title: Solid-Pattern Desmoplastic Small Round Cell Tumor.
abstract: Desmoplastic small round cell tumor (DSRCT) is an aggressive small round cell sarcoma that typically occurs intra-abdominally in adolescents and young adults, and is characterized by a recurrent t(11;22)(p13;q12) translocation leading to generation of the EWSR1-WT1 fusion gene, which codes for a chimeric protein with transcriptional regulatory activity. DSRCT has a characteristic histologic appearance of nests of uniform small cells within prominent fibroblastic stroma and immunohistochemically it shows multidirectional differentiation, with expression of epithelial, neural, and muscle markers. We illustrate a case of DSRCT that presented as a large intra-abdominal mass, which harbored EWSR1 rearrangement by fluorescence in situ hybridization and EWSR1-WT1 fusion transcripts by reverse transcription-polymerase chain reaction (RT-PCR), and which histologically had an entirely solid morphology, lacking evidence of desmoplastic stroma. This purely solid variant emphasizes that even when occurring at a typical location, DSRCT may be difficult to recognize when lacking nonclassical morphology. This is of clinical relevance, as DSRCT with this pattern could be misdiagnosed as Ewing sarcoma if RT-PCR is not performed, with resulting prognostic and therapeutic implications.
authors.affiliation: 1 Royal Marsden Hospital, London, UK.
authors.forename: Ahmed
authors.initials: A
authors.lastname: Ali
authors.affiliation: 1 Royal Marsden Hospital, London, UK.
authors.forename: Mustafa
authors.initials: M
authors.lastname: Mohamed
authors.affiliation: 1 Royal Marsden Hospital, London, UK.
authors.forename: Julia
authors.initials: J
authors.lastname: Chisholm
authors.affiliation: 1 Royal Marsden Hospital, London, UK.
authors.forename: Khin
authors.initials: K
authors.lastname: Thway
mesh_terms: D000293:Adolescent; D002148:Calmodulin-Binding Proteins / Q000235:genetics; D058405:Desmoplastic Small Round Cell Tumor / Q000235:genetics / Q000473:pathology*; D005260:Female; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D015514:Oncogene Proteins, Fusion / Q000235:genetics; D034802:RNA-Binding Protein EWS; D016601:RNA-Binding Proteins / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012983:Soft Tissue Neoplasms / Q000235:genetics / Q000473:pathology*; D025721:WT1 Proteins / Q000235:genetics
chemical_list: D002148:Calmodulin-Binding Proteins; C500986:EWSR1 protein, human; D015514:Oncogene Proteins, Fusion; D034802:RNA-Binding Protein EWS; D016601:RNA-Binding Proteins; D025721:WT1 Proteins; C583751:WT1 protein, human
keywords: EWSR1-WT1; desmoplastic small round cell tumor; morphology; pathology; sarcoma; solid pattern