Extragastrointestinal stromal tumor of prostate.

Gastrointestinal stromal tumors (GISTs) that originate outside the GI tract are extremely uncommon. In this case report, we describe a GIST of primary origin in the prostate gland of an 84-year-old male who presented with severe urinary retention at King Abdulaziz University Hospital in Saudi Arabia. Diagnosis was based on patient history, radiological studies, pathologic findings, and immunohistochemical data. Digital rectal examination revealed a hugely enlarged prostate encroaching upon the rectal lumen with a smooth and firm surface. Transrectal ultrasound showed a markedly enlarged prostate with an estimated volume of 360 ml; prostate-specific antigen was 5.4 ng/ml. Immediate preoperative cystoscopy demonstrated only a moderate enlargement of the prostate, which was disproportionate to its actual size. Postoperative abdominal computed tomography showed residual prostatic tissue with an estimated weight of 78 g, multiple diffuse colonic diverticulosis, and scattered subcentimeter mesenteric lymph nodes. Histopathological examination of the prostatic tissue showed cellular spindle cell neoplastic proliferation which was diffusely positive for CD117 (c-kit), DOG1, and CD34. GISTs must be considered in the differential diagnosis of spindle cell tumors detected in the prostate.