What is hiding behind S100 protein and SOX10 positive oncocytomas? Oncocytic pleomorphic adenoma and myoepithelioma with novel gene fusions in a subset of cases

Atypical and worrisome histological features in pleomorphic adenoma: challenging and potentially significant diagnostic pitfall

Pleomorphic adenoma (PA), the most prevalent salivary gland tumor, exhibits a diverse histological spectrum characterized by epithelial, myoepithelial, and mesenchymal patterns, and secretory products. However, a subset of PAs presents microscopic features suggestive of malignancy, leading to challenging and potentially significant diagnostic pitfalls. A comprehensive retrospective analysis was conducted on the Salivary Gland Tumor Registry, compiled by the authors. A total of 104 cases diagnosed between 1960 and 2023 were retrieved. Clinical findings, pathological features, and molecular genetic results were analyzed. In the study of 104 PA cases, 23 (22.1%) presented features suggestive of pseudoinvasion, with satellite nodules being the most common (43.5%) along with capsular penetration, irregular growth, pseudopodia, lipomatous changes, and vascular permeation. Features of pseudomalignant cytomorphology were found in 97 cases (93.3%), characterized by increased cellularity, cellular atypia, heightened proliferative activity, oncocytic metaplasia, and necrosis. Additionally, 30 cases (28.8%) displayed features resembling other defined malignant salivary gland tumors, particularly myoepithelial carcinoma, adenoid cystic carcinoma, and polymorphous adenocarcinoma. Despite PA's generally straightforward diagnosis, cases with these features may be mistakenly interpreted as malignant tumors. The shared morphocytological features underscore the complexity of an accurate diagnosis, emphasizing the need for meticulous examination and a comprehensive assessment, incorporating morphological, molecular, and immunohistochemical analyses to differentiate between benign and malignant salivary gland tumors, in selected cases.

The Transcriptomic and Gene Fusion Landscape of Pleomorphic Salivary Gland Adenomas

Pleomorphic adenoma (PA) is the most common salivary gland tumor. PAs are characterized by chromosomal rearrangements of 8q12 and 12q14-15, leading to gene fusions involving the PLAG1 and HMGA2 oncogenes. Here, we performed the first comprehensive study of the transcriptomic and gene fusion landscape of 38 cytogenetically characterized PAs. RNA-seq identified PLAG1 or HMGA2 fusions in 33/38 cases (87%), of which 15 were novel fusions. Fusions were found also in tumors with normal karyotype, demonstrating that they are generated by cryptic rearrangements. PLAG1 was mainly activated by promoter swapping and HMGA2 by truncation of its 3'-part. RNA-seq revealed upregulation of genes involved in extracellular matrix production, WNT-signaling, and epithelial-mesenchymal transition in PA compared to normal salivary tissue. Principal component analysis identified two PA subclusters characterized by PLAG1- and HMGA2-activation, respectively, that differed in expression of genes involved in the immune system, cell adhesion, and microenvironment remodeling. Moreover, comparative analyses of PA and salivary carcinomas revealed that PA resembles myoepithelial carcinoma. Our study reveals new oncogenic gene fusions and expands our knowledge about the molecular underpinnings of PA.

SARCP, a Clinical Next-Generation Sequencing Assay for the Detection of Gene Fusions in Sarcomas: A Description of the First 652 Cases

An amplicon-based targeted next-generation sequencing (NGS) assay for the detection of gene fusions in sarcomas was developed, validated, and implemented. This assay can detect fusions in targeted regions of 138 genes and BCOR internal tandem duplications. This study reviews our experience with testing on the first 652 patients analyzed. Gene fusions were detected in 238 (36.5%) of 652 cases, including 83 distinct fusions in the 238 fusion-positive cases, 10 of which had not been previously described. Among the 238 fusion-positive cases, the results assisted in establishing a diagnosis for 137 (58%) cases, confirmed a suspected diagnosis in 66 (28%) cases, changed a suspected diagnosis in 25 (10%) cases, and were novel fusions with unknown clinical significance in 10 (4%) cases. Twenty-six cases had gene fusions (ALK, ROS1, NTRK1, NTRK3, and COL1A1::PDGFB) for which there are targetable therapies. BCOR internal tandem duplications were identified in 6 (1.2%) of 485 patients. Among the 138 genes in the panel, 66 were involved in one or more fusions, and 72 were not involved in any fusions. There was little overlap between the genes involved as 5'-partners (31 different genes) and 3'-partners (37 different genes). This study shows the clinical utility of a next-generation sequencing gene fusion detection assay for the diagnosis and treatment of sarcomas.

