Gastrointestinal stromal tumor with an unusual presentation as an enlarged prostate gland: a case report and review of the literature.

We report a case of a 78-year-old male who presented with urinary retention, constipation and an enlarged prostate gland. A transurethral resection of the prostate (TURP) was performed. Pathologic examination revealed a hypercellular-spindled neoplasm with frequent mitoses, nuclear pleomorphism, and multifocal geographic tumoral necrosis. A pathologic diagnosis of gastrointestinal stromal tumor (GIST) was made based on morphologic and immunohistochemical findings, and was later reinforced by molecular study results. This lesion was initially thought to represent a primary prostatic GIST. To the best of our knowledge, there have been only five cases of primary prostatic GISTs. Subsequent imaging studies revealed the mass to be contiguous with the anterior rectal wall, suggesting the possibility of a rectal primary with extension to the prostate gland. The patient was treated with imatinib mesylate, and after twelve months of follow up failed to demonstrate any evidence of progression or metastatic disease. GIST should be considered in cases of prostatic tumors with a spindled or epithelioid morphology, and immunohistochemistry and possible molecular studies are recommended to aid in diagnosis and guide treatment decisions.