2020-7 / FEBRUARY 17

A 72-year old patient underwent a transurethral resection of the prostate due to clinical diagnosis of nodular hyperplasia. He had a previous transurethral resection of the prostate 18 months earlier. Micrographs show one or two areas of interest in the specimen, the largest area measuring 2.5 mm. The lesion was positive for PAX8 (photo), negative for PSA and Ki67 stained less than 5% of the cells.


1. What is the correct diagnosis?

a. Bladder adenocarcinoma involving the prostate

b. Prostate acinar adenocarcinoma

c. Nephrogenic adenoma with signet ring morphology

d. Clear cell carcinoma of prostatic urethra

e. Urothelial carcinoma with plasmacytoid morphology

1. Nephrogenic adenoma with signet ring morphology

Nephrogenic adenoma is an uncommon lesion that occurs throughout the urinary tract that is typically preceded by some kind of injury, in particular transurethral resection of prostate or bladder. It may show a wide range of patterns including tubules, cysts, papillae, and focal solid growth pattern. It is rare but well documented that the tubules in nephrogenic adenoma may be strikingly tiny and closely packed, mimicking signet ring cells.
The presence of signet ring morphology should alert the pathologist to consider the diagnosis of primary and metastatic malignancies in the prostate; however, it does not exclude the possibility of nephrogenic adenoma. Lesions in association with the urethra forming small tubules and showing PAX8 positivity have a differential diagnosis that should include nephrogenic adenoma and clear cell carcinoma. In this case, a low Ki67 index, lack of atypia, small size and the typical prior history of surgical trauma favored the interpretation of the lesion as nephrogenic adenoma.

Rahemtullah A, Oliva E. Nephrogenic adenoma: an update on an innocuous but troublesome entity.
Adv Anat Pathol. 2006 Sep;13(5):247-55.

Kunju LP. Nephrogenic adenoma: report of a case and review of morphologic mimics.
Arch Pathol Lab Med. 2010 Oct;134(10):1455-9.

Daniel Athanazio
Federal University of Bahia, Imagepat, Laboratory of Pathology, Salvador, Bahia, Brazil


Prostate; nephrogenic adenoma; signet ring cell