Synovial chondromatosis and soft tissue chondroma: extraosseous cartilaginous tumor defined by FN1 gene rearrangement

CD34+ synovial fibroblasts exhibit high osteogenic potential in synovial chondromatosis

Synovial chondromatosis (SC) is a disorder of the synovium characterized by the formation of osteochondral nodules within the synovium. This study aimed to identify the abnormally differentiated progenitor cells and possible pathogenic signaling pathways. Loose bodies and synovium were obtained from patients with SC during knee arthroplasty. Single-cell RNA sequencing was used to identify cell subsets and their gene signatures in SC synovium. Cells derived from osteoarthritis (OA) synovium were used as controls. Multi-differentiation and colony-forming assays were used to identify progenitor cells. The roles of transcription factors and signaling pathways were investigated through computational analysis and experimental verification. We identified an increased proportion of CD34+ sublining fibroblasts in SC synovium. CD34+CD31- cells and CD34-CD31- cells were sorted from SC synovium. Compared with CD34- cells, CD34+ cells had larger alkaline phosphatase (ALP)-stained area and calcified area after osteogenic induction. In addition, CD34+ cells exhibited a stronger tube formation ability than CD34- cells. Our bioinformatic analysis suggested the expression of TWIST1, a negative regulator of osteogenesis, in CD34- sublining fibroblasts and was regulated by the TGF-β signaling pathway. The experiment showed that CD34+ cells acquired the TWIST1 expression during culture and the combination of TGF-β1 and harmine, an inhibitor of Twist1, could further stimulate the osteogenesis of CD34+ cells. Overall, CD34+ synovial fibroblasts in SC synovium have multiple differentiation potentials, especially osteogenic differentiation potential, and might be responsible for the pathogenesis of SC.

Calcified Chondroid Mesenchymal Neoplasms

Calcified chondroid mesenchymal neoplasms (CCMN) represent a morphologic spectrum of related tumors. Historically, chondroid matrix or chondroblastoma-like features have been described in soft tissue chondroma, tenosynovial giant cell tumors (especially of the temporomandibular joint (TMJ) region), and in a subset of tophaceous pseudogout. Recently, these tumors have been found to share FN1-receptor tyrosine kinase (RTK) fusions. This review discusses the clinical, morphologic, immunohistochemical, and molecular genetic features of CCMN. The distinction from morphologic mimics is also discussed.

Pathology of intra-articular tumours and tumour-like lesions: pearls, pitfalls and rarities from a general surgical pathology practice

Intra-articular tumours are uncommonly encountered in routine practice and may present diagnostic challenges to pathologists. Challenges unique to this site include distinction from more common reactive synovial conditions, which are far more common; histologic variability; superimposed reactive changes; and often, lack of provided clinicoradiological context. This article reviews the pathology of the synovial tumours and tumour-like lesions, including diagnostic pearls, pitfalls and rare entities.

Calcified chondroid mesenchymal neoplasm: report of a case involving the temporomandibular joint region and review of the literature

The calcified chondroid mesenchymal neoplasm (CCMN) represents a recently recognized tumor type with only 50 well-documented cases in the English-language literature. Herein we report an additional case of CCMN presenting as a large mass in the temporomandibular joint region of a 41-year-old female. A review of previously reported cases and the current case of CCMN shows the following features: 1) average age 52 years (range 14-87 years) and an approximately even sex distribution; 2) most frequently involved sites: distal extremities (including foot, hand, wrist, forearm) (n=41) and temporomandibular joint/temporal/parotid region (n=9); 3) multilobular soft tissue tumor with chondroid to cartilaginous matrix, often grungy or lace-like calcifications, and variable cytologic atypia; 4) frequently detected FN1 rearrangement (n=15), including FN1 fusion with FGFR2 (n=7) or other receptor tyrosine kinases; 5) 2 reported local recurrences (after incomplete excision); 6) no reports of malignant biologic behavior.

FGFR1 gene fusions in a subset of pediatric mesenchymal tumors: Expanding the genetic spectrum of tumors sharing histologic overlap with infantile fibrosarcoma and "NTRK-rearranged" spindle cell neoplasms

As the classification of kinase-driven spindle cell tumors continues to evolve, we describe the first series of pediatric mesenchymal tumors harboring FGFR1 gene fusions that share histologic overlap with infantile fibrosarcoma and "NTRK-rearranged" spindle cell neoplasms. Herein, we present three cases of FGFR1-rearranged pediatric mesenchymal tumors, including one case with FGFR1::PARD6B gene fusion and two cases with FGFR1::EBF2 gene fusion. The tumors involved infants ranging from 3 to 9 months in age with a male-to-female ratio of 2:1. All tumors involved the deep soft tissue of the gluteal, pelvic, or perirectal region. Histologically, the tumors comprised a cellular spindle cell neoplasm with primitive stellate cells, focal myxoid stroma, focal epithelioid features, no necrosis, and occasional mitotic figures (2-6 per 10 high-power field). By immunohistochemistry, the neoplastic cells focally expressed CD34 but lacked expression of S100 protein, SMA, desmin, myogenin, MyoD1, pan-TRK, and ALK. These three cases, including a case with long-term clinical follow-up, demonstrate that FGFR1 fusions occur in a subset of newly described pediatric kinase-driven mesenchymal tumors with locally aggressive behavior. Importantly, knowledge of these genetic alterations in this spectrum of pediatric tumors is key for diagnostic and targeted therapeutic purposes.

RNA Sequencing Reveals Novel Oncogenic Fusions and Depicts Detailed Fusion Transcripts of FN1-FGFR1 in Phosphaturic Mesenchymal Tumors

