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.

Detection of mesenchymal chondrosarcoma in pleural effusion with immunocytochemistry and determination of HEY1::NCOA2 fusion by next-generation sequencing on cell block.

Mesenchymal chondrosarcoma (MC) is a rare but extremely aggressive type of chondrosarcoma distinguished by the presence of both primitive mesenchymal cells and fully developed chondroid tissue. The identification of a biphasic morphology in pleural effusion, along with detection of the HEY1::NCOA2 fusion using next-generation sequencing, serve as vital indicators for an accurate diagnosis.

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.

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.

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.

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.

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.

A mesenchymal chondrosarcoma with aberrant nuclear expression of STAT6: a potential diagnostic pitfall.

STAT6 is usually considered to be a very sensitive and specific immunomarker for diagnosis of solitary fibrous tumor (SFT), being a surrogate of the NAB2-STAT6 fusion gene identified in most cases of this tumor. STAT6 expression has also been reported in rare cases of other soft tissue tumors, such as low-grade fibromyxoid sarcoma, myxoid/round cell liposarcoma, dedifferentiated liposarcoma and deep fibrous histiocytoma. The aim of this study was to report, for the first time, a case of mesenchymal chondrosarcoma showing diffuse aberrant immunohistochemical expression of STAT6. Molecular biology, showing the HEY1-NCOA2 fusion gene, was crucial to rule out SFT.

Mesenchymal PLAG1 Tumor With PCMTD1-PLAG1 Fusion in an Infant: A New Type of "Plagoma".

ABSTRACT: In the past decade, there have been major advances in knowledge related to mesenchymal tumors, and new genetic alterations are being delineated. We report a mesenchymal spindle cell neoplasm harboring a novel gene fusion in an infant. Histopathologically, the neoplasm shared some features with sclerosing perineurioma, but immunohistochemically, EMA was negative, whereas GLUT1, NK1-C3, and BCOR were positive. Next-generation sequencing revealed a PCMTD1-pleomorphic adenoma gene 1 (PLAG1) fusion. PLAG1 contributes to the expression of a variety of genes implicated in regulating cell proliferation, and PCMTD1 has been related to the development of certain carcinomas. Recently, other soft tissue tumors in young children associated with PLAG1 fusion variants have been reported. Perhaps, mesenchymal neoplasms presenting PLAG1 fusions with different genes would confirm a specific group (PLAG mesenchymal tumours or "plagomas") in the near future.

[Extraskeletal mesenchymal chondrosarcoma in central nerve system: a clinicopathological analysis].

Objective: To investigate the clinicopathological features, immunophenotype, molecular genetics and prognosis of extraskeletal mesenchymal chondrosarcoma in central nerve system (CNS). Methods: The clinicopathological findings, immunohistochemistry and genetic analysis of four cases of extraskeletal mesenchymal chondrosarcoma in Xuanwu Hospital between 2014 and 2019 were reviewed and followed up. Results: The ages of patients ranged from 20-35 years. Three patients had intracranial lesions and one had intradural tumor. The characteristic histologic features were undifferentiated small cells together with scattered islands of hyaline cartilage. There was hemangiopericytoma-like pattern with calcification and ossification. The tumor cells were positive for VIM and SOX9; and the small cells were positive for CD99, NSE and NKX3.1. The cells in chondroid matrix were positive for S-100. All tumor cells were negative for markers including CKpan, EMA and desmin. At molecular analysis, HEY1-NCOA2 fusion transcripts were identified in three patients. The fusion points were between exon 4 of HEY1 and exon 13 of NCOA2. Follow-up information was obtained in two patients, and both were free from recurrence or metastasis at 8 and 20 months. Conclusions: Extraskeletal mesenchymaI chondrosarcoma is a rare CNS disease with poor prognosis. In addition to SOX9, NKX3.1 can be another useful antibody for the differential diagnosis. The combination of pathological characteristics, immunophenotype and genetic profile of tumor is essential for diagnosis.

