Identification of a novel, recurrent HEY1-NCOA2 fusion in mesenchymal chondrosarcoma based on a genome-wide screen of exon-level expression data

Case report: A mesenchymal chondrosarcoma with alternative HEY1::NCOA2 fusions in the sella turcica

Introduction

Mesenchymal chondrosarcoma (MCS) is a rare subtype of chondrosarcoma that occurs at widespread anatomical locations, such as bone, soft tissue, and intracranial sites. The central nervous system (CNS) is one of the most common origins of extraosseous MCS. However, alternative HEY1::NCOA2 fusions have not been reported in this tumor.

Case report

We report a case of intracranial MCS with HEY1::NCOA2 rearrangement. A 52-year-old woman presented with a 15-mm calcified mass around the sella turcica. She initially underwent transsphenoidal surgery for tumor resection and then additional resections for five local recurrences over 5 years. Histologically, the tumor was composed of small round to spindle-shaped cells admixed with well-differentiated hyaline cartilaginous islands. A hemangiopericytoma-like vascular pattern and small sinusoid-like vessels were also observed. RNA sequencing using RNA extracted from formalin-fixed paraffin-embedded samples from the last operation revealed two alternative variants of the HEY1::NCOA2 fusion: HEY1(ex4)::NCOA2 (ex13) and HEY1(ex4)::NCOA2(ex14). Both variants were confirmed as in-frame fusions using reverse transcription-polymerase chain reaction.

Discussion

Cartilaginous components were often not apparent during the recurrences. In addition to the non-typical pathological finding, the correct diagnosis was hampered by the poor RNA quality of the surgical specimens and non-specific STAT6 nuclear staining.

Conclusion

This is the first reported case of intracranial MCS with an alternative HEY1::NCOA2 fusion.

Uterine Tumor Resembling Ovarian Sex-Cord Tumor (UTROSCT): A Rare Polyphenotypic Neoplasm

Uterine tumor resembling ovarian sex-cord tumor (UTROSCT) is a rare form of uterine mesenchymal neoplasm. Although UTROSCT generally exhibits benign behavior with a favorable prognosis, this neoplasm is nevertheless classified as being of uncertain malignant potential, given its low rate of recurrence and the fact that it rarely produces metastases (e.g., in the lymph nodes, epiploic appendix, omentum, small bowel, subcutaneous tissue, lungs). Its histogenesis is also uncertain. Typically, UTROSCT occurs in peri-menopausal or menopausal women, but it can sometimes be observed in young women. Usually, this neoplasm can be found in the uterine corpus as a nodular intramural lesion, while it is less frequently submucosal, subserosal, or polypoid/intracavitary. UTROSCT can cause abnormal bleeding, pelvic pain, enlarged uterus, and mass sensation, but sometimes it is found purely by chance. This neoplasm can be considered polyphenotypic on morphological, immunohistochemical, and genetic analyses. Generally, upon microscopic examination, UTROSCT shows a predominant pattern of the cords, nests, and trabeculae typical of sex-cord tumors of the ovary, while immunohistochemically it is characterized by a coexpression of epithelial, smooth muscle, and sex-cord markers. The aim of this review is to report clinical and pathological data and genetic alterations to establish their impact on the prognosis and management of patients affected by this rare entity.

Molecular Alterations in Pediatric Solid Tumors

Pediatric tumors can be divided into hematologic malignancies, central nervous system tumors, and extracranial solid tumors of bone, soft tissue, or other organ systems. Molecular alterations that impact diagnosis, prognosis, treatment, and familial cancer risk have been described in many pediatric solid tumors. In addition to providing a concise summary of clinically relevant molecular alterations in extracranial pediatric solid tumors, this review discusses conventional and next-generation sequencing-based molecular techniques, relevant tumor predisposition syndromes, and the increasing integration of molecular data into the practice of diagnostic pathology for children with solid tumors.

Biological and therapeutic insights from animal modeling of fusion-driven pediatric soft tissue sarcomas

Survival for children with cancer has primarily improved over the past decades due to refinements in surgery, radiation and chemotherapy. Although these general therapies are sometimes curative, the cancer often recurs, resulting in poor outcomes for patients. Fusion-driven pediatric soft tissue sarcomas are genetically defined by chromosomal translocations that create a chimeric oncogene. This distinctive, almost 'monogenic', genetic feature supports the generation of animal models to study the respective diseases in vivo. This Review focuses on a subset of fusion-driven pediatric soft tissue sarcomas that have transgenic animal tumor models, which includes fusion-positive and infantile rhabdomyosarcoma, synovial sarcoma, undifferentiated small round cell sarcoma, alveolar soft part sarcoma and clear cell sarcoma. Studies using the animal models of these sarcomas have highlighted that pediatric cancers require a specific cellular state or developmental stage to drive tumorigenesis, as the fusion oncogenes cause different outcomes depending on their lineage and timing of expression. Therefore, understanding these context-specific activities could identify targetable activities and mechanisms critical for tumorigenesis. Broadly, these cancers show dependencies on chromatin regulators to support oncogenic gene expression and co-opting of developmental pathways. Comparative analyses across lineages and tumor models will further provide biological and therapeutic insights to improve outcomes for these children.

VGLL2 and TEAD1 fusion proteins drive YAP/TAZ-independent transcription and tumorigenesis by engaging p300

Studies on Hippo pathway regulation of tumorigenesis largely center on YAP and TAZ, the transcriptional co-regulators of TEAD. Here, we present an oncogenic mechanism involving VGLL and TEAD fusions that is Hippo pathway-related but YAP/TAZ-independent. We characterize two recurrent fusions, VGLL2-NCOA2 and TEAD1-NCOA2, recently identified in spindle cell rhabdomyosarcoma. We demonstrate that, in contrast to VGLL2 and TEAD1, the fusion proteins are strong activators of TEAD-dependent transcription, and their function does not require YAP/TAZ. Furthermore, we identify that VGLL2 and TEAD1 fusions engage specific epigenetic regulation by recruiting histone acetyltransferase p300 to control TEAD-mediated transcriptional and epigenetic landscapes. We showed that small molecule p300 inhibition can suppress fusion proteins-induced oncogenic transformation both in vitro and in vivo. Overall, our study reveals a molecular basis for VGLL involvement in cancer and provides a framework for targeting tumors carrying VGLL, TEAD, or NCOA translocations.

Uncovering the WWTR1::NCOA2 Gene fusion in low-grade myoepithelial-rich neoplasm with HMGA2 expression: A case report

We describe a case of a pleomorphic adenoma (PA) arising from the para-tracheal accessory salivary gland in a 44-year-old male harboring a novel WWTR1::NCOA2 gene fusion. To our knowledge, this novel gene fusion has not been described previously in salivary gland tumors. The patient presented with hoarseness of voice. The radiological exam revealed a mass in the upper third of the trachea involving the larynx. Histologically, the tumor consisted of bland-looking monocellular eosinophilic epithelial cells arranged in cords and sheets separated by thin fibrous stroma, focally forming a pseudo-tubular pattern. In immunohistochemistry, the tumor cells demonstrated positivity for CK7, PS100, SOX10, and HMGA2; and negativity for CK5/6, p40 p63, and PLAG1. In addition, the clustering analysis clearly demonstrates a clustering of tumors within the PA group. In addition to reporting this novel fusion in the PA spectrum, we discuss the relevant differential diagnoses and briefly review of NCOA2 and WWTR1 gene functions in normal and neoplastic contexts.

p160 nuclear receptor coactivator family members and their role in rare fusion‑driven neoplasms (Review)

Gene fusions with translocations involving nuclear receptor coactivators (NCoAs) are relatively common among fusion-driven malignancies. NCoAs are essential mediators of environmental cues and can modulate the transcription of downstream target genes upon binding to activated nuclear receptors. Therefore, fusion proteins containing NCoAs can become strong oncogenic drivers, affecting the cell transcriptional profile. These tumors show a strong dependency on the fusion oncogene; therefore, the direct pharmacological targeting of the fusion protein becomes an attractive strategy for therapy. Currently, different combinations of chemotherapy regimens are used to treat a variety of NCoA-fusion-driven tumors, but given the frequent tumor reoccurrence, more efficient treatment strategies are needed. Specific approaches directed towards inhibition or silencing of the fusion gene need to be developed while minimizing the interference with the original genes. This review highlights the relevant literature describing the normal function and structure of NCoAs and their oncogenic activity in NCoA-gene fusion-driven cancers, and explores potential strategies that could be effective in targeting these fusions.

