CIC-DUX sarcomas demonstrate frequent MYC amplification and ETS-family transcription factor expression

Case of a CIC::DUX4 fusion gene in a vascular neoplasm extends the spectrum of CIC-rearranged sarcomas

CIC-rearranged sarcomas comprise a group of exceptionally aggressive round-cell sarcomas. These tumors most commonly demonstrate CIC::DUX4 fusion and show similar histopathology to Ewing sarcomas, though lesions mimicking vascular neoplasms have recently been described. Here, we describe a case of a patient with CIC::DUX4 fusion sarcoma identified using RNA-based molecular testing who was initially diagnosed with an endothelial neoplasm. The tumor showed extensive vasoformative growth, complete WT1 negativity, and global positive staining for ERG, CD31, and DUX4 by immunohistochemistry. Methylation testing of the tumor clustered more closely with angiosarcomas than with CIC-rearranged sarcomas. Our findings suggest that CIC::DUX4 fused neoplasms may demonstrate a more diverse phenotypic range than previously appreciated and offer evidence that both molecular and immunohistochemical studies are needed for accurate diagnosis.

CIC-Rearranged Sarcoma

CIC-rearranged sarcoma is a rare type of small round cell sarcoma. The tumors often affect the deep soft tissues of patients in a wide age range. They are highly aggressive, respond poorly to chemotherapy, and have a worse outcome than Ewing sarcoma. CIC-rearranged sarcoma has characteristic and recognizable histology, including lobulated growth, focal myxoid changes, round to epithelioid cells, and minimal variation of nuclear size and shape. Nuclear ETV4 and WT1 expression are useful immunohistochemical findings. CIC fusion can be demonstrated using various methods; however, even next-generation sequencing suffers from imperfect sensitivity, especially for CIC::DUX4.

A Practical Approach to Small Round Cell Tumors Involving the Gastrointestinal Tract and Abdomen

Small round cell neoplasms are diagnostically challenging owing to their clinical and pathologic overlap, necessitating use of large immunopanels and molecular analysis. Ewing sarcomas (ES) are the most common, but EWSR1 is translocated in several diverse neoplasms, some with round cell morphology. Molecular advances enable classification of many tumors previously termed 'atypical ES'. The current WHO Classification includes two new undifferentiated round cell sarcomas (with CIC or BCOR alterations), and a group of sarcomas in which EWSR1 partners with non-Ewing family transcription factor genes. This article reviews the spectrum of small round cell sarcomas within the gastrointestinal tract and abdomen.

Renal CIC-LEUTX rearranged sarcoma with multiple pulmonary metastases: a case report and literature review

BACKGROUND

CIC-rearranged sarcomas (CRS) are a group of heterogeneous tumors which mostly occur in the soft tissues of limbs and trunk, and are highly invasive with poor prognosis. Here, we describe a rare case of CRS that occurred in the left kidney with a CIC-LEUTX rearrangement.

CASE PRESENTATION

A 45-year-old male was admitted to hospital with a dry cough for more than two months without obvious cause. Physical examination and laboratory tests revealed no notable abnormality. The CT scan demonstrated a mass in the left kidney and multiple nodules in both lungs. The percutaneous core needle biopsy showed similar histomorphology and immunophenotype of small round cell malignant tumors. Genetic test revealed a CIC-LEUTX gene fusion.

CONCLUSIONS

We present a rare primary renal CRS with multiple pulmonary metastases, and LEUTX is confirmed as the fusion partner of CIC gene for the first time in a renal case.

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

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

POU2AF3-rearranged sarcomas: A novel tumor defined by fusions of EWSR1 or FUS to a gene formerly designated COLCA2

Gene fusions involving EWSR1 or FUS as the 5' partner have been reported in a diverse array of sarcomas. Here, we characterize the histopathology and genomics of six tumors harboring a gene fusion between EWSR1 or FUS and POU2AF3, an understudied, putative colorectal cancer predisposition gene. Striking morphologic features reminiscent of synovial sarcoma were observed including a biphasic appearance with variable fusiform to epithelioid cytomorphology and staghorn-type vasculature. RNA sequencing demonstrated variable breakpoints in EWSR1/FUS along with similar breakpoints in POU2AF3 that encompassed a 3' portion of this gene. For cases in which additional information was available, the behavior of these neoplasms was aggressive with local spread and/or distant metastases. Although further studies are needed to confirm the functional significance of our findings, POU2AF3 fusions to EWSR1 or FUS may define a novel type of POU2AF3-rearranged sarcomas with aggressive, malignant behavior.

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.

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.

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.

The Recent Advances in Molecular Diagnosis of Soft Tissue Tumors

Soft tissue tumors are rare mesenchymal tumors with divergent differentiation. The diagnosis of soft tissue tumors is challenging for pathologists owing to the diversity of tumor types and histological overlap among the tumor entities. Present-day understanding of the molecular pathogenesis of soft tissue tumors has rapidly increased with the development of molecular genetic techniques (e.g., next-generation sequencing). Additionally, immunohistochemical markers that serve as surrogate markers for recurrent translocations in soft tissue tumors have been developed. This review aims to provide an update on recently described molecular findings and relevant novel immunohistochemical markers in selected soft tissue tumors.

E26 transformation-specific transcription variant 5 in development and cancer: modification, regulation and function

E26 transformation-specific (ETS) transcription variant 5 (ETV5), also known as ETS-related molecule (ERM), exerts versatile functions in normal physiological processes, including branching morphogenesis, neural system development, fertility, embryonic development, immune regulation, and cell metabolism. In addition, ETV5 is repeatedly found to be overexpressed in multiple malignant tumors, where it is involved in cancer progression as an oncogenic transcription factor. Its roles in cancer metastasis, proliferation, oxidative stress response and drug resistance indicate that it is a potential prognostic biomarker, as well as a therapeutic target for cancer treatment. Post-translational modifications, gene fusion events, sophisticated cellular signaling crosstalk and non-coding RNAs contribute to the dysregulation and abnormal activities of ETV5. However, few studies to date systematically summarized the role and molecular mechanisms of ETV5 in benign diseases and in oncogenic progression. In this review, we specify the molecular structure and post-translational modifications of ETV5. In addition, its critical roles in benign and malignant diseases are summarized to draw a panorama for specialists and clinicians. The updated molecular mechanisms of ETV5 in cancer biology and tumor progression are delineated. Finally, we prospect the further direction of ETV5 research in oncology and its potential translational applications in the clinic.

