Cystosarcoma phyllodes of the seminal vesicle

An unique case of high‐grade phyllodes tumor (cystosarcoma phyllodes) arising in the seminal vesicle is reported. A 61‐year‐old man had symptoms of urinary obstruction, and ultrasonography and computed tomography showed a large mass posterior to the bladder. Using cystoprostatoseminovesiculectomy, a high‐grade phyllodes tumor of the left seminal vesicle was found that did not involve the bladder or prostate. Histologically, the tumor consisted of benign irregular slit‐like glands set in a mitotically active cellular sarcomatous stroma. The epithelium displayed intense cytoplasmic immunoreactivity with all keratin proteins (AE1/AE3, CAM 5.2, and high‐molecular‐weight keratin [clone 34βTE12]). The stromal cells were strongly positive for vimentin, and approximately 30% were positive for muscle‐specific actin and desmin. Four years after resection, a lung metastasis was removed, which was histologically and immunohistochemically identical to the seminal vesicle tumor. This case represents the malignant end of the range of phyllodes tumors (cystosarcoma phyllodes). Like similar tumors in the breast and prostate, phyllodes tumors of the seminal vesicle should be considered high‐grade lesions (malignant) in which there is significant mitotic activity, stromal pleomorphism, and stromal overgrowth.