Low-grade undifferentiated sarcoma with MEIS1::NCOA2-rearrangement primary to the lung: a case report

BACKGROUND

MEIS1::NCOA2 is a rare fusion gene that has been recently described in a subset of spindle cell rhabdomyosarcomas and multiple low-grade undifferentiated spindle cell sarcomas predominantly arising in the genitourinary and gynecologic tracts with no specific line of differentiation. We present the first documented case of this neoplasm arising as a lung primary tumor.

CASE PRESENTATION

A 74-year-old woman with a 40-year smoking history presented with a 2.1 × 1.7 cm lung nodule discovered on computed tomography (CT) scan. A biopsy and subsequent lobe resection were performed, as well as an extensive metastatic work up, which revealed no additional masses. No specific line of differentiation was found by immunohistochemical staining, and an RNA-based fusion panel revealed a MEIS1::NCOA2 fusion, at which point a diagnosis of Low-Grade Undifferentiated Sarcoma with MEIS1::NCOA2-Rearrangement was rendered.

CONCLUSIONS

This report represents the first diagnosis of this tumor primary to the lung, and provides additional insight into the origin and localization of these rare tumors.

Unraveling molecular signatures in rare bone tumors and navigating the cancer pathway landscapes for targeted therapeutics

Rare cancers (RCs), which account for over 20% of cancer cases, face significant research and treatment challenges due to their limited prevalence. This results in suboptimal outcomes compared to more common malignancies. Rare bone tumors (RBTs) constitute 5-10% of rare cancer cases and pose unique diagnostic complexities. The therapeutic potential of anti-cancer drugs for RBTs remains largely unexplored. Identifying molecular alterations in cancer-related genes and their associated pathways is essential for precision medicine in RBTs. Small molecule inhibitors and monoclonal antibodies targeting specific RBT-associated proteins show promise. Ongoing clinical trials aim to define RBT biomarkers, subtypes, and optimal treatment contexts, including combination therapies and immunotherapeutic agents. This review addresses the challenges in diagnosing, treating, and studying RBTs, shedding light on the current state of RBT biomarkers, potential therapeutic targets, and promising inhibitors. Rare cancers demand attention and innovative solutions to improve clinical outcomes.

NR1D1-rearranged soft tissue tumour: A clinicopathological and molecular analysis of four additional cases

AIMS

Nuclear receptor subfamily 1 group D member 1 (NR1D1)-rearranged soft tissue tumour is a newly described entity with an epithelioid morphology and a potential for aggressive behaviour. Largely due to under-recognition, this tumour type has not yet been widely acknowledged. Herein, we report four additional cases to further expand its clinicopathological and molecular spectrum.

METHODS AND RESULTS

Four mesenchymal tumours with NR1D1 rearrangement were identified from our consultation files. There were one male and three females with ages ranging from 19 to 47 years (median = 28.5 years). Tumour occurred in the tongue, neck, hip and index finger, respectively. Histologically, two tumours were composed predominantly of epithelioid cells; one tumour had admixed epithelioid-spindle cells and one tumour consisted of monomorphic small round to ovoid cells. By immunohistochemistry, none of the tumours expressed lineage-specific markers. Targeted RNA-sequencing identified NR1D1 fusions in all four tumours, the partner genes being MAML2, MAML3, KMT2A and NCOA2, respectively. The novel MAML3 and NCOA2 rearrangements were confirmed by fluorescence in-situ hybridisation analysis. On follow-up (2-23 months), one patient experienced local recurrence due to incomplete resection and one patient developed lung metastasis. The other two patients were alive without disease.

CONCLUSIONS

This study adds more support for NR1D1-rearranged soft tissue tumour as an emerging entity. The occurrence of two additional tumours in the head and neck region, description of a small round cell variant and identification of novel MAML3, KMT2A and NCOA2 partners further expand its clinicopathological and molecular spectrum. More studies on larger series are necessary to validate the fully malignant potential of NR1D1-rearranged soft tissue tumour.

Sclerosing Epithelioid Fibrosarcoma

Sclerosing epithelioid fibrosarcoma (SEF) is a distinctive sarcoma that may arise in nearly any soft tissue site or bone. While there has been past controversy as to whether it is related to low-grade fibromyxoid sarcoma (LGFMS), it has been shown to behave far more aggressively than LGFMS. SEF has a propensity to metastasize to the lungs and bone and arise within the abdominal cavity. Histologically, it is characterized by uniform nuclei embedded in a densely collagenous stroma simulating osteoid. By immunohistochemistry, it is often strongly positive for MUC4. The majority (75%) have EWSR1 gene rearrangement, most commonly with CREB3L1 as a fusion partner, although a variety of FUS/EWSR1 and CREB3L1/CREB3L2/CREB3L3 fusions have been described in addition to others. SEF is currently recalcitrant to nearly all chemotherapy and radiation therapy.

Myxoid epithelioid smooth muscle tumor of the vulva: A distinct entity with MEF2D::NCOA2 gene fusion

Smooth muscle tumors are the most common mesenchymal tumors of the female genital tract, including the vulva. Since vulvar smooth muscle tumors are rare, our understanding of them compared to their uterine counterparts continues to evolve. Herein, we present two cases of morphologically distinct myxoid epithelioid smooth muscle tumors of the vulva with novel MEF2D::NCOA2 gene fusion. The tumors involved 24 and 37-year-old women. Both tumors presented as palpable vulvar masses that were circumscribed, measuring 2.8 and 5.1 cm in greatest dimension. Histologically, they were composed of epithelioid to spindle-shaped cells with minimal cytologic atypia and prominent myxoid matrix. Rare mitotic figures were present (1-3 mitotic figures per 10 high-power field (HPF)), and no areas of tumor necrosis were identified. By immunohistochemistry, the neoplastic cells strongly expressed smooth muscle actin, calponin, and desmin, confirming smooth muscle origin. Next-generation sequencing identified identical MEF2D::NCOA2 gene fusions. These two cases demonstrate that at least a subset of myxoid epithelioid smooth muscle tumors of the vulva represent a distinct entity characterized by a novel MEF2D::NCOA2 gene fusion. Importantly, recognition of the distinct morphologic and genetic features of these tumors is key to understanding the biological potential of these rare tumors.