Ewing and Ewing-like sarcomas: A morphological guide through genetically-defined entities

The fifth edition of the World Health Organization classification of soft tissue and bone tumors redefined Ewing sarcoma by fusions between EWSR1/FUS and ETS family of transcription factors, and recognized three tumor groups among Ewing-like sarcoma: CIC-rearranged sarcoma, sarcoma with BCOR genetic alterations, and round cell sarcoma with EWSR1::non-ETS fusions. Although this classification underscores the critical role of molecular genetics in the diagnosis of small round cell sarcoma, each entry is recognized as a specific entity not only because they have different genetics but because their phenotypes are distinct and reasonably robust to support the diagnosis. This review focuses on the morphological aspects of Ewing sarcoma and a subset of Ewing-like sarcomas (CIC-rearranged sarcoma, BCOR-associated sarcoma, and EWSR1::NFATC2 sarcoma) for which phenotypic characteristics have been well established. Classic histological findings, uncommon variations, and recurrent diagnostic pitfalls are addressed, along with the utility of recently developed immunohistochemical markers (NKX2.2, PAX7, ETV4, BCOR, CCNB3, and NKX3.1). Phenotypic expertise would significantly expedite the diagnostic process and complement (or sometimes outperform) genetic testing, even in well-resourced settings. Morphological knowledge plays an even more substantial role in facilities that do not have easy access to molecular testing.

Patterns of care and outcome of CIC ‐rearranged sarcoma patients: A nationwide study of the French sarcoma group

BACKGROUND

CIC-rearranged sarcomas (CIC-RS) represent the most frequent subset of "Ewing-like" undifferentiated small round cell sarcomas. These tumors tend to be more aggressive than Ewing sarcomas. Moreover, treatment strategy can differ according to teams. The primary aim of this retrospective study was to describe the characteristics, treatments, and outcome for patients with CIC-RS included in the French NETSARC+ database.

METHODS

Pediatric and adult patients from 13 French centers with a diagnosis of CIC-RS were registered from October 2008 to March 2021. Patients and tumors characteristics were collected from the national network NETSARC+ database (http://netsarc.sarcomabcb.org). CIC-RS diagnosis was pathologically and molecularly confirmed with a central review by expert pathologists. Two groups of patients were studied: those treated as classical Ewing sarcomas (cohort EwS) and those treated as high-grade soft tissue sarcomas (cohort STS) according to ESMO and/or EpSSG guidelines. Survival was calculated using the Kaplan-Meier method and the log-rank test was used to compare survival.

RESULTS

Among 79 patients, the male/female sex ratio was 0.7 and the median age at diagnosis was 27 years (range 2-87). With a median follow-up of 37 months, 39 patients died of the disease. Median overall survival from diagnosis was 18 months, with no significant difference between both cohorts (p = 0.9). Nevertheless, when focusing on patients with metastatic disease at diagnosis (N = 21), all patients from cohort STS died of disease while some patients from cohort EwS were still alive and in complete remission.

CONCLUSION

FSG experience confirms the aggressive clinical course of CDS patients regardless of chemotherapy regimen.

A case report of CIC-DUX4 fusion-positive sarcoma in the pelvic cavity with targeted next-generation sequencing results

CIC-DUX4 fusion-positive sarcoma is a subtype of undifferentiated small round cell sarcoma that is rarely reported. As far as we know, less than 200 cases have been reported worldwide to date. The clinicopathologic characteristics of this kind of tumor are non-specific, which makes it difficult to be diagnosed. Therefore, more cases are required to enrich the diagnosis and treatment experience. Here, we present a 17-year-old Asian girl diagnosed with CIC-DUX4 fusion-positive sarcoma after targeted next-generation sequencing. Her clinical manifestation was abdominal pain. Furthermore, a mass in the pelvic cavity and massive ascites were found after an imaging examination. After resection, the mass was sent to the pathology department for a definite diagnosis, and the micromorphology showed an undifferentiated sarcoma with massive necrosis. The tumor cells were round to spindle with clear to eosinophilic cytoplasm and vesicular nuclei. Rhabdoid cells and myxoid mesenchyme were focally shown. Immunohistochemical staining showed diffusely positive for vimentin, cyclin D1, Fli-1, and WT-1 and very focally positive for CD99. Moreover, the targeted next-generation sequencing also revealed other genetic changes in this tumor including LongInDel of POLE, copy number variation of CD79, low tumor mutational burden, and microsatellite stability. With a follow-up time of 6 months, the patient survived the disease and received chemotherapy routinely. This report presented a rare primary site CIC-DUX4 fusion-positive sarcoma (CDS) and revealed novel genetic changes that enrich the manifestation, histology, and cytogenetic scales of this rare sarcoma. In addition, we have summarized the clinicopathologic characteristics of this tumor by reviewing the literature to have a better understanding of CIC-DUX4 fusion-positive sarcomas, which may be helpful for diagnosis and treatment.

Co-expression of ERG and CD31 in a subset of CIC-rearranged sarcoma: a potential diagnostic pitfall

CIC-rearranged sarcoma is characterized by round cell undifferentiated histology, frequent expression of ETV4 and WT1, and aggressive behavior. A clinical encounter of a case with CIC-DUX4 fusion and ERG/CD31 co-expression prompted us to systematically investigate ERG and CD31 expression status in 30 archival cases of CIC-rearranged sarcoma. Half (15) of them showed moderate or strong ERG expression in <5-100% of tumor cells, among which nine showed heterogeneous membranous CD31 reactivity, including four cases each showing diffuse or strong expression. None of them showed uniformly strong and diffuse ERG/CD31 co-expression; however, three cases were initially interpreted and treated as angiosarcoma without response. Except for smaller superficial tumor enrichment, the clinicopathological characteristics of these nine cases of ERG+/CD31+ CIC-rearranged sarcoma did not differ from those of remaining 21 cases. Five showed focal hemorrhagic clefts/cysts, mimicking vascular spaces. All tumors expressed ETV4 and/or nuclear WT1, and fusion to DUX4 was confirmed in seven cases. Four tumors examined by next-generation sequencing harbored no CIC missense mutations. Using DNA methylation profiling, one CD31+ CIC-rearranged sarcoma was clustered with CD31- CIC-rearranged sarcomas, but distant from angiosarcomas. When compared with epithelioid angiosarcomas lacking CIC rearrangements, ERG+/CD31+ CIC-rearranged sarcomas were distinguished by focal myxoid change and the entire lack of vasoformative architecture. The angiosarcomas were characterized by uniform strong expression of ERG and CD31, but none of them were found positive for ETV4 or nuclear WT1. Heterogeneous ERG/CD31 co-expression in a subset of CIC-rearranged sarcoma is a clinically relevant pitfall for angiosarcoma, as these two diseases are treated differently.