[Mesenchymal chondrosarcoma in central nervous system: a clinicopathological analysis].

Objective: To investigate the clinicopathological features of central nervous system (CNS) mesenchymal chondrosarcoma (MCS). Methods: Nine cases of CNS MCS were collected at the First Affiliated Hospital of Fujian Medical University from September 2010 to September 2020. The clinical,imaging,histopathological and immunohistochemical features were reviewed. NCOA2 gene rearrangement was evaluated by fluorescence in situ hybridization (FISH). Results: There were three male and six female patients, with age range of 1 to 59 years (median 31 years). Six cases were intracranial and three cases were intraspinal, and the tumors showed dural attachment. They were often diagnosed as meningioma basing on preoperative imaging. Microscopically, the tumors showed a characteristic biphasic histologic pattern composed of undifferentiated mesenchymal small cells and well-differentiated hyaline cartilage islands. The small cells area were positive for SOX9 (9/9), CD99 (8/9), and without BRG1 and INI1 deletion. The cartilaginous component expressed SOX9 (9/9) and S-100 protein (8/9). NCOA2 gene break apart signal was identified in five cases (5/5). Eight patients were followed up for 4-124 months. Three patients (3/8) had recurrences within one year and two patients died of the tumor. Conclusions: CNS MCS is an extremely rare malignant neoplasm with a propensity to dural involvement. Preoperative imaging has low diagnostic accuracy. CNS MCS should be differentiated from other CNS small round cell tumors and chondrosarcoma. FISH detection of NCOA2 gene rearrangement will assist the diagnosis of MCS.

Clinical Efficacy of Olaparib in IDH1/IDH2-Mutant Mesenchymal Sarcomas.

PURPOSE: Tumors with neomorphic mutations in IDH1/2 have defective homologous recombination repair, resulting in sensitivity to poly (ADP-ribose) polymerase (PARP) inhibition. The Olaparib Combination trial is a phase II, open-label study in which patients with solid tumors harboring IDH1/2 mutations were treated with olaparib as monotherapy, with objective response and clinical benefit rates as the primary end points. METHODS: Ten patients with IDH1/2-mutant tumors by next-generation sequencing were treated with olaparib 300 mg twice daily. RESULTS: Three of five patients with chondrosarcomas had clinical benefit, including one patient with a partial response and two with stable disease lasting > 7 months. A patient with pulmonary epithelioid hemangioendothelioma had stable disease lasting 11 months. In contrast, clinical benefit was not observed among four patients with cholangiocarcinoma. CONCLUSION: These results indicate preliminary activity of PARP inhibition in patients with IDH1/2-mutant chondrosarcoma and pulmonary epithelioid hemangioendothelioma. Further studies of PARP inhibitors alone and in combination in this patient population are warranted.

OLIG2 Immunolabeling of Mesenchymal Chondrosarcoma: Report of 14 Cases.

Mesenchymal chondrosarcoma (MC) is a rare aggressive mesenchymal sarcoma. Specific markers for the differential diagnosis of MCs remain to be developed. OLIG2 expression has been reported only in neuroepithelial tumors. Recently, OLIG2 expression was found to be involved in the development of NCOA2 fusion-positive alveolar rhabdomyosarcomas. Therefore, we investigated whether OLIG2 expression could be used as a diagnostic marker for MC. We report the clinical pathological and immunohistochemical features of 14 MCs. All tumors showed typical pathological features including biphasic patterns with sheets of primitive round mesenchymal cells and interspersed islands of cartilage. These tumors expressed BCL2, SOX9, and CD99. OLIG2 was robustly expressed in 12/14 of MCs. NCOA2 rearrangement was found in 12 cases. OLIG2 expression was not found in the NCOA2 rearrangement-negative MCs. Notably, OLIG2 expression was not detected in 52 neoplasms (8 Ewing sarcomas, 23 hemangiopericytomas, and 21 chondrosarcomas) that are frequently misdiagnosed as MC. Our findings provide convincing evidence that OLIG2 can serve as a reliable marker in the differential diagnosis of MC and may be a unique neurodevelopmental gene expression signature for the NCOA2 rearranged MCs.

