Desmoplastic Small Round Cell Tumor with"Pure"Spindle Cell Morphology and Novel EWS- WT1 Fusion Transcript: Expanding the Morphological and Molecular Spectrum of This Rare Entity

Background: Desmoplastic small round cell tumor (DSRCT) is a rare pediatric soft tissue neoplasm composed of small round tumor cells with prominent stromal desmoplasia, polyphenotypic differentiation and EWSR1‐WT1 gene fusion. We, herein, present a unique case of DSRCT, exhibiting a pure spindle cell morphology, absence of desmoplastic stroma and showing a novel EWS‐WT1 fusion transcript. Methods: A 12‐year‐old boy presented multiple intra‐abdominal, confluent and mass‐forming nodules that affected the entire abdominal and pelvic cavities. Results: Histologically, the nodules were composed of spindle cells with scant cytoplasm and oval nuclei arranged into short, intersecting fascicles and set in a scant, non‐desmoplastic, stroma. Immunohistochemically, neoplastic cells were stained with vimentin, desmin, WT‐1 (C‐terminus antibodies) and EMA. Reverse‐transcriptase polymerase chain reaction (RT‐PCR) analysis showed the presence of an unusual chimeric transcript, composed of an in‐frame junction of exon 9 of EWS to exon 7 of WT1, confirming the histological diagnosis of DSRCT. Conclusions: The present case contributes to widen the morphological spectrum of this entity; notably, the additional presence of a novel chimeric fusion transcript contributes to making the present case even more unique. Whether the detection of the above‐mentioned fusion transcripts could explain the unusual morphology of the tumor remains to be established