Reappraisal of Oncocytic Adenocarcinoma: Unveiling Its Connection to Oncocytic Variants of Salivary Duct Carcinoma and Mucoepidermoid Carcinoma Through ImmunoHisto-Molecular Perspectives

Oncocytic adenocarcinoma (OC) of the salivary glands is a rare and controversial entity. It was recently reclassified as "salivary carcinoma NOS and emerging entities" in the 2022 WHO classification of head and neck tumors. The lack of specific molecular alterations and its potential affiliation with other salivary gland carcinomas, such as the oncocytic mucoepidermoid carcinomas (OMEC) or the oncocytic subtype of salivary duct carcinomas (OSDC) justified this reclassification. It is becoming essential to clarify the complex spectrum of potential diagnoses surrounding oncocytic tumors. The objective of this study was to explore the histologic features, as well as the immunohistochemical and molecular profiles, of cases previously diagnosed as OC or OMEC of the salivary glands. This study involved 28 cases of carcinomas with a predominantly oncocytic component. The sex distribution was equal. The median age was 59 years (range 10 to 89). Most of these cases originated from the parotid gland (25/28). The mean tumor size was 2.4 cm (range 0.5 to 6.5). Primary immuno-morphological and mutation/gene fusion profiles reclassified mainly (64.3%, 18/28). Most of them were reclassified in descending order as OSDC (8/18), OMEC (5/18), and OC (2/18). But 3 cases remained unclassified (3/18). The transcriptomic analysis found a proximity of their transcriptomic profile with the OMEC group and a distance from the OSDCs. These findings imply that OC is not distinct but represents oncocytic variants of other salivary carcinomas. It underscores the importance of thorough morphologic, immunohistochemical, and molecular examinations to accurately diagnose carcinomas with predominant oncocytic components in the salivary glands.

[Fusion genes in salivary gland tumors]

Salivary gland tumors represent a diagnostic challenge for pathologists due to their rarity, their very wide histopathological and immuno-phenotypic spectrum, and the recent identification of new entities. This article presents the main molecular characteristics of these tumors in order to allow any pathologist to perceive the diagnostic tracks of these ENT tumors and to better guide the molecular approach to establish the diagnosis and guide therapy.

Understanding and overcoming the pitfalls in the diagnosis of pleomorphic and carcinoma ex-pleomorphic adenoma of salivary glands

The study illustrates a recurrent pitfall in the diagnosis of pleomorphic adenoma and carcinoma ex pleomorphic adenoma.

Insights into the molecular alterations of PLAG1 and HMGA2 associated with malignant phenotype acquisition in pleomorphic adenoma

Pleomorphic adenoma (PA) is the most common neoplasm of the salivary gland, presenting with a variety of histological features. In some cases, PA can undergo malignant transformation to carcinoma ex pleomorphic adenoma (CXPA). The transition from PA to CXPA is associated with complex molecular alterations, particularly involving the pleomorphic adenoma gene 1 (PLAG1) and high mobility group protein gene (HMGA2). This review investigates the molecular alterations of PLAG1 and HMGA2 in all domains in the malignant transformation of PA. Our analysis highlights that these markers are key alterations in the etiopathogenesis of PA and CXPA, with gene fusion and amplification being frequently reported mechanisms. Although the exact role of PLAG1 and HMGA2 in the oncogenic process remains unclear, further studies on the HMGA2 and PLAG1, are needed particularly in HMGA2-PLAG1-IGF2 which is proving to be a potential pathway for the development of clinically applicable therapies, especially for CXPA management.

The Impact of Inflammation on the Etiopathogenesis of Benign Salivary Gland Tumors: A Scoping Review

Salivary gland tumors are rare head and neck tumors constituting up to 6% of all head and neck neoplasms; despite being mostly benign, these tumors present in diverse histological subtypes, making them challenging to diagnose and treat. Our research aims to investigate the link between inflammation and tumorigenesis within the salivary glands based on the literature regarding the etiopathogenesis of benign salivary gland tumors. This scoping review was conducted following the PRISMA extension for scoping reviews and reporting guidelines. The search was conducted using the Pubmed and Embase databases. Articles published between 2004 and May 2024 were included in the review. A total of 1097 papers were collected and identified. After 271 duplicates were removed, 826 titles and abstracts were independently reviewed by two researchers. Based on the title and abstract, 735 citations were excluded, and 91 articles were assessed for eligibility. Data were extracted from 46 articles that met the inclusion criteria. The review highlights the significance of inflammation-related factors and its relations with benign salivary gland tumors (SGTs). Knowledge of the etiopathogenesis of these tumors remains insufficient, and their rich immunological background poses challenges in diagnosis. The findings also point to directions for further clinical research, which will be necessary to implement these molecules in clinical practice.