Phosphaturic mesenchymal tumors (PMTs) are rare neoplasms of soft tissue or bone. Although previous studies revealed that approximately 50% of PMTs harbor FN1::FGFR1 fusions, the molecular mechanisms in the remaining cases are largely unknown. In this study, fusion genes were investigated using RNA-based next-generation sequencing in 76 retrospectively collected PMTs. Novel fusions were validated with Sanger sequencing and fluorescence in situ hybridization. Fusion genes were detected in 52/76 (68.4%) PMTs, and 43/76 (56.6%) harbored FN1::FGFR1 fusions. Fusion transcripts and breakpoints of the FN1::FGFR1 fusions were diverse. The most common fusion transcript was between exon 20 of FN1 and exon 9 of FGFR1 (7/43, 16.3%). The most upstream breakpoint of the FN1 gene was located at the 3' end of exon 12, and the most downstream breakpoint of the FGFR1 gene was at the 5' end of exon 9, suggesting the inessential nature of the third fibronectin-type domain of FN1 and the necessity of the transmembrane domain of FGFR1 in the FN1::FGFR1 fusion protein, respectively. Moreover, the reciprocal FGFR1::FN1 fusions, which had not been identified in previous studies, were detected in 18.6% (8/43) of FN1::FGFR1 fusion-positive PMTs. Novel fusions were identified in 6/76 (7.9%) FN1::FGFR1 fusion-negative PMTs, including 2 involving FGFR: FGFR1::USP33 (1/76, 1.3%) and FGFR1::TLN1 (1/76, 1.3%). Other novel fusions identified were the PDGFRA::USP35 (1/76, 1.3%), SPTBN1::YWHAQ (1/76, 1.3%), GTF2I::RALGPS1 (1/76, 1.3%), and LTBP1::VWA8 (1/76, 1.3%) fusions. In addition to these novel fusions, FN1::FGFR2 (1/76, 1.3%), NIPBL::BEND2 (1/76, 1.3%), and KIAA1549::BRAF fusions (1/76, 1.3%) were also identified in FN1::FGFR1-negative cases arising from the thigh, ilium, and acetabulum, respectively. The frequency of oncogenic fusions was significantly higher (P = .012) in tumors derived from extremities (29/35, 82.9%) compared with other locations (23/41, 56.1%). No significant correlation was identified between fusions and recurrence (P = .786). In conclusion, we report fusion transcripts and breakpoints of FN1::FGFR1 in PMTs in detail, providing insights into fusion protein functions. We also revealed that a considerable proportion of PMTs without FN1::FGFR1 fusion carried novel fusions, providing further insight into the genetic basis of PMTs.

Myoepithelioma, myoepithelioma-like, and chondroid soft-tissue tumors arising at acral sites: a review

Myoepithelial neoplasms comprise a histologically and immunophenotypically diverse spectrum of entities. The following review is a comprehensive summary of acral lesions demonstrating myoepithelial-like and chondroid histomorphology, as well as recently described mimics that are diagnostically challenging to distinguish. The salient clinicopathologic, immunophenotypic, and molecular features of each entity are described.

Synovial chondromatosis: a case series and review of the literature

This case series reviews 2 patients worked up and treated for unilateral synovial chondromatosis of the temporomandibular joint (TMJ). The first was a 58-year-old female evaluated and treated for synovial chondromatosis of the left TMJ using an arthrotomy of the joint to remove the cartilaginous and osteocartilaginous nodules. The second is a 63-year-old male who was evaluated and treated for synovial chondromatosis of the right TMJ with the removal of extracapsular masses and an arthrotomy with intra-joint removal of nodules. Six-year radiographic follow-up demonstrated no recurrence of the pathology in his case. The cases are reviewed in this article, along with a current review of the literature.

Small biopsies in the head and neck: Bone and soft tissue

Bone and soft tissue lesions in the head and neck encompass not only a broad morphologic spectrum but also significant inherent clinicopathologic overlap. Epidemiology, radiology, and location - similar to the diagnostic assessment in other sites - are especially important considerations in the context of an established mesenchymal proliferation. Herein, the approach towards diagnosis is stratified by morphology (spindle, sarcomatoid, epithelioid, round cell), cellular lineage (fibroblastic, nerve sheath, rhabdomyogenic), and tumor grade (benign, low- to high-grade malignant) as the basis of further immunohistochemical or molecular investigation.

Integrated computational screening and liquid biopsy approach to uncover the role of biomarkers for oral cancer lymph node metastasis

Cancer is an abnormal, heterogeneous growth of cells with the ability to invade surrounding tissue and even distant organs. Worldwide, GLOBOCAN had an estimated 18.1 million new cases and 9.6 million death rates of cancer in 2018. Among all cancers, Oral cancer (OC) is the sixth most common cancer worldwide, and the third most common in India, the most frequent type, oral squamous cell carcinoma (OSCC), tends to spread to lymph nodes in advanced stages. Throughout the past few decades, the molecular landscape of OSCC biology has remained unknown despite breakthroughs in our understanding of the genome-scale gene expression pattern of oral cancer particularly in lymph node metastasis. Moreover, due to tissue variability in single-cohort studies, investigations on OSCC gene-expression profiles are scarce or inconsistent. The work provides a comprehensive analysis of changed expression and lays a major focus on employing a liquid biopsy base method to find new therapeutic targets and early prediction biomarkers for lymph node metastasis. Therefore, the current study combined the profile information from GSE9844, GSE30784, GSE3524, and GSE2280 cohorts to screen for differentially expressed genes, and then using gene enrichment analysis and protein-protein interaction network design, identified the possible candidate genes and pathways in lymph node metastatic patients. Additionally, the mRNA expression of discovered genes was assessed using real-time PCR, and the Human Protein Atlas database was utilized to determine the protein levels of hub genes in tumor and normal tissues. Angiogenesis was been investigated using the Chorioallentoic membrane (CAM) angiogenesis test. In a cohort of OSCC patients, fibronectin (FN1), C-X-C Motif Chemokine Ligand 8 (CXCL8), and matrix metallopeptidase 9 (MMP9) were significantly upregulated, corroborating these findings. Our identified significant gene signature showed greater serum exosome effectiveness in early detection and clinically linked with intracellular communication in the establishment of the premetastatic niche. Also, the results of the CAM test reveal that primary OC derived exosomes may have a function in angiogenesis. As a result, our study finds three potential genes that may be used as a possible biomarker for lymph node metastasis early detection and sheds light on the underlying processes of exosomes that cause a premetastatic condition.

Calcified Chondroid Mesenchymal Neoplasm: Exploring the Morphologic and Clinical Features of an Emergent Entity With a Series of 33 Cases

Calcified chondroid mesenchymal neoplasm is a term proposed for tumors with a spectrum of morphologic features, including cartilage/chondroid matrix formation, that frequently harbor FN1 gene fusions. We report a series of 33 cases of putative calcified chondroid mesenchymal neoplasms, mostly referred for expert consultation out of concern for malignancy. Patients included 17 males and 16 females, with a mean age of 51.3 years. Anatomic locations include the hands and fingers, feet and toes, head and neck, and temporomandibular joint; 1 patient presented with multifocal disease. Radiologic review showed soft tissue masses with variable internal calcification, which occasionally scalloped bone but in all cases appeared indolent/benign. Tumors had a mean gross size of 2.1 cm and a homogenous rubbery to fibrous/gritty tan-white cut surface. Histology demonstrated multinodular architecture with a prominent chondroid matrix and increased cellularity towards the periphery of the nodules. The tumor cells were polygonal with eccentric nuclei and bland cytologic features and showed a variable amount of increased spindled / fibroblastic forms in the perinodular septa. The majority of cases had notable grungy and/or lacy calcifications. A subset of cases demonstrated at least focal areas of increased cellularity and osteoclast-like giant cells. Herein, we confirm the distinct morphologic and clinicopathologic features associated with this entity with the largest series to date, with a focus on practical diagnostic separation from similar chondroid neoplasms. Awareness of these features is critical in avoiding pitfalls, including a malignant diagnosis of chondrosarcoma.

