Paratesticular desmoplastic small round cell tumour: an unusual tumour with an unusual fusion; cytogenetic and molecular genetic analysis combining RT-PCR and COBRA-FISH

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.Desmoplastic small round cell tumour (DSRT) was first described as a distinct entity by Gerald and Rosai now about 23 years ago [1]. The tumour is nowadays well-characterized histologically and at the immunohistochemical level and involves serosal surfaces. Microscopically, 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. The cells show a multidirectional phenotype with epithelial, myogenic and neural marker expression. The tumour is located in the abdominal and pelvic peritoneal cavity in the vast majority of cases. Extra-abdominal sites are rare. Cases were described however in the cranial cavity, lung, head and neck, salivary gland [2], limbs, pancreas and paratesticular region. Although most cases have been described in young men and children, several cases have been described in older patients [3-5] and in women, sometimes simulating ovarian tumours [3,4,6], even with high CA125 le