Myoepithelial-Rich Pleomorphic Adenoma With Novel PLAG1 Inversion on Chromosome 8, and LRP1B, PBRM1 and TCF3 Mutations

Pleomorphic adenoma (PA) is the most common salivary gland neoplasm worldwide (50%-70%). Most cases of PA are straightforward diagnoses. However, the diagnosis may be challenging due to the morphological diversity of PAs, which in many cases is caused by the predominance of one of the three components or the presence of metaplastic epithelium. We present the case of a 64-year-old male with a history of prostate cancer and right submandibular gland excision 16 years ago with an unknown previous diagnosis and recent regrowth of his mass in the surgical bed. The tumour showed a predominant spindle cell morphology, cytokeratin-positivity, variable expression of myoepithelial markers in the cytology and surgical pathology specimens, and novel inversion of the chromosome 8, and LRP1B, PBRM1 and TCF3 mutations.

Fusions in salivary gland neoplasms: a review of practical diagnostic applications

There is an ongoing explosion of new information regarding the underlying molecular alterations driving a variety of salivary gland neoplasms. The volume of this emerging data makes it difficult to keep up with and may cause pathologists to believe that salivary gland neoplasms cannot be diagnosed without genetic analysis. This review focuses on the practical diagnostic applications of molecular tools in surgical pathology specimens.

Expanding the Molecular Spectrum of Carcinoma Ex Pleomorphic Adenoma: An Analysis of 84 Cases With a Novel HMGA2::LINC02389 Fusion

Carcinoma ex pleomorphic adenoma (CXPA) is an aggressive epithelial and/or myoepithelial neoplasm that arises in association with a pleomorphic adenoma (PA). Its etiopathogenesis remains poorly understood, but it is believed that the development of this tumor is due to the accumulation of genetic, protein, metabolic, and epigenetic alterations in a PA. A retrospective review of the Salivary Gland Tumor Registry in Pilsen yielded 84 CXPA, namely 25/84 salivary duct carcinoma (SDC), 15/84 myoepithelial carcinoma (MC), 1/84 epithelial-myoepithelial carcinoma (EMC), and 1/84 adenoid cystic carcinoma (AdCC). All 84 CXPA cases were analyzed by next-generation sequencing (NGS) and/or fluorescence in situ hybridization (FISH). Forty-three tumors originally diagnosed as CXPA (43/84, 51.2%) showed some molecular alteration. Fusion transcripts were identified in 12/16 (75%) CXPA, including LIFR::PLAG1, CTNNB1::PLAG1, FGFR1::PLAG1, and a novel fusion, HMGA2::LINC02389. Most of the fusions were confirmed by FISH using PLAG1 (6/11) and HMGA2 (1/1) gene break probes. Split signals indicating gene break were identified by FISH for PLAG1 (12/17), HMGA2 (3/4), EWSR1 (7/22), and MYB (2/7). Concerning pathogenic mutations, only CXPA with epithelial differentiation (SDC) presented these alterations, including HRAS mutation (2/4), TP53 (1/4), PTEN (1/4), and ATK1 (1/4). In addition, amplifications in ERBB2 (17/35), MDM2 (1/4), and EWSR1 (1/7) were detected. A novel finding was the discovery of an HMGA2::LINC02389 fusion in 1 patient with EMC ex-PA. The present results indicate that molecular profiling of CXPA with myoepithelial differentiation (MC) tends to reveal chromosomal fusion events, whereas CXPA with epithelial differentiation (SDC) tends to have a higher frequency of pathogenic mutations and gene amplifications.