Novel NCOA2/3-rearranged low-grade fibroblastic spindle cell tumors: A report of five cases

Spindle cell mesenchymal neoplasms are a diverse and often challenging diagnostic group. While morphological impression is sufficient for some diagnoses, increasingly immunohistochemical and even molecular data is required to render an accurate diagnosis, which can lead to the characterization of new entities. We describe five cases of novel mesenchymal neoplasms with rearrangements in the NCOA2 and NCOA3 genes partnered with either CTCF or CRTC1. Three tumors occurred in the head and neck (palate, auditory canal), while the other two were in visceral organs (lung, urinary bladder). All cases occurred in adults (range 33-86) with a median age of 42 and fairly even sex distribution = (male-to-female = 3:2). Morphologically, they had similar features consisting of monotonous, bland spindle to ovoid cells with fascicular and reticular arrangements in a myxohyaline to collagenous stroma. However, immunophenotypically they had essentially a null phenotype, with only two tumors staining partially for CD34 and smooth muscle actin. Targeted RNA sequencing detected in-frame CTCF::NCOA2 (one case), CRTC1::NCOA2 (two cases), and CTCF::NCOA3 (two cases) fusions. Treatment was surgical resection in all cases. Local recurrence and/or distant metastases were not observed in any case (median follow-up, 7.5 months; range, 2-19 months). Given their morphologic, immunohistochemical, and molecular similarities, we believe that these cases may represent an emerging family of low-grade NCOA2/3-rearranged fibroblastic spindle cell neoplasms.

Uterine MEIS1::NCOA2 Fusion Sarcoma With Lung Metastasis: A Case Report and Review of the Literature

MEIS1::NCOA1/2 fusion sarcomas are a recently described novel entity arising in a variety of locations with a predilection for the genitourinary tract and gynecologic organs. Despite multiple locoregional recurrences, these tumors are thought to behave in a low-grade malignant manner. Here we report a uterine MEIS1::NCOA2 fusion sarcoma with lung metastasis. The patient was a 47-yr-old woman with a history of abnormal uterine bleeding who was found to have a myometrial mass confirmed by pathology to be uterine sarcoma. The tumor was predominantly composed of monotonous spindle cells with scant cytoplasm, crowded nuclei, and brisk mitotic activity, growing in a fascicular and streaming pattern. The morphologic and immunophenotypic features were nonspecific and a diagnosis of high-grade uterine sarcoma with a differential of leiomyosarcoma versus high-grade endometrial stromal sarcoma was rendered. At the 27-mo follow-up, the patient was found to have a lung metastasis consisting of a monotonous round cell sarcoma. A retrospective RNA-based and DNA-based next-generation sequencing of the primary uterine sarcoma revealed a MEIS1::NCOA2 gene fusion, a c.94G>C/p.D32H mutation in exon 3 of CTNNB1 gene, HMGA2 , and CDK4 gene amplification, and an intermediate/marginal level of MDM2 gene amplification. Polymerase chain reaction-based molecular analysis further demonstrated that the MEIS1::NCOA2 gene fusion and CTNNB1 somatic mutation were also present in the lung metastasis. This case represents the first case of such gynecologic sarcoma with distant (lung) metastasis, and the second metastatic case among all reported MEIS1::NCOA1/2 fusion sarcomas, highlighting the malignant metastatic potential of this emerging entity. Our case also indicates that HMGA2/CDK4/MDM2 region amplification and CTNNB1 somatic mutation might be recurrent genetic events in this rare sarcoma subtype.

Extensive analysis of 59 sarcoma-related fusion genes identified pazopanib as a potential inhibitor to COL1A1-PDGFB fusion gene

Sarcomas are malignant mesenchymal tumors that are extremely rare and divergent. Fusion genes are involved in approximately 30% of sarcomas as driver oncogenes; however, their detailed functions are not fully understood. In this study, we determined the functional significance of 59 sarcoma-related fusion genes. The transforming potential and drug sensitivities of these fusion genes were evaluated using a focus formation assay (FFA) and the mixed-all-nominated-in-one (MANO) method, respectively. The transcriptome was also examined using RNA sequencing of 3T3 cells transduced with each fusion gene. Approximately half (28/59, 47%) of the fusion genes exhibited transformation in the FFA assay, which was classified into five types based on the resulting phenotype. The sensitivity to 12 drugs including multityrosine kinase inhibitors was assessed using the MANO method and pazopanib was found to be more effective against cells expressing the COL1A1-PDGFB fusion gene compared with the others. The downstream MAPK/AKT pathway was suppressed at the protein level following pazopanib treatment. The fusion genes were classified into four subgroups by cluster analysis of the gene expression data and gene set enrichment analysis. In summary, the oncogenicity and drug sensitivity of 59 fusion genes were simultaneously evaluated using a high-throughput strategy. Pazopanib was selected as a candidate drug for sarcomas harboring the COL1A1-PDGFB fusion gene. This assessment could be useful as a screening platform and provides a database to evaluate customized therapy for fusion gene-associated sarcomas.

Mesenchymal Chondrosarcoma from Diagnosis to Clinical Trials

Mesenchymal chondrosarcoma (MCS) is a rare subtype of chondrosarcoma with a poor prognosis. Although these tumors are sensitive to radiotherapy/chemotherapy, the standard treatment for localized MCS is only surgical resection, and there are no established treatment guidelines for patients with advanced and metastatic MCS. Due to the low incidence of MCS, the pathology of these tumors is still unknown, and other therapeutic options are lacking. Some studies show the potential role of the PDGF/PPI3K/AKT, PKC/RAF/MEK/ERK, and pRB pathways, and BCL2 overexpression in the pathogenesis of MCS. These findings provide an opportunity to use protein kinases and BCL2 inhibitors as potential therapy in MCS. In this review, we summarize the current knowledge about MCS diagnosis and treatment options. We show the immunological and molecular biomarkers used in the diagnosis of MCS. In addition, we discuss the known prognostic and predictive factors in MCS. Finally, we present the novel trends, including targeted therapies and ongoing clinical trials using protein kinase inhibitors and the death receptor 5 (DR5) agonist, which may be the focus of future MCS treatment studies.

Clinical diagnostic and radiographic features of a primary intradural spinal chondrosarcoma in a young adult: illustrative case

BACKGROUND

Mesenchymal chondrosarcoma (MCS) is an aggressive subtype of chondrosarcoma that occurs extremely rarely in the central nervous system. Patients often present with pain or sensorimotor deficits, and resection is considered the gold standard. The role of adjuvant radiation and/or chemotherapy is largely unknown.

OBSERVATIONS

A 22-year-old male presented with a 4-month history of progressive back and bilateral leg pain. He underwent imaging workup with magnetic resonance imaging of the lumbar spine and was found to have an intradural, extramedullary, heterogeneously enhancing mass spanning the L4-5 vertebral levels. Intraoperatively, a lobular, partially calcified mass with a ventral dural attachment displacing the nerve roots laterally was observed. The mass was removed en bloc, and the patient later underwent adjuvant radiotherapy, with no evidence of recurrence 2 years following surgery.

LESSONS

Spinal MCS is extremely rare and often presents with a more aggressive course than conventional chondrosarcoma. Radiological diagnosis is challenging, as the tumor mimics different pathologies. The presence of calcifications, heterogeneous enhancement, and a more rapid clinical course as well as the presence of HEY1::NCOA2 gene fusion, which can be detected by surrogate immunohistochemistry, aids in diagnosis. Resection is the standard of care, and adjuvant radiation may be considered to reduce local recurrence, although further studies are warranted.

