Case Report: Refractory desmoplastic small round cell tumor: a report of a molecularly confirmed case with EWSR1-WT1...

Desmoplastic small round cell tumor (DSRCT) is an extremely rare and highly aggressive soft-tissue sarcoma that predominantly affects adolescents and young male patients. This malignancy is defined by the t(11;22) (p13;q12) chromosomal translocation, which generates the EWSR1-WT1 fusion gene. Owing to its rarity and aggressive clinical behavior, standardized treatment strategies for DSRCT have not yet been established.

A 13-year-old boy presented with increased defecation frequency and progressive weight loss. Serum cancer antigen 125 (CA125) levels were markedly elevated at 187.00 U/mL. Contrast-enhanced abdominal computed tomography (CT) revealed a large heterogeneous mass with calcifications in the left epigastrium, invading the adjacent intestinal loops. CT-guided biopsy combined with immunohistochemical staining demonstrated positive expression of desmin, cytokeratin pan (CKpan), and vimentin in the tumor. Targeted next-generation sequencing (NGS) confirmed the presence of EWSR1-WT1 fusion, supporting the diagnosis of DSRCT. The patient received comprehensive multimodal treatment, including neoadjuvant chemotherapy, cytoreductive surgery, multiple lines of systemic chemotherapy, combined chemoimmunotherapy, and tyrosine kinase inhibitor (TKI) therapy. Nevertheless, the tumor relapsed repeatedly, and chemotherapy resistance gradually emerged during sequential treatment.

We report a pediatric case of intra-abdominal DSRCT harboring EWSR1-WT1 fusion. The patient was diagnosed with an advanced stage disease at the initial presentation. Immunohistochemical and molecular analyses revealed a WT1-negative phenotype and dual EWSR1-WT1 fusion breakpoints, which are atypical findings compared with most reported DSRCT cases. Despite these unusual molecular features, a definitive diagnosis of DSRCT was established. The tumor inevitably progressed despite intensive multimodal intervention. This case further demonstrates the highly aggressive nature of DSRCT, which is associated with a high risk of local recurrence and distant metastasis. Novel systemic and targeted therapies are urgently needed to improve the clinical outcomes of affected patients.