CIC-DUX4 sarcomas

PURPOSE OF REVIEW

CIC-DUX4 sarcoma (CDS) is a high-grade undifferentiated round cells sarcoma that belongs to the undifferentiated round cell sarcomas family. It represents less than one percent of sarcomas, defining a rarest among rare malignancies. It affects young adults, displaying soft tissue mass. Considered very aggressive, a high proportion of cases display an advanced disease with lung metastasis at diagnosis. Here we discuss recent progress in molecular characterization of CDS, the main tracks of CDS biology and the current and future prospects of therapeutic approaches.

RECENT FINDINGS

CDS is characterized by a specific oncogenic translocation CIC::DUX4 that induce ETV4 overexpression. Patients with CDS show an aggressive clinical course and have a significantly unfavorable outcome compared to Ewing sarcoma. As of today, there is a lack of consensus on whether they should be treated with an Ewing-like approach, as currently done by most sites, or regarded as high-grade soft tissue sarcoma (STS). Anyway, when feasible, combination regimens including anthracycline and alkylating agents should be favored and patients should not benefit from a therapeutic de-escalation. Overall, registration within clinical trials and prospective registries is recommended.

SUMMARY

Overall, CDS showed a poor prognosis regardless of the patterns of treatment that warrant biological studies to better understand the disease.

Central nervous system sarcoma with ATXN1::DUX4 fusion expands the concept of CIC-rearranged sarcoma

CIC-rearranged sarcoma is a high-grade sarcoma, most often harboring CIC::DUX4 fusion, and is characterized by a distinct round cell histology, co-expression of ETV4 and WT1, and a specific DNA methylation class. Herein, we report a brain tumor with ATXN1::DUX4 that had an indistinguishable phenotype and DNA methylation profile from CIC-rearranged sarcoma. A 40-year-old man presented with a 5 cm hemorrhagic mass in the right frontal lobe of the cerebrum. The tumor was resected and histologically showed a dense proliferation of relatively monomorphic round cells with multifocal myxoid changes. Immunohistochemically, the tumor was diffusely positive for ETV4, WT1, and DUX4. Through classic histomorphology and immunoprofile, the tumor was provisionally diagnosed as CIC-rearranged sarcoma. However, no CIC fusions or mutations were identified using CIC break-apart fluorescence in situ hybridization (FISH) or FoundationOne CDx. Despite multiple surgeries and adjuvant chemoradiation therapy, the patient succumbed 16 months after presentation. RNA exome sequencing detected an in-frame intraexonic ATXN1 (exon 9)::DUX4 (exon 1) fusion, which was validated by reverse transcription-polymerase chain reaction and ATXN1 FISH assay. Upon DNA methylation analysis, the tumor matched with CIC-rearranged sarcoma both by the Deutsche Krebsforschungszentrum classifier and t-distributed stochastic neighbor embedding. Along with a recent report of a similar pediatric brain tumor, the present case suggests that ATXN1::DUX4 is a recurrent alternative molecular event in the sarcoma type that is presently defined by CIC rearrangement, which prompts an expansion of the tumor concept. This article is protected by copyright. All rights reserved.

Comorbidities rather than older age define outcome in adult patients with tumors of the Ewing sarcoma family

Background

Ewing family of tumors (EFT) is rarely diagnosed in patients (pts) over the age of 18 years (years), and data on the clinical course and the outcome of adult EFT pts is sparse.

Methods

In this retrospective analysis, we summarize our experience with adult EFT pts. From 2002 to 2020, we identified 71 pts of whom 58 were evaluable for the final analysis.

Results

Median age was 31 years (18–90 years). Pts presented with skeletal (n = 26), and extra‐skeletal primary disease (n =32). Tumor size was ≥8 cm in 20 pts and 19 pts were metastasized at first diagnosis. Between the age groups (≤25 vs. 26–40 vs. ≥41 years) we observed differences of Charlson comorbidity index (CCI), tumor origin, as well as type and number of therapy cycles. Overall, median overall survival (OS) was 79 months (95% confidence interval, CI; 28.5–131.4 months), and median progression‐free survival (PFS) 34 months (95% CI; 21.4–45.8 months). We observed a poorer outcome (OS, PFS) in older pts. This could be in part due to differences in treatment intensity and the CCI (<3 vs. ≥3; hazard ratio, HR 0.334, 95% CI 0.15–0.72, p = 0.006). In addition, tumor stage had a significant impact on PFS (localized vs. metastasized stage: HR 0.403, 95% CI 0.18–0.87, p = 0.021).

Conclusions

Our data confirms the feasibility of intensive treatment regimens in adult EFT pts. While in our cohort outcome was influenced by age, due to differences in treatment intensity, CCI, and tumor stage, larger studies are warranted to further explore optimized treatment protocols in adult EFT pts.

Primary cardiac CIC-rearranged undifferentiated sarcoma in an infant

INTRODUCTION

Cardiac neoplasms are particularly rare in children, and the majority of these tumors are benign. Approximately 10% of cardiac neoplasms are malignant, including soft tissue sarcomas and lymphomas. Cardiac tumors could also be metastases. Primitive EWSR1-negative round or spindle cell undifferentiated sarcoma harboring CIC gene translocation is a highly aggressive malignancy mainly occurring in soft tissues. However, it has not yet been described in the heart.

CASE PRESENTATION

We report a sarcoma that arose from the right ventricle in a 1-year-old girl. Histologically, it was composed of closely arranged small round or oval undifferentiated cells with fibrovascular separation, hyaline degeneration, and geographical necrosis. Immunohistochemically, the neoplastic cells exhibited focal membrane positivity for CD99 and diffuse positivity for WT1 and ETV4. Fluorescent in situ hybridization analysis showed EWSR1-negative but CIC-positive split signals. The breakpoint was also confirmed by whole genome sequencing.

CONCLUSION

Based on morphological, immunohistochemical and molecular findings, this cardiac mass was diagnosed as CIC-rearranged sarcoma.

