Undifferentiated Round Cell Sarcomas Research Articles

Primary CIC-rearranged Gastric sarcoma: A rare diagnosis

Gastric sarcoma is rare, accounting for 1-3% of all gastric neoplasms. WHO has published a new classification of soft tissue tumors and a group of undifferentiated round cell sarcomas, including CIC-rearranged sarcoma has been added. CIC-rearranged sarcoma has not been reported till date. We report a case of CIC-rearranged gastric sarcoma which was managed with chemotherapy and multivisceral resection.

Undifferentiated Small Round Cell Sarcoma of the Hypopharynx in a 7-Month-Old Patient.

Undifferentiated small round cell sarcoma is an extremely rare and highly aggressive tumor touching the soft tissues and bones. Here, we report the case of a 7-month-old girl who presented to our department with respiratory distress due to a hypopharyngeal mass causing airway obstruction. The patient underwent a tracheotomy and had a direct laryngoscopy. Histological examination confirmed the diagnosis of an undifferentiated small round cell sarcoma. The patient received chemotherapy and radiotherapy and underwent neck dissection. One year later, the patient was diagnosed with local recurrence as well as metastatic cervical nodes and liver and pulmonary metastases. The case is original by the tumor's location and the age of onset. To the best of our knowledge, this could be the first case in English and French literature reporting an undifferentiated small round cell sarcoma affecting the hypopharynx among infants. The purpose of this article is to report our case and discuss its clinical and anatomopathological features as well as its prognosis and treatment options.

PATH-63. NEXT GENERATION SEQUENCING FOR CNS TUMORS IN CHILDREN; DOES IT ADD VALUE IN A MIDDLE-INCOME COUNTRY SETUP?

Abstract INTRODUCTION Advances in molecular diagnostics led to improved targeted interventions in the treatment of pediatric CNS tumors. However, the capacity to do these diagnostics is limited in LMICs, and consequently their value is questionable. METHODS We reviewed our experience of Next Generation Sequencing (NGS) testing (TruSight RNA Pan-Cancer seq panel) for pediatric CNS tumors at KHCC/Jordan (March/2022- April/2023). Paraffin blocks’ scrolls were shipped to Sickkids laboratory based on local multidisciplinary team recommendations. We reviewed patients’ clinical characteristics, tumor types and the impact on treatment. RESULTS There were 16 boys and 16 girls; median age at time of testing was 9.5 years (range, 0.9- 21.9 years). Twenty samples were sent at diagnosis and twelve upon tumor progression. Main diagnoses were Low-grade glioma (15), High-grade glioma (10), and other tumors (7). Reasons for NGS testing were: to find a molecular target (20), and to characterize more tumor/behavior (12). The median time from shipping the samples to receive the NGS result was 22 days (range, 15-49 days) at a cost of US$1000. Twenty (63%) tumors had targetable alterations (MAPK/PI3K inhibitors (16), NTRK inhibitors (2), check point inhibitors (2)). Two rare BRAF mutations were identified (BRAFp.G469A, BRAFp.K601E). One tumor diagnosed initially as undifferentiated round-cell sarcoma found to have NAB2::STAT6 fusion and re-diagnosed as aggressive metastatic solitary fibrous tumor. Eight patients received targeted therapy; Dabrafenib/Trametinib (5), Pembrolizumab (2), Entrectinib (1), while radio-chemotherapy was used in the others. Three patients died from disease progression (one used Entrectinib). CONCLUSIONS Sent abroad NGS testing was feasible, however local capacity building is necessary. In this highly selected tumor cohort, high percentage of targetable alterations were identified. NGS was helpful to characterize tumors more and to offer alternative therapies. Nevertheless, interpretation of the significance of NGS results and access to those “new” therapies continues to be a challenge in LMICs

The efficacy of the TRK inhibitor entrectinib in patients with extracranial <i>NTRK</i> fusion-positive tumors

