Primary spinal intramedullary Ewing-like sarcoma harboring CIC-DUX4 translocation: a similar cytological appearance as its soft tissue counterpart but no lobulation in association with desmoplastic stroma

Primary Central Nervous System Mesenchymal Neoplasms in the Pediatric Population-An Update

This article reviews the latest updates in the classification and understanding of pediatric primary central nervous system mesenchymal tumors. It highlights changes in the World Health Organization Classification, including new tumor entities and refined prognostic criteria. Also, the review emphasizes the need for continued research to address diagnostic challenges and improve therapeutic approaches for these rare tumors.

CIC/ATXN1-rearranged tumors in the central nervous system are mainly represented by sarcomas: A comprehensive clinicopathological and epigenetic series

CIC fusions have been described in two different central nervous system (CNS) tumor entities. On one hand, fusions of CIC or ATXN1 genes belonging to the same complex of transcriptional repressors, were reported in the CIC-rearranged, sarcoma (SARC-CIC). The diagnosis of this tumor type, which was recently added to the World Health Organization (WHO) Classification of CNS tumors, is difficult mainly because the data concerning its histopathology (as compared to its soft tissue counterpart), immunoprofile, and clinical as well as radiological characteristics are scarce in the literature. On the other hand, a recent study, based on DNA-methylation profiling, has identified a novel high-grade neuroepithelial tumor characterized by recurrent CIC fusions (HGNET-CIC). The aim of this multicentric study was to characterize a cohort of 15 primary CNS tumors harboring a CIC or ATXN1 fusion in terms of clinical, radiological, histopathological, immunophenotypical, and epigenetic characteristics. According to the integrated diagnoses, 14/15 tumors corresponded to SARC-CIC, and only one to HGNET-CIC. The tumors showed similar clinical (mainly pediatric), radiological (mostly supratentorial, cystic, and contrast enhancing), immunophenotypical (common expression of glioneuronal markers), and genetic (similar spectrum of fusions) profiles but their histopathological appearance was clearly distinct. Moreover, we found a novel fusion transcript (CIC::EWSR1) in a SARC-CIC. Most DNA methylation profiles using the Heidelberg Brain Tumor Classifier (v12.8) annotated the samples to the methylation class "SARC-CIC" (9/14 tumors with available data). By using uniform manifold approximation and projection analysis, four other samples were classified as SARC-CIC and another clustered within the methylation class of HGNET-CIC. Our findings confirm that CNS CIC-fused tumors do not represent a single molecular tumor entity. Further analyses are needed to characterize HGNET-CIC in more detail. These results may help to refine the essential diagnostic criteria for SARC-CIC and their terminology (with a suggested consensual name of sarcoma, CIC/ATXN1-complex rearranged).

Molecular and therapeutic advancements in Capicua (CIC)-rearranged sarcoma

Capicua (CIC)-rearranged sarcomas are an aggressive subset of undifferentiated round cell sarcomas. CIC::DUX4, the proto-typical CIC fusion oncoprotein is associated with rapid clinical progression and chemotherapy resistance leading to poor clinical outcomes. Recent studies have identified additional CIC fusions (CIC::NUTM1, CIC::FOXO4, and CIC::LEUTX) that largely retain CIC-binding specificity but leverage C-terminal binding partners (NUTM1, FOXO4, and LEUTX) to potentially activate transcriptional programs that drive oncogenesis. Moreover, the recent development of preclinical models to study CIC::DUX4 sarcoma have advanced our understanding of the underlying biological mechanisms and uncovered key dependencies that can be translated into rational therapies. In this review, we will highlight these recent advancements in CIC-rearranged sarcoma biology with a vision for clinical translation to improve patient outcomes.

CIC-DUX4 Sarcoma Involving the Skull Base: A Rare Presentation and Review of the Literature

Background  CIC-DUX4 sarcoma is a rare, aggressive tumor that is difficult to diagnose. Although it is closely related to Ewing's sarcoma, each is a distinct pathologic entity and both have been previously reported in the skin, lymph nodes, and viscera. We report the first description of CIC-DUX4 involving the posterior cranial fossa and review the distinctive symptomatology, morphology, immunoprofile, and genetic signature that differentiate this rare tumor. Case Report  A 32-year-old man presented with an enlarging right lateral neck mass, progressive hoarseness, and orofacial pain. Biopsy revealed a high-grade undifferentiated malignant neoplasm. Imaging demonstrated an 8-cm mass in the right neck extending to the skull base and abutting the carotid sheath, in addition to pulmonary nodules and pelvic lymphadenopathy. Despite initial response to chemotherapy, he experienced disease progression and underwent surgical resection, radical neck dissection, and brachytherapy. Definitive pathologic diagnosis was achieved with next-generation sequencing. Within weeks of treatment, he developed symptoms reflecting progression of disease involving the neck, posterior cranial fossa, and lung. Adjuvant chemotherapy was planned, but the patient succumbed to his disease prior to initiation of further therapy. Conclusion  CIC-DUX4 sarcomas are uncommon and can progress rapidly. Diagnosis requires either fluorescence in situ hybridization or next-generation sequencing. Due to its rarity, there is no standard-of-care treatment for this tumor and further investigations are needed to understand disease behavior and develop targeted therapeutic modalities.

