A t(4;19) pediatric undifferentiated sarcoma with a novel variant of the CIC-DUX4 fusion transcript

CIC-DUX4 Sarcoma of the Skin: A Rare Case Report and Literature Review

CIC::DUX4 fusion sarcoma represents a rare and aggressive subtype of undifferentiated small round blue cell tumors. We report on a 23-year-old African male who developed a rapidly enlarging inferolateral left buttock nodule with ulceration. After debulking excision of the lesion, histologic sections demonstrated sheets and lobules of atypical round blue cells with significant cytologic atypia. Prominent foci of atypical mitotic figures and tissue necrosis were present. Tumoral cells stained strongly and diffusely using MDM2, vimentin, WT1 and CD99 immunohistochemical (IHC) markers. Molecular testing was performed and highlighted CIC::DUX4 gene fusion positivity, making the diagnosis of a CIC::DUX4 sarcoma (CDS). Post-surgical excision, the patient showed no disease on imaging and underwent five cycles of adjuvant chemotherapy with no recurrence observed at the eight-month follow-up. With fewer than 200 cases reported in the literature and somewhat nonspecific clinicopathologic characteristics, CIC::DUX4 sarcoma presents a diagnostic challenge. This case underlines the importance of molecular diagnostics in undifferentiated sarcomas and presents a rare primary cutaneous manifestation of CIC::DUX4 fusion sarcoma. Additionally, we provide a review of the literature to aid in recognition, diagnosis, and treatment of this rare entity.

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

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

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.

Ewing-like sarcoma: An emerging family of round cell sarcomas

Ewing-like sarcomas are an emerging subgroup of small round blue cell sarcomas that share various degrees of morphological, immunohistochemical, molecular, and clinical similarity with Ewing sarcoma. Despite these similarities, Ewing-like sarcomas lack the pathognomonic molecular hallmark of Ewing sarcoma: A translocation between a gene of the RNA-binding TET family (EWSR1 or FUS) with a gene of the ETS-transcription family ( FLI1, ERG, ETV1, ETV4, or FEV). Recently, increased use of modern molecular methods based on next-generation sequencing have enabled the identification of distinct subgroups within this previously uncharacterized group of Ewing-like sarcomas based on the discovery of novel molecular driving events. The focus of this review is to provide an update on the main subcategories of Ewing-like sarcomas discovered to date: CIC-rearranged sarcomas, BCOR-rearranged sarcomas, sarcomas with a rearrangement between EWSR1 and a non-ETS family gene, and the substantial fraction of tumors which remain uncharacterized by molecular methods. There is increasing evidence that these tumors represent stand-alone entities with unique characteristics rather than simply a subgroup of Ewing sarcoma; thus, the question of the best therapeutic approach for these often aggressive sarcomas remains of primary importance. Ultimately, large collaborative efforts will be necessary to better determine the characteristics of this rare, heterogeneous family of tumors.