Somatic translocations involving the NTRK genes occur in 0.34–2.2% of all malignant neoplasms in children. TRK inhibitors whose efficacy has been demonstrated in prospective clinical studies expand treatment options for patients with solid tumors harboring NTRK gene rearrangements. The aim of our study was to summarize the first Russian experience with the use of the TRK inhibitor entrectinib in patients with extracranial NTRK fusion-positive solid tumors included in the compassionate use program. This study was approved by the Independent Ethics Committee and the Academic Council of the Dmitry Rogachev National Medical Research Center of Pediatric Hematology, Oncology and Immunology. The study included 8 patients who had been treated at the Dmitry Rogachev National Medical Research Center of Pediatric Hematology, Oncology and Immunology and the N.N. Blokhin National Medical Research Center of Oncology. The main criteria for inclusion in the compassionate use program were a confirmed rearrangement of either NTRK1/2/3 genes in a solid tumor in patients with unresectable disease for whom no effective standard systemic therapy was available, progressive or recurrent disease during therapy prescribed according to the established diagnosis, risk group and risk stratification criteria, and the infeasibility of non-mutilating radical surgery. The median age at diagnosis was 4.3 months (range 1.2–83.6). The male to female ratio was 1:1. The primary site distribution was as follows: head and neck (n = 6; 75%), chest wall (n = 1; 12.5%), pelvis (n = 1; 12.5%). None of the patients had regional lymph node involvement or distant metastases at diagnosis. The distribution by histology (according to histopathology reports) was as follows: infantile fibrosarcoma (n = 4; 50%), undifferentiated round cell sarcoma, low-grade (n = 1; 12.5%), undifferentiated spindle cell sarcoma, high-grade (n = 1; 12.5%), NTRK-rearranged spindle cell sarcoma, low-grade (n = 1; 12.5%), spindle cell tumor associated with an NTRK rearrangement (n = 1; 12.5%). Immunohistochemistry (IHC) with a pan-Trk monoclonal antibody was performed in 7/8 (87.5%) patients. Pan-Trk IHC was positive in 4/7 (57%) patients. Rearrangements in the NTRK1 and NTRK3 genes were confirmed in all the patients. The final methods used for the detection of fusion transcripts were as follows: reverse transcription polymerase chain reaction (n = 4; 50%) and RNA-based next-generation sequencing (n = 4; 50%). NTRK1 and NTRK3 gene translocations were detected in 3/8 (37.5%) and 5/8 (62.5%) patients, respectively. The following fusion transcripts were identified: ETV6::NTRK3 (n = 4), DIP2C::NTRK3 (n = 1), TPR::NTRK1 (n = 1), TPM3::NTRK1 (n = 1), MYH10::NTRK1 (n = 1). One (12.5%) patient received entrectinib as first-line therapy, other patients (7/8, 87.5%) received entrectinib as secondor subsequent-line therapy. Three (37.5%) patients had undergone surgery before treatment with entrectinib: 2 had R2 resection, 1 had R0/R1 resection (resection margins were not evaluated). None of the patients received radiation therapy. The median duration of entrectinib therapy at the time of analysis was 11.8 months (range 2.3–20.1). Delayed surgery was performed in 2/8 patients; according to the histopathology reports, they achieved grade IV pathomorphosis. Three patients experienced adverse events during treatment with entrectinib. The median time to adverse events was 0.23 months (range 0.2–7.96). Three patients required temporary interruption in treatment to relieve symptoms, a subsequent dose reduction by one dose level was necessary when resuming therapy in two patients. The median follow-up since diagnosis was 19.5 months (range 14.9–75.0). All the patients included in our analysis were alive, three of them had no radiologic evidence of disease. Fifty percent of the patients completed targeted therapy, another 50% of the patients continued treatment with entrectinib. Complete and very good partial response was achieved in 3/8 and 2/8 patients, respectively. Partial response, minor partial response and stable disease were observed in one patient each. These results indicate high efficacy and safety of entrectinib in pediatric patients with extracranial NTRK fusion-positive solid tumors. Further studies are needed to determine the therapeutic potential of TRK inhibitors in the treatment of different solid malignant neoplasms in children and to assess long-term treatment results.

Genetically Engineered Mouse Models of CIC-DUX4 Sarcoma Reveal an Unexpected Sensitivity to Histone Deacetylase (HDAC) Inhibition

