A case of primary spindle cell variant of embryonal rhabdomyosarcoma of the prostate.

We treated a rare case of spindle cell variant of embryonal rhabdomyosarcoma (RMS) of the prostate of a patient referred to our hospital for gross hematuria. Computed tomography and magnetic resonance imaging revealed a 4-cm-diameter mass with focal cystic change. Transurethral resection (TUR) of the prostate was performed to diagnosis and treat for complete urinary retention. Microscopically, the TUR specimen almost comprised a fascicular proliferation of spindle-shaped tumor cells, leading to the diagnosis of spindle cell sarcoma. The consequent total prostatectomy revealed the presence of rhabdomyoblasts in addition to the spindle cell proliferation. A MyoD1 p.L122R mutation was not detected in this tumor. The tumor recurred locally, with multiple metastatic lesions found soon after surgery. The patient received chemotherapy and radiation therapy but died 10 months after initial presentation. Although MyoD1 mutation is reported to define a clinically aggressive subset of embryonal RMS, spindle cell variant of embryonal RMS shows extremely adverse clinical outcomes irrespective of MyoD1 mutation.