Subcutaneous chondromyxoid fibroma with a novel PNISR::GRM1 fusion-report of a primary soft tissue tumour without connection to an underlying bone

Chondromyxoid fibroma (CMF) is a rare benign bone tumour. While CMF located entirely on the surface of a bone (i.e. juxtacortical CMF) has been well characterised, CMF has not so far been convincingly documented to arise in soft tissues without connection to an underlying bone.We report a subcutaneous CMF in a 34-year-old male, located on the distal medial aspect of the right thigh without any connection with the femur. The tumour measured 15 mm, it was well-circumscribed and displayed typical morphological features of a CMF. At the periphery, there was a small area of metaplastic bone. Immunohistochemically, the tumour cells were diffusely positive for smooth muscle actin and GRM1, and negative for S100 protein, desmin and cytokeratin AE1AE3. Whole transcriptome sequencing revealed a novel PNISR::GRM1 gene fusion.Our case indicates that CMF should be included in the differential diagnosis of soft tissue (including subcutaneous) tumours composed of spindle/ovoid cells, with a lobular architecture and chondromyxoid matrix. The diagnosis of CMF arising in soft tissues can be confirmed by identifying a GRM1 gene fusion or GRM1 expression by immunohistochemistry.

Soft Tissue Masses of the Hand: A Review of Clinical Presentation and Imaging Features

More than 15% of all soft-tissue tumors arise in the hand. Because of the location of these tumors, even small abnormalities may be alarming to patients on presentation. Although the majority of lesions are benign and can be diagnosed solely by history and physical examination, additional imaging workup may be required to confirm a diagnosis or define anatomic extent of involvement. This paper aims to review the basic epidemiology, clinical presentation, imaging findings, and treatment options of the more common soft-tissue tumors of the hand.

Anti-histone H3.3K36M Antibody is a Highly Sensitive and Specific Immunohistochemistry Marker for the Diagnosis of Chondroblastoma. A Validation Based on Study 136 Cases Comprising Chondroblastoma and its Mimics from Single a Centre in India

Introduction: Chondroblastoma has a wide range of differential diagnosis encompassing various benign and malignant entities. The closest differential diagnosis is giant cell tumor of the bone due to overlapping radiological and histomorphological features. Extensive aneurysmal bone cyst like changes and lack of adequately sampled chondroid matrix often masquerades the primary bone lesion and amplifies the diagnostic difficulty in small biopsies with limited tissue. Immunohistochemistry is helpful in such instances to resolve the diagnostic dilemma. Objectives: To analyze the immunohistochemical expression of anti-histone H3F3K36M antibody inchondroblastoma and validate its utility in differentiating chondroblastomafrom its histological mimics. Material and methods: Immunohistochemistry was performed using anti-histone antibody H3.3K36M in 44 histologically diagnosed chondroblastoma and 92 other histological mimickers. All chondroblastoma and giant cell tumor of the bone included in the study were also tested for anti-histone H3.3 G34W antibody. Of the 33 giant cell tumors of bone with classic morphology and imaging findings, 24 H3.3 G34W positive and 9 negative tumors were included intentionally to rule out the possibility of chondroblastoma. The sensitivity, specificity, positive and negative predictive value of marker with regard to chondroblastoma was calculated. Results: Immunohistochemistry revealed unequivocal nuclear positivity for H3.3K36M in the mononuclear cells in all the 44 Chondroblastoma tested, denoting a sensitivity of 100% cases. Allthesetumors tested simultaneously for anti-histone H3.3G34W were negative. None of the histological mimickers were positive H3.3K36M indicating a specificity of 100%. The positive and negative predictive value was 100%. Conclusion: H3.3K36M mutant antibody is highly sensitive and specific IHC marker and can be used as a valuable adjunct to distinguish chondroblastomafrom its histological mimics especially on small biopsies.

[Bone tumours-What's new in the 2020 WHO classification and beyond]

The recent WHO classification of Bone Tumours (2020) has introduced several changes. Conceptionally, small round cell sarcomas are now summarized in a distinct chapter, acknowledging their occurrence in both, bone and soft tissue. In the light of new molecular findings some diagnostic categories, such as fibrohistiocytic tumors, have been abandoned, and a few new entities have been added to the classification. Finally, systematic changes were made with regard to the terminology employed in the classification of chondrogenic tumours, and modifications have been made with respect to the biological potential of some lesions. This article summarizes the major changes made, underscoring the elementary role of an interdisciplinary approach in the diagnosis and management of bone lesions.

A Comprehensive Understanding of the Genomic Bone Tumor Landscape: A Multicenter Prospective Study

Complexity and heterogeneity increases the difficulty of diagnosis and treatment of bone tumors. We aimed to identify the mutational characterization and potential biomarkers of bone tumors. In this study, a total of 357 bone tumor patients were recruited and the next generation sequencing (NGS)-based YuanSu450 panel, that includes both DNA and RNA sequencing, was performed for genomic alteration identification. The most common mutated genes in bone tumors included TP53, NCOR1, VEGFA, RB1, CCND3, CDKN2A, GID4, CCNE1, TERT, and MAP2K4. The amplification of genes such as NCOR1, VEGFA, and CCND3 mainly occurred in osteosarcoma. Germline mutation analysis reveal a high frequency of HRD related mutations (46.4%, 13/28) in this cohort. With the assistance of RNA sequencing, 16.8% (19/113) gene fusions were independently detected in 20% (16/79) of patients. Nearly 34.2% of patients harbored actionable targeted mutations, of which the most common mutation is CDKN2A deletion. The different mutational characterizations between juvenile patients and adult patients indicated the potential effect of age in bone tumor treatment. According to the genomic alterations, the diagnosis of 26 (7.28%) bone tumors were corrected. The most easily misdiagnosed bone tumor included malignant giant cell tumors of bone (2.8%, 10/357) and fibrous dysplasia of bone (1.7%, 6/357). Meanwhile, we found that the mutations of MUC16 may be a potential biomarker for the diagnosis of mesenchymal chondrosarcomas. Our results indicated that RNA sequencing effectively complements DNA sequencing and increased the detection rate of gene fusions, supporting that NGS technology can effectively assist the diagnosis of bone tumors.

