Giant cystosarcoma phyllodes of the prostate associated with adenocarcinoma.

Cystosarcoma phyllodes of the prostate is a rare neoplasm, occurring in adult men. It closely resembles the not uncommon tumor of the female breast and usually behaves in a similar manner. This case of benign cystosarcoma phyllodes of the prostate occurred in a 53-year-old man who presented with increasing abdominal girth and underwent exploratory laparotomy and removal of the 11.2-kg tumor. It was remarkable for its very large size and the presence of foci of well-differentiated adenocarcinoma, prostatic acinar type. The glandular epithelium of both the phyllodes tumor and the carcinoma were immunoreactive for cytokeratin, epithelial membrane antigen, prostate-specific antigen, and prostate-specific acid phosphatase. The presence of typical prostatic type adenocarcinoma and this immunoreactivity pattern strongly supports a prostatic origin for this rare neoplasm.