Gastrointestinal stromal tumor of the prostate.

We present a unique case of an atypical prostate tumor in a 49-year-old man with acute urinary retention. Digital rectal examination revealed a large prostate with a parenchymal mass on the left side. Radiologic imaging showed a 14.2 x 9.6 x 14.0-cm prostatic mass and multiple liver metastases. A pathologic diagnosis of a prostatic gastrointestinal stromal tumor was made and was confirmed by molecular analysis. Therapy consisted of a tyrosine kinase inhibitor, resulting in prostate mass reduction. After 100 weeks, the patient was in good physical condition with a continuing partial response with a reduced mass volume and liver nodules.