH
• Adult MeSH
• Gene Rearrangement MeSH
• In Situ Hybridization, Fluorescence MeSH
• Middle Aged MeSH
• Humans MeSH
• Young Adult MeSH
• Carcinoma, Mucoepidermoid * pathology   genetics   MeSH
• Biomarkers, Tumor genetics   analysis   MeSH
• Salivary Gland Neoplasms * pathology   genetics   MeSH
• Aged MeSH
• Sclerosis MeSH
• Trans-Activators genetics   MeSH
• Transcription Factors genetics   MeSH
• High-Throughput Nucleotide Sequencing MeSH
• Check Tag
• Adult MeSH
• Middle Aged MeSH
• Humans MeSH
• Young Adult MeSH
• Male MeSH
• Aged MeSH
• Female MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• DNA-Binding Proteins MeSH
• MAML2 protein, human MeSH Browser
• Biomarkers, Tumor MeSH
• Trans-Activators MeSH
• Transcription Factors MeSH

Nodular fasciitis is a benign myofibroblastic tumor characterized by rapid growth and spontaneous regression. While nodular fasciitis is typically an indolent process, rare cases with benign morphologic features have developed metastases. Conversely, nodular fasciitis with malignant histologic features and benign clinical course have also been reported. In this study, we present seven nodular fasciitis cases with novel USP6 gene fusion partners, in addition to two cases with rare fusions that displayed aggressive clinical behavior. The cohort comprised five females and four males with a median age of 36 years (range 13-59). Tumors were located in the forearm (n = 3), thigh (n = 2), and shoulder, abdominal wall, chest wall, and oral cavity (one each), ranging from 1.4 to 24.0 cm in size (median, 2.2 cm). Except for the clinically aggressive cases, patients presented with painless masses of varying onset from days to months. Of the clinically aggressive cases, one patient presented with a slowly growing subfascial thigh/hip mass over nine years, leading to erosion of the femur and pelvis; the other presented with a painful subfascial thigh mass of several months' duration. Histologically, all cases, including the clinically aggressive ones, showed conventional nodular fasciitis features without nuclear pleomorphism or atypical mitotic figures; one case with aggressive clinical behavior exhibited focal infarction-type necrosis. Break-apart FISH analysis using USP6 flanking probes failed to detect USP6 rearrangement in two cases (false negatives) and was inconclusive in one case. Next-generation RNA sequencing identified USP6 fusions in all cases. The clinically aggressive cases showed fusions with COL1A1 (exon 1) and PPP6R3 (exon 1), while novel fusions were identified in the remaining cases including EIF4A1 (exon 1), FILIP1L (exon 2), NF1 (exon 33), OMD (exon 1), PFN1 (exon 1), RLIM (exon 1), and SETD5 (exon 1). Six patients underwent surgical resection; three were managed conservatively, with two experiencing spontaneous tumor resolution. Of the clinically aggressive cases, one patient had progression of the tumor with erosion of the underlying bone, and the second patient developed local recurrence at 14 months and lung metastasis at 19 months, ultimately dying of disease at 22 months. The remaining patients showed no recurrence or metastasis. Our findings expand the spectrum of USP6 gene fusion partners in nodular fasciitis and, for the first time, report cases with conventional morphology exhibiting aggressive behavior, including death. These observations raise the question of whether a subset of deep lesions with conventional nodular fasciitis histology but unusual clinical features, such as large tumor size, represents malignant nodular fasciitis or alternatively a nodular fasciitis-like myofibroblastic sarcoma.

• Keywords
• Aggressive behavior, Nodular fasciitis, Novel gene fusions, Rare partners,
• MeSH
• Adult MeSH
• Fasciitis * genetics   pathology   MeSH
• Gene Fusion * MeSH
• In Situ Hybridization, Fluorescence MeSH
• Middle Aged MeSH
• Humans MeSH
• Adolescent MeSH
• Young Adult MeSH
• Biomarkers, Tumor * genetics   MeSH
• Proto-Oncogene Proteins genetics   MeSH
• Ubiquitin Thiolesterase * genetics   MeSH
• Check Tag
• Adult MeSH
• Middle Aged MeSH
• Humans MeSH
• Adolescent MeSH
• Young Adult MeSH
• Male MeSH
• Female MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Biomarkers, Tumor * MeSH
• Proto-Oncogene Proteins MeSH
• Ubiquitin Thiolesterase * MeSH
• USP6 protein, human MeSH Browser

