Interesting cases

Fibromyxoid pattern nephrogenic adenoma

Fibromyxoid pattern nephrogenic adenoma

The cytologically bland tubular epithelial elements in this case were positive for PAX8 and negative for p63. Congo red histochemical stain was negative for amyloid deposition. Admixed refractile material was not identified under polarization. The diagnosis for this case was fibromyxoid pattern nephrogenic adenoma (NA).
Fibromyxoid pattern NA is one of the more recently described morphologies that NA can exhibit, in addition to tubular, papillary, cystic, and flat patterns. Helpful clues including finding admixed classic patterns. There should be minimal atypia without increased mitotic activity. Most cases often show admixed amyloid-like background stroma. Immunohistochemically, fibromyxoid NA stains like typical NA in being positive for PAX8 and AMACR; caution should be exhibited on GATA3/PSA/PSAP as these can be positive in NA (particularly a pitfall in bladder specimens and/or in patient’s with a history of prostate cancer). In the past, fibromyxoid pattern NA was reported exclusively in patients prior therapy; however, a larger recent study has shown that patients without prior treatment can also show this diagnosis. Nephrogenic adenoma can occur anywhere in the genitourinary tract, with most patients having a prior associated urothelial injury, procedure, infection, or biopsy.

PMID: 36395466
PMID: 17667548

Ankