Extragastrointestinal stromal tumor of the urinary wall bladder: case report and review of the literature.

Most mesenchymal tumours of the gastrointestinal tract are now referred to as gastrointestinal stromal tumours (GISTs). These tumours typically express c-kit (CD117) and CD34; 30-50% are (often focally) positive for alpha-smooth muscle actin, and all are negative for desmin and S100 protein. Recently, mutations in exon 11 of the c-kit gene have been identified as a molecular genetic marker for the subset of GISTs. In this report, we describe a mesenchymal tumour removed from the pelvic cavity of a 34-year-old man. The tumour was strongly attached to the external wall of the urinary bladder. The neoplasm grossly resembled a leiomyoma, and was histologically composed of sheets of spindle cells with a dense collagenous background. The mitotic activity was low (less then 1 per 50 high-power fields). Immunohistochemically, tumour cells were negative for alpha-smooth muscle actin and desmin and positive for CD117 and CD34. This case illustrates that tumours which are phenotypically and genotypically similar to GISTs may present in sites other than the tubular gastrointestinal tract.