A Rare Case of Myxochondroid Metaplasia of the Plantar Foot With Review of Histopathological Mimics

ABSTRACT

Chondromyxoid metaplasia can rarely lead to the formation of a distinctive tumor-like proliferation in the plantar foot. This is thought to represent a reactive or reparative process, possibly due to chronic trauma. For the unwary dermatopathologist, this could represent a diagnostic challenge. Herein, we review the clinical, histopathological, and molecular presentation of an athletic 17-year-old boy with a soft tissue mass arising in the right plantar foot. Microscopic examination showed a relatively circumscribed proliferation of spindle cells with abundant chondromyxoid stroma, hyalinization, and diffuse ERG reactivity. We also review characteristics of this entity that help differentiate it from clinical and histopathologic mimics and postulate possible links with soft tissue chondromas and immature chondroid choristoma.

Two Cases of Temporomandibular Synovial Chondromatosis Associated with Gli1 Gene Mutation

Synovial chondromatosis (SC) is a rare benign disease involving multifocal generation of ectopic cartilage in the synovial tissue. Herein, we report two cases of SC in the temporomandibular joint: a 38-year-old woman (patient 1) and 39-year-old woman (patient 2). Both patients had trismus, jaw joint noises, and jaw-opening pain in the temporomandibular joint. Cone-beam computed tomography (CT) and magnetic resonance imaging (MRI) in patient 1 showed multiple calcified loose bodies around the right mandibular condyle. In addition, CT and MRI in patient 2 showed multiple calcified loose bodies around the left mandibular condyle and temporal bone perforation. Following establishing a diagnosis of SC, both patients underwent tumor resection via open surgery. In immunohistochemical examinations of the resected tissues, tumor cells showed intense nuclear staining with labeled anti-Gli1 antibody. Gene sequencing revealed that both patients had a homozygous mutation in the Gli1 gene (rs2228226 G>C). In conclusion, we suggest that the Gli1 gene (rs2228226 G>C) may be involved in the etiology of SC.

Periarticular calcifications

Periarticular calcification and ossification is a frequent finding on imaging and may sometimes pose a diagnostic challenge. The differential diagnoses for this radiological finding are wide and can be classified into broad groups such as idiopathic, developmental, trauma, burns, infection, tumor, connective tissue disease, crystalline, metabolic, vascular, and foreign bodies. With careful consideration of the clinical and imaging findings as well as awareness of mimickers of periarticular mineralization, the list of differential diagnoses can be narrowed down. This article aims to review the clinical-radiologic findings of periarticular calcified or ossified lesions with relevant imaging illustrations.

Update from the 5th Edition of the World Health Organization Classification of Head and Neck Tumors: Soft Tissue Tumors

The fifth (5th) edition of the World Health Organization (WHO) Classification of Head and Neck Tumors introduces a new chapter dedicated to soft tissue neoplasms commonly affecting the head and neck. While the diversity, rarity, and wide anatomic range of soft tissue tumors precludes a discussion of all entities that may be found in the head and neck, the addition of this new chapter to the head and neck "blue book" aims to provide a more comprehensive and uniform reference text, including updated diagnostic criteria, of mesenchymal tumor types frequently (or exclusively) arising at head and neck sites. Since publication of the previous edition in 2017, there have been numerous advances in our understanding of the pathogenesis of many soft tissue tumors which have facilitated refinements in tumor classification, identification of novel entities, development of diagnostic markers, and improved prognostication. This review will provide a focused discussion of the soft tissue tumors included in the 5th edition WHO Head and Neck classification, with an emphasis on updates.

[Soft tissue tumours with FN1 (Fibronectin 1) fusion gene]

Translocations involving FN1 gene have been described in several tumours, which share the presence of a cartilaginous matrix with or without calcifications and a good prognosis. They encompass: soft tissue chondroma, synovial chondromatosis, calcifying aponeurotic fibroma, phosphaturic mesenchymal tumour and a new spectrum of tumours: "the calcified chondroid mesenchymal neoplasms". We review all the clinical, histopathological and molecular data of these tumours and discuss the differential diagnoses.

Identification and development of the novel 7-genes diagnostic signature by integrating multi cohorts based on osteoarthritis

Background

A chronic progressive degenerative joint disease, such as osteoarthritis (OA) is positively related to age. The medical economy is facing a major burden, because of the high disability rate seen in patients with OA. Therefore, to prevent and treat OA, exploring the diagnostic biomarkers of OA will be of great significance.

Methods

Differentially expressed genes (DEGs) were obtained from the Gene Expression Omnibus database using the RobustRankAggreg R package, and a protein–protein interaction network was constructed. The module was obtained from Cytoscape, and the four algorithms of degree, MNC, closeness, and MCC in CytoHubba were used to identify the hub genes. A diagnostic model was constructed using Support Vector Machines (SVM), and the ability of the model to predict was evaluated by other cohorts.

Results

From normal and OA samples, 136 DEGs were identified, out of which 45 were downregulated in the normal group and 91 were upregulated in the OA group. These genes were associated with the extracellular matrix-receptor interactions, the PI3K-Akt signaling pathway, and the protein digestion and absorption pathway, as per a functional enrichment analysis. Finally, we identified the 7 hub genes (COL6A3, COL1A2, COL1A1, MMP2, COL3A1, POST, and FN1). These genes have important roles and are widely involved in the immune response, apoptosis, inflammation, and bone development. These 7 genes were used to construct a diagnostic model by SVM, and it performed well in different cohorts. Additionally, we verified the methylation expression of these hub genes.

Conclusions

The 7-genes signature can be used for the diagnosis of OA and can provide new ideas in the clinical decision-making for patients with OA.

Recurrent driver mutations in benign tumors

The understanding of the molecular pathogenesis of benign tumors may bring essential information to clarify the process of tumorigenesis, and ultimately improve the understanding of events such as malignant transformation. The definition of benign neoplasia is not always straightforward and herein the issues surrounding this concept are discussed. Benign neoplasms share all cancer hallmarks with malignancies, except for metastatic potential. Recently, next-generation sequencing has provided unprecedented opportunities to unravel the genetic basis of benign neoplasms and, so far, we have learned that benign neoplasms are indeed characterized by the presence of genetic mutations, including genes rearrangements. Driver mutations in advanced cancer are those that confer growth advantage, and which have been positively selected during cancer evolution. Herein, some discussion will be brought about this concept in the context of cancer prevention, involving precursor lesions and benign neoplasms. When considering early detection and cancer prevention, a driver mutation should not only be advantageous (i.e., confer survival advantage), but predisposing (i.e., promoting a cancer phenotype). By including the benign counterparts of malignant neoplasms in tumor biology studies, it is possible to evaluate the risk posed by a given mutation and to differentiate advantageous from predisposing mutations, further refining the concept of driver mutations. Therefore, the study of benign neoplasms should be encouraged because it provides valuable information on tumorigenesis central for understanding the progression from initiation to malignant transformation.