Cytarabine and EIP co-administration synergistically reduces viability of acute lymphoblastic leukemia cells with high ERG expression

The E26 transformation sequence-related gene ERG encodes a transcription factor involved in normal hematopoiesis, and its expression is abnormal in leukemia. Especially in a type of acute lymphoblastic leukemia (ALL) that is refractory and easy to relapse, the expression of ERG protein is abnormally increased. Chemotherapy can alleviate the condition of ALL, but the location and survival mechanism of the remaining ALL cells after chemotherapy are still not fully understood. It is becoming increasingly clear that the interaction between leukemia cells and their microenvironment plays an important role in the acquisition of drug resistance mutations and disease recurrence. We selected an acute lymphocytic leukemia cell line with high ERG expression, and studied the synergistic effect of chemotherapeutics and small molecule peptides through cell proliferation, apoptosis, and cell cycle experiments; At the same time, we inoculated acute lymphocytic leukemia cells with high ERG expression into mice with severe immunodeficiency to simulate human ALL and investigated (i) the effects of co-administration on the nesting and invasion of leukemia cells and (ii) the effects of the small molecule peptide drug EIP, which targets ERG, on the sensitivity of ALL chemotherapy and the underlying mechanisms.Ara-c and EIP synergistically reduces viability of ALL cells with high ERG expression may be achieved by promoting their apoptosis and inhibiting their nesting.

Control of DUX4 Expression in Facioscapulohumeral Muscular Dystrophy and Cancer

DUX4, a gene encoding a transcription factor involved in early embryogenesis, is located within the D4Z4 subtelomeric repeat on chromosome 4q35. In most healthy somatic tissues, DUX4 is heavily repressed by multiple genetic and epigenetic mechanisms, and its aberrant expression is linked to facioscapulohumeral muscular dystrophy (FSHD) where it has been extensively studied. Recently, DUX4 expression has been implicated in oncogenesis, although this is much less explored. In this review, we discuss multiple levels of control of DUX4 expression, including enhancer-promoter interactions, DNA methylation, histone modifications, noncoding RNAs, and telomere positioning effect. We also connect disparate data on intrachromosomal contacts involving DUX4 and emphasize the feedback loops in DUX4 regulation. Finally, we bridge data on DUX4 in FSHD and cancer and discuss prospective approaches for future FSHD therapies and the potential outcomes of DUX4 inhibition in cancer.

Round Cell Sarcomas: Newcomers and Diagnostic Approaches

Undifferentiated sarcomas of soft tissue and bone have been defined as tumors with no identifiable morphologic, immunohistochemical, or molecular features indicating tumor cell origin. In young patients, these tumors frequently have a round or spindle cell morphology. Recently described recurrent translocations within this category have led to the recognition of new molecular subtypes of round cell sarcomas, and several of them have a more aggressive clinical course and less chemosensitivity. Because these "newcomers" are diagnosed based on their molecular characteristics, molecular investigation is key in the diagnosis and optimal treatment of these challenging tumors.

Subcutaneous desmoplastic small round-cell tumor: An unusual primary location expanding the differential of superficial round-cell tumors

Desmoplastic small round-cell tumor (DSRCT) is a rare, aggressive malignant tumor, which in the great majority of cases arises at abdominal-pelvic sites. Nevertheless, rare cases of primary extra-abdominal tumors have been reported. In challenging cases, its molecular hallmark, the EWSR1-WT1 reciprocal translocation, can be exploited diagnostically by various molecular techniques. Herein, we report an extremely rare case of primary subcutaneous DSRCT in an effort to raise awareness among our dermatopathology colleagues by expanding the differential of superficial round-cell tumors.

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

The CIC-DUX4 translocation is the most common genetic alteration of small round cell sarcomas without EWSR1 rearrangement. These "Ewing-like sarcomas" usually occur in peripheral soft tissues, and rare primary central nervous system (CNS) tumors have been described. We report a rare case of primary spinal intramedullary Ewing-like sarcoma harboring CIC-DUX4 translocation. A 23-year-old man presented with weakness in the extremities. Magnetic resonance imaging revealed a large intramedullary tumor spanning C3-C5 with heterogeneous enhancement following gadolinium administration. Histologically, most of the tumor displayed dense myeloid proliferation composed of medium- to slightly small-sized primitive cells. Postoperatively, he received local adjuvant radiation therapy without tumor progression for 10 months. Target RNA sequencing analysis revealed the CIC-DUX4 fusion gene. Methylation array analysis resulted in a diagnosis of "methylation class CNS Ewing sarcoma family tumor with CIC alteration". Although this tumor lacked characteristic histological features such as lobular structures in association with desmoplastic stroma, relatively uniform nuclei with prominent nucleoli and eosinophilic cytoplasm, which are often found in CIC-rearranged sarcomas of soft tissue, were identified. Recently, many CNS and soft tissue tumors require genetic analysis for precise diagnosis. To consider certain molecular testing, careful histological examination is essential.

Pancreaticoduodenectomy for a primary duodenal capicua transcriptional repressor (CIC) -rearranged sarcoma with severe bleeding: a case report

BACKGROUND

Capicua transcriptional repressor (CIC) -rearranged sarcoma is characterized by small round cells, histologically similar to Ewing sarcoma. However, CIC-rearranged sarcoma has different clinical, histological, and immunohistochemical features from Ewing sarcoma. It is important to differentiate between these tumors.

CASE PRESENTATION

The patient is a 44-year-old man with a duodenal tumor diagnosed in another hospital who presented with a history of melena. Laboratory studies showed anemia with a serum hemoglobin of 6.0 g/dL. He was hospitalized and gastrointestinal bleeding was controlled successfully with endoscopy. However, he suffered from appetite loss and vomiting and progression of anemia a few weeks after presentation. Upper gastrointestinal endoscopy showed a circumferential soft tumor in the second portion of the duodenum and the endoscope could not pass distally. Computed tomography scan showed a greater than 10 cm tumor in the duodenum, with compression of the inferior vena cava and infiltrating the ascending colon. A definitive pathologic diagnosis could not be established despite four biopsies from the tumor edge. Due to gastrointestinal obstruction and progression of anemia, a pylorus-preserving pancreaticoduodenectomy with partial resection of the inferior vena cava and right hemicolectomy was performed as a complete tumor resection. The tumor was diagnosed as a CIC-rearranged sarcoma, but 2 months postoperatively local recurrence and distant metastases to the liver and lung were found. The patient died 3 months after surgery.

CONCLUSIONS

Although the only definitive treatment for CIC-rearranged sarcoma is surgical resection, the CIC-rearranged sarcoma is highly malignant with a poor prognosis even after radical resection. More research is needed to establish optimal treatment strategies.

Capicua Transcriptional Repressor-Rearranged Undifferentiated Round Cell Sarcoma Metastatic to the Brain Treated with Surgery and Stereotactic Radiosurgery

BACKGROUND

Ewing-like sarcoma with capicua transcriptional repressor (CIC) rearrangement is a unique class of undifferentiated round cell sarcomas characterized by CIC-double homeobox 4 gene fusion. Despite showing great histologic resemblance to Ewing sarcomas, they have proved to be a distinct pathological entity from the immunohistochemistry and genetic examinations and the response to treatment. We have presented a case of CIC-rearranged Ewing-like sarcoma with cerebral metastasis managed with operative resection and gamma knife radiosurgery.

CASE DESCRIPTION

A 56-year-old woman had initially presented with an ulcerating lesion of the right fifth toe. The histological and immunohistochemical analysis revealed features consistent with CIC-rearranged Ewing-like sarcoma, which was confirmed with genetic analysis. Despite aggressive local control and a multidrug chemotherapy regimen, the patient developed multifocal metastases involving the lungs, femur, and cerebrum. The cerebral lesions were managed with surgery and gamma knife radiosurgery, with mixed results.

CONCLUSION

CIC-rearranged Ewing-like sarcomas have recently been recognized as a distinct disease entity with a highly aggressive course. Treatment paradigms have yet to be defined to properly manage such an aggressive pathological process.

[Malignant round cell tumors : The Ewing sarcoma and beyond]

Ewing sarcomas are highly malignant tumors that are mainly found in children and adolescents. In addition to early clinical diagnosis, correct histopathological and molecular genetic classification is the most important step. Although EWSR1-FLI1 fusion is by far the most common detectable change, there are also other representatives of the Ewing sarcoma family that cannot be distinguished histopathologically and immunohistochemically from classical Ewing sarcomas and that have different molecular genetic profiles. Although a precise molecular genetic differentiation of the various representatives of small round blue cell tumors does not yet lead to any change in the standard chemotherapy and surgical treatment applied, it does allow an estimation of the prognosis and will probably contribute in the future to an even more individualized treatment of Ewing sarcomas within the framework of personalized medicine.

DNA Methylation Profiling for Diagnosing Undifferentiated Sarcoma with Capicua Transcriptional Receptor (CIC) Alterations

Undifferentiated soft tissue sarcomas are a group of diagnostically challenging tumors in the pediatric population. Molecular techniques are instrumental for the categorization and differential diagnosis of these tumors. A subgroup of recently identified soft tissue sarcomas with undifferentiated round cell morphology was characterized by Capicua transcriptional receptor (CIC) rearrangements. Recently, an array-based DNA methylation analysis of undifferentiated tumors with small blue round cell histology was shown to provide a highly robust and reproducible approach for precisely classifying this diagnostically challenging group of tumors. We describe the case of an undifferentiated sarcoma of the abdominal wall in a 12-year-old girl. The patient presented with a voluminous mass of the abdominal wall, and multiple micro-nodules in the right lung. The tumor was unclassifiable with current immunohistochemical and molecular approaches. However, DNA methylation profiling allowed us to classify this neoplasia as small blue round cell tumor with CIC alterations. The patient was treated with neoadjuvant chemotherapy followed by complete surgical resection and adjuvant chemotherapy. After 22 months, the patient is disease-free and in good clinical condition. To put our experience in context, we conducted a literature review, analyzing current knowledge and state-of-the-art diagnosis, prognosis, and clinical management of CIC rearranged sarcomas. Our findings further support the use of DNA methylation profiling as an important tool to improve diagnosis of non-Ewing small round cell tumors.

Superficial sarcomas with CIC rearrangement are aggressive neoplasms: A series of eight cases

CIC rearranged sarcomas have significant overlap with Ewing sarcoma, are aggressive, and typically present in deep soft tissue. They most commonly have a t(4;19)(q35;q13) with CIC-DUX4 fusion. Superficial presentation is rare. We report eight (6F, 2M; median 45-years-old, range 14-65) superficial CIC-rearranged sarcomas, involving the extremities (n = 4), vulva (n = 2), and trunk (n = 2). The tumors were composed of nodules/sheets of round cells with necrosis and hemorrhage separated by dense hyaline bands. Tumor cells had vesicular chromatin, prominent nucleoli and frequent mitotic figures. One showed pagetoid spread. Targeted next-generation sequencing was positive for CIC-DUX4 fusion (6/6); fluorescence in situ hybridization (FISH) was positive for CIC rearrangement (2/3). Eight of eight had evidence of CIC-DUX4 fusion/rearrangement by molecular techniques. Immunohistochemistry was positive for CD99+ (8/8) and DUX4+ (4/4). FISH for EWSR1 rearrangement was negative (5/5). Of five patients with at least 6 months follow-up, three of five died of disease, all within 2 years of presentation. One is alive with disease at 48 months. One is disease free at 3 months. Superficial CIC-rearranged sarcomas should be considered in cases exhibiting features reminiscent of Ewing sarcoma, but with increased pleomorphism and/or geographic necrosis. In contrast to superficial Ewing sarcomas, superficial CIC-rearranged sarcomas are aggressive.

Expanding the differential of superficial tumors with round-cell morphology: Report of three cases of CIC-rearranged sarcoma, a potentially under-recognized entity

Among sarcomas with a round-cell morphology that lack rearrangement of the EWSR1 gene, rearrangements involving the CIC gene are the most common. In comparison with Ewing Sarcoma, CIC-rearranged sarcomas present at an older average age, arise almost exclusively in soft tissues, are clinically more aggressive, and are more likely to be resistant to the chemotherapy regimens used for Ewing sarcoma. CIC-rearranged sarcomas present more commonly in a deep location, and we suspect that superficial presentations may be under-recognized. In this case series, we report three of such cases. Overall, the morphology is similar to CIC-rearranged sarcomas of deeper locations. We hope to raise awareness among the dermatopathology community by expanding the differential of superficial tumors with round cell morphology.

Ewing sarcoma and Ewing-like tumors

Ewing sarcoma (ES) and Ewing-like sarcomas are highly aggressive round cell mesenchymal neoplasms, most often occurring in children and young adults. The identification of novel molecular alterations has greatly contributed to a profound reappraisal of classification, to the extent that the category of undifferentiated round cell sarcoma has significantly shrunk. In fact, in addition to Ewing sarcoma, we currently recognize three main categories: round cell sarcomas with EWSR1 gene fusion with non-ETS family members, CIC-rearranged sarcomas, and BCOR-rearranged sarcomas. Interestingly, despite significant morphologic overlap, most of these entities tend to exhibit morphologic features predictive of the underlying molecular alteration. Ewing sarcoma is the prototype of round cell sarcoma whereas in CIC sarcomas, focal pleomorphism and epithelioid morphology can predominate. BCOR sarcomas often exhibit a spindled neoplastic cell population. NFATC2 sarcoma may exhibit remarkable epithelioid features, and PATZ1 sarcomas often feature a sclerotic background. The differential diagnosis for these tumors is rather broad, and among round cell sarcomas includes alveolar rhabdomyosarcoma, desmoplastic small round cell tumor, poorly differentiated round cell synovial sarcoma, small cell osteosarcoma, and mesenchymal chondrosarcoma. A combination of morphologic, immunohistochemical, and molecular findings allows accurate classification in most cases. A granular diagnostic approach to Ewing sarcoma and Ewing-like sarcomas is justified by significant differences in terms of both response to chemotherapy and overall survival. As all these entities are in part defined by specific fusion genes, a molecular diagnostic approach based on NGS technology should be considered. In consideration of the extreme rarity of many of these tumor entities, referral to expert rare cancer centers or to rare cancer networks represents the best strategy in order to minimize diagnostic inaccuracy, and allow proper patient management.