Primary intradural extramedullary spinal mesenchymal chondrosarcoma: case report and literature review.

BACKGROUND: Mesenchymal chondrosarcoma (MCS) is a rare malignant variant of chondrosarcoma with a high tendency of recurrence and metastasis. Intradural extramedullary spinal MCS is exceedingly rare and usually found in pediatric patients. Herein, we present an elderly patient with primary intradural extramedullary spinal MCS. Relevant literatures are reviewed to disclose characteristics of intradural extramedullary spinal MCS. CASE PRESENTATION: A 64-year-old female presented with urinary difficulty and tightness of upper back preceding progressive weakness of right lower extremity. Magnetic resonance imaging revealed an intradural extramedullary tumor at the level of 3rd thoracic vertebra. This patient underwent total tumor resection and then received adjuvant radiotherapy. Histopathological examination showed that the tumor composed of spindle and round cells with high nucleocytoplasmic ratio accompanied by scattered eosinophilic chondroid matrix. Along with immunohistochemical findings and the existence of HEY1-NCOA2 fusion transcript, the diagnosis of MCS was confirmed. Neurologic deficit recovered nearly completely after surgery. No evidence of local recurrence or distant metastasis was found 5 years after treatments. Including the current case, a total of 18 cases have been reported in the literature with only one case with local recurrence and one case of mortality. The current case was the eldest patient diagnosed with primary intraspinal MCS in the literature. CONCLUSIONS: MCS rarely appears in the intradural space of the spine. In contrast to classic MCS, treatment outcome of primary intradural extramedullary spinal MCS is usually excellent as total tumor resection is commonly achievable. Adjuvant radiotherapy may reduce local recurrence and chemotherapy may be associated with fewer recurrences especially for unresectable tumors.

Primary paediatric epidural sarcomas: molecular exploration of three cases.

BACKGROUND: Primary paediatric epidural sarcomas are extremely rare. Overall, there remains a paucity of knowledge in paediatric epidural sarcomas owing to the infrequent number of cases. The Archer FusionPlex Sarcoma Kit (ArcherDX, Inc) is a next-generation sequencing assay that has been reported to be a useful technique to detect recurrent fusion in sarcomas. We report the molecular exploration of 3 primary paediatric epidural sarcomas-one in the cranium (mesenchymal chondrosarcoma) and 2 in the spine (mesenchymal chondrosarcoma and Ewing sarcoma respectively). CASE PRESENTATION: This is a study approved by the hospital ethics board. Clinico-pathological information from 3 consenting patients with primary epidural sarcomas was collected. These selected tumours are interrogated via Archer FusionPlex Sarcoma Kit (ArcherDX, Inc) for genomic aberrations. Results were validated with RT-PCR and Sanger sequencing. All findings are corroborated and discussed in concordance with current literature. Our findings show 2 variants of the HEY1-NCOA2 gene fusion: HEY1 (exon 4)-NCOA2 (exon 13) and HEY1 (exon 4)-NCOA2 (exon 14), in both mesenchymal chondrosarcoma patients. Next, the Ewing sarcoma tumour is found to have EWSR1 (exon 10)-FLI1 (exon 8) translocation based on NGS. This result is not detected via conventional fluorescence in situ testing. CONCLUSIONS: This is a molecularly-centered study based on 3 unique primary paediatric epidural sarcomas. Our findings to add to the growing body of literature for these exceptionally rare and malignant neoplasms. The authors advocate global collaborative efforts and in-depth studies for targeted therapy to benefit affected children.

Establishment and characterization of a novel dedifferentiated chondrosarcoma cell line, NCC-dCS1-C1.