Update on MR Imaging of Soft Tissue Tumors of Head and Neck

This article reviews soft tissue tumors of the head and neck following the 2020 revision of WHO Classification of Soft Tissue and Bone Tumours. Common soft tissue tumors in the head and neck and tumors are discussed, along with newly added entities to the classification system. Salient clinical and imaging features that may allow for improved diagnostic accuracy or to narrow the imaging differential diagnosis are covered. Advanced imaging techniques are discussed, with a focus on diffusion-weighted and dynamic contrast imaging and their potential to help characterize soft tissue tumors and aid in distinguishing malignant from benign tumors.

Intra-Articular Tumors

The intra-articular space is a relatively rare site of occurrence of neoplastic diseases. The 2 distinct groups of clinicopathologic entities that exhibit an almost exclusive tropism for the joints are represented by synovial chondromatosis and tenosynovial giant cell tumors (TGCT). Synovial chondromatosis is a locally aggressive chondrogenic neoplasm that very rarely can show malignant behavior. TGCT occur in 2 main variants, the localized variant and the more locally aggressive diffuse type. Malignant TCGT is exceedingly rare and is characterized by significant rates of both local recurrence and metastatic spread.

Primary soft tissue chondroma of the posterior mediastinum: a rare case report and literature review

A chondroma is a common benign cartilaginous tumor. However, a primary soft tissue chondroma of the posterior mediastinum is very rare. We herein report a case involving a 51-year-old man with a posterior mediastinal mass. The mass was dissected by thoracoscopy through the eighth intercostal space. Pathological examination led to a definitive diagnosis of a primary mediastinal chondroma with no criteria of malignancy. Preoperative diagnosis of a posterior mediastinal soft tissue chondroma is not easy because of its rarity and lack of typical features other than calcification. When a posterior mediastinal well-circumscribed soft tissue mass contains calcification and shows no obvious enhancement, the possibility of a soft tissue chondroma should be considered.

SPP1 and FN1 are significant gene biomarkers of tongue squamous cell carcinoma

Tongue squamous cell carcinoma (TSCC) is one of the most common malignant tumor types in the oral and maxillofacial region. The etiology and pathogenesis behind TSCC is complicated. In the present study, three gene expression profiles, namely GSE31056, GSE13601 and GSE78060, were downloaded from the Gene Expression Omnibus (GEO). The GEO2R online tool was utilized to identify differentially expressed genes (DEGs) between TSCC and normal tissue samples. Furthermore, a protein-protein interaction (PPI) network was constructed and hub genes were validated and analyzed. A total of 83 common DEGs were obtained in three datasets, including 48 upregulated and 35 downregulated genes. Pathway enrichment analysis indicated that DEGs were primarily enriched in cell adhesion, extracellular matrix (ECM) organization, and proteolysis. A total of 63 nodes and 218 edges were included in the PPI network. The top 11 candidate hub genes were acquired, namely plasminogen activator urokinase (PLAU), signal transducer and activator of transcription 1, C-X-C motif chemokine ligand 12, matrix metallopeptidase (MMP) 13, secreted phosphoprotein 1 (SPP1), periostin, MMP1, MMP3, fibronectin 1 (FN1), serpin family E member 1 and snail family transcriptional repressor 2. Overall, 83 DEGs and 11 hub genes were screened from TSCC and normal individuals using bioinformatics and microarray technology. These genes may be used as diagnostic and therapeutic biomarkers for TSCC. In addition, SPP1 and FNl were identified as potential biomarkers for the progression of TSCC.

Calcified chondroid mesenchymal neoplasms with FN1-receptor tyrosine kinase gene fusions including FGFR2, FGFR1, MERTK, NTRK1, and TEK: a molecular and clinicopathologic analysis

Translocations involving FN1 have been described in a variety of neoplasms that share the presence of a cartilage matrix and may also contain a variable extent of calcification. Fusions of FN1 to FGFR1 or FGFR2 have been reported in nine soft tissue chondromas, mostly demonstrated indirectly by FISH analysis. Delineation of FN1 fusions with various partner genes will facilitate our understanding of the pathogenesis and diagnostic classification of these neoplasms. In this study, we present molecular, clinical, and pathologic features of 12 cartilaginous soft tissue neoplasms showing a predilection for the TMJ region and the distal extremities. We analyzed for gene fusions with precise breakpoints using targeted RNA-seq with a 115-gene panel. We detected gene fusions in ten cases, including three novel fusions, FN1-MERTK, FN1-NTRK1, and FN1-TEK, each in one case, recurrent FN1-FGFR2 fusion in five cases, FN1-FGFR1 in one case, and FGFR1-PLAG1 in one case. The breakpoints in the 5' partner gene FN1 ranged from exons 11-48, retaining the domains of a signal peptide, FN1, FN2, and/or FN3, while the 3' partner genes retained the transmembrane domain, tyrosine kinase (TK) domains, and/or Ig domain. The tumors are generally characterized by nodular/lobular growth of polygonal to stellate cells within a chondroid matrix, often accompanied by various patterns of calcification, resembling those described for the chondroblastoma-like variant of soft tissue chondroma. Additional histologic findings include extensive calcium pyrophosphate dihydrate deposition in two cases and features resembling tenosynovial giant cell tumor (TGCT). Overall, while the tumors from our series show significant morphologic overlap with chondroblastoma-like soft tissue chondroma, we describe findings that expand the morphologic spectrum of these neoplasms and therefore refer to them as "calcified chondroid mesenchymal neoplasms." These neoplasms represent a spectrum of chondroid/cartilage matrix-forming tumors harboring FN1-receptor TK fusions that include those classified as soft tissue chondroma as well as chondroid TGCT.

The Role of IGF/IGF-IR-Signaling and Extracellular Matrix Effectors in Bone Sarcoma Pathogenesis

Simple Summary

Bone sarcomas are mesenchymal origin tumors. Bone sarcoma patients show a variable response or do not respond to chemotherapy. Notably, improving efficient chemotherapy approaches, dealing with chemoresistance, and preventing metastasis pose unmet challenges in sarcoma therapy. Insulin-like growth factors 1 and 2 (IGF-1 and -2) and their respective receptors are a multifactorial system that significantly contributes to bone sarcoma pathogenesis. Most clinical trials aiming at the IGF pathway have had limited success. Developing combinatorial strategies to enhance antitumor responses and better classify the patients that could best benefit from IGF-axis targeting therapies is in order. A plausible approach for developing a combinatorial strategy is to focus on the tumor microenvironment (TME) and processes executed therein. Herewith, we will discuss how the interplay between IGF-signaling and the TME constituents affects bone sarcomas’ basal functions and their response to therapy. Potential direct and adjunct therapeutical implications of the extracellular matrix (ECM) effectors will also be summarized.