"PRRX1-rearranged mesenchymal tumors": expanding the immunohistochemical profile and molecular spectrum of a recently described entity with the proposed revision of nomenclature

Since the publication of the 2020 World Health Organization classification of soft tissue and bone tumors, the classification of "fibroblastic" tumors has expanded to include a novel subset of tumors characterized by PRRX1::NCOA1/2 gene fusions. These tumors defy conventional classification and are morphologically distinct, characterized by a multi-nodular growth of bland spindle cells suspended in a myxo-collagenous stroma with mild cytologic atypia, "staghorn-like" vessels, and variable perivascular hyalinization. Mitotic activity is rare, and necrosis is not identified. Herein, we present six additional cases of PRRX1-rearranged mesenchymal tumors, including five cases with PRRX1::NCOA1 fusion and one case with PRRX1::KMT2D fusion. Three cases (3/6, 50%) demonstrated focal co-expression of S100 protein and SOX10, thereby expanding the immunohistochemical profile of this emerging entity. Like prior reported cases, there was no evidence of malignant behavior on short-term follow-up. The novel fusion, PRRX1::KMT2D, further expands the molecular spectrum of this entity and leads to a proposed revision of the provisional nomenclature to "PRRX1-rearranged mesenchymal tumor" to both accommodate non-NCOA1/2 fusion partners and allow for the possibility of partial neural or neuroectodermal differentiation.

HEY1-NCOA2 expression modulates chondrogenic differentiation and induces mesenchymal chondrosarcoma in mice

Mesenchymal chondrosarcoma affects adolescents and young adults, and most cases usually have the HEY1::NCOA2 fusion gene. However, the functional role of HEY1-NCOA2 in the development and progression of mesenchymal chondrosarcoma remains largely unknown. This study aimed to clarify the functional role of HEY1-NCOA2 in transformation of the cell of origin and induction of typical biphasic morphology of mesenchymal chondrosarcoma. We generated a mouse model for mesenchymal chondrosarcoma by introducing HEY1-NCOA2 into mouse embryonic superficial zone (eSZ) followed by subcutaneous transplantation into nude mice. HEY1-NCOA2 expression in eSZ cells successfully induced subcutaneous tumors in 68.9% of recipients, showing biphasic morphologies and expression of Sox9, a master regulator of chondrogenic differentiation. ChIP sequencing analyses indicated frequent interaction between HEY1-NCOA2 binding peaks and active enhancers. Runx2, which is important for differentiation and proliferation of the chondrocytic lineage, is invariably expressed in mouse mesenchymal chondrosarcoma, and interaction between HEY1-NCOA2 and Runx2 is observed using NCOA2 C-terminal domains. Although Runx2 knockout resulted in significant delay in tumor onset, it also induced aggressive growth of immature small round cells. Runx3, which is also expressed in mesenchymal chondrosarcoma and interacts with HEY1-NCOA2, replaced the DNA-binding property of Runx2 only in part. Treatment with the HDAC inhibitor panobinostat suppressed tumor growth both in vitro and in vivo, abrogating expression of genes downstream of HEY1-NCOA2 and Runx2. In conclusion, HEY1::NCOA2 expression modulates the transcriptional program in chondrogenic differentiation, affecting cartilage-specific transcription factor functions.

NKX3.1 immunohistochemistry and methylome profiling in mesenchymal chondrosarcoma: additional diagnostic value for a well-defined disease?

Mesenchymal chondrosarcoma (MCS) is a rare and highly aggressive tumour of soft tissue and bone that is defined by an underlying and highly specific fusion transcript involving HEY1 and NCOA2. Histologically, the tumours show a biphasic appearance consisting of an undifferentiated blue and round cell component as well as islands of highly differentiated cartilage. Particularly in core needle biopsies, the chondromatous component can be missed and the non-specific morphology and immunophenotype of the round cell component can cause diagnostic challenges. We applied NKX3.1 immunohistochemistry which was recently reported as a highly specific marker as well as methylome and copy number profiling to a set of 45 well characterised MCS cases to evaluate their potential diagnostic value. Methylome profiling revealed a highly distinct cluster for MCS. Notably, the findings were reproducible also when analysing the round cell and cartilaginous component separately. Furthermore, four outliers were identified by methylome profiling for which the diagnosis had to be revised. NKX3.1 immunohistochemistry showed positivity in 36% of tumours, the majority of which was rather focal and weak. Taken together, NKX3.1 expression showed a low sensitivity but a high specificity in our analysis. Methylome profiling on the other hand represents a sensitive, specific and reliable tool to support the diagnosis of MCS, particularly if only the round cell component is obtained in a biopsy and the diagnosis is not suspected. Furthermore, it can aid in confirming the diagnosis in case RNA sequencing for the HEY1::NCOA2 fusion transcript is not available.

Bad to the Bone: Emerging Approaches to Aggressive Bone Sarcomas

Bone sarcomas are rare heterogeneous tumors that affect patients of all ages including children, adolescent young adults, and older adults. They include many aggressive subtypes and patient groups with poor outcomes, poor access to clinical trials, and lack of defined standard therapeutic strategies. Conventional chondrosarcoma remains a surgical disease, with no defined role for cytotoxic therapy and no approved targeted systemic therapies. Here, we discuss promising novel targets and strategies undergoing evaluation in clinical trials. Multiagent chemotherapy has greatly improved outcomes for patients with Ewing sarcoma (ES) and osteosarcoma, but management of those with high-risk or recurrent disease remains challenging and controversial. We describe the impact of international collaborative trials, such as the rEECur study, that aim to define optimal treatment strategies for those with recurrent, refractory ES, and evidence for high-dose chemotherapy with stem-cell support. We also discuss current and emerging strategies for other small round cell sarcomas, such as CIC-rearranged, BCOR-rearranged tumors, and the evaluation of emerging novel therapeutics and trial designs that may offer a new paradigm to improve survival in these aggressive tumors with notoriously bad (to the bone) outcomes.

Molecular In-Depth Characterization of Chondrosarcoma for Current and Future Targeted Therapies

Chondrosarcoma (CHS) are heterogenous, but as a whole, represent the second most common primary malignant bone tumor entity. Although knowledge on tumor biology has grown exponentially during the past few decades, surgical resection remains the gold standard for the treatment of these tumors, while radiation and differentiated chemotherapy do not result in sufficient cancer control. An in-depth molecular characterization of CHS reveals significant differences compared to tumors of epithelial origin. Genetically, CHS are heterogenous, but there is no characteristic mutation defining CHS, and yet, IDH1 and IDH2 mutations are frequent. Hypovascularization, extracellular matrix composition of collagen, proteoglycans, and hyaluronan create a mechanical barrier for tumor suppressive immune cells. Comparatively low proliferation rates, MDR-1 expression and an acidic tumor microenvironment further limit therapeutic options in CHS. Future advances in CHS therapy depend on the further characterization of CHS, especially the tumor immune microenvironment, for improved and better targeted therapies.

Spindle Cell Sarcoma of the Uterus Harboring MEIS1::NCOA1 Fusion Gene and Mimicking Endometrial Stromal Sarcoma

MEIS1::NCOA1/2 sarcomas are a newly recognized group of exceedingly rare low-grade spindle cell sarcomas that often involve the genitourinary and gynecologic tracts. Due to its deceptively low-grade morphology and the non-specific immunoprofile, these neoplasms may pose a diagnostic challenge by histologically mimicking other entities such as endometrial stromal sarcoma, smooth muscle tumor, or uterine perivascular epithelioid cell tumor (PEComa). Histologically, MEIS1::NCOA1/2 sarcomas typically show spindle cell proliferation with hyperchromatic nuclei and a generalized cytologic uniformity, arranged in short fascicles and exhibiting alternating zones of hypo- and hypercellularity. Among the previously reported cases, molecular analysis revealed the MEIS1::NCOA2 fusion as the most commonly detected fusion gene, whereas the MEIS1::NCOA1 fusion gene has been reported in only a single case that involved kidney. Herein we report the first case of uterine sarcoma harboring the MEIS1::NCOA1 fusion gene that was initially misclassified as low-grade endometrial stromal sarcoma, demonstrating its clinicopathologic features, and highlighting the essential role of molecular pathology to arrive at the accurate diagnosis that may alter disease classification and inform therapy.

