Nephrogenic adenoma is a benign condition of the urinary tract resulting from the displacement and seeding of renal tubular cells from the renal pelvis to the urethra. A retrospective series of 134 cases collected from four hospitals in three different countries was analyzed in this study. Recorded clinical data included age and sex, topography, urological antecedents, coexistent lesions, and follow-up. Cytonuclear and architectural features were reviewed, and PAX-8, p63, PSMA, S100A1, CEA, EMA, CD117, cannabinoid receptor CB1, AMACR, E-cadherin, and CD10 antibodies were included in an immunohistochemical panel. Males predominated (105 M/29 F) with an average age of 66 years (range, 14-96). Urothelial carcinoma was the most frequent clinical antecedent (43.2 %) and also the most common coexisting lesion (14 %). Tubular architecture was the most frequent pattern detected (40 %) although most cases showed a mixed pattern (45.5 %). Deep infiltrative growth into the muscularis propria occurred in two cases. EMA and PAX-8 were expressed in 100 % of nephrogenic adenomas, while E-cadherin reactivity was observed in 66.6 % of cases, cannabinoid receptor CB1 in 25 %, CD10 in 13.6 %, CD117 in 4.1 %, and AMACR in 2.7 %. For the rest of the antigens, no reactivity was found. The average time lapse between the pathological antecedent and the discovery of a nephrogenic adenoma was 32 months. We conclude that nephrogenic adenoma displays a broad spectrum of histological features that may mimic malignancy. In our experience, CB1 immunostaining adds a further argument in favor of a renal origin of this lesion. The combination of PAX-8+, p63-, and EMA + distinguishes nephrogenic adenoma from urothelial and prostate carcinoma, its most frequent malignant look-alikes.