Abstract

Bone sarcomas, mesenchymal origin tumors, represent a substantial group of varying neoplasms of a distinct entity. Bone sarcoma patients show a limited response or do not respond to chemotherapy. Notably, developing efficient chemotherapy approaches, dealing with chemoresistance, and preventing metastasis pose unmet challenges in sarcoma therapy. Insulin-like growth factors 1 and 2 (IGF-1 and -2) and their respective receptors are a multifactorial system that significantly contributes to bone sarcoma pathogenesis. Whereas failures have been registered in creating novel targeted therapeutics aiming at the IGF pathway, new agent development should continue, evaluating combinatorial strategies for enhancing antitumor responses and better classifying the patients that could best benefit from these therapies. A plausible approach for developing a combinatorial strategy is to focus on the tumor microenvironment (TME) and processes executed therein. Herewith, we will discuss how the interplay between IGF-signaling and the TME constituents affects sarcomas’ basal functions and their response to therapy. This review highlights key studies focusing on IGF signaling in bone sarcomas, specifically studies underscoring novel properties that make this system an attractive therapeutic target and identifies new relationships that may be exploited. Potential direct and adjunct therapeutical implications of the extracellular matrix (ECM) effectors will also be summarized.

The 2020 WHO Classification of Tumors of Bone: An Updated Review

Bone tumors are a rare and heterogeneous group of neoplasms that occur in the bone. The diversity and considerable morphologic overlap of bone tumors with other mesenchymal and nonmesenchymal bone lesions can complicate diagnosis. Accurate histologic diagnosis is crucial for appropriate management and prognostication. Since the publication of the fourth edition of the World Health Organization (WHO) classification of tumors of soft tissue and bone in 2013, significant advances have been made in our understanding of bone tumor molecular biology, classification, prognostication, and treatment. Detection of tumor-specific molecular alterations can facilitate the accurate diagnosis of histologically challenging cases. The fifth edition of the 2020 WHO classification of tumors of soft tissue and bone tumors provides an updated classification scheme and essential diagnostic criteria for bone tumors. Herein, we summarize these updates, focusing on major changes in each category of bone tumor, the newly described tumor entities and subtypes of existing tumor types, and newly described molecular and genetic data.

Surgical hip dislocation for treatment of synovial chondromatosis of the hip

PURPOSE

In the present study, we aimed to evaluate the clinical outcomes of surgical hip dislocation in patients with synovial chondromatosis (SC) of the hip.

METHODS

Seven patients with primary SC of the hip treated with open synovectomy and removal of loose bodies by surgical hip dislocation from 2016 to 2019 were retrospectively reviewed. All patients had numerous and widespread loose bodies based on pre-operative images, including routine radiographs, CT, and MRI. The visual analog scale (VAS) score and Harris hip score (HHS) were collected and analyzed before and after surgery. The post-operative radiographs were reviewed to evaluate disease recurrence and osteoarthritis progression.

RESULTS

The mean operative time was 61 minutes (range, 42-75 min). An average of 33 loose bodies in each patient (range, 16-67) was removed, and extra-articular pathology was found in one patient. Patients were followed up for a mean duration of 30 months (range, 18-42 months). The average VAS scores were decreased from 3.7 (range, 2-6) pre-operatively to 0.9 (range, 0-2) at the last follow-up, and the HHS was improved from 60.1 (range, 50-73) to 90.1 (range, 82-95). All results demonstrated significant improvements (P < 0.05). Post-operative radiographs showed no recurrence, osteoarthritis progression, or osteonecrosis of the femoral head in all hips.

CONCLUSIONS

Surgical hip dislocation was a practical approach for managing both intra-articular and extra-articular pathologic lesions around the hip. It was an effective treatment for SC of the hip with short surgical time, good joint functions, a lower recurrence rate, and few complications.

Juvenile Dysplasia Epiphysealis Hemimelica with Multiple Ankle Free Body

Dysplasia epiphysealis hemimelica (DEH), also known as Trevor's disease, is a rare overgrowth of cartilage that commonly arises in the epiphyseal bone of children. We report a rare case of DEH originating from a talus accompanied by multiple intra-articular free bodies in a 7-year-old patient with ankle instability. After the primary surgery for free body removal and microfracture technique for the cartilage defects in the ankle joint, the free body recurred. Secondary surgery of arthroscopic free body removal with lateral ankle ligament repair succeeded in treating the patient, without further recurrence of the free body.

Acral FibroChondroMyxoid tumor: imaging features of a new entity

"Acral FibroChondroMyxoid tumor" (AFCMT) is a recently described distinctive subtype of acral soft tissue tumor that typically arises on the fingers and toes. We herein present the unreported imaging features of AFCMT in a 44-year-old woman. This otherwise healthy patient was referred for a painful, slow-growing, soft tissue mass in the middle finger of her right hand. Initial radiographs and computed tomography showed a small lesion centered in the soft tissue of the ulnar aspect of the proximal phalanx, associated with scalloping of the underlying bone. Magnetic resonance imaging confirmed the presence of a well-circumscribed soft tissue tumor that exhibited relatively high T2-weighted signal intensity and marked enhancement after contrast administration. Subsequent excisional biopsy was performed. Histologically, the tumor was characterized by an abundant stroma displaying fibrous, chondroid, and myxoid areas. By immunohistochemistry, tumor cells stained for CD34, ERG, and focally S100 protein. RNA-sequencing allowed detection of THBS1-ADGFR5 gene fusion which confirmed the diagnosis of AFCMT. At 2-year follow-up, the patient remains free of recurrence. AFCMT is a previously unrecognized entity that may mimic chondroma and should be considered in the differential diagnosis of soft tissue tumors with cartilaginous or myxoid stroma in the extremities.

Updates from the 2020 World Health Organization Classification of Soft Tissue and Bone Tumours

The fifth edition of the World Health Organization (WHO) classification of soft tissue and bone tumours was published in May 2020. This 'Blue Book', which is also available digitally for the first time, incorporates an array of new information on these tumours, amassed in the 7 years since the previous edition. Major advances in molecular characterisation have driven further refinements in classification and the development of ancillary diagnostic tests, and have improved our understanding of disease pathogenesis. Several new entities are also included. This review summarises the main changes introduced in the 2020 WHO classification for each subcategory of soft tissue and bone tumours.