Myoepithelial carcinoma of the parotid gland with a novel CTCF::NCOA2 fusion

We describe a case of a myoepithelial carcinoma of the superficial parotid gland in a 46-year-old male harboring a novel CTCF::NCOA2 gene fusion. To our knowledge, this novel gene fusion has not been described previously in myoepithelial carcinoma. A 46-year-old male patient presented with a mass involving the superficial left parotid gland with extension into the external auditory canal (EAC) and erosion of the conchal cartilage. Histologically, the neoplasm was composed of uniform spindled, epithelioid/ovoid cells arranged in cords and nests within hyalinized to myxoid stroma. On immunohistochemistry (IHC), the tumor cells demonstrated patchy and variable staining for low molecular weight cytokeratin (CAM5.2), pan-cytokeratin (OSCAR), and S-100. Overall, the morphological and immunohistochemical attributes supported a locally aggressive tumor of myoepithelial differentiation consistent with myoepithelial carcinoma. Molecular analysis using a custom 115-gene gene panel by targeted RNA sequencing, showed an in-frame CTCF::NCOA2 fusion. In addition to reporting this novel fusion in myoepithelial carcinoma, we also discuss relevant differential diagnosis, and provide a brief review of NCOA2 gene function in both normal and neoplastic contexts.

Novel low-grade renal spindle cell neoplasm with HEY1::NCOA2 fusion that is distinct from mesenchymal chondrosarcoma

HEY1-NCOA2 fusion is most described in mesenchymal chondrosarcoma. This is the first case report of a primary renal spindle cell neoplasm of uncertain malignant potential with a HEY1::NCOA2 fusion identified by Fusionplex RNA-sequencing that is histologically distinct from mesenchymal chondrosarcoma. The neoplasm was identified in a 33-year-old woman without significant past medical history who underwent partial nephrectomy for an incidentally discovered renal mass. The histologic features of the mass included spindle cells with variable cellularity and monotonous bland cytology forming vague fascicles and storiform architecture within a myxoedematous and collagenous stroma with areas of calcification. The morphologic and immunophenotypic features were not specific for any entity but were most similar to low-grade fibromyxoid sarcoma. To date, the patient has not had recurrence, and the malignant potential of the neoplasm is uncertain.

Exploring real-world practices and challenges of sarcoma diagnosis in Morocco: A survey-based study among 144 pathologists

BACKGROUND AND AIM

Sarcoma diagnosis is a challenge for laboratories of cytopathology and anatomic pathology. We conducted this survey-based study to better elucidate real-world practices and challenges of sarcoma diagnosis.  Methods: This was a cross-sectional study using an anonymous questionnaire. The survey was distributed among pathologists using snowball sampling. Descriptive statistics were used to report the finding of this survey.

RESULTS

A total of 144 Moroccan pathologists were surveyed. Most respondents were from academic institutions (41.7%) and those with a specialization in sarcoma diagnosis represented 57%, through training using post-graduate fellowships followed by internships abroad and inter-university diplomas. Remarkably, 36.8% of participants reported no training on sarcoma pathology during their career. Regarding frequency of sarcoma diagnosis, 64.6% of pathologists reported having received less than one case of sarcoma per week and more than 70% did not receive sufficient information from referring clinicians. The majority of pathologists reported their nonattendance in multidisciplinary meetings. Morphology and immunohistochemistry were the most frequently used diagnostic tools, while fluorescence in situ hybridization and other molecular biology techniques were accessible for only 27% and 20.1% of pathologists, respectively. Response time during pathological diagnosis of sarcoma was 14 days according to 52.8% of surveyed participants. In addition, a second opinion was needed for 66% of pathologists.

CONCLUSIONS

Specialized training on sarcoma pathology in Morocco is lacking. A national working group on sarcoma pathology is needed to provide second opinions, and therefore, improve the management of this malignancy of poor prognosis. (www.actabiomedica.it).

VGLL2-NCOA2 leverages developmental programs for pediatric sarcomagenesis

Clinical sequencing efforts are rapidly identifying sarcoma gene fusions that lack functional validation. An example is the fusion of transcriptional coactivators, VGLL2-NCOA2, found in infantile rhabdomyosarcoma. To delineate VGLL2-NCOA2 tumorigenic mechanisms and identify therapeutic vulnerabilities, we implement a cross-species comparative oncology approach with zebrafish, mouse allograft, and patient samples. We find that VGLL2-NCOA2 is sufficient to generate mesenchymal tumors that display features of immature skeletal muscle and recapitulate the human disease. A subset of VGLL2-NCOA2 zebrafish tumors transcriptionally cluster with embryonic somitogenesis and identify VGLL2-NCOA2 developmental programs, including a RAS family GTPase, ARF6. In VGLL2-NCOA2 zebrafish, mouse, and patient tumors, ARF6 is highly expressed. ARF6 knockout suppresses VGLL2-NCOA2 oncogenic activity in cell culture, and, more broadly, ARF6 is overexpressed in adult and pediatric sarcomas. Our data indicate that VGLL2-NCOA2 is an oncogene that leverages developmental programs for tumorigenesis and that reactivation or persistence of ARF6 could represent a therapeutic opportunity.

NCOA1/2/3 rearrangements in uterine tumor resembling ovarian sex cord tumor: A clinicopathological and molecular study of 18 cases

Recurrent NCOA1/2/3 gene fusions emerged in uterine tumor resembling ovarian sex cord tumor (UTROSCT). More cases are required to consolidate these molecular alterations. In this study, the clinicopathological features and immunostaining profiles were reviewed in 18 UTROSCT. Fluorescence in situ hybridization for dual color break-apart probes of NCOA1, NCOA2, NCOA3, BCOR, YWHAE, PHF1 and JAZF1 were performed on 16 tumors. Eight cases were subjected to targeted next-generation sequencing to detect genomic alterations. We found that the tumors predominantly showed various sex-cord patterns without a recognizable endometrial stromal component. They exhibited a diverse immunohistochemical profile, frequently co-expressing sex cord (calretinin, inhibin, WT1, SF-1, and FOXL2), smooth muscle (SMA, desmin and caldesmon), epithelial (CK) and other markers (CD10 and IFITM1). Fourteen of 16 tumors (87.5%) showed NCOA1-3 gene rearranges, but none had BCOR, YWHAE, PHF1 and JAZF1 fusions. Five tumors contained 6 non-recurrent pathogenic (likely) mutations and one had gains in c-MYC. Our study supports frequent NCOA1-3 rearrangements in UTROSCT. Rare, non-recurrent mutations suggest that these gene rearrangements be potential drivers in tumorigenesis. Detection of gene rearrangements can contribute to the correct interpretation of UTROSCT. However, large comparative studies with molecular tests are required to confirm these findings.

