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

Updates on WHO classification for small round cell tumors: Ewing sarcoma vs. everything else

The WHO Classification of Soft Tissue and Bone Tumours currently recognizes four categories of undifferentiated small round cell sarcoma: Ewing sarcoma, round cell sarcoma with EWSR1-non-ETS fusions including NFATc2 and PATZ1, CIC-rearranged sarcoma, and sarcoma with BCOR genetic alterations. These neoplasms frequently pose significant diagnostic challenges due to rarity and overlapping morphologic and immunohistochemical findings. Further, molecular testing, with accompanying pitfalls, may be needed to establish a definitive diagnosis. This review summarizes the clinical, histologic, immunohistochemical, and molecular features of these neoplasms. In addition, differential diagnosis and areas of uncertainty and ongoing investigation are discussed.

A Rare Case of a Malignant Epithelioid Neoplasm With an Underlying Novel EWSR1::ZBT44 Fusion, Identified on Next-Generation Sequencing (NGS)

The clinicopathological spectrum of undifferentiated round cell sarcomas of bone and soft tissues is expanding after the 5th edition of the WHO classification. A 23-year-old male patient presented with a lump in his left thigh of 3 months' duration. Radiological examination revealed a well-defined, solid-cystic lobulated, soft tissue lesion in the proximal medial region of his left thigh, measuring 7.7 cm in the largest dimension. The referring diagnosis was an epithelioid sarcoma. Histopathological review of the tumor sections revealed a cellular tumor composed of malignant epithelioid to focally "rhabdoid-like" cells in a variable hyalinized and myxoid stroma with geographic areas of necrosis. In addition, there were areas reminiscent of hemangiopericytomatous vasculature. By immunohistochemistry, the tumor cells were diffusely positive for CD34, focally and distinctly for pan keratin (AE1/AE3). INI1/SMARCB1 and SMARCA4 (BRG1) were diffusely positive (normal). Next-generation sequencing with a wide sarcoma panel revealed EWSR1exon8::ZBT44exon4 fusion. The present example constitutes the first malignant epithelioid tumor with a hemangiopericytomatous growth pattern, exhibiting this rare fusion. The differential diagnoses of this tumor and their corresponding immunohistochemical profile are discussed. This example highlights the value of NGS in unraveling rare fusions and in differentiating these tumors from their several mimics.

Clinical outcomes of patients with CIC-rearranged sarcoma: a single institution retrospective analysis

PURPOSE

CIC-rearranged sarcomas represent a type of undifferentiated small round cell sarcoma (USRCS) characterized by poor survival, rapid development of chemotherapy resistance, and high rates of metastasis. We aim to contribute to the growing body of knowledge regarding diagnosis, treatment, clinical course, and outcomes for these patients.

METHODS

This case series investigates the clinical courses of ten patients with CIC-rearranged sarcoma treated at the Johns Hopkins Hospital from July 2014 through January 2024. Clinical data were retrospectively extracted from electronic medical records.

RESULTS

Patients ranged from 10 to 67 years of age at diagnosis, with seven patients presenting with localized disease and three with metastatic disease. Tumors originated from soft tissues of various anatomic locations. Mean overall survival (OS) was 22.1 months (10.6-52.2), and mean progression-free survival (PFS) was 16.7 months (5.3-52.2). Seven patients received intensive systemic therapy with an Ewing sarcoma-directed regimen or a soft tissue sarcoma-directed regimen. Three patients experienced prolonged disease-free survival without systemic treatment.

CONCLUSION

Most patients in this case series demonstrated aggressive clinical courses consistent with those previously described in the literature, although we note a spectrum of clinical outcomes not previously reported. The diversity of clinical courses underscores the need for an improved understanding of individual tumor biology to enhance clinical decision-making and patient prognosis. Despite its limitations, this article broadens the spectrum of reported clinical outcomes, providing a valuable addition to the published literature on this rare cancer.

CIC-DUX4 Chromatin Profiling Reveals New Epigenetic Dependencies and Actionable Therapeutic Targets in CIC-Rearranged Sarcomas

CIC-DUX4-rearranged sarcoma (CDS) is a rare and aggressive soft tissue tumor that occurs most frequently in young adults. The key oncogenic driver of this disease is the expression of the CIC-DUX4 fusion protein as a result of chromosomal rearrangements. CIC-DUX4 displays chromatin binding properties, and is therefore believed to function as an aberrant transcription factor. However, the chromatin remodeling events induced by CIC-DUX4 are not well understood, limiting our ability to identify new mechanism-based therapeutic strategies for these patients. Here, we generated a genome-wide profile of CIC-DUX4 DNA occupancy and associated chromatin states in human CDS cell models and primary tumors. Combining chromatin profiling, proximity ligation assays, as well as genetic and pharmacological perturbations, we show that CIC-DUX4 operates as a potent transcriptional activator at its binding sites. This property is in contrast with the repressive function of the wild-type CIC protein, and is mainly mediated through the direct interaction of CIC-DUX4 with the acetyltransferase p300. In keeping with this, we show p300 to be essential for CDS tumor cell proliferation; additionally, we find its pharmacological inhibition to significantly impact tumor growth in vitro and in vivo. Taken together, our study elucidates the mechanisms underpinning CIC-DUX4-mediated transcriptional regulation.

Case Report: Colon malignant tumor caused by retroperitoneal small round cell undifferentiated sarcoma

Small round cell undifferentiated sarcoma is a rare and highly invasive group of malignant bone and soft tissue tumors, often associated with a high misdiagnosis rate. The patient in this case was a 34-year-old male who presented with a two-month history of abdominal pain that worsened over the past two weeks. Elevated levels of tumor markers CA19-9 and CA72-4 were observed. Imaging revealed a substantial, well-vascularized mass in the lower left abdomen, located in the posterior abdominal cavity, invading the descending colon and the root of the small mesentery, and infiltrating the serous layer. The lesion was extensively resected without any postoperative complications. Microscopic examination indicated a combination of mucinous adenocarcinoma (approximately 30%) and small round cell undifferentiated sarcoma (approximately 70%). The patient was followed up for six months, and one month after surgery, a recurrence of the tumor was observed in the left paracolonic sulcus area, with metastases to the abdominal wall, peritoneum, and medial iliac muscles. Chemotherapy and targeted therapy were administered, and the patient currently survives with the presence of tumors. Small round cell undifferentiated sarcoma is an uncommon and highly invasive tumor, and clinical surgeons need to raise their awareness and realize to the maximum extent possible that this disease can be described through a multi-modal combination of immunohistochemistry and genetic test to improve diagnostic accuracy and reduce missed diagnoses. Further research in the field of biology is necessary to explore targeted drugs specifically suitable for this disease.

Gene partners of the EWSR1 fusion may represent molecularly distinct entities

EWSR1 fusions are highly promiscuous and are associated with unique malignancies, clinical phenotypes, and molecular subtypes. However, rare fusion partners (RFP) of EWSR1 has not been well described. Here, we conducted a cross-sectional, retrospective study of 1,140 unique tumors harboring EWSR1 fusions. We identified 64 unique fusion partners. RFPs were identified more often in adults than children. Alterations in cell cycle control and DNA damage response genes as driving the differences between fusion partners. Potentially clinically actionable genomic variants were more prevalent in tumors harboring RFP than common fusions. While the data presented here is limited, tumors harboring RFP of EWSR1 may represent molecularly distinct entities and may benefit from further molecular testing to identify targeted therapeutic options.

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.