Comparative transcriptome analysis of sinonasal inverted papilloma and associated squamous cell carcinoma: Out-HOXing developmental genes

BACKGROUND

Sinonasal papilloma has a tendency toward local destruction, recurrence, and malignant transformation. This study aimed to unravel mechanisms in the malignant transformation of sinonasal papillomas using RNA-seq.

METHODS

The cohort consisted of 37 consecutive patients; tumor histology included a continuum spectrum (sinonasal papillomas/dysplastic/carcinomas-in-situ/invasive squamous cell carcinomas). These were microdissected and RNA was subjected to whole-transcriptome shotgun sequencing.

RESULTS

RNA-seq and pathway analysis showed that the highest expressed genes/potential drivers were development- and differentiation-related genes. The protein expression of six highly upregulated genes (HOXA9, EN1, DUX4, CA9, CD1a, and CK5/6) validated the RNA-seq results. HOXA9 and CA9 were found to be expressed in most of the carcinoma samples but were largely negative in papillomas; all of the CA9-negative carcinomas were recurrent.

CONCLUSIONS

We conclude that sinonasal carcinomas arising from papillomas are mainly defined by overexpressed developmental/homeobox genes, which provide the potential for transformation/plasticity, along with differentiation and proliferation behavior of neoplastic cells. Our results support HOXA9 and CA9 as biomarkers for carcinomas, with CA9 emerging as a predictive marker of recurrence.

Important Recently Characterized Non-Ewing Small Round Cell Tumors

Round cell sarcomas morphologically similar to Ewing sarcoma, but lacking the classic immunohistochemical features, EWSR-ETS family fusions, and other signs of differentiation, are classified as Ewing-like sarcomas. Recent molecular advances led to the discovery and characterization of two recurrent oncogenic fusion rearrangements, CIC-DUX4 and BCOR-CCNB3, in a significant subset of Ewing-like sarcomas. Uncovered alternate fusion partners broadened the proposed classification of these tumors to CIC-rearranged sarcomas and BCOR-rearranged sarcomas. This article summarizes the clinicopathologic and molecular features of these entities, with particular attention paid to those features that overlap with and distinguish these sarcomas from other round cell sarcomas.

Duxbling Stem Cells Meet Tumorigenesis

Identification of tumor-initiating populations could provide insights into tumor heterogeneity and responses to treatments, but this has proven difficult in most cancers. Now in Cell Stem Cell, Preussner et al. (2018) provide direct evidence that regenerating muscle satellite cells can be transformed to initiate and propagate rhabdomyosarcoma tumors.

Clinical Utility of In Situ Hybridization Assays in Head and Neck Neoplasms

Head and neck pathology present a unique set of challenges including the morphological diversity of the neoplasms and presentation of metastases of unknown primary origin. The detection of human papillomavirus and Epstein-Barr virus associated with squamous cell carcinoma and newer entities like HPV-related carcinoma with adenoid cystic like features have critical prognostic and management implications. In salivary gland neoplasms, differential diagnoses can be broad and include non-neoplastic conditions as well as benign and malignant neoplasms. The detection of specific gene rearrangements can be immensely helpful in reaching the diagnosis in pleomorphic adenoma, mucoepidermoid carcinoma, secretory carcinoma, hyalinizing clear cell carcinoma and adenoid cystic carcinoma. Furthermore, molecular techniques are essential in diagnosis of small round blue cell neoplasms and spindle cell neoplasms including Ewing sarcoma, rhabdomyosarcoma, synovial sarcoma, biphenotypic sinonasal sarcoma, dermatofibrosarcoma protuberans, nodular fasciitis and inflammatory myofibroblastic tumor. The detection of genetic rearrangements is also important in lymphomas particularly in identifying 'double-hit' and 'triple-hit' lymphomas in diffuse large B cell lymphoma. This article reviews the use of in situ hybridization in the diagnosis of these neoplasms.

Genomics of a pediatric ovarian fibrosarcoma. Association with the DICER1 syndrome

Ovarian fibrosarcomas are extremely rare tumors with little genomic information available to date. In the present report we present the tumoral exome and transcriptome and the germinal exome of an ovarian fibrosarcoma from a 9-years old child. We found a paucity of mutations (0.77/Mb) and CNV alterations. Of these, the most relevant were a point mutation in the metal-binding site of the microRNA-processing DICER1 enzyme and a frame-shift alteration in the tumor suppressor gene NF1. We validated a germinal truncating mutation in DICER1, which was consistent with a DICER1 Syndrome diagnosis, providing the first example of an ovarian fibrosarcoma as the presenting neoplasia in this syndrome. Network and enrichment analyses showed that both a mesenchymal signature and a Hedgehog cascade could be driving the progression of this tumor. We were also able to find a global lincRNA deregulation, as the number of lincRNAs transcripts expressed in the tumor was decreased, with a concomitant upregulation of previously described non-coding transcripts associated with cancer, such as MALAT1, MIR181A1HG, CASC1, XIST and FENDRR. DICER1 Syndrome should be considered as a possible diagnosis in children ovarian fibrosarcoma. The role of lncRNAs in neoplasias associated with DICER1 alterations need to be studied in more detail.

Primary Spinal Epidural CIC-DUX4 Undifferentiated Sarcoma in a Child

Primitive round- or spindle-cell EWSR1-negative undifferentiated sarcomas harboring CIC-DUX4 gene fusion are the most common form of Ewing-like sarcomas. These tumors primarily occur in peripheral soft tissues, but examples have been described within viscera and the brain. As far as we are aware, CIC-DUX4 positive primary epidural spinal sarcoma has not been reported. Herein, we describe a T5-T6 epidural tumor in a 15-year-old girl in which many neoplastic cells had moderate and focally abundant cytoplasm, including plasmacytoid or rhabdoid cells, rather than the more common Ewing-like morphology described in the majority of such tumors. The diagnosis was confirmed by fluorescent in situ hybridization after the tumor was found to be WT-1 positive, and comprehensive genomic profiling demonstrated breakpoints in exon 20 and exon 1 of the CIC and DUX4 genes, respectively. After treatment with local radiation and systemic chemotherapy, resected recurrent tumor demonstrated more pleomorphic neoplastic cells as well as intracytoplasmic eosinophilic globules and nuclear pseudoinclusions which may reflect therapy-related changes. Unfortunately, there was further progression of tumor including the development of intracranial lesions, and the patient succumbed to her tumor 22 months after the original resection.