A Radiologist's Guide to the 2021 WHO Central Nervous System Tumor Classification: Part 2-Newly Described and Revised Tumor Types

The fifth edition of the World Health Organization classification of tumors of the central nervous system (CNS), published in 2021, introduces major shifts in the classification of brain and spine tumors. These changes were necessitated by rapidly increasing knowledge of CNS tumor biology and therapies, much of which is based on molecular methods in tumor diagnosis. The growing complexity of CNS tumor genetics has required reorganization of tumor groups and acknowledgment of new tumor entities. For radiologists interpreting neuroimaging studies, proficiency with these updates is critical in providing excellent patient care. This review will focus on new or revised CNS tumor types and subtypes, beyond infiltrating glioma (described in part 1 of this series), with an emphasis on imaging features.

Mesenchymal non-meningothelial tumors of the central nervous system: a literature review and diagnostic update of novelties and emerging entities

The fifth edition of the World Health Organization Classification of Tumors of the Central Nervous System (CNS) now includes mesenchymal tumors that occur uniquely or frequently in the CNS. Moreover, this version has aligned the terminology of mesenchymal tumors with their soft tissue counterparts. New tumor types have been added, such as the "intracranial mesenchymal tumor, FET-CREB fusion-positive", the "CIC-rearranged sarcoma", and the "Primary intracranial sarcoma, DICER1-mutant". Other entities (such as rhabdomyosarcoma) have remained in the current WHO classification because these tumor types may present specificities in the CNS as compared to their soft tissue counterparts. Based on an extensive literature review, herein, we will discuss these newly recognized entities in terms of clinical observation, radiology, histopathology, genetics and outcome, and consider strategies for an accurate diagnosis. In light of this literature analysis, we will also introduce some potentially novel tumor types.

Rare embryonal and sarcomatous central nervous system tumours: State-of-the art and future directions

The introduction of molecular methods into the diagnostics of central nervous system (CNS) tumours and the subsequent deciphering of their molecular heterogeneity has resulted in a significant impact on paediatric neurooncology. Particularly in the field of rare embryonal and sarcomatous CNS tumours, novel tumour types have been delineated and introduced in the recent 5th edition of the WHO classification of CNS tumours. The rarity and novelty of these tumour types result in diagnostic and therapeutic challenges. Apart from distinct histopathological and molecular features, these tumour types exhibit characteristic clinical properties and require different therapeutic approaches for optimal patient management. However, based on the limited availability of clinical data, current therapeutic recommendations have to be based on data from small, predominantly retrospective patient cohorts. Within this article, we provide guidance for diagnostic work-up and clinical management of rare CNS embryonal tumours ('embryonal tumour with multi-layered rosettes', ETMR; 'CNS neuroblastoma, FOXR2-activated', CNS NB-FOXR2; 'CNS tumour with BCOR-ITD, CNS BCOR-ITD) and rare CNS sarcomatous tumours ('primary intracranial sarcoma, DICER1-mutant', CNS DICER1; 'CIC-rearranged sarcoma', CNS CIC). By emphasizing the significant consequences on patient management in paediatric CNS tumours, we want to encourage wide implementation of comprehensive molecular diagnostics and stress the importance for joint international efforts to further collect and study these rare tumour types.

A case of CIC-rearranged sarcoma with CIC-LEUTX gene fusion in spinal cord

A 16-year-old male was admitted to the hospital for weakness of both lower extremities. Magnetic resonance imaging revealed an intraspinal extramedullary subdural mass at the thoracic 9 level. Microscopically, the tumor cells were small to medium sized and round to ovoid in shape. They were distributed in diffuse sheets or showed nodular appearance. The nucleus of the tumor had mild-to-moderate atypia, with vesicular chromatin and prominent nucleoli. A smaller proportion of tumor cells demonstrated rhabdoid morphology. Focal myxoid stromal change was present, in which tumor cells exhibited spindle shapes. Approximately two mitoses were counted per 10 high-power fields. No necrosis was observed. The tumor cells were focal positive for CD99; multifocal positive for WT1; diffuse positive for nestin, synaptophysin, and D2-40; partial positive for GFAP; focal positive for desmin and SSTR2; and scattered positive for S-100 protein. The Ki-67 labeling index was approximately 20%. Genetic testing revealed CIC-LEUTX gene fusion. Considering the patient's history, clinical data, pathological findings and genetic findings, we rendered a rare tumor named CIC-rearranged sarcoma with CIC-LEUTX gene fusion.

