Extragastrointestinal stromal tumor of the retroperitoneum mimicking kidney tumor

A case of extragastrointestinal tumor of the retroperitoneum in a 48-year-old woman complaining right sided flank pain without hematuria is reported. The mass was excised from the kidney without a positive margin. The histopathological examination revealed an extragastrointestinal stromal tumor of the retroperitoneum. These tumors usually originate from the small intestine or stomach. On the other hand, they are rarely located in the retroperitoneum. These tumors typically exhibit CD117 immunoreactivity, whereas they may reveal CD34, neuron specific enolase, smooth muscle actin, desmin and S-100 protein. In our case the specimen of the patient was positive for CD117, actin and desmin.