Introduction: Despite its macroscopic similarity to bladder cancer, nephrogenic adenoma is a rare lesion. However, the incidence has been on the rise in recent years. It is a urothelial metaplasia in the form of a polypoid or papillary lesion. The macroscopic appearance is difficult to distinguish from bladder cancer.
We present two cases of nephrogenic adenoma and a systematic review of the literature.
Clinical findings: Male, 84 years old and 75 years old, both with a history of prostate adenocarcinoma treated with radiotherapy (RT) and former smokers. Under follow-up for high grade T1 bladder carcinoma. Both urologically asymptomatic.
In the first case, in a control urethrocystoscopy 3 years after transurethral resection of the bladder, a polypoid lesion was observed in the left lateral wall.
In the second case, also at a follow-up urethrocystoscopy 6 years after transurethral resection of the bladder, a 2-cm flat lesion was observed in the trigone.
Diagnosis & Treatment: Due to the suspicion of bladder neoformation, transurethral resection of the described lesions was performed.
In the first case, the anatomopathological result of the lesion was nephrogenic adenoma and low grade non-invasive urothelial carcinoma. Subsequently, the patient suffered a recurrence in the form of invasive urothelial carcinoma.
In the second case, the histological result was compatible with nephrogenic adenoma. No recurrences of nephrogenic adenoma or urothelial cancer have been diagnosed in follow-up urethrocystoscopies.
Conclusions: Nephrogenic adenoma is a rare bladder lesion, with fewer than 70 cases published in the literature. It is usually diagnosed in adult males. They are often asymptomatic, although the most common form of presentation is voiding symptoms in the form of urgency and urinary frequency. Hematuria is less frequent than in bladder cancer.
Its incidence is higher in renal transplant patients. It has also been associated with other antecedents such as permanent bladder catheter, repeated infections, interstitial cystitis, previous bladder surgeries, intravesical instillations of BCG, urinary lithiasis, etc. In our case, both patients had received external RT for the treatment of prostate adenocarcinoma and bladder TUR for urothelial carcinoma prior to the appearance of the nephrogenic adenoma.
Published studies have failed to demonstrate malignant transformation of nephrogenic adenoma. In our case, one of the patients developed invasive urothelial carcinoma 3 years later.
There aren't generalized action protocols at present. Experts recommend complete transurethral resection of these lesions and periodic monitoring with urethrocystoscopy, since they are lesions with a risk of recurrence.

Nephrogenic adenoma: an unusual lesion of urothelium