DNA Methylation-Based Classifier for Accurate Molecular Diagnosis of Bone Sarcomas

Purpose

Pediatric sarcomas provide a unique diagnostic challenge. There is considerable morphologic overlap between entities, increasing the importance of molecular studies in the diagnosis, treatment, and identification of therapeutic targets. We developed and validated a genome-wide DNA methylation based classifier to differentiate between osteosarcoma, Ewing's sarcoma, and synovial sarcoma.

Materials and Methods

DNA methylation status of 482,421 CpG sites in 10 Ewing's sarcoma, 11 synovial sarcoma, and 15 osteosarcoma samples were determined using the Illumina Infinium HumanMethylation450 array. We developed a random forest classifier trained from the 400 most differentially methylated CpG sites within the training set of 36 sarcoma samples. This classifier was validated on data drawn from The Cancer Genome Atlas (TCGA) synovial sarcoma, TARGET Osteosarcoma, and a recently published series of Ewing's sarcoma.

Results

Methylation profiling revealed three distinct patterns, each enriched with a single sarcoma subtype. Within the validation cohorts, all samples from TCGA were accurately classified as synovial sarcoma (10/10, sensitivity and specificity 100%), all but one sample from TARGET-OS were classified as osteosarcoma (85/86, sensitivity 98%, specificity 100%) and 14/15 Ewing's sarcoma samples classified correctly (sensitivity 93%, specificity 100%). The single misclassified osteosarcoma sample demonstrated high EWSR1 and ETV1 expression on RNA-seq although no fusion was found on manual curation of the transcript sequence. Two additional clinical samples, that were difficult to classify by morphology and molecular methods, were classified as osteosarcoma when previously suspected to be a synovial sarcoma and Ewing's sarcoma on initial diagnosis, respectively.

Conclusion

Osteosarcoma, synovial sarcoma, and Ewing's sarcoma have distinct epigenetic profiles. Our validated methylation-based classifier can be used to provide diagnostic assistance when histological and standard techniques are inconclusive.

EWSR1 fusion proteins mediate PAX7 expression in Ewing sarcoma

PAX7 is a paired-box transcription factor that is required for the developmental specification of adult skeletal muscle progenitors in mice. We previously demonstrated PAX7 expression as a marker of skeletal muscle differentiation in rhabdomyosarcoma. Here, using analyses of published whole-genome gene expression microarray data, we identify PAX7 as a gene with significantly increased expression in Ewing sarcoma in comparison to CIC-DUX4 round cell sarcoma. Analysis of PAX7 in a large cohort of 103 Ewing sarcoma cases by immunohistochemistry revealed expression in 99.0% of cases (102/103). PAX7 expression was noted in cases demonstrating three distinct Ewing sarcoma EWSR1 translocations involving FLI1, ERG, and NFATc2. No PAX7 expression was observed in any of 27 cases of CIC-DUX4 sarcoma by immunohistochemistry (0%; 0/27). Exploring the mechanism of PAX7 expression in Ewing sarcoma using curated RNA- and ChIP-sequencing data, we demonstrate that the EWSR1 fusion protein is required for PAX7 expression in Ewing sarcoma and identify a candidate EWSR1-FLI1-bound PAX7 enhancer that coincides with both a consensus GGAA repeat-containing binding site and a peak of regulatory H3K27 acetylation. Taken together, our findings provide mechanistic support for the utility of PAX7 immunohistochemistry in the diagnosis of Ewing sarcoma, while linking this sarcoma of uncertain histogenesis to a key transcriptional regulator of mammalian muscle progenitor cells.

INI Expressing Epithelioid Sarcoma with Osteoclastic Giant Cells in a Child: A Case Report with Summary of Prior Published Cases

BACKGROUND

Epithelioid sarcoma is a heterogeneous tumor with 2 subtypes, classic and proximal. The proximal variant is more aggressive and occurs in proximal location in young adults.

CASE REPORT

We present a proximal epithelioid sarcoma in the leg of an 8 year old girl with rhabdoid morphology and scattered osteoclastic giant cells. Nuclear INI-1 was retained. Despite wide local excision, local recurrence occurred at 8 months. Following re-excision, she developed a chest wall metastasis after 9 months.

CONCLUSION

Epithelioid sarcoma, proximal type with osteoclastic giant cells in the pediatric age group has not been reported previously and should be considered in the differential diagnoses of tumors with epithelioid cell morphology and scattered osteoclastic giant cells. Retained INI expression helped to differentiate this tumor from malignant rhabdoid tumor.

DUX4 Immunohistochemistry Is a Highly Sensitive and Specific Marker for CIC-DUX4 Fusion-positive Round Cell Tumor

The histologic differential diagnosis of pediatric and adult round cell tumors is vast and includes the recently recognized entity CIC-DUX4 fusion-positive round cell tumor. The diagnosis of CIC-DUX4 tumor can be suggested by light microscopic and immunohistochemical features, but currently, definitive diagnosis requires ancillary genetic testing such as conventional karyotyping, fluorescence in situ hybridization, or molecular methods. We sought to determine whether DUX4 expression would serve as a fusion-specific immunohistochemical marker distinguishing CIC-DUX4 tumor from potential histologic mimics. A cohort of CIC-DUX4 fusion-positive round cell tumors harboring t(4;19)(q35;q13) and t(10;19)(q26;q13) translocations was designed, with additional inclusion of a case with a translocation confirmed to involve the CIC gene without delineation of the partner. Round cell tumors with potentially overlapping histologic features were also collected. Staining with a monoclonal antibody raised against the C-terminus of the DUX4 protein was applied to all cases. DUX4 immunohistochemistry exhibited diffuse, crisp, strong nuclear staining in all CIC-DUX4 fusion-positive round cell tumors (5/5, 100% sensitivity), and exhibited negative staining in nuclei of all of the other tested round cell tumors, including 20 Ewing sarcomas, 1 Ewing-like sarcoma, 11 alveolar rhabdomyosarcomas, 9 embryonal rhabdomyosarcomas, 12 synovial sarcomas, 7 desmoplastic small round cell tumors, 3 malignant rhabdoid tumors, 9 neuroblastomas, and 4 clear cell sarcomas (0/76, 100% specificity). Thus, in our experience, DUX4 immunostaining distinguishes CIC-DUX4 tumors from other round cell mimics. We recommend its use when CIC-DUX4 fusion-positive round cell tumor enters the histologic differential diagnosis.