Characterization of a Molecularly Distinct Subset of Oncocytic Pleomorphic Adenomas/Myoepitheliomas Harboring Recurrent ZBTB47-AS1::PLAG1 Gene Fusion

Recurrent gene fusions are common in salivary gland tumors including benign tumors, such as pleomorphic adenoma (PA) and myoepithelioma (ME). In cases where chromosomal rearrangement is identified in the pleomorphic adenoma gene 1 (PLAG1) gene, different gene partners are found. Oncocytic metaplasia, characterized by oncocytes with abundant eosinophilic granular cytoplasm and hyperchromatic nuclei, is a well-known phenomenon in salivary gland neoplasms. However, the pure oncocytic variant of PA/ME showed PLAG1 gene rearrangements involving various gene partners at the molecular level, without any recurrent fusion being found. Our study includes 20 cases of PA/ME, with 11 females and 9 males. The age of patients ranged from 37 to 96 years, with a median age of 62.8 years. Most tumors originate from the parotid gland. The median size of the tumor was 26.5 mm (range: 13 to 60 mm). Among the 20 cases, 14 were a pure oncocytic variant of PA/ME, whereas 6 cases showed focal oncocytic or oncocytic-like aspects. Molecular studies on 20 cases of PA/ME were conducted. A novel recurrent ZBTB47-AS1::PLAG1 fusion was identified in 6 of 12 cases with pure oncocytic metaplasia, whereas the other cases had PLAG1 gene fusion with different gene partners. The transcriptomic analysis of the cases harboring ZBTB47-AS1::PLAG1 fusion demonstrated that these tumors have a distinct molecular profile from conventional PA/ME. This study reveals a unique subset in the oncocytic PA/ME spectrum characterized by pure oncocytic morphology with larger oncocytic cells and recurrent ZBTB47-AS1::PLAG1 fusion. It also highlights the transcriptomic distinctness of salivary gland adenomas with pure oncocytic metaplasia in the spectrum of salivary gland neoplasms. Further studies are needed to better understand the oncocytic variant of PA/ME and to determine the true nature of oncocytic cells in PA/ME.

Updates in head and neck cytopathology: Insights from European Congress of Pathology Short Course

Cytological specimens play a pivotal role in head and neck nodule/mass work up and diagnoses. The specimens´ importance has grown with the onset of personalized medicine and the routine use of molecular markers in the diagnostic work up. The Updates in Head and Neck Cytopathology Short Course ran during the 35th European Congress of Pathology held in Dublin, Ireland, in 2023 and brought together experts in cytopathology, pathology, and related fields to share their expertise and experience in the field of head and neck cytopathology and its future directions. Topics such as a one-stop clinic, the Milan System for Reporting Salivary Gland Cytopathology, next generation sequencing, and human papilloma virus detection in the head and neck area were covered during the short course. These topics are briefly summarized in the present review.

Molecular testing in salivary gland cytopathology: A practical overview in conjunction with the Milan system

Recently, significant advances in the molecular characterization of salivary gland neoplasms have facilitated the classification and diagnosis of specific diagnostic entities. In the highly challenging diagnostic scenario of salivary malignancies, molecular testing is increasingly being adopted in routine practice to refine the cytological diagnosis of salivary lesions. Here, we reviewed the most recent evidence in the field of salivary glands molecular cytopathology.

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.

Top Ten Differentials to Mull Over for Head and Neck Myoepithelial Neoplasms

BACKGROUND

Myoepithelial neoplasms of the salivary gland are benign or malignant neoplasms composed exclusively of neoplastic myoepithelial cells. These tumors, including the benign myoepithelioma and the malignant counterpart myoepithelial carcinoma, exhibit a wide range of cytomorphologic features and architectural patterns.

METHODS

Review.

RESULTS

Myoepithelial cells can be epithelial, plasmacytoid, clear cell, spindle cell, and/or oncocytic cell, arranging as trabeculae, solid sheets, nests, cords, and/or single cells. A stromal component is commonly but not universally present, Therefore, their differential diagnoses are quite broad, including salivary gland neoplasms especially those with a myoepithelial component, plasmacytoma, melanoma, and various mesenchymal tumors.

CONCLUSION

In this review, we summarize the characteristic histologic features, useful immunohistochemical panel, and common molecular alterations of myoepithelial tumors and their top differential diagnoses. A logical stepwise algorithmic approach and an immunohistochemical panel to include multiple myoepithelial markers are essential to establish the correct diagnosis.