Undifferentiated small round cell sarcomas constitute a highly aggressive subtype of soft tissue sarcoma that affects adolescents and young adults. Frequently, these cancers are caused by a gene fusion between the DNA binding domain of capicua (CIC), a canonical tumor suppressor that normally acts as a transcriptional repressor, with the transcriptional activation domain of double homeobox 4 (DUX4). Given the rare nature of CIC-DUX4 sarcoma (CDS), obtaining patient tissues to study the mechanisms of disease is very challenging. Moreover, conducting clinical trials to identify radiosensitizers or other novel treatments is not possible underscoring the need for a primary animal model. Here, we report the development and characterization of the first genetically engineered mouse model of CDS and the use of this model to investigate novel therapies. Using Cre-loxP technology, three genetically engineered mouse models of CDS were developed. The resulting tumors were characterized by hematoxylin and eosin (H&E) staining, immunohistochemistry (IHC), and RNA-sequencing. Cell lines from multiple primary and metastatic tumors were derived and used for Chromatin Immunoprecipitation (ChiP) sequencing, Rapid Immunoprecipitation mass spectrometry of Endogenous proteins (RIME), and targeted drug screening. In all three models, spontaneous (Cre-independent) recombination occurred in chimeric animals resulting in the formation of soft tissue tumors, widespread metastasis to the lungs, liver, and brain, and 100% lethality within 4-8 weeks of life. The tumors histologically resembled human CDS and stained positive for an HA (hemagglutinin) epitope tag confirming transgene expression. Of 108 chimeric pups (generation 0, G0), only one male bred before succumbing to metastatic disease. G2 progeny now exhibit resistance to spontaneous recombination and tumor development enabling reliable propagation of one of the models for experimentation. Using tumor derived cell lines for integrative analyses of multi-omics datasets, we find evidence for a model where CIC-DUX4 functions as a neomorphic and oncogenic transcriptional activator, which cooperates with ETS family transcription factors to drive the CDS transcriptional program. Lastly, small molecule epigenetic drug screens in mouse and human CDS cell lines point to an unexpected sensitivity to HDAC inhibitors, which we hypothesize may be attributable to ETS factor hyperactivity. Genetically engineered mouse models of CIC-DUX4 sarcoma form tumors that recapitulate the human disease. Using mouse tumors and tumor-derived cell lines, we identify a mechanistic role and potential therapeutic vulnerability that converges on the ETS family transcription factors.

Giant middle mediastinal lesions: when tumor size correlates with mesenchymal origin-a retrospective single-center analysis.

The International Thymic Malignancy Interest Group (ITMIG) proposed an internationally accepted division of the mediastinum into three compartments based on computed tomography (CT): anterior (prevascular), middle (visceral) and posterior (paravertebral) compartment. There is no generally accepted definition for the term "giant" when applied to middle mediastinal lesions. We defined the term "giant" and described our surgical experience in treating patients with giant lesions of the middle mediastinum. CT imaging of patients operated in our center from January 2016 to August 2021 for mediastinal lesions was reviewed. Lesions were categorized to one of the ITMIG-defined compartments. Lesion size at diagnosis was measured at its largest diameter on axial CT imaging. Giant middle mediastinal lesions were defined as lesions having a size ≥90th percentile of our middle mediastinal lesion cohort. Patients with giant middle mediastinal lesions were further analyzed. Thirty-six patients (23%) had lesions located in the middle mediastinal compartment. Most common diagnoses were mediastinal cysts (n=10, 28%), metastatic lesions (n=6, 17%), lymphomas (n=5, 14%), and sarcomas (n=3, 8%). Ninetieth percentile lesion size was 73 mm. As per definition, four patients had giant middle mediastinal lesions. All these four lesions were of mesenchymal origin including oesophageal leiomyoma, synovial sarcoma, leiomyosarcoma and undifferentiated round cell sarcoma. Resection was performed through posterolateral thoracotomy or sternotomy, with or without cardiopulmonary bypass. The term "giant" could be defined as a mass larger or equal to 73 mm. This definition selected specifically lesions with mesenchymal origin and may therefore guide diagnostic algorithm and patient management.

458 Primary Renal Mesenchymal Neoplasms: A Retrospective Clinicopathological Study

Abstract Aim Mesenchymal tumors are rare primary neoplasms of the kidney with limited demographic data in literature. We sought to study the prevalence of this rare subset of tumors in adults, at our tertiary care hospital focusing on the pathological and radiological characteristics. Method Clinico-radiological and intra-operative details were retrospectively analyzed for adult primary renal mesenchymal neoplasms received between 2006 and 2021 and correlated with the histopathology data. Results Of 2164 nephrectomies performed for neoplastic conditions, 97 (4.5%) were diagnosed as renal mesenchymal tumors. There were 59 (60.8%) benign, 10 (10.3%) with intermediate biologic behavior and 28 (28.9%) malignant tumors. The mean age was similar across these categories. Hematuria was seen in 11 of 38 (29%) intermediate grade and malignant tumors and in only 6 of 59 (10%) benign tumors a difference that was statistically significant (p = 0.017). Tumors ≥ 7cm were more likely to be malignant/intermediate grade than benign (p = 0.027). Classical angiomyolipomas constituted 90% of the benign tumors. Epithelioid angiomyolipomas and solitary fibrous tumors were the common intermediate grade tumors. Undifferentiated small round cell sarcoma was the most common malignant neoplasm. Immunohistochemical and molecular studies were useful for confirmation of diagnosis, particularly in cases of intermediate/malignant tumors. Conclusions Mesenchymal tumors constitute 4.5% of adult primary renal tumors, are predominantly benign tumors but are malignant in 1/4 th of cases. Malignant tumors are typically larger and more often present with hematuria. Immunohistochemistry (IHC) and molecular studies play a role in the diagnosis of intermediate and malignant mesenchymal tumors.

Impact of age on survival according to molecular tumor findings in children and adolescents with soft-tissue and bone sarcoma: The BIOSCA project

BackgroundAdolescents (15–19 years) with sarcoma are known to have significantly worse survival than children (0–14 years). One possible reason may be that the adolescent sarcomas exhibit specific biological characteristics resulting in differences in clinical presentation and treatment resistance behaviors. The BIOSCA project aims to further explore these age-related differences in survival accounting for molecular tumor characteristic in children and adolescents with sarcoma. MethodsA retrospective national population-based observational study with documented somatic genetic analyses was conducted between 2011 and 2016 of all patients aged from 0 to 17 years with a diagnosis of sarcoma using the National Registry of Childhood Cancers Database. ResultsA total of 1637 children (0–9years: 40%), preadolescents (10–14years: 35%) and adolescents (15–17 years: 25%) with a diagnosis of bone (N = 845) or soft-tissue (N = 792) sarcoma were included. Adolescents had significantly worse outcome for undifferentiated small round cell sarcoma (USRCS), alveolar rhabdomyosarcoma (ARMS), and epithelioid sarcoma. Five-year overall survivals were worse among CIC-rearranged USRCS cases (47% [95%CI:21–69]) as compared to other USRCS, and PAX3::FOXO1 ARMS patients (44% [95%CI:32–55]) as compared to other ARMS. Adjusting for stage and genomic-profiling status, adolescents with USRCS were 1.6-fold more likely to die than children (P = 0.05), while the difference in survival between age of ARMS patients was weaken. Indeed, the prevalence of PAX3::FOXO1 increased significantly with age. ConclusionAge was an independent prognostic factor of outcome only in patients with USRCS, while the association between age and survival of patients with ARMS could be partly explained by differences in prevalence of PAX3::FOXO1.

Identification of novel actionable SNVs using targeted comprehensive genome profiling in patients with sarcoma.

e23520 Background: The utility of comprehensive genome profiling is not well validated in early-stage sarcoma. The 5-year survival rate for metastatic sarcoma is less than 20%. The application of comprehensive Next Generation Sequencing (NGS) on tumor DNA has led to the identification of a multitude of actionable alterations in oncogenes & tumor suppressor genes alongside the detection of immunotherapy markers like microsatellite instability, tumor mutational burden, and homologous recombinant deficiency. Methods: We retrospectively analyzed ccfDNA and gDNA in 13 sarcoma patients by targeted Next Generation Sequencing (NGS) using OncoIndx proprietary gene panel that targets exonic regions of 600 cancer-related genes. Illumina-compatible libraries were prepared by the target hybridization method and sequenced on Nextseq 2000 platform in a pair-end fashion. Variant calling was performed using an indigenously developed bioinformatics pipeline. Results: Here we report for the first time the identification of several, novel mutations in rare sarcomas such as IDH2R140W (in epithelioid hemangioendothelioma), CTNNB1D32V (in undifferentiated small round cell sarcoma) and DDR2M754I (in osteosarcoma). Furthermore, we observed, JAK1 amplification and BRAF-GUSBP1 fusion in osteosarcoma and a sarcomatoid carcinoma case, respectively. JAK1 amplification and DDR2M754I were found in the same patient. The IDH2 mutation and JAK1 amplification could find potential applications for JAK1 and IDH2 inhibitors respectively. Similarly, cancers having DDR2 mutations are known to respond to multikinase inhibitors such as Imatinib and Dasatinib, thus making a strong case for the potential repurposing of these drugs in sarcomas. ~93% of patients demonstrated genome-wide instabilities as evidenced by LOH, LST, TAI, and high TMB. Homologous Recombinant deficiency was found in 66.7% of patients. Although this is a small patient population, the high HRD+ percentages point to the underappreciated importance of HRD testing in sarcoma and herald the use of PARPi therapy for sarcoma. Conclusions: We identified several actionable mutations in rare sarcoma cases. These findings highlight the power of comprehensive genome profiling like the OncoIndx panel and warrant further studies on the role of IDH2, JAK1, and BRAF fusion in sarcomas. Moreover, they also present a strong potential case for repurposing of TKI such as Imatinib and Dasatinib in sarcomas.