Biology and Management of High-Grade Chondrosarcoma: An Update on Targets and Treatment Options

This review provides an overview of histopathology, clinical presentation, molecular pathways, and potential new systemic treatments of high-grade chondrosarcomas (CS), including grade 2−3 conventional, dedifferentiated, and mesenchymal CS. The diagnosis of CS combines radiological and histological data in conjunction with patient clinical presentations. Conventional CS is the most frequent subtype of CS (85%) and represents about 25% of primary bone tumors in adults; they can be categorized according to their bone location into central, peripheral, and periosteal chondrosarcomas. Central and peripheral CS differ at the molecular level with either IDH1/2 mutations or EXT1/2 mutations, respectively. CDKN2A/B deletions are also frequent in conventional CS, as well as COL2A1 mutations. Dedifferentiated CS develops when low-grade conventional CS transforms into a high-grade sarcoma and most frequently exhibits features of osteosarcoma, fibrosarcoma, or undifferentiated pleomorphic sarcoma. Their molecular characteristics are similar to conventional CS. Mesenchymal CS is a totally different pathological entity exhibiting recurrent translocations. Their clinical presentation and management are different too. The standard treatment of CSs is wide en-bloc resection. CS are relatively radiotherapy resistant; therefore, doses >60 Gy are needed in an attempt to achieve local control in unresectable tumors. Chemotherapy is possibly effective in mesenchymal chondrosarcoma and is of uncertain value in dedifferentiated chondrosarcoma. Due to resistance to standard anticancer agents, the prognosis is poor in patients with metastatic or unresectable chondrosarcomas. Recently, the refined characterization of the molecular profile, as well as the development of new treatments, allow new therapeutic options for these rare tumors. The efficiency of IDH1 inhibitors in other malignancies suggests that these inhibitors will be part of IDH1/2 mutated conventional CS management soon. Other treatment approaches, such as PIK3-AKT-mTOR inhibitors, cell cycle inhibitors, and epigenetic or immune modulators based on improving our understanding of CS molecular biology, are emerging.

Molecular testing of soft tissue tumors

BACKGROUND

The diagnosis of soft tissue tumors is challenging, especially when the evaluable material procured is limited. As a result, diagnostic ancillary testing is frequently needed. Moreover, there is a trend in soft tissue pathology toward increasing use of molecular results for tumor classification and prognostication. Hence, diagnosing newer tumor entities such as CIC-rearranged sarcoma explicitly requires molecular testing. Molecular testing can be accomplished by in situ hybridization, polymerase chain reaction, as well as next generation sequencing, and more recently such testing can even be accomplished leveraging an immunohistochemical proxy.

CONCLUSION

This review evaluates the role of different molecular tests in characterizing soft tissue tumors belonging to various cytomorphologic categories that have been sampled by small biopsy and cytologic techniques.

Metastatic mesenchymal chondrosarcoma showing a sustained response to cabozantinib: A case report

Mesenchymal chondrosarcoma is a rare and aggressive sarcoma subtype with high risk for distant metastases and poor prognosis. Currently NCCN- and ESMO-Guidelines recommend using Ewing sarcoma protocols as standard treatment. Nevertheless, in localized disease overall 5-year survival rates are below 50% whereas in metastatic spread median progression-free survival rates of only 5 months can be expected. Here we present a patient with metastatic osseous spread of mesenchymal chondrosarcoma that showed a sustained clinical improvement and a good partial response on imaging over a period of one year when treated with the multi-tyrosine kinase inhibitor cabozantinib. Although we cannot explain the exact mechanism underlying this treatment effect, tumors with similar genetic patterns might respond to the same therapy as well.

Melanoma cell plasticity poses diagnostic challenges: a case series

Phenotype switching is an emerging concept in melanoma research and deals with the cancer cell plasticity. In this paper, we present five cases of patients with metastatic malignant melanoma where the tumor underwent dramatic morphological and immunohistochemical changes thereby mimicking other types of malignancies. The diagnosis of melanoma in all these cases was based on the mutational profile of the tumor assessed by next-generation sequencing compared to the primary lesion or local regional lymph nodes. These cases highlight the importance of thorough diagnostic measures in patients with metastatic melanoma who show progressive disease and where basic pathological assessment shows a diagnostic discrepancy.

ZFP64::NCOA3 gene fusion defines a novel subset of spindle cell rhabdomyosarcoma

Spindle cell rhabdomyosarcoma represents a rare neoplasm characterized by monomorphic spindle cells with a fascicular architecture and variable skeletal muscle differentiation. Following incidental identification of a ZFP64::NCOA3 gene fusion in an unclassified spindle cell sarcoma resembling adult-type fibrosarcoma, we performed a retrospective archival review and identified four additional cases with a similar histology and identical gene fusion. All tumors arose in adult males (28-71 years). The neoplasms were found in the deep soft tissues, two were gluteal, and one each arose in the thigh, abdominal wall, and chest wall. Morphologically, the tumors were characterized by spindle cells with a distinctive herringbone pattern and variable collagenous to myxoid stroma. The nuclei were relatively monomorphic with variable mitotic activity. Three tumors had immunoreactivity for MyoD1, and four contained variable expression of desmin and smooth muscle actin. All cases tested for myogenin, CD34, S100, pankeratin, and epithelial membrane antigen were negative. Targeted RNA sequencing revealed a ZFP64::NCOA3 fusion product in all five tumors. Three patients developed distant metastases, and two ultimately succumbed to their disease within 2 years of initial diagnosis. This study suggests ZFP64::NCOA3 fusions define a novel subtype of rhabdomyosarcoma with a spindle cell morphology and aggressive clinical behavior. The potential for morphologic and immunohistochemical overlap with several other sarcoma types underscores the value of molecular testing as a diagnostic adjunct to ensure accurate classification and management of these neoplasms.

Mesenchymal chondrosarcoma of the head and neck with HEY1::NCOA2 fusion: A clinicopathologic and molecular study of 13 cases with emphasis on diagnostic pitfalls

BACKGROUND

Mesenchymal chondrosarcoma (MCS) is a rare translocation-associated sarcoma, driven by a canonical HEY1::NCOA2 fusion. The tumors typically have a biphasic phenotype of primitive small blue round cells intermixed with hyaline cartilage. The head and neck (HN) region is a common site for MCS, accounting for 12-45% of all cases reported.

AIMS

We assembled a relatively large cohort of 13 molecularly confirmed HN MCS for a detailed clinicopathologic analysis. The underlying fusion events were determined using fluorescence in situ hybridization and/or targeted RNA sequencing.

RESULTS

The median age of presentation was 19 years. Five MCSs (39%) had an intraosseous presentation (skull, maxilla, palate, and mandible), while the remaining eight cases occurred in the brain/meninges, orbit, and nasal cavity. Microscopically, HN MCSs were characterized by primitive round cells arranged in a distinctive nested architecture and a rich staghorn vasculature. A cartilaginous component of hyaline cartilage islands and/or single chondrocytes were present in 69% cases. A combined immunoprofile of CD99(+)/SATB2(+)/CD34(-)/STAT6(-) was typically noted. As this immunoprofile is non-specific, the referral diagnoses in cases lacking a cartilaginous component included Ewing sarcoma family and osteosarcoma. Among the seven patients with follow-up data, three developed distant metastasis and one died of disease.

CONCLUSION

HN MCS may arise at intra- or extra-osseous sites. The HN MCS appears to have a more prolonged survival compared other MCS sites. Testing for HEY1::NCOA2 fusion is recommended in HN tumors with nested round cell morphology and staghorn vasculature that lack a distinctive cartilaginous component.