CIC break-apart fluorescence in-situ hybridization misses a subset of CIC-DUX4 sarcomas: a clinicopathological and molecular study

AIMS

Approximately 60-70% of high-grade round-cell sarcomas that lack the Ewing sarcoma breakpoint region 1 (EWSR1) rearrangement harbour a rearrangement of the CIC gene, most commonly CIC-DUX4. Recent studies have established that CIC-rearranged sarcomas constitute a distinct group characterized by recognizable histology and immunoprofiles, such as positivity for ETV4 and WT1 and negativity for NKX2.2. Although these sarcomas are diagnosed increasingly in practice by fluorescence in-situ hybridization (FISH) with CIC break-apart probes, the optimal modality to diagnose these sarcomas has not been determined. In this study, we describe four round-cell sarcomas that showed false-negative results by CIC break-apart FISH assays.

METHODS AND RESULTS

These sarcomas showed characteristic histology of CIC-rearranged sarcomas, and all were immunohistochemically positive for ETV4 and WT1 and negative for NKX2.2. Although FISH showed non-atypical negative signals for CIC rearrangement, high-throughput RNA sequencing identified CIC-DUX4 and its fusion breakpoint in all cases. Their clinical and histological findings, as well as fusion points determined by RNA sequencing, did not differ significantly from those of nine FISH-positive CIC-DUX4 sarcoma cases. We estimated that the FISH false-negative rate for CIC-rearranged sarcomas was 14%. Although neither histology nor immunoprofiles (e.g. ETV4 and WT1) are entirely sensitive or specific for CIC-rearranged sarcomas, the observation that these four cases were identified successfully by such phenotypes suggested their practical utility.

CONCLUSIONS

CIC break-apart FISH assays missed a significant minority of CIC-DUX4 sarcomas, and full awareness of typical morphology and judicious immunohistochemical work-ups, including analyses of ETV4 and WT1, should complement diagnostic assessment.

Update on Families of Round Cell Sarcomas Other than Classical Ewing Sarcomas

This article focuses on families of round cell sarcomas other than classical Ewing sarcomas. Until recently, these tumors were referred to as so-called Ewing-like tumors, as they morphologically resemble Ewing sarcomas but are negative for canonical fusion transcripts of Ewing sarcomas involving gene members of the ETS family of transcription factors. Clinicopathologic and molecular evidence has dramatically influenced the diagnostic approach of these tumors in recent years. Molecular data that support these sarcoma subtypes are biologically distinct from those of Ewing sarcomas, thereby advocating discarding the all-embracing and confusing terminology of "Ewing-like tumors."

Primary undifferentiated small round cell sarcoma of the deep abdominal wall with a novel variant of t(10;19) CIC-DUX4 gene fusion

We experienced a 38-year-old Japanese male with t(10;19) CIC-DUX4 -positive undifferentiated small round cell sarcoma in the deep abdominal wall. Three months before his first visit to our hospital, he noticed a mass in his right abdominal wall. Computed tomography on admission revealed a solid abdominal tumor 70×53mm in size and multiple small tumors in both lungs. The biopsy of the abdominal tumor revealed undifferentiated small round cell sarcoma, suggestive of Ewing sarcoma. Under the clinical diagnosis of Ewing-like sarcoma of the abdominal wall with multiple lung metastases, several cycles of ICE (ifosfamide, carboplatin and etoposide) therapy were performed. After the chemotherapy, the lung metastases disappeared, while the primary lesion rapidly grew. Additional VDC (vincristine, doxorubicin and cyclophosphamide) therapy was carried out without apparent effect. Although the surgical removal of the primary lesion was done, peritoneal dissemination and a huge metastatic liver tumor appeared thereafter. The patient died of disease progression two months after the surgery. The total clinical course was approximately one year, showing that the tumor was extremely aggressive. The tumor cells of the surgical specimen were positive for CD99, WT1, calretinin, INI1, ERG and Fli1 by immunohistochemistry. Fusion gene analyses using the frozen surgical material revealed negativity for EWSR1-Fli1, EWSR1-ERG and t(4;19) CIC-DUX4 fusions, but positivity for t(10;19) CIC-DUX4 fusion. Thus, we made a final pathological diagnosis of t(10;19) CIC-DUX4-positive undifferentiated small round cell sarcoma. To our knowledge, this is the 13th case of t(10;19) CIC-DUX4 undifferentiated small round cell sarcoma with precise clinicopathological information. Especially in our case, two types of t(10;19) CIC-DUX4 fusion transcripts were observed, both of which are in-frame and novel.

The utility of ETV1, ETV4 and ETV5 RNA in-situ hybridization in the diagnosis of CIC-DUX sarcomas

AIMS

A recently characterized group of undifferentiated small round cell sarcomas harbours fusions of the genes CIC and DUX4. Studies report a distinctive gene expression profile for these sarcomas, including expression of E26 transformation-specific (ETS) family proto-oncogenic transcription factors ETV1, ETV4 and ETV5. To test the utility of an ancillary diagnostic technique for these tumours, we evaluated chromogenic RNA in-situ hybridization assays for ETV1, ETV4 and ETV5 as diagnostic adjuncts for this emerging group of highly malignant sarcomas.

METHODS AND RESULTS

We tested six confirmed CIC-DUX4 sarcomas and 105 lesions in the differential, including 48 Ewing sarcomas for expression of ETV1, ETV4 and ETV5, scoring expression utilizing a previously validated scale. ETV1 and ETV4 were positive in five of six cases, while ETV5 was positive in six of six. No Ewing sarcoma or other sarcoma tested showed coexpression of these transcripts, while one ETV1/ETV4/ETV5 triple positive previously unclassified round cell sarcoma was identified as harbouring a CIC rearrangement by break-apart fluorescence in-situ hybridization (FISH).

CONCLUSION

We identified overexpression of ETV1, ETV4 and ETV5 transcripts in situ in CIC-DUX4 sarcomas using a robust assay in routine archival sections. One previously unclassified round cell sarcoma showed ETV1/4/5 positivity, and was proved to harbour a CIC rearrangement by break-apart FISH. The sensitivity and specificity observed with our in-situ hybridization assay implies potential utility as an ancillary diagnostic technique, particularly when faced with limited biopsy samples.