Nephrogenic adenomas of the urethra involving the prostate gland: a report of two cases of a lesion that may be confused with prostatic adenocarcinoma.

Two cases of urethral nephrogenic adenoma involving the prostate are described. A diagnosis of prostatic carcinoma was raised in both cases and was seriously entertained in one of them. The patients, who were 65 and 68 yr old, underwent transurethral resection because of difficulty voiding; both had had a prior similar procedure. Microscopic examination in each case showed small tubules and clusters of cells in the fibromuscular stroma of the prostate. In one case the lesional cells had abundant clear cytoplasm, and in both cases some of the nuclei had prominent nucleoli. In each case a minor component of the cystic pattern of nephrogenic adenoma was also present. Features pointing to a diagnosis of nephrogenic adenoma were a morphology that was diagnosis of nephrogenic adenoma were a morphology that was focally characteristic of that lesion, an origin from overlying prostatic urethra in both cases, and negative immunohistochemical staining of the lesional cells for prostate-specific antigen and prostate-specific acid phosphatase. These cases illustrate that nephrogenic adenoma occasionally involves the prostate and in these cases can potentially be confused with prostatic adenocarcinoma.