The clinical value of tumor-informed minimal residual disease detection in sarcoma.

11510 Background: The high recurrence and metastasis rates lead to poor survival of patients with sarcoma. At present, circulating tumor DNA-based minimal residual disease (MRD) has been studied in varies solid tumors and proved to be valuable in guiding treatment and predicting recurrence, but its application in sarcomas is rarely reported. Methods: Tumor tissue samples were used for whole exome sequencing (WES) and clonal mutations were selected for the customized MRD panel. Blood samples were collected for MRD detection. Experiments were conducted at OrigiMed, a College of American Pathologists accredited and Clinical Laboratory Improvement Amendments certified laboratory. Results: A total of 84 sarcoma patients including 47 bone tumor (BT), 32 soft-tissue sarcoma (STS), and 5 undifferentiated small round cell sarcoma (USRCS) patients were enrolled. Patients consisted of 49 (58.3%) males and 35 (41.7%) females, with a median age of 23 years old (1-85 years old). Based on WES, we found that 64% (4936/7715) of the mutated genes were unique to each patient, and 70.4% (859/1220) of selected tumor-informed single nucleotide variants (SNV) were variants with unknown significance, suggesting that tumor-informed MRD is superior to panel-based MRD in sarcomas. In this cohort, 78.6% (66/84) of patients successfully constructed MRD panels, including 85.1% (40/47) of BT patients, 75% (24/32) of STS patients, and 40% (2/5) of USRCS patients. The main reason for failure was the scarcity of SNVs detected. Preoperative MRD detection was performed on 6 cases and revealed a positive rate of 100%. MRD detection was performed twice on 2 patients during preoperative neoadjuvant therapy. For the patient with constant allele frequencies detected throughout the treatment course, imaging showed tumor enlargement; While for another patient with a trend of reduction in allelic frequency, imaging showed tumor shrinkage and necrotic tumor tissue was observed in surgery one month later. These two patients had not recurred after surgery at the time of analysis. Post-surgery MRD detection were performed on 27 patients, of which 1 STS and 7 BTs were positive (30%, 8/27). Three of them confirmed recurrence by imaging at 12, 30, and 101 days after detection of positive MRD, respectively. However, there were still no imaging recurrence in the other patients so far, including the 5 remaining patients with positive MRD and 19 patients with negative MRD. Follow-up is still ongoing. Conclusions: MRD tests had been successfully performed in most of the sarcoma patients. Due to the heterogeneity of sarcomas, about 64% of mutated genes of sarcomas are unique individually, which may be more suitable for monitoring with tumor-informed MRD panel. Tumor-informed MRD could be used to predict the efficacy of preoperative neoadjuvant therapy and discover recurrence earlier than imaging in sarcoma.

P424 MEDIASTINAL ROUND CELL SARCOMA WITH PULMONARY ARTERY STENOSIS: CLINICAL USEFULNESS OF CARDIAC MRI IN CARDIO–ONCOLOGY

Abstract Case description: a previously healthy 26–year–old man presented with dyspnea on exertion and dry cough. CT scan revealed a large mediastinal mass with displacement of great vessels and trachea and pericardial effusion. Cardiac MRI showed the huge mediastinal mass, literally leaning on the heart with signs of compression of the pulmonary artery (Figure 1) with the typical D–shape of inter ventricular septum. Pericardial effusion did not compress the RV due to high intraventricular pressure. At baseline echo the mass simulated pulmonary artery stenosis as a consequence of pulmonary artery “ab extrinseco” compression. Surgical biopsy showed Ewing sarcoma lately redefined into undifferentiated round cell sarcoma so the patient started chemotherapy with VAI (vincristine, adriblastine, and ifosfamide) x6 followed by maintenance etoposide and ifosfamide (no anthraciclines for risk of cardiac toxicity). After induction phase MRI showed a partial response to treatment; mediastinal mass further reduced at the end of maintenance (Figure 2). Pericardial effusion disappeared and peak velocity of pulmonary artery went back to normal level at echo. Our patient underwent surgery with en–block removal of mediastinal mass with pericardium and anonymous vein and partial pulmonary upper left lobe resection with R0 resection. Pathology report confirmed an undifferentiated round cell sarcoma (possible embryonal origin, FISH analysis for EWS/FUS genes and 12p negative). Adjuvant mediastinal radiotherapy was delivered. The patient is alive without disease recurrence at one–year follow–up. Conclusions cardiac MR offer great tissue characterization (differential diagnosis between malignant and benign masses) inside/outside the heart. CMR is non–invasive/non radiation and ideal technique for surgery indication and follow–up imaging.