Plexiform Myofibroblastoma: Clinicopathologic Analysis of 36 Cases of a Distinctive Benign Tumor of Soft Tissue Affecting Mainly Children and Young Adults

The spectrum of benign superficial fibroblastic/myofibroblastic tumors continues to expand and includes entities such as plexiform fibrohistiocytic tumor, dermatomyofibroma and fibroblastic connective tissue nevus. Here, we describe a seemingly distinctive group of lesions which we have labeled "plexiform myofibroblastoma" (PM). PM is a rare superficial mesenchymal tumor of fibroblastic/myofibroblastic lineage that predominantly occurs in children and young adults. Thirty-six cases from the consultation archives of one of the authors have been studied to characterize the clinicopathologic characteristics of PM. 19 patients (53%) were female and 17 were male, with age at presentation ranging from congenital (2 cases) to 50 years of age (median: 9.5 y). Three patients had multiple lesions. Males tended to develop tumors during childhood (median: 2 y; range: congenital-37 y), while in females the age distribution was relatively uniform from childhood through adulthood (median age: 25 y; range: 4 mo to 50 y). Most tumors occurred in truncal locations (25/40), including the back (11), anterolateral chest wall (4), axilla (4), abdominal wall (4), perineum (1) and suprapubic region (1). Other tumor sites were the neck (10/40), occiput (2), lower extremity (2) and breast (1). The average greatest dimension was 2.7±1.7 cm (range: 0.6 to 8 cm). Three male patients, 2 of whom were brothers, presented between 6 months and 1 year of age with multiple lesions variably involving the back, occiput and axillae; these lesions spontaneously regressed after being present for about 2 years, with no evidence of recurrence at a mean follow-up of 11.4±3.2 years. Histologically, PM was composed of plexiform fascicles of fibroblastic/myofibroblastic spindle cells that ramify through the subcutis and reticular dermis. The bland neoplastic cells had indistinct cell borders, palely eosinophilic cytoplasm and ovoid or tapered nuclei. There was no histiocytoid component in any case, and no cases contained osteoclast-like giant cells. Twelve of thirty-four (35%) reviewed cases showed at least focal keloidal hyalinization, 6/34 (18%) contained somewhat fasciitis-like areas and 6/34 (18%) contained focal myxoid stroma. Immunohistochemical studies were positive for SMA (27/32 cases), desmin (9/21) and CD34 (13/24) and negative for β-catenin (0/14) and S-100 (0/22). EMA was weakly positive in 2/15 cases. An FGFR2 M535L tyrosine kinase domain variant of unknown significance was detected in 1/7 sequenced cases, and no somatic alterations, copy number alterations or gene fusions were detected in the other 6. Clinical follow-up data were available for 16/36 patients (44%; median duration: 5.5 y). Although most excisions had positive margins (11/16), only 1 patient developed a local recurrence 4 years after initial excision. No tumors metastasized. PM is a benign tumor with characteristic histology, epidemiology and anatomic site distribution. Because PM rarely recurs, a watchful waiting approach would be reasonable for lesions excised with positive margins.

Chondrogenic Bone Tumors: The Importance of Imaging Characteristics

BACKGROUND

 Chondrogenic tumors are the most frequent primary bone tumors. Malignant chondrogenic tumors represent about one quarter of malignant bone tumors. Benign chondrogenic bone tumors are frequent incidental findings at imaging. Radiological parameters may be helpful for identification, characterization, and differential diagnosis.

METHODS

 Systematic PubMed literature research. Identification and review of studies analyzing and describing imaging characteristics of chondrogenic bone tumors.

RESULTS AND CONCLUSIONS

 The 2020 World Health Organization (WHO) classification system differentiates between benign, intermediate (locally aggressive or rarely metastasizing), and malignant chondrogenic tumors. On imaging, typical findings of differentiated chondrogenic tumors are lobulated patterns with a high signal on T2-weighted magnetic resonance imaging (MRI) and ring- and arc-like calcifications on conventional radiography and computed tomography (CT). Depending on the entity, the prevalence of this chondrogenic pattern differs. While high grade tumors may be identified due to aggressive imaging patterns, the differentiation between benign and intermediate grade chondrogenic tumors is challenging, even in an interdisciplinary approach.

KEY POINTS

  · The WHO defines benign, intermediate, and malignant chondrogenic bone tumors. · Frequent benign tumors: osteochondroma and enchondroma; Frequent malignant tumor: conventional chondrosarcoma. · Differentiation between enchondroma versus low-grade chondrosarcoma is challenging for radiologists and pathologists. · Pain, deep scalloping, cortical destruction, bone expansion, soft tissue component: favor chondrosarcoma. · Potential malignant transformation of osteochondroma: progression after skeletal maturity, cartilage cap thickness (> 2 cm adult; > 3 cm child). · Potentially helpful advanced imaging methods: Dynamic MRI, texture analysis, FDG-PET/CT.

CITATION FORMAT

· Engel H, Herget GW, Füllgraf H et al. Chondrogenic Bone Tumors: The Importance of Imaging Characteristics. Fortschr Röntgenstr 2021; 193: 262 - 274.

Clinicopathologic and molecular features of six cases of phosphaturic mesenchymal tumor

Phosphaturic mesenchymal tumors (PMT) are rare neoplasms characterized by secretion of FGF23, resulting in renal phosphate wasting and osteomalacia. This tumor-induced osteomalacia (TIO) is cured by complete resection; thus, diagnosis is important, particularly on biopsy. Although PMT have a classic histologic appearance of bland spindled cells with conspicuous vascular network and characteristic smudgy basophilic matrix, there is a broad histologic spectrum and variant histologic patterns can make recognition difficult. Recent studies have demonstrated FN1-FGFR1 and FN1-FGF1 gene fusions in PMT; however, approximately 50% of cases are negative for these fusions. We sought to characterize 6 cases of PMT in-depth, compare fusion detection methods, and determine whether alternative fusions could be uncovered by targeted RNA sequencing. Of the 6 cases of PMT in our institutional archive, 3 were not given diagnoses of PMT at the time of initial pathologic examination. We characterized the immunoprofile (SMA, D2-40, CD56, S100 protein, desmin, SATB2, and ERG) and gene fusion status (FN1 and FGFR1 rearrangements by fluorescent in situ hybridization (FISH) and two targeted RNA sequencing approaches) in these cases. Tumors were consistently positive for SATB2 and negative for desmin, with 5/6 cases expressing ERG and CD56. One specimen was acid-decalcified and failed FISH and RNA sequencing. We found FN1 gene rearrangements by FISH in 2/5 cases, and a FN1-FGFR1 fusion by targeted RNA sequencing. No alternative gene fusions were identified by RNA sequencing. Our findings suggest that IHC and molecular analysis can aid in the diagnosis of PMT, guiding excision of the tumor and resolution of osteomalacia.

The distribution of chondromas: Why the hand?

