Abstract
Desmoplastic small round cell tumour is a rare malignant tumour with a male to female ratio of 4:1. It manifests mostly at serosal sites. Here we present a case of a 28-year-old male patient, who presented with a fast growing paratesticular mass. On biopsy nests and cords of small round cells, without a clear morphological lineage of differentiation were seen. Occasionally desmoplatic small round cell tumour shows different lines of differentiation. An unequivocal histological diagnosis might be difficult in such cases. Here we demonstrate by a combination of methods the characteristic immunohistochemical profile and - albeit unusual - molecular background and discuss the eventual link with Ewing sarcoma.Immunohistochemical studies showed a membranous staining of Keratine AE1/3 and a dot-like staining of Desmine, confirming its diagnosis. Using COBRA-FISH following a metaphase approach we demonstrated a balanced translocation, t(11;22)(p13;q12) and in RT-PCR formation of the EWSR1-WT1 fusion product, a specific translocation of desmoplastic round cell tumour. The fusion involves exon 9 of EWSR1 to exon 8 of WT1, an unusual fusion product, though earlier described in a case of a desmoplastic small round cell tumour of the hand. The EWSR1-WT1 chimera seems to function as an oncogenic transcription factor. Here the zinc finger domain of the WT1 acts with affinity with certain promoter domains influencing the expression of various downstream proteins such as: PDGFA, PAX2, insulin-like growth factor 1 receptor, epidermal growth factor receptor, IL2 receptor beta, BAIAP3, MLF1, TALLA-1, LRRC15 and ENT. We discuss their potential oncogenic roles and potential therapeutic consequences.
Highlights
Desmoplastic small round cell tumour (DSRT) was first described as a distinct entity by Gerald and Rosai about 23 years ago [1]
We present a rare case of desmoplastic round cell tumour presenting as a paratesticular mass and with cytogenetic analysis using a multicolour Combined Binary RAtio labelling Fluorescence In-situ Hybridization (COBRA-FISH) method and with a rare translocation variant detected by reverse transcriptasepolymerase chain reaction (RT-PCR) analysis of the t (11;22) fusion gene product
The typical presentation is with a paraserosal mass and a predilection for serosal surfaces, mainly the peritoneum and - as in our case - the paratesticular region
Summary
Desmoplastic small round cell tumour (DSRT) was first described as a distinct entity by Gerald and Rosai about 23 years ago [1]. The morphologic prototype of the tumour shows nests of small, round cells embedded within a desmoplastic stroma, giving it its descriptive name as an entity. DSRCT is associated with a distinct translocation which shows a fusion between Ewing sarcoma gene (EWSR1) and Wilms tumour gene (WT1). There are at least two reports of hybrid tumours with features of both DSRCT and Ewing sarcoma, one with an EWSR1-FLI1 fusion gene [8] and one with an EWSR1-ERG fusion gene [6]. The reported prognosis is poor, with a median survival of 17 months only [9,10,11,12,13,14,15]. At the meeting of the Connective Tissue Oncology Society, November 2010, Subbiah et al presented data from 161 patients, with a median survival duration of 2.4 years
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