Dedifferentiated chondrosarcoma is an aggressive mesenchymal tumor of the bone, and novel therapies are needed to improve its clinical outcomes. Patient-derived cell lines are essential tools for elucidating disease mechanisms associated with poor prognosis and for developing therapies. However, few lines and xenografts have been previously reported in dedifferentiated chondrosarcoma. We established a novel patient-derived dedifferentiated chondrosarcoma cell line, NCC-dCS1-C1. Primary dedifferentiated chondrosarcoma tissues were obtained at the time of surgery and subjected to primary tissue culture. The cell line was established and authenticated by assessing DNA microsatellite short tandem repeats. The cells maintained in monolayer cultures exhibited constant growth, spheroid formation capacity, and invasion ability. When the cells were implanted into mice, they exhibited histological features similar to those of the original tumor. Genomic analysis of single nucleotide polymorphisms showed aberrant genomic contents. The DNA sequencing revealed the absence of IDH1/2 mutations. The global targeted sequencing revealed that the cell line preserved homozygous deletion of CDKN2A and CREBBP. A proteomic study by mass spectrometry unveiled similar but distinct molecular backgrounds in the original tumor and the established cell line, suggesting that tumor cell functions might be altered during the establishment of the cell line. Using a screening approach, four anti-cancer drugs with anti-proliferative effects at a low concentration were identified. In conclusion, a novel dedifferentiated chondrosarcoma cell line, NCC-dCS1-C1, was successfully established from primary tumor tissues. The NCC-dCS1-C1 cell line will be a useful tool for investigations of the mechanisms underlying dedifferentiated chondrosarcomas.

Minute mesenchymal chondrosarcoma within osteochondroma: an unexpected diagnosis confirmed by HEY1-NCOA2 fusion.

Mesenchymal chondrosarcoma is rare and can be challenging to diagnose. Herein, we report a minute mesenchymal chondrosarcoma within an osteochondroma. A 12-year-old girl presented with an asymptomatic exophytic lesion of the rib. The tumor was clinically diagnosed as osteochondroma and was excised after observation for 3 years. The resected specimen revealed an unexpected minute (0.9 cm) "monophasic" mesenchymal chondrosarcoma in the apex of the lesion. The sarcoma consisted of monomorphic spindle cells without hyaline cartilage. Fluorescence in situ hybridization detected NCOA2 rearrangement, and reverse-transcription polymerase chain reaction and sequencing detected a HEY1 (exon 4)-NCOA2 (exon 13) fusion transcript. The patient did not receive adjuvant therapy and is alive with no recurrence 6 years after surgery. The present case highlights the value of careful pathological examination of specimens submitted as osteochondroma and emphasizes the usefulness of molecular assays in the diagnosis of mesenchymal chondrosarcoma in an atypical setting.

Mesenchymal Chondrosarcoma: a Review with Emphasis on its Fusion-Driven Biology.

Mesenchymal chondrosarcoma is a rare but deadly form of chondrosarcoma that typically affects adolescents and young adults. While curative intent is possible for patients with localized disease, few options exist for patients in the unresectable/metastatic setting. Thus, it is imperative to understand the fusion-driven biology of this rare malignant neoplasm so as to lead to the future development of better therapeutics for this disease. This manuscript will briefly review the clinical and pathologic features of mesenchymal chondrosarcoma followed by an appraisal of existing data linked to the fusions, HEY1-NCOA2 and IRF2BP2-CDX1, and the associated downstream pathways.

Integrating Morphology and Genetics in the Diagnosis of Cartilage Tumors.

Cartilage-forming tumors of bone are a heterogeneous group of tumors with different molecular mechanisms involved. Enchondromas are benign hyaline cartilage-forming tumors of medullary bone caused by mutations in IDH1 or IDH2. Osteochondromas are benign cartilage-capped bony projections at the surface of bone. IDH mutations are also found in dedifferentiated and periosteal chondrosarcoma. A recurrent HEY1-NCOA2 fusion characterizes mesenchymal chondrosarcoma. Molecular changes are increasingly used to improve diagnostic accuracy in chondrosarcomas. Detection of IDH mutations or HEY1-NCOA2 fusions has already proved their immense value, especially on small biopsy specimens or in case of unusual presentation.