Chondroma is a benign hyaline cartilage tumor and is a relatively common skeletal neoplasm. Uneven distribution of this tumor among the various bones and regions of the skeleton is known but no explanation of this phenomenon followed. The current research aimed to document the exact chondroma distribution in the body. We hypothesized that the cases of all subtypes of chondroma have to be investigated in complex and that obtaining combined data from a large cohort of cases may explain the logic of chondroma distribution and may answer the question of why the hand is the main target of the tumor. We retrospectively analyzed 1529 cases of various subtypes of chondroma. Enchondroma was the most frequent type (65.4%) and the hand was the main target location (49.8% of all cases). The right side of the body was affected in 900 cases (58.9%) and in 629 cases (41.1%) the left side was affected (p = 0.03). The general results for tumor distribution are as follows: head and extremities - 92.8%; head, hands, and feet - 71.8%; and hands and feet - 62.8%. In the hand and the feet, multiple chondromas were distributed along the same digital ray in all cases. The anatomical distribution of various subtypes of chondroma follows "the periphery of the being", the uneven lateral distribution, and the "same digital ray" patterns that permits to suggest that genetic mutations affecting the development of the body during the embryonic period are the main etiological component for this tumor.

Recurrent novel THBS1-ADGRF5 gene fusion in a new tumor subtype "Acral FibroChondroMyxoid Tumors"

Acral soft tissue tumors are common neoplasms, a subset of which pose a diagnostic challenge. We report 10 cases of a previously unrecognized acral benign soft tissue tumor. These tumors arose on the fingers and toes and involved bone in half of cases. Histologically, the tumors were lobulated and displayed an abundant stroma made of variable fibrous, chondroid and myxoid material reminiscent of cartilaginous or myoepithelial differentiation. Tumor cells harbored small round to reniform nuclei with clear chromatin and inconspicuous nucleoli along with scant eosinophilic cytoplasm. The cells were mostly arranged haphazardly in the stroma but also in small clusters. No mitotic activity was detected. No specific feature was identified in recurrent cases. By immunohistochemistry, the cells consistently stained for CD34 (10/10), ERG (9/10), and SOX9 (7/10). Whole RNA sequencing identified a previously undescribed recurrent in frame THBS1-ADGRF5 gene fusion in all cases. The transcript was confirmed by RT-PCR and was not found in the control group of mimickers including soft tissue chondromas. We propose the name of Acral FibroChondroMyxoid Tumors for this new entity.

Key Genes Associated with Prognosis and Tumor Infiltrating Immune Cells in Gastric Cancer Patients Identified by Cross-Database Analysis

Background: The molecular mechanisms underlying gastric cancer (GC) progression are unclear. The authors examined key genes associated with the prognosis and tumor-infiltrating immune cells in patients with GC. Materials and Methods: Gene expression omnibus (GEO) was used to filter and obtain GC-related differentially expressed genes (DEGs). The molecular functions, biological processes, and cellular components of the DEGs were subjected to enrichment analysis. Protein-protein interaction networks of proteins encoded by the DEGs were analyzed using STRING. The authors also identified hub genes of GC, as well as their expression levels in GC and their relationship with patient prognosis. The relationship between hub genes and tumor-infiltrating immune cells was analyzed by Tumor IMmune Estimation Resource. Results: Six GEO datasets were included in this study, and 265 DEGs were identified. These DEGs were enriched in different signaling pathways and had different biological functions. Six hub genes were potentially significantly related to the molecular mechanisms of GC (TOP2A, FN1, SPARC, COL3A1, COL1A1, and TIMP1). These genes are potential markers of prognosis. Five hub genes were significantly positively correlated with the number of macrophages, neutrophils, and dendritic cells. Conclusions: The authors provide a theoretical basis for exploring the molecular regulation mechanism underlying GC and identifying therapeutic targets.

Genomics and Therapeutic Vulnerabilities of Primary Bone Tumors

Osteosarcoma, Ewing sarcoma and chondrosarcoma are rare diseases but the most common primary tumors of bone. The genes directly involved in the sarcomagenesis, tumor progression and treatment responsiveness are not completely defined for these tumors, and the powerful discovery of genetic analysis is highly warranted in the view of improving the therapy and cure of patients. The review summarizes recent advances concerning the molecular and genetic background of these three neoplasms and, of their most common variants, highlights the putative therapeutic targets and the clinical trials that are presently active, and notes the fundamental issues that remain unanswered. In the era of personalized medicine, the rarity of sarcomas may not be the major obstacle, provided that each patient is studied extensively according to a road map that combines emerging genomic and functional approaches toward the selection of novel therapeutic strategies.

Soft Tissue Special Issue: Chondroid Neoplasms of the Skull

Clinically, radiologically, and pathologically, chondroid neoplasms of the skull can be diagnostically challenging due to overlapping features in each of these domains. Compounding the problem for the pathologist, there is also significant morphologic, immunophenotypic, and molecular genetic overlap between benign and malignant cartilaginous lesions, and the majority of these lesions are encountered quite rarely in routine surgical pathology practice. Each of these factors contribute to the diagnostic difficulty posed by these lesions, highlighting the importance of radiologic-pathologic correlation in the diagnosis. This review is intended to provide an update for surgical pathologists on some of the most commonly encountered chondroid neoplasms in the skull, and includes the following lesions: chondromyxoid fibroma, synovial chondromatosis, chondrosarcoma and variants, and chordoma and variants. For each of these lesions, the differential diagnosis and useful ancillary tests will be discussed in the context of a broad range of additional primary and secondary lesions.

A molecular study of synovial chondromatosis

Synovial chondromatosis (SC) is a rare benign cartilaginous neoplasm in which recurrent fibronectin 1 (FN1) and activin receptor 2A (ACVR2A) gene rearrangements have been recently reported. Triggered by a case of malignant transformation in SC (synovial chondrosarcoma) showing a novel KMT2A-BCOR gene fusion by targeted RNA sequencing, we sought to evaluate the molecular abnormalities in a cohort of 27 SC cases using a combined methodology of fluorescence in situ hybridization (FISH) and/or targeted RNA sequencing. Results showed that FN1 and /or ACVR2A gene rearrangements were noted in 18 cases (67%), with an FN1-ACVR2A fusion being confirmed in 15 (56%) cases. Two cases showed only FN1 gene rearrangement, without other abnormalities. A novel FN1-NFATc2 gene fusion was noted in one case by RNA sequencing. The remaining nine cases showed no abnormalities in FN1 and ACVR2A genes. No additional cases showed BCOR gene alterations. In conclusion, this study confirms that FN1-ACVR2A fusion is the leading pathogenetic event in SC, at even higher frequency than previously reported. FISH methodology emerges as an appropriate tool in the identification of FN1 and ACVR2A gene abnormalities, which can be used in challenging cases. Further studies are needed to determine the recurrent potential of BCOR abnormalities in this disease.