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.

Clinicopathological features of five cases of CIC::DUX4 positive sarcomas, including literature review

According to the recent World Health Organization (WHO) classification, CIC-rearranged sarcomas, including CIC::DUX4-positive sarcomas constitute an aggressive subtype of undifferentiated round cell sarcomas. There is a single study on these tumors from our subcontinent. We present clinicopathological features of 5 additional cases of this tumor entity, including literature review.Thirty-nine undifferentiated round cell sarcomas, excluding Ewing sarcomas (ES), were tested for CIC::DUX4 fusion, including Type I (165 base pair size) and II (230 bp) by reverse transcription-polymerase chain reaction. Twenty-five of those tumors were tested for EWSR1 gene rearrangement, 5 for SS18 and 4 for SS18::SSX fusion, and were negative for those tests. Five tumors (12.8 %) were positive for CIC::DUX4(Type II) fusion.Five CIC:: DUX4-positive sarcomas occurred in 4 males and one female; of 25–43 years of age, in soft tissues, including thigh (n = 2), chest wall (n = 1), iliac region (n = 1) and foot (n = 1). Tumor size varied from 2.2 to 19 cm. Microscopically, the tumors were predominantly composed of nodules and sheets of malignant round to epithelioid cells, including “rhabdoid-like” (n = 2) and spindle-shaped (n = 2) with eosinophilic to vacuolated cytoplasm (4/5), distinct nucleoli (4/5), brisk mitoses, focal myxoid to hyalinised stroma (4/5) and necrosis (5/5). Immunohistochemically, tumor cells were positive for WT1 (5/5), calretinin (3/4), pan-keratin (1/4), CD99/MIC2 (“dot-like” to cytoplasmic membranous) (4/4), while negative for desmin (0/4), S100P (0/4), and NKX2.2 (0/5). INI1/SMARCB1 was retained (3/3). All patients underwent excision with adjuvant radiotherapy and chemotherapy (Ewing sarcoma regimen). A single patient developed recurrence, and 2 developed pulmonary metastasis, including one with brain metastasis.CIC:: DUX4-positive sarcomas are ultra-rare tumors, that mainly occur in the soft tissues and in young adult patients. Histopathologically, these tumors display a wide spectrum, including round to epithelioid cells, variable amount of cytoplasmic vacuolization and myxoid stroma with necrosis.Immunohistochemically, these tumors express WT1 and calretinin. Despite adjuvant therapies, these tumors have dismal outcomes, especially in large-sized tumors. CIC::DUX4-positive sarcomas need to be differentiated from their histopathological mimics, including ES, in view of significant treatment-related implications.

Ewing sarcoma

Ewing sarcoma, according to the latest 2020 WHO classification of tumors of bone and soft tissue, belongs to the category of “undifferentiated small round cell sarcomas of bone and soft tissue.” After osteosarcoma, it is the second most common malignant bone tumor in children and young adults. Most Ewing sarcomas develop in the bone and about 30% of soft tissues. In this paper, all the epidemiological, clinical and imaging characteristics will be reviewed.

Expanding the Molecular Diversity of CIC-Rearranged Sarcomas With Novel and Very Rare Partners