Expanding the spectrum of "mesenchymal" tumors of the central nervous system

In this review, we summarize the clinical, histopathological, and molecular features of central nervous system (CNS) tumors with BCOR internal tandem duplication, intracranial mesenchymal tumor with FET/CREB fusion, CNS CIC-rearranged sarcomas and primary intracranial sarcoma DICER1-mutant, now included in the 2021 WHO classification of CNS tumors. Possible relationships between tumors occurring in the CNS and their systemic counterparts are discussed.

Metastatic thoracic and lumbar intramedullary and extramedullary Ewing's sarcoma: a rare case report and literature review

Ewing sarcoma (ES) is a highly aggressive bone and soft tissue tumor that occurs mainly in young children and adolescents and is associated with primary and metastatic disease. Intramedullary ES (either primary or secondary) is rare, and the ideal management remains inconclusive. We herein report intramedullary and extramedullary metastatic ES in a single patient. A 46-year-old woman was referred to our outpatient clinic from the oncology clinic with progressive paraparesis and paresthesia for 1 week prior to presentation. She had developed left clavicular ES 2 years earlier for which surgery and chemoradiotherapy had been performed. At the present evaluation, she was diagnosed with intramedullary thoracic and lumbar extradural masses. Thoracic surgery was performed, and a biopsy of the lesion was obtained. The diagnosis of ES was confirmed histopathologically, and she underwent adjuvant chemotherapy. Her neurological status did not improve after surgery, and she underwent rehabilitation and physical therapy. The lumbar lesion resolved with chemotherapy. Metastasis of ES to the spinal cord, especially intramedullary lesions, is extremely rare, and there is no standard management guideline. However, surgical decompression and adjuvant chemotherapy are the main treatments in these cases.

Major Changes in 2021 World Health Organization Classification of Central Nervous System Tumors

The World Health Organization (WHO) published the fifth edition of the WHO Classification of Tumors of the Central Nervous System (WHO CNS5) in 2021, as an update of the WHO central nervous system (CNS) classification system published in 2016. WHO CNS5 was drafted on the basis of recommendations from the Consortium to Inform Molecular and Practical Approaches to CNS Tumor Taxonomy (cIMPACT-NOW) and expounds the classification scheme of the previous edition, which emphasized the importance of genetic and molecular changes in the characteristics of CNS tumors. Multiple newly recognized tumor types, including those for which there is limited knowledge regarding neuroimaging features, are detailed in WHO CNS5. The authors describe the major changes introduced in WHO CNS5, including revisions to tumor nomenclature. For example, WHO grade IV tumors in the fourth edition are equivalent to CNS WHO grade 4 tumors in the fifth edition, and diffuse midline glioma, H3 K27M-mutant, is equivalent to midline glioma, H3 K27-altered. With regard to tumor typing, isocitrate dehydrogenase (IDH)-mutant glioblastoma has been modified to IDH-mutant astrocytoma. In tumor grading, IDH-mutant astrocytomas are now graded according to the presence or absence of homozygous CDKN2A/B deletion. Moreover, the molecular mechanisms of tumorigenesis, as well as the clinical characteristics and imaging features of the tumor types newly recognized in WHO CNS5, are summarized. Given that WHO CNS5 has become the foundation for daily practice, radiologists need to be familiar with this new edition of the WHO CNS tumor classification system. Online supplemental material and the slide presentation from the RSNA Annual Meeting are available for this article. ^©RSNA, 2022.

[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.

Advances in the classification of round cell sarcomas

Round cell sarcomas represent a diagnostic challenge for pathologists, owing to the poorly differentiated features of these high-grade tumours. The diagnosis of round cell sarcoma requires large immunohistochemical panels and molecular testing in many cases. This spectrum of malignancies is largely dominated by Ewing sarcomas (ESs), which represent the most common family of these tumours. Nonetheless, new families have been delineated in the past few years, with the addition of two additional families in the 2020 World Health Organization classification of bone and soft tissue tumours, namely sarcomas with CIC rearrangements and sarcomas with BCOR alterations. EWSR1, one of the genes involved in the driver fusion of ESs, is also implicated in the translocation of many other tumours with heterogeneous lineages and variable levels of aggressiveness. Round cell sarcomas associated with fusions inwhichEWSR1is partnered with genes encoding transcription factors distinct from those of the 'Ewing family' represent a heterogeneous group of rare tumours that require further study to determine whether their fusions may or not define a specific subgroup. They include mainly sarcomas with NFATc2 rearrangements and sarcomas with PATZ1 rearrangements. At this point, PATZ1 fusions seem to be associated with tumours of high clinical and morphological heterogeneity. Molecular studies have also helped in the identification of more consistent biomarkers that give tremendous help to pathologists in triaging, if not diagnosing, these tumours in practice. This review compiles the latest accumulated evidence regarding round cell sarcomas, and discusses the areas that are still under investigation.