[Salivary gland tumors-an overview : Advances in molecular characterization: Part II]

The second part of the article is devoted to the molecular characteristics of epithelial-myoepithelial carcinoma, polymorphous adenocarcinoma, myoepithelial carcinoma, basal cell adenocarcinoma, and salivary duct carcinoma. In addition, the new entities mucinous adenocarcinoma, sclerosing microcystic adenocarcinoma, and microsecretory adenocarcinoma are summarized. The molecular genotype can also be very helpful in diagnosing most of these entities. In this regard, overexpression of the androgen receptor and/or human epidermal growth factor receptor 2 (HER2)/neu can support diagnosis in the appropriate histopathologic context and may serve as a potential target for therapy in salivary duct carcinoma.

Chromosome Translocations, Gene Fusions, and Their Molecular Consequences in Pleomorphic Salivary Gland Adenomas

Salivary gland tumors are a heterogeneous group of tumors originating from the major and minor salivary glands. The pleomorphic adenoma (PA), which is the most common subtype, is a benign lesion showing a remarkable morphologic diversity and that, upon recurrence or malignant transformation, can cause significant clinical problems. Cytogenetic studies of >500 PAs have revealed a complex and recurrent pattern of chromosome rearrangements. In this review, we discuss the specificity and frequency of these rearrangements and their molecular/clinical consequences. The genomic hallmark of PA is translocations with breakpoints in 8q12 and 12q13-15 resulting in gene fusions involving the transcription factor genes PLAG1 and HMGA2. Until recently, the association between these two oncogenic drivers was obscure. Studies of the Silver−Russel syndrome, a growth retardation condition infrequently caused by mutations in IGF2/HMGA2/PLAG1, have provided new clues to the understanding of the molecular pathogenesis of PA. These studies have demonstrated that HMGA2 is an upstream regulator of PLAG1 and that HMGA2 regulates the expression of IGF2 via PLAG1. This provides a novel explanation for the 8q12/12q13-15 aberrations in PA and identifies IGF2 as a major oncogenic driver and therapeutic target in PA. These studies have important diagnostic and therapeutic implications for patients with PA.

Pediatric fibromyxoid tumor with PLAG1 fusion: An emerging entity with a novel intracranial location

Translocations involving PLAG1 occur in several tumors, most commonly pleomorphic adenoma and lipoblastoma. Recently, a distinctive soft tissue tumor with a PLAG1 fusion has been reported in the pediatric age group. These are low grade tumors with a fibroblastic or mixed fibroblastic and myxoid morphology but no other lines of differentiation. They are typically immunopositive for desmin and CD34. The partner genes for these tumors have included YWHAZ, EEF1A1, ZFHX4l, CHCHD7, and PCMTD1. We report another case of this fibromyxoid tumor with a PLAG1 fusion, this time with COL3A1 as the partner gene. The fusion placed expression of a full-length PLAG1 protein under the control of the constitutively active COL3A1 promoter. Overexpression of PLAG1 was confirmed by diffusely positive immunostaining for PLAG1. The most novel aspect of this tumor is the intracranial location. Opinion has been divided over whether these tumors are a specific entity, or related to lipoblastoma, since that tumor also typically occurs in soft tissue in the pediatric age group and shows many of the same gene fusions. However, lipoblastoma has never been reported in an intracranial location and, thus, our case provides compelling evidence that this fibromyxoid tumor is indeed a distinct entity.

Myoepithelial carcinoma of major salivary glands: Analysis of population-based clinicopathologic and prognostic features

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The demographic features of major salivary glands myoepithelial carcinoma has been analyzed using propensity score-matching.

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The correlation between tumor stage and prognostic for patients with myoepithelial carcinoma is conformed.

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The radiotherapy is a favorable factor for overall survival in patients with myoepithelial carcinoma.

Background

This study aimed to investigate the effect of demographic characteristics and disease stage on the survival outcomes of patients with myoepithelial carcinoma (MECA) of the salivary glands, and to assess the role of radiotherapy in these patients.

Methods

The Epidemiology, Surveillance and End Results database was queried from 2000 to 2018 to identify patients with MECA. Data pertaining to the tumor stage, size, histological grade, and demographic characteristics were analyzed. The relationship between clinicopathological features and overall survival (OS) was assessed using statistical analyses.

