Nephrogenic Adenoma of the Prostatic Urethra Mimicking Prostatic and Bladder Carcinomas

A nephrogenic adenoma is a benign lesion consisting of the proliferation of tubules and glands in the urinary tract. The lesion, thought to be originated from renal tubules, is commonly seen in the urinary bladder. Microscopically, nephrogenic adenoma is composed of a proliferation of small tubules and microcysts encircled by a narrow rim of basement membrane-like hyaline material. There are tubules and microcysts lined by atrophic to undulating hobnail-appearing epithelial cells with bland nuclei and pale eosinophilic to clear cytoplasm. Focal cellular atypia characterized by somewhat coarse chromatin and prominent nucleoli may be present. The stroma is edematous and reveals a granulation tissue-like appearance. By immunohistochemical staining, nephrogenic adenoma is positive for PAX-2, PAX-8, P504S (α-methylacyl-CoA racemase), pan cytokeratin AE1/AE3, CK7, CAM5.2, epithelial membrane antigen (EMA), CD10, and napsin A. Occasionally the lesions are incidentally encountered in the prostatic urethra, which may lead to a misdiagnosis as prostatic adenocarcinoma, clear cell adenocarcinoma or urothelial carcinoma of the urinary bladder. Herein we present a case of nephrogenic adenoma which has been incidentally found in a transurethral resection of a prostate specimen for the management of benign prostatic hypertrophy. The evaluation of morphology, immunohistochemistry, and differential diagnoses have also been discussed.