Capicua transcriptional repressor (CIC)-rearranged sarcoma represents a distinct pathologic entity and constitutes the second most prevalent category of undifferentiated round cell sarcomas (URCSs) after Ewing sarcoma. The 2 most common translocations are t(4;19) and t(10;19), resulting in CIC fusions with either DUX4 and DUX4L paralog, respectively; however, other rare variant fusions have also been reported. In this study, we expand the molecular spectrum of CIC-gene partners, reporting on 5 cases of URCSs showing CIC fusions with AXL, CITED1, SYK, and LEUTX by targeted RNA or DNA sequencing. There were 4 female patients and 1 male patient with a wide age range (12-70 years; median, 36 years). Four cases occurred in the deep soft tissues (lower extremity, 3; neck, 1) and 1 case in the central nervous system (midbrain/thalamus). All cases showed similar histologic findings within the spectrum of URCSs. Immunohistochemistry, showed variable positivity for ETV4 in 4 of the 4 cases and positive results for ERG in 3 of the 4 cases and for WT1 in 1 of the 4 cases. CD31 showed positivity in 2 of the 3 cases, including one coexpressing ERG. Unsupervised clustering of methylation profiles by T-distributed stochastic neighborhood embedding performed in 4 cases showed that all clustered tightly together and along the CIC sarcoma methylation class. RNA-sequencing data showed consistent upregulation of ETV1 and ETV4 mRNA in all cases examined, at similar levels to CIC::DUX4 URCSs. Our study expands the molecular diversity of CIC-rearranged URCSs to include novel and rare partners, providing morphologic, immunohistochemical, gene expression, and methylation evidence supporting their classification within the family of tumors harboring the more common DUX4/DUX4L partner genes.

Update of pediatric bone tumors-other mesenchymal tumors of bone, hematopoietic neoplasms of bone, and WHO classification of undifferentiated small round cell sarcomas of bone.

There are numerous bone tumors in the pediatric population, with imaging playing an essential role in diagnosis and management. Our understanding of certain bone tumors has rapidly evolved over the past decade with advancements in next-generation genetic sequencing techniques. This increased level of understanding has altered the nomenclature, management approach, and prognosis of certain lesions. We provide a detailed update of bone tumors that occur in the pediatric population with emphasis on the recently released nomenclature provided in the 5th edition of the World Health Organization Classification of Soft Tissue and Bone Tumours. We discuss other mesenchymal tumors of bone, hematopoietic neoplasms of bone, and WHO classification of undifferentiated small round cell sarcomas of bone. We have detailed osteogenic tumors and osteoclastic giant cell-rich tumors, as well as notochordal tumors, chondrogenic tumors, and vascular tumors of the bone in separate manuscripts.

A global collaboRAtive study of CIC-rearranged, BCOR::CCNB3-rearranged and other ultra-rare unclassified undifferentiated small round cell sarcomas (GRACefUl)

BackgroundUndifferentiated small round cell sarcomas (URCSs) represent a diagnostic challenge, and their optimal treatment is unknown. We aimed to define the clinical characteristics, treatment, and outcome of URCS patients. MethodsURCS patients treated from 1983 to 2019 at 21 worldwide sarcoma reference centres were retrospectively identified. Based on molecular assessment, cases were classified as follows: (1) CIC-rearranged round cell sarcomas, (2) BCOR::CCNB3-rearranged round cell sarcomas, (3) unclassified URCSs. Treatment, prognostic factors and outcome were reviewed. ResultsIn total, 148 patients were identified [88/148 (60%) CIC-rearranged sarcoma (median age 32 years, range 7–78), 33/148 (22%) BCOR::CCNB3-rearranged (median age 17 years, range 5–91), and 27/148 (18%) unclassified URCSs (median age 37 years, range 4–70)]. One hundred-one (68.2%) cases presented with localised disease; 47 (31.8%) had metastases at diagnosis. Male prevalence, younger age, bone primary site, and a low rate of synchronous metastases were observed in BCOR::CCNB3-rearranged cases. Local treatment was surgery in 67/148 (45%) patients, and surgery + radiotherapy in 52/148 (35%). Chemotherapy was given to 122/148 (82%) patients. At a 42.7-month median follow-up, the 3-year overall survival (OS) was 92.2% (95% CI 71.5–98.0) in BCOR::CCNB3 patients, 39.6% (95% CI 27.7–51.3) in CIC-rearranged sarcomas, and 78.7% in unclassified URCSs (95% CI 56.1–90.6; p < 0.0001). ConclusionsThis study is the largest conducted in URCS and confirms major differences in outcomes between URCS subtypes. A full molecular assessment should be undertaken when a diagnosis of URCS is suspected. Prospective studies are needed to better define the optimal treatment strategy in each URCS subtype.

Strategies for the Treatment of Infantile Soft Tissue Sarcomas With BCOR Alterations.