Results

In total, 290 patients (137 men and 153 women) were identified. The parotid gland was the most common tumor location (76.6% patients). Approximately half of the patients had locally advanced tumors, and 14.5 and 6.6% had lymph node and distant organ involvement, respectively. The median OS was 142 months, while the survival rates at 120 months and 180 months were 53% and 39%, respectively. In the cohort, 160 patients (55.2%) underwent surgery alone, while 130 patients (44.8%) underwent surgery combined with radiotherapy. Multivariate Cox analysis revealed that histopathological grade, stage, T3 stage (hazard ratio [HR]: 2.47, P = 0.039), T4 stage (HR: 3.33, P = 0.011), N2 stage (HR: 6.59, P = 0.002), and M1 stage (HR: 2.72, 95%confidence interval [CI]: 1.03–7.19; P = 0.044) were associated with poor prognosis. Radiotherapy (HR: 0.58, P = 0.042) was a favorable factor for OS, and it reduced the mortality risk by 42%.

Conclusions

Histological grade, stage, and radiotherapy are independent risk factors for OS. The decision to administer chemotherapy for MECA should be made with caution. Adjuvant radiotherapy is recommended in high-risk patients.

S-100 Immunohistochemical Positivity in Rhabdomyoma: An Underestimated Potential Diagnostic Pitfall in Routine Practice

A 66-year-old man presented with a 2.8 cm lesion of the left vocal cord. On contrast-enhanced computed tomography scans, the tumor extended to the supraglottis, subglottis, paraglottic space and anterior commissure, causing partial obstruction of the laryngeal lumen. At another hospital, a fragmented incisional biopsy was diagnosed as a granular cell tumor, as to the S-100 immunohistochemical positivity. After excision, the tumor revealed to be an adult-type laryngeal rhabdomyoma. The typical cytoplasmic rod-like inclusions and cross striations were more evident in the second specimen. We confirmed the unusual S-100 immunohistochemical positivity (variable intensity, >90% of tumor cells). Muscle markers were not performed on the previous biopsy, resulting positive in our specimen (Desmin: strong, diffuse expression; Smooth Muscle Actin: strong staining in 10% of tumor cells). Melan-A, CD68, GFAP, pan-cytokeratins, CEA, calretinin and neurofilaments resulted negative. To our brief, systematic literature review, S-100 positivity (usually variable, often weak or patchy/focal) was globally found in 19/34 (56%) adult-type rhabdomyomas of the head and neck region. Especially on fragmented biopsy material, the differential diagnoses of laryngeal rhabdomyomas may include granular cell tumors, oncocytic tumors of the salivary glands or of different origin, and paragangliomas.

Expression of cartilage oligomeric matrix protein (COMP) associates with capsular invasion in salivary gland pleomorphic adenoma

BACKGROUND

Accumulating evidence shows that pleomorphic adenoma (PA) exhibits a unique capsular invasion and with a crucial role in recurrence. This study was designed to explore RNA expression profiles in salivary gland PA in an attempt to further analyse genes associate with capsule invasion.

METHODS

We evaluated the expression profiles of 4 salivary gland PA patients by RNA-sequencing. The principal functions of the differentially expressed mRNAs (DEGs) were explored using GO and KEGG analysis. Then, RT-qPCR and correlation analyses were performed to verify the candidate DEGs in 59 PA patients, and immunohistochemical examinations were conducted to validate candidate DEGs. Finally, the COMP-related genes were screened using correlation and biological pathway enrichment analysis, and further validated by RT-qPCR.

RESULTS

A total of 974 DEGs were significantly upregulated and 1464 were downregulated (fold change ≥2.0; p < 0.05). Based on GO and KEGG analyses, extracellular matrix organization and the PI3K-Akt signaling pathway might play pivotal roles in the tumorigenesis of PA. 40 DEGs were screened and validated by RT-qPCR, 11 upregulated and 5 downregulated DEGs were consistent with the sequencing results. Cartilage oligomeric matrix protein (COMP) was identified to have a significant correlation with the capsular invasion of PA and expression of COMP in patients with invasive capsular PA was significantly stronger than PA. Finally, further results could reveal that 5 highest-scoring genes were screened as hub genes for COMP.

CONCLUSIONS

These findings suggested that COMP may be a prognostic target for PA and might contribute to its capsular invasion.