Small round cell sarcomas

Undifferentiated small round cell sarcomas (SRCSs) of bone and soft tissue comprise a heterogeneous group of highly aggressive tumours associated with a poor prognosis, especially in metastatic disease. SRCS entities mainly occur in the third decade of life and can exhibit striking disparities regarding preferentially affected sex and tumour localization. SRCSs comprise new entities defined by specific genetic abnormalities, namely EWSR1-non-ETS fusions, CIC-rearrangements or BCOR genetic alterations, as well as EWSR1-ETS fusions in the prototypic SRCS Ewing sarcoma. These gene fusions mainly encode aberrant oncogenic transcription factors that massively rewire the transcriptome and epigenome of the as yet unknown cell or cells of origin. Additional mutations or copy number variants are rare at diagnosis and, depending on the tumour entity, may involve TP53, CDKN2A and others. Histologically, these lesions consist of small round cells expressing variable levels of CD99 and specific marker proteins, including cyclin B3, ETV4, WT1, NKX3-1 and aggrecan, depending on the entity. Besides locoregional treatment that should follow standard protocols for sarcoma management, (neo)adjuvant treatment is as yet ill-defined but generally follows that of Ewing sarcoma and is associated with adverse effects that might compromise quality of life. Emerging studies on the molecular mechanisms of SRCSs and the development of genetically engineered animal models hold promise for improvements in early detection, disease monitoring, treatment-related toxicity, overall survival and quality of life.

Patient-derived xenografts and in vitro model show rationale for imatinib mesylate repurposing in HEY1-NCoA2-driven mesenchymal chondrosarcoma

Mesenchymal chondrosarcoma (MCS) is a high-grade malignancy that represents 2-9% of chondrosarcomas and mostly affects children and young adults. HEY1-NCoA2 gene fusion is considered to be a driver of tumorigenesis and it has been identified in 80% of MCS tumors. The shortage of MCS samples and biological models creates a challenge for the development of effective therapeutic strategies to improve the low survival rate of MCS patients. Previous molecular studies using immunohistochemical staining of patient samples suggest that activation of PDGFR signaling could be involved in MCS tumorigenesis. This work presents the development of two independent in vitro and in vivo models of HEY1-NCoA2-driven MCS and their application in a drug repurposing strategy. The in vitro model was characterized by RNA sequencing at the single-cell level and successfully recapitulated relevant MCS features. Imatinib, as well as specific inhibitors of ABL and PDGFR, demonstrated a highly selective cytotoxic effect targeting the HEY1-NCoA2 fusion-driven cellular model. In addition, patient-derived xenograft (PDX) models of MCS harboring the HEY1-NCoA2 fusion were developed from a primary tumor and its distant metastasis. In concordance with in vitro observations, imatinib was able to significantly reduce tumor growth in MCS-PDX models. The conclusions of this study serve as preclinical results to revisit the clinical efficacy of imatinib in the treatment of HEY1-NCoA2-driven MCS.

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.

Mesenchymal chondrosarcoma: An Australian multi-centre cohort study

BACKGROUND

Mesenchymal chondrosarcoma (MCS) is an ultra-rare sarcoma that follows a more aggressive course than conventional chondrosarcoma. This study evaluates prognostic factors, treatments (surgery, chemotherapy, and radiation), and outcomes in an Australian setting.

METHODS

We collected demographics, clinicopathological variables, treatment characteristics, and survival status from patients with MCS registered on the national ACCORD sarcoma database. Outcomes include overall survival (OS) and progression-free survival (PFS).

RESULTS

We identified 22 patients with MCS between 2001-2022. Median age was 28 (range 10-59) years, 19 (86%) had localised disease at diagnosis of whom 16 had surgery (84%), 11 received radiation (58%), and 10 chemotherapy (53%). Ten (52%) developed recurrence and/or metastases on follow-up and three patients with initial metastatic disease received surgery, radiation, and chemotherapy. At a median follow-up of 50.9  (range 0.4-210) months nine patients had died. The median OS was 104.1 months (95% CI 25.8-182.3). There was improved OS for patients with localised disease who had surgical resection of the primary (p = 0.003) and those with ECOG 0-1 compared to 2-3 (p = 0.023) on univariate analysis.

CONCLUSIONS

This study demonstrates contemporary Australian treatment patterns of MCS. The role of chemotherapy for localised disease remains uncertain. Understanding treatment patterns and outcomes help support treatment decisions and design of trials for novel therapeutic strategies.

Pigmented PRRX1::NCOA1-rearranged Fibroblastic Tumor: A Rare Morphologic Variant of an Emerging Mesenchymal Tumor

PRRX::NCOAx-rearranged fibroblastic tumor is a recently described, morphologically distinctive subcutaneous fibroblastic tumor with benign behavior. To date, 12 cases have been reported. Here, we report a new case of PRRX::NCOAx-rearranged fibroblastic tumor showing a prominent pigmented component. The lesion occurred on the shoulder of a 23-year-old male. It was an at least 2.5 cm subcutaneous tumor with a multinodular and plexiform appearance. Morphologically, the tumor was characterized by a variably cellular proliferation of uniform oval to spindle cells arranged in fascicles and cords within a myxo-collagenous stroma. Irregular, elongated, dilated vessels were prominent at the periphery of tumor nodules. In addition, nests and clusters of pigment-laden epithelioid and dendritic cells were present. Immunohistochemically, the non-pigmented tumor cells showed patchy positivity for factor XIIIa and focal positivity for S100 protein. The pigmented cells were positive for S100 protein, SOX10, MITF, and a pan-melanocytic cocktail (Melan A, HMB-45, and tyrosinase). Next-generation RNA sequencing identified an in-frame PRRX1::NCOA1 fusion. In summary, this case highlights a rare pigmented variant of PRRX::NCOAx-rearranged fibroblastic tumor, expanding the morphologic spectrum of this newly described mesenchymal tumor. This article is protected by copyright. All rights reserved.

The Small Round Cell Sarcomas Complexities and Desmoplastic Presentation

Background

Small round cell sarcomas (SRCSs) account for most solid malignancies in the pediatric age group and are a part of group of malignant tumors characterized by heterogenous clinical presentation and overlapping microscopic features of small, round, primitive cells. In addition to the recently established certain genetically defined subset of undifferentiated round cell sarcomas of soft tissue and bone, this group of sarcomas include desmoplastic small round cell tumor, poorly differentiated synovial sarcoma, alveolar rhabdomyosarcoma, mesenchymal chondrosarcoma, and small cell osteosarcoma. Although, those entities share clinical and cytomorphologic features and cannot be unequivocally classified based on clinical presentation and morphology alone. Most of SRCSs characterizes of particular patterns of protein expression or genetic changes and ancillary tests remain necessary to confirm or rule out a specific diagnosis. Subtle but occasionally distinctive cytologic features narrows the number of differential diagnoses and helps to select appropriate ancillary tests necessary for the final diagnosis. Thus, when adequate fine needle aspiration (FNA) biopsy specimen is combined with ancillary tests, a specific histologic diagnosis can be made in almost all cases. However, due to complex cytologic features of SRCS as well as various quality and diversity of FNA smears, there are cases in that cytologic features which do not entirely match the known diagnostic criteria.

Summary

The aim of this review was to summarize cytomorphologic criteria and to present rare and divergent cytological features of SRCSs. Careful assessment of clinical presentation, cytological features, immunohistochemical patterns, and molecular alternations is necessary for an accurate diagnosis. Knowing of rare and divergent microscopic findings that does not fit with the known cytological criteria will help to avoid misdiagnosis.

Key Messages

The role of FNA biopsies diagnosing soft tissue and bone tumors has been increasing because of the ability of ancillary tests to assist in the diagnosis of specific tumors. SRCSs may be diagnosed accurately in cytology specimens. Access to clinical and radiographic presentation, utility of ancillary tests, understanding complexity of cytological features, and awareness of the rare cytologic findings that differ from that of the established diagnostic criteria are essential to make correct diagnosis.

