Pseudosarcomatous Proliferation of Cx43- and Kit-Expressing Interstitial Cell in the Urinary Bladder

The authors report a case showing proliferation of KIT- and connexin 43-expressing mesenchymal cells of the urinary bladder. A 75-year-old woman had an ulcerated endophytic mass (size, approximately 2 × 2？cm) in the left posterolateral wall. She underwent transurethral resection and subsequent partial cystectomy. The suburothelial mass extended to the muscularis propria. The histopathological analysis revealed spindle-shaped mesenchymal cells that were loosely arranged with myxoid stroma and showed a focal compact fascicular arrangement. In the immunohistochemical analysis, these spindle cells were stained with specific antibodies to KIT and connexin 43. The patient is currently free of disease at 5 years after operation. The proliferating spindle cells in the present case might represent a phenotype of interstitial cells of the lamina propria. 1. Introduction Although proliferation of various nonepithelial cells can occur in the urinary bladder, this phenomenon is rather rare. However, a fundamental understanding of the proliferation of these cells is important to determine the appropriate treatment approach for patients presenting with this phenomenon. Interstitial cells of the urinary bladder belong to a group of nonepithelial mesenchymal cells that exhibit elongated or satellite-shaped cell bodies and express KIT [1]. Suburothelial ICCs are characterized by the expression of both KIT and a gap-junction protein, connexin 43 (Cx43), to form an interconnection with neighboring interstitial cells [2]. Piotrowska et al. reported that the ICCs were absent in the urinary bladder of patients with megacystis-microcolon-intestinal peristalsis syndrome, which is characterized by a distended unobstructed urinary bladder [3]. Roosen et al. also showed that the cell number of the Cx43-expressing ICCs was significantly increased in the urinary bladder of patients with detrusor overactivity [4]. These findings may support the idea that ICCs act as a pacemaker or a neurotransmitter in the urinary bladder. KIT expression is clinical important because of the existence of a compound, imatinib mesylate that specifically inhibits tyrosine kinase receptors [5]. Therefore, it is important to know whether KIT-expressing ICCs could be a source for tumorous or pseudosarcomatous proliferation in the urinary bladder. Here, we report a case of proliferation of suburothelial KIT- and Cx43-expressing mesenchymal spindle cells in an adult urinary bladder. 2. Case Report The patient was a 75-year-old woman with diabetes mellitus and hypertension, but without any history of