PLAG1-rearrangment in a uterine leiomyosarcoma with myxoid stroma and heterologous differentiation

A variety of molecular alterations have been reported in uterine leiomyosarcomas, but most are considered nondiagnostic. There are, however, rare exceptions including PLAG1 rearrangement which has recently been identified in a subset of myxoid leiomyosarcomas. A 41-year-old woman presented with symptoms of a fibroid. She underwent a myomectomy which revealed a high-grade uterine sarcoma with areas of myxoid stroma and heterologous elements. The tumor expressed desmin, smooth muscle actin, H-caldesmon, and estrogen and progesterone receptors. RNA sequencing revealed a novel TRIM13-PLAG1 fusion gene which was subsequently independently confirmed by fluorescence in situ hybridization. On further evaluation the patient was found to have multiple pulmonary metastases and died due to disease progression shortly after diagnosis. This report describes a novel fusion partner of PLAG1 in a uterine leiomyosarcoma with myxoid leiomyosarcoma and heterologous elements, thereby broadening the spectrum of morphologic and genetic findings within this rare group of neoplasms.

Targeted RNA sequencing in the routine clinical detection of fusion genes in salivary gland tumors

Salivary gland tumors represent a diverse group of neoplasms that occasionally pose a diagnostic challenge for pathologists, particularly with limited sampling. Gene fusions, which may reflect genetic drivers, are increasingly recognized in a subset of these neoplasms, and can be leveraged for diagnostic purposes. We performed a retrospective analysis on a cohort of 80 benign and malignant salivary gland tumors, enriched for subtypes known to harbor recurrent fusion events, to validate the diagnostic use of a targeted RNA sequencing assay to detect fusion transcripts. Testing identified fusion genes in 71% (24/34) of pleomorphic adenoma and carcinoma-ex-pleomorphic adenoma, with 56% of cases showing rearrangement of PLAG1 and 15% HMGA2. In addition to confirming known partners for these genes, novel PLAG1 fusion partners were identified, including DSTN, NTF3, and MEG3; CNOT2 was identified as a novel fusion partner for HMGA2. In adenoid cystic carcinoma, 95% of cases (19/20) were positive for a fusion event. MYB was rearranged in 60% (12/20), MYBL1 in 30% (6/20), and NFIB in 5% (1/20); two tumors exhibited novel fusion products, including NFIB-TBPL1 and MYBL1-VCPIP1. Fusion genes were identified in 64% (9/14) of cases of mucoepidermoid carcinoma; MAML2 was confirmed to partner with either CRTC1 (43%) or CRTC3 (21%). One salivary duct carcinoma was found to harbor a novel RAPGEF6-ACSL6 fusion gene. Finally, as anticipated, gene fusions were not detected in any of the five acinic cell carcinomas included in the cohort. In summary, targeted RNA sequencing represents a diagnostically useful ancillary technique for identifying a variety of existing, and novel, fusion transcripts in the classification of salivary gland neoplasms.

Oncocytic Lipoadenoma: Report of 3 Rare Cases Involving the Parotid Gland, Including a Synchronous Presentation With Paraganglioma of the Right Carotid Bifurcation and Literature Review

Oncocytic lipoadenoma (OL) is a rare salivary gland tumor characterized by the presence of oncocytic cells and mature adipose tissue. To date, only 30 cases of OL have been reported in the English-language literature. We present 3 additional OL cases involving the parotid, including a synchronous presentation with paraganglioma of the right carotid bifurcation. Microscopically, both the OLs were composed of a mixed population of oncocytes and adipocytes in varying proportions surrounded by a thin, connective tissue fibrous capsule. Oncocytes were positive for pan-cytokeratins (CKs) AE1/AE3, epithelial membrane antigen, CK5, CK7, CK14, CK18, and CK19. Calponin, p63, alpha-smooth muscle actin, and carcinoembryonic antigen were negative. Vimentin and S-100 protein were positive only in adipose cells. Despite distinctive morphologic features, OL is often misdiagnosed, given its rarity. We hope to contribute to surgeons' and pathologists' awareness and knowledge regarding the existence of this tumor and provide adequate management through conservative surgical excision.

Pleomorphic adenoma: the great mimicker of malignancy

Pleomorphic adenoma (PA) is the most common salivary gland neoplasm, and its diagnosis is straightforward in the majority of cases. However, not infrequently, PA shows unusual and uncommon histological features that can be confused with those of malignancy. The difficulties in diagnosing PA arise from its ability to mimic invasion, show atypical or metaplastic cytomorphology, and show morphological features that overlap with those of established salivary gland carcinomas. In addition, recognising early malignant transformation to carcinoma ex-pleomorphic adenoma continues to be a frequent challenge. This review describes the diagnostic pitfalls of PA, and offers a systematic approach to avoid them by combining classic histopathology with novel immunohistochemical and molecular tests.