BCOR alterations are described in ultra-rare infantile soft tissue sarcomas including primitive myxoid mesenchymal tumor of infancy and undifferentiated round cell sarcoma (URCS). Previous reports often describe dismal outcomes. Thus, we undertook a retrospective, multi-institutional study of infants with BCOR -rearranged soft tissue sarcomas. Nine patients aged 6 weeks to 15 months were identified. One tumor carried a BCOR :: CCNB3 fusion, whereas 7 tumors harbored internal tandem duplication of BCOR , including 4 cases classified as primitive myxoid mesenchymal tumor of infancy, 1 case as URCS, and 2 cases characterized by a "hybrid morphology" in our evaluation. Four patients underwent upfront surgery with residual disease that progressed locally after a median of 2.5 months. Locoregional recurrences were observed in hybrid patients, and the URCS case recurred with brain metastases. Complete radiographic responses after chemotherapy were achieved in patients treated with vincristine/doxorubicin/cyclophosphamide alternating with ifosfamide/etoposide, vincristine/doxorubicin/cyclophosphamide alternating with cyclophosphamide/etoposide (regimen I), and ifosfamide/carboplatin/etoposide. Seven patients received radiotherapy. With a median of 23.5 months off therapy, 8 patients are with no evidence of disease. In our study, observation was inadequate for the management of untreated postsurgical residual disease. Tumors demonstrated chemosensitivity with anthracycline-based regimens and ifosfamide/carboplatin/etoposide. Radiotherapy was required to achieve durable response in most patients.

Clinical and morphological characteristics of Ewing's sarcoma and the algorithm for diagnosing undifferentiated round cell sarcomas

The group of undifferentiated round cell sarcomas, according to the World Health Organization Classification, in addition to Ewing's sarcoma (ES), includes round cell sarcoma with rearrangement of the EWSR1 gene with partners not from the ETS gene family, sarcoma with BCOR gene alterations, CIC -rearranged sarcoma. Despite the fact that all tumors have clear histological and immunological criteria, their diagnosis can be difficult, given the fact that there are overlapping variants of the morphological picture and immunophenotype both within the group and with other round cell tumors. Present a comparative analysis of genetically verified ES, sarcoma with BCOR gene alterations and CIC-rearranged sarcoma. A comparative study of biopsy specimens of bones, soft tissues and internal organs was carried out in 118 patients with ES, 10 with BCOR gene alterations and 8 with CIC-rearranged sarcomas. All cases were genetically verified. The following research methods were used: histological, immunohistochemical, RT-PCR, RNA sequencing and FISH. Within our cohort, it was shown that ES predominantly affects bones, while soft tissue localization is more typical for the other two undifferentiated round cell sarcomas. Histologically, in the overwhelming majority of cases, ES is characterized by a monomorphic round-cell structure; on the contrary, heterogeneous structure is typical for sarcoma with alterations of the BCOR gene, CIC-rearranged sarcoma. High sensitivity and specificity of CD99/NKX2.2 co-expression for ES, BCOR/SATB2/TLE1 for sarcoma with BCOR gene alterations, high specificity and low sensitivity of WT1/ETV4 co-expression for CIC-rearranged sarcoma was shown. For the differential diagnosis of undifferentiated round-cell sarcomas, it is necessary to take into account the clinical, morphology when compared with the data of the IHC study, and verification by molecular genetic methods is necessary to improve the accuracy of diagnosis.

Ganglioneuronal Differentiation in Ewings Sarcoma of the Chest Wall (Askin Tumour): An Uncommon Post-Chemotherapy Change

Ewing sarcoma is classified under undifferentiated small round cell sarcomas of bone and soft tissue. Such tumours arising in the chest wall were previously called Askin’s tumour, however this terminology is not preferred at present. These tumours classically have a small round cell morphology and fusion of FET family of genes (usually EWSR1) with a member of the ETS family of transcription factors. Rare cases of Ewing sarcoma are found to have extensive neural differentiation with ganglion cells and neuropil at diagnosis as well as following chemotherapy. We report a 12 year old boy who presented with a large mass in the right hemi-thorax, which was diagnosed as Ewing sarcoma with EWSR1 translocation by FISH. However, following four cycles of chemotherapy (Vincristine, Doxorubicin, Cyclophosphamide alternating with ifosphamide and etoposide), the resection specimen showed predominantly neural differentiation mimicking a ganglioneuroma with only small areas of small round cell component. EWSR1 translocation was also demonstrated in the resection specimen. After a period of nine months, the child presented with recurrence at the same site and was treated with Irinotecan, cyclophosphamide with topotecan and temozolamide giving excellent clinical response. In this paper, we emphasize the rare occurrence of extensive neural differentiation in Ewing sarcoma and the need to revisit the upfront chemotherapy protocols for patients who exhibit this rare phenomenon