Genomic profiling identifies genes and pathways dysregulated by HEY1-NCOA2 fusion and shines a light on mesenchymal chondrosarcoma tumorigenesis

Mesenchymal chondrosarcoma is a rare, high‐grade, primitive mesenchymal tumor. It accounts for around 2–10% of all chondrosarcomas and mainly affects adolescents and young adults. We previously described the HEY1–NCOA2 as a recurrent gene fusion in mesenchymal chondrosarcoma, an important breakthrough for characterizing this disease; however, little study had been done to characterize the fusion protein functionally, in large part due to a lack of suitable models for evaluating the impact of HEY1–NCOA2 expression in the appropriate cellular context. We used iPSC‐derived mesenchymal stem cells (iPSC‐MSCs), which can differentiate into chondrocytes, and generated stable transduced iPSC‐MSCs with inducible expression of HEY1–NCOA2 fusion protein, wildtype HEY1 or wildtype NCOA2. We next comprehensively analyzed both the DNA binding properties and transcriptional impact of HEY1–NCOA2 expression by integrating genome‐wide chromatin immunoprecipitation sequencing (ChIP‐seq) and expression profiling (RNA‐seq). We demonstrated that HEY1–NCOA2 fusion protein preferentially binds to promoter regions of canonical HEY1 targets, resulting in transactivation of HEY1 targets, and significantly enhances cell proliferation. Intriguingly, we identified that both PDGFB and PDGFRA were directly targeted and upregulated by HEY1‐NCOA2; and the fusion protein, but not wildtype HEY1 or NCOA2, dramatically increased the level of phospho‐AKT (Ser473). Our findings provide a rationale for exploring PDGF/PI3K/AKT inhibition in treating mesenchymal chondrosarcoma. © 2022 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Primary intra- and extradural extramedullary mesenchymal chondrosarcoma with isolated punctate calcification: case report and literature review

Background

Mesenchymal chondrosarcoma (MCS) is an ultra-rare, high-grade subtype of chondrosarcoma affecting both bone and soft tissues. Extra-skeletal MCS rarely occurs in intra- and extradural regions.

Case presentation

We presented a case of intraspinal dumbbell-shaped MCS at the T12-L2 level with isolated punctate calcification in a 19-year-old male complaining of progressive lower back pain. Surgical treatment for removal of the tumor was performed. The postoperative pathological result confirmed MCS. The patient showed symptomatic improvement and follow-up MRI showed no evidence of recurrence or metastasis for nearly 1 year after surgery.

Conclusions

CT and MRI play an important role in differential diagnosis for intraspinal MCS. MCS should be added to the differential diagnosis of intraspinal dumbbell-shaped tumors, especially when radiological examinations reveal punctate calcification in a homogeneous enhanced tumor without dural tail sign. However, the final diagnosis depends on histopathological results. Despite the good prognosis of intraspinal MCS, close follow-up after operation is still necessary.

[Fusion-related round and spindle cell sarcomas of the bone (beyond Ewing)]

Round cell sarcomas represent a diagnostic challenge for pathologists due to the poorly differentiated pattern of these high-grade tumors. Their diagnosis often requires large immunohistochemical panels and the use of molecular pathology. These tumors are largely dominated by Ewing sarcomas, but new families are now well characterized, including in decreasing frequency order in bone, BCOR-altered sarcomas, NFATc2-rearranged sarcomas, mesenchymal chondrosarcomas and more rarely CIC-rearranged sarcomas and myoepithelial tumors. This progress report presents microscopic, immunohistochemical and molecular features of these tumors previously named by the inappropriate term "Ewing-like" sarcomas, in order to enable any pathologist to perceive the morphological features of these sarcomas, to select the immunohistochemical panel that will lead to the diagnosis and to better guide the molecular approach needed to establish the final diagnosis.

Primary Chondrosarcoma in L-shaped Crossed Fused Renal Ectopia Coexisting with Papillary Urothelial Carcinoma in Urinary Bladder - An Enigmatic Entity with Poor Prognosis

Primary renal chondrosarcomas are rare tumors that are high-grade in nature and, unfortunately, have poorly understood pathogenesis and extremely low prognosis. The coexistence of a discrete malignancy in the urinary bladder is even rarer, with the occurrence of distinct papillary urothelial carcinoma in the urinary bladder in this case. The clinical presentation is nonspecific, and the primary radiological investigations have a limited scope in providing specific diagnosis of this entity. The final diagnosis is possible on thorough histopathological examination of the resected specimen, which requires extensive sampling and meticulous reporting. As of now, the only way to achieve a better prognosis is by early diagnosis. It is necessary to keep the possibility of occurrence of sarcomas at rare sites in the differential diagnoses. The cytogenetic and molecular abnormalities associated with this entity need to be elucidated to achieve a more satisfactory outcome concerning the overall management of the patient.

Update of Key Clinical, Histological and Molecular Features of Malignant Bone Tumours Arising in the Craniofacial Skeleton

The craniofacial skeleton is a highly complex and specialized anatomic region containing and protecting the brain and sensory organs. Bone sarcomas arising here comprise a heterogeneous group of tumours, some of which differ in their biological behaviour compared to their peripheral counterparts. The reasons for this seem to lie, at least partially, in the embryonal development of the craniofacial bones. For reaching the correct diagnosis as the cornerstone of optimal personalised treatment planning, a multidisciplinary team of specialists, including pathologists, radiologists, oncologists, and head and neck surgeons needs to be involved. The most common tumours arising in the craniofacial bones are bone-forming tumours, cartilage-forming tumours, fibro-osseous lesions, giant cell-rich lesions, and notochordal tumours. While morphology remains the backbone for the diagnosis, the last decade has witnessed tremendous advances in the molecular characterization of tumours, and molecular testing is increasingly becoming a part of the diagnostic process. The integration of these new molecular markers into the diagnostic approach has undoubtedly increased the diagnostic accuracy and objectivity, and holds great promise to also identify new therapeutic targets for precision medicine in the future. Examples include HEY1-NCOA2 in mesenchymal chondrosarcoma, IDH1/2 mutations in chondrosarcoma and TFCP2 rearrangements in rhabdomyosarcoma. In this article, key clinical, histological and molecular features of malignant bone tumours arising in the craniofacial region are discussed, with a special focus on the differential diagnosis and prognostic considerations.

Diagnosis of soft tissue tumors using immunohistochemistry as a surrogate for recurrent fusion oncoproteins

Soft tissue neoplasms encompass a broad spectrum of clinicopathologic manifestations. In a subset of soft tissue tumors, spanning a wide range of clinical behavior from indolent to highly aggressive, recurrent genetic translocations yield oncogenic fusion proteins that drive neoplastic growth. Beyond functioning as primary mechanisms of tumorigenesis, recurrent translocations represent key diagnostic features insofar as the presence of a particular oncogenic gene fusion generally points to specific tumor entities. In addition to more direct methods for identifying recurrent translocations, such as conventional cytogenetics or fluorescence in situ hybridization, immunohistochemistry for a component of the fusion oncoprotein increasingly is being used as a surrogate marker, exploiting the tendency of these fusion components to be distinctively overexpressed by translocation-bearing tumor cells. Diagnostic immunohistochemistry can also be used to identify the characteristic gene expression changes that occur downstream of oncogenic fusions. Here, we review the use of immunohistochemistry to detect surrogate markers of recurrent translocations in soft tissue tumors, focusing on the practical applications and limitations of this diagnostic approach.