Nephrogenic adenoma in elderly patients: Three case reports.

Nephrogenic adenoma (NA), referred to as nephrogenic metaplasia, is a rare benign lesion of the urinary tract. NA is histologically characterized by tubular and papillary formations lined by low cuboidal to columnar epithelial cells. NA is also immunohistochemically characterized by positivity for paired box (PAX) 2, PAX8 and cytokeratin 7, and negative for p63 and prostate-specific antigen. In this study, we present 3 cases of NA arising in the urinary bladder of elderly male patients with predisposing factors: patient 1 had undergone transurethral lithotripsy due to a ureteral stone; patient 2 had undergone transurethral resection of a urothelial carcinoma in the urinary bladder; and patient 3 had been treated with Bacillus-Calmettle-Guérin due to a urothelial carcinoma in the urinary bladder. The characteristics of the NAs of our 3 cases were histologically and immunohistologically consistent with previously reported cases, although 1 patient exhibited a pseudoinvasive pattern. Since NA is a tumor-like benign lesion, it should be clearly differentiated morphologically and immunohistologically from other tumors arising in the urinary tract and from invasion by prostate cancer.