The diagnosis of Ewing sarcoma can be challenging, particularly when the tumor is present in an atypical location and resembles histologic mimics. The hallmark feature of Ewing sarcoma is chromosomal translocation, t(11;22)(q24;q12), involving EWSR1 and ETS gene family members. For decades, fluorescence in situ hybridization with a break-apart EWSR1 probe has been the diagnostic gold standard. However, EWSR1 rearrangements have been identified in other malignancies; thus, the detection of chimeric EWSR1 transcripts has become a preferable approach. Occasionally, insufficient tissue, severe RNA degradation, or economic constraints hamper molecular testing. This study evaluated Protein Kinase C Beta II (PKC β II) expression in >1000 tumors and assessed the utility of PKC β II immunohistochemistry in the differential diagnosis of Ewing sarcoma. Tumors harboring EWSR1 :: FLI1 (n=26), EWSR1 :: ERG , EWSR1 :: ETV4 (n=1), and FUS :: ERG (n=6) fusions were evaluated, revealing strong diffuse immunoreactivity, although a patchy pattern was seen in 3 cases. Undifferentiated round cell sarcomas (n=46), including BCOR -, CIC -, NFATC2 -, NUTM1 -, and PATZ1 rearranged/fusion-sarcomas were negative. Two of the 130 synovial sarcomas, including 1 with a poorly differentiated morphology, showed diffuse, moderate-to-strong positivity. One of the 26 poorly differentiated carcinomas from the head and neck region, probably small cell lung carcinoma metastasis, showed strong PKC β II expression. Neuroblastomas (>50%) expressed PKC β II, although none showed a strong diffuse pattern. Diffuse moderate-to-strong immunoreactivity was observed in 2 sarcomatoid mesotheliomas and 2 metastatic melanomas. Diffuse but weak staining was observed in 73% (11/15) of the T-cell lymphoblastic lymphomas, including 10 CD99-positive cases. Similarly, weak predominantly patchy staining was seen in half (40/80) of other non-Hodgkin lymphomas and sporadically in embryonal rhabdomyosarcoma, Merkel cell carcinoma, small cell lung carcinoma, and Wilms tumor. Thus, diffuse and strong PKC β II immunoreactivity appears to be a reliable diagnostic marker for distinguishing classic Ewing sarcoma from histologic mimics.

• Keywords
• Ewing sarcoma, Ewing-like sarcoma, immunohistochemistry, oncogenic fusions, undifferentiated round cell sarcoma,
• MeSH
• Diagnosis, Differential MeSH
• Child MeSH
• Adult MeSH
• Sarcoma, Ewing * diagnosis   genetics   enzymology   pathology   MeSH
• Immunohistochemistry * MeSH
• Middle Aged MeSH
• Humans MeSH
• Adolescent MeSH
• Young Adult MeSH
• Biomarkers, Tumor * analysis   genetics   MeSH
• Bone Neoplasms * diagnosis   enzymology   genetics   pathology   MeSH
• Predictive Value of Tests MeSH
• RNA-Binding Protein EWS MeSH
• Protein Kinase C beta * analysis   MeSH
• Check Tag
• Child MeSH
• Adult MeSH
• Middle Aged MeSH
• Humans MeSH
• Adolescent MeSH
• Young Adult MeSH
• Male MeSH
• Female MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• EWSR1 protein, human MeSH Browser
• Biomarkers, Tumor * MeSH
• PRKCB protein, human MeSH Browser
• RNA-Binding Protein EWS MeSH
• Protein Kinase C beta * MeSH

Adenoid cystic carcinomas (AdCC) of salivary gland origin have long been categorized as fusion-defined carcinomas owing to the almost universal presence of the gene fusion MYB::NFIB , or less commonly MYBL1::NFIB. Sinonasal AdCC is an aggressive salivary gland malignancy with no effective systemic therapy. Therefore, it is urgent to search for potentially targetable genetic alterations associated with AdCC. We have searched the authors' registries and selected all AdCCs arising in the sinonasal tract. The tumors were examined histologically, immunohistochemically, by next generation sequencing (NGS) and/or fluorescence in situ hybridization (FISH) looking for MYB/MYBL1 and/or NFIB gene fusions or any novel gene fusions and/or mutations. In addition, all tumors were tested for HPV by genotyping using (q)PCR. Our cohort comprised 88 cases of sinonasal AdCC, predominantly characterized by canonical MYB::NFIB (49 cases) and MYBL1::NFIB (9 cases) fusions. In addition, noncanonical fusions EWSR1::MYB ; ACTB::MYB; ESRRG::DNM3 , and ACTN4::MYB were identified by NGS, each of them in 1 case. Among nine fusion-negative AdCCs, FISH detected rearrangements in MYB (7 cases) , NFIB (1 case), and EWSR1 (1 case). Six AdCCs lacked fusions or gene rearrangements, while 11 cases were unanalyzable. Mutational analysis was performed by NGS in 31/88 (35%) AdCCs. Mutations in genes with established roles in oncogenesis were identified in 21/31 tumors (68%), including BCOR (4/21; 19%), NOTCH1 (3/21; 14%), EP300 (3/21; 14%), SMARCA4 (2/21; 9%), RUNX1 (2/21; 9%), KDM6A (2/21; 9%), SPEN (2/21; 9%), and RIT1, MGA, RB1, PHF6, PTEN, CREBBP, DDX41, CHD2, ROS1, TAF1, CCD1, NF1, PALB2, AVCR1B, ARID1A, PPM1D, LZTR1, GEN1 , PDGFRA , each in 1 case (1/21; 5%). Additional 24 cases exhibited a spectrum of gene mutations of uncertain pathogenetic significance. No morphologic differences were observed between AdCCs with MYBL1::NFIB and MYB::NFIB fusions. Interestingly, mutations in the NOTCH genes were seen in connection with both canonical and noncanonical fusions, and often associated with high-grade histology or metatypical phenotype, as well as with poorer clinical outcome. Noncanonical fusions were predominantly observed in metatypical AdCCs. These findings emphasize the value of comprehensive molecular profiling in correlating morphologic characteristics, genetic landscape, and clinical behavior in AdCC.

• MeSH
• Carcinoma, Adenoid Cystic * genetics   pathology   chemistry   MeSH
• Adult MeSH
• Phenotype MeSH
• Gene Fusion * MeSH
• Oncogene Proteins, Fusion * genetics   MeSH
• Genetic Predisposition to Disease MeSH
• In Situ Hybridization, Fluorescence MeSH
• Immunohistochemistry MeSH
• Middle Aged MeSH
• Humans MeSH
• Young Adult MeSH
• Mutation * MeSH
• DNA Mutational Analysis MeSH
• Biomarkers, Tumor * genetics   analysis   MeSH
• Paranasal Sinus Neoplasms * genetics   pathology   chemistry   MeSH
• Proto-Oncogene Proteins MeSH
• Aged, 80 and over MeSH
• Aged MeSH
• Gene Expression Profiling MeSH
• Trans-Activators genetics   MeSH
• NFI Transcription Factors genetics   MeSH
• High-Throughput Nucleotide Sequencing MeSH
• Check Tag
• Adult MeSH
• Middle Aged MeSH
• Humans MeSH
• Young Adult MeSH
• Male MeSH
• Aged, 80 and over MeSH
• Aged MeSH
• Female MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Oncogene Proteins, Fusion * MeSH
• MYBL1 protein, human MeSH Browser
• Biomarkers, Tumor * MeSH
• NFIB protein, human MeSH Browser
• Proto-Oncogene Proteins MeSH
• Trans-Activators MeSH
• NFI Transcription Factors MeSH

The immunohistochemical (IHC) or fluorescence/chromogenic in situ hybridization (FISH/CISH) assays for assessing HER2 are now recommended by the American Society of Clinical Oncologists and the College of American Pathologists, but there are an increasing number of published studies describing alternative diagnoses at the molecular level. Inspired by these studies, we established a laboratory-developed test (LDT) to analyze HER2 status not only at the gene expression level but also at the gene copy number. A precise copy number calculation was fulfilled including the Control Genomic DNA of known concentration, which allowed subsequent assay validation at the DNA level. The results were reported according to the concordant results of the DNA and RNA approaches. By comparing with IHC determination, completely identical results were found in ten blank samples, which underlines the legitimacy of molecular biological approaches in this diagnostic field. An equivocal sample that was positive by IHC and qPCR was found to be negative by the FISH and so it may change the choice of personalized medicine. The topic of this short communication will hopefully contribute to allowing IVD-certified diagnostics based on the HER2 gene expression profile or copy number to be tested in the Czech Republic as well.

• Keywords
• HER2/ERBB2, gene copy number, gene expression, quantitative PCR assessment,
• MeSH
• DNA * genetics   MeSH
• Gene Dosage MeSH
• In Situ Hybridization, Fluorescence methods   MeSH
• Immunohistochemistry methods   MeSH
• Humans MeSH
• Biomarkers, Tumor genetics   MeSH
• Breast Neoplasms * genetics   diagnosis   metabolism   MeSH
• Receptor, ErbB-2 * genetics   metabolism   MeSH
• RNA * genetics   MeSH
• Check Tag
• Humans MeSH
• Female MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• DNA * MeSH
• ERBB2 protein, human MeSH Browser
• Biomarkers, Tumor MeSH
• Receptor, ErbB-2 * MeSH
• RNA * MeSH

TFE3 rearrangements characterize histogenetically, topographically, and biologically diverse neoplasms. Besides being a universal defining feature in alveolar soft part sarcoma (ASPS) and clear cell stromal tumor of the lung, TFE3 fusions have been reported in subsets of renal cell carcinoma, perivascular epithelioid cell tumor (PEComa), epithelioid hemangioendothelioma and ossifying fibromyxoid tumors. TFE3 -related neoplasms are rare in the head and neck and may pose diagnostic challenges. We herein describe 22 TFE3 fusion neoplasms affecting 11 males and 11 females aged 4 to 79 years (median, 25) and involving different head and neck sites: sinonasal cavities (n = 8), tongue (n = 4), oral cavity/oropharynx (n = 3), salivary glands (n = 2), orbit (n = 2), and soft tissue or unspecified sites (n = 3). Based on morphology and myomelanocytic immunophenotype, 10 tumors qualified as ASPS, 7 as PEComas (3 melanotic; all sinonasal), and 5 showed intermediate (indeterminate) histology overlapping with ASPS and PEComa. Immunohistochemistry for TFE3 was homogeneously strongly positive in all cases. Targeted RNA sequencing/FISH testing confirmed TFE3 fusions in 14 of 16 successfully tested cases (88%). ASPSCR1 was the most frequent fusion partner in ASPS (4 of 5 cases); one ASPS had a rare VCP::TFE3 fusion. The 6 successfully tested PEComas had known fusion partners as reported in renal cell carcinoma and PEComas ( NONO, PRCC, SFPQ , and PSPC1 ). The indeterminate tumors harbored ASPSCR1::TFE3 (n = 2) and U2AF2::TFE3 (n = 1) fusions, respectively. This large series devoted to TFE3-positive head and neck tumors illustrates the recently proposed morphologic overlap in the spectrum of TFE3 -associated mesenchymal neoplasms. While all PEComas were sinonasal, ASPS was never sinonasal and occurred in diverse head and neck sites with a predilection for the tongue. The indeterminate (PEComa-like) category is molecularly more akin to ASPS but shows different age, sex, and anatomic distribution compared with classic ASPS. We report VCP as a novel fusion partner in ASPS and PSPC1 as a novel TFE3 fusion partner in PEComa (detected in one PEComa). Future studies should shed light on the most appropriate terminological subtyping of these highly overlapping tumors.

• MeSH
• Sarcoma, Alveolar Soft Part * genetics   pathology   chemistry   MeSH
• Child MeSH
• Adult MeSH
• Phenotype MeSH
• Gene Fusion MeSH
• Gene Rearrangement * MeSH
• In Situ Hybridization, Fluorescence MeSH
• Immunohistochemistry MeSH
• Middle Aged MeSH
• Humans MeSH
• Adolescent MeSH
• Young Adult MeSH
• Biomarkers, Tumor * genetics   analysis   MeSH
• Head and Neck Neoplasms * genetics   pathology   chemistry   MeSH
• Perivascular Epithelioid Cell Neoplasms * genetics   pathology   chemistry   MeSH
• Child, Preschool MeSH
• Aged MeSH
• Basic Helix-Loop-Helix Leucine Zipper Transcription Factors * genetics   MeSH
• Check Tag
• Child MeSH
• Adult MeSH
• Middle Aged MeSH
• Humans MeSH
• Adolescent MeSH
• Young Adult MeSH
• Male MeSH
• Child, Preschool MeSH
• Aged MeSH
• Female MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Biomarkers, Tumor * MeSH
• TFE3 protein, human MeSH Browser
• Basic Helix-Loop-Helix Leucine Zipper Transcription Factors * MeSH

Myoepithelial neoplasms of the skin and soft tissue still represent a confusing and somewhat controversial field in pathology as it appears that this category includes several different entities. However, recent studies have suggested that both apocrine mixed tumors (AMT) and cutaneous myoepitheliomas (CM) harbor identical chromosomal rearrangements involving the PLAG1 gene and hence may represent a morphological spectrum. The aim of the present study was to share our institutional experience with these tumors and specifically focus on studying their immunohistochemical and molecular features to further assess their relatedness. Eleven cases of AMT and 7 cases of CM were collected and analyzed using immunohistochemistry (IHC), PLAG1 FISH, and Archer FusionPlex assay. There were 14 male and 4 female patients with ages ranging from 26 to 85 years (median 55.8 years, mean 58.5 years). AMTs were mainly located in the head and neck (n = 10), while CMs were mainly located in the acral sites (n = 5). PLAG1 IHC was diffusely strongly positive in 14/17 (82%) cases, whereas a single case of AMT diffusely expressed HMGA2. Both tumor groups showed PLAG1 gene fusions which were detected in 6/13 analyzable samples (AMT, n = 4 and CM, n = 2), and included TRPS1::PLAG1 (n = 3), NDRG1::PLAG1 (n = 1), CTNNB1::PLAG1 (n = 1) and a novel PXDNL::PLAG1 fusion (n = 1). The remaining 5 cases were negative, 5 were not analyzable and the single case positive for HMGA2 by IHC revealed a potential HMGA2 gene rearrangement. The cases were further studied by FISH, with 12/17 cases showing PLAG1 gene rearrangement (AMT, n = 8 and CM, n = 4). Altogether, 14/18 cases showed PLAG1 gene rearrangement by at least one of the methods. PLAG1 immunohistochemistry had a 92% specificity and sensitivity. Our study provided additional data to suggest that AMT and CM share overlapping morphological and immunohistochemical features as well as molecular background characterized by PLAG1 gene fusions and thus represent a morphological spectrum. In addition, we identified a novel PXDNL::PLAG1 fusion and suggested that rare cases may harbor HMGA2 gene alterations which seem to be mutually exclusive with PLAG1 gene fusions. The relatedness of these tumors to salivary gland myoepithelial neoplasms and distinctness from eccrine mixed tumors and other skin and soft tissue myoepithelial neoplasms with EWSR1/FUS fusions is discussed.

• Keywords
• HMGA2, PLAG1, Apocrine mixed tumors, Cutaneous myoepitheliomas, Myoepithelial neoplasm, Targeted RNA sequencing,
• MeSH
• Apocrine Glands * pathology   MeSH
• DNA-Binding Proteins * genetics   MeSH
• Adult MeSH
• Gene Rearrangement * MeSH
• In Situ Hybridization, Fluorescence MeSH
• Immunohistochemistry MeSH
• Middle Aged MeSH
• Humans MeSH
• Myoepithelioma * genetics   pathology   chemistry   MeSH
• Biomarkers, Tumor * genetics   analysis   MeSH
• Skin Neoplasms * genetics   pathology   chemistry   MeSH
• Sweat Gland Neoplasms * genetics   pathology   MeSH
• HMGA2 Protein * genetics   MeSH
• Aged, 80 and over MeSH
• Aged MeSH
• Check Tag
• Adult MeSH
• Middle Aged MeSH
• Humans MeSH
• Male MeSH
• Aged, 80 and over MeSH
• Aged MeSH
• Female MeSH
• Publication type
• Journal Article MeSH
• Comparative Study MeSH
• Names of Substances
• DNA-Binding Proteins * MeSH
• HMGA2 protein, human MeSH Browser
• Biomarkers, Tumor * MeSH
• PLAG1 protein, human MeSH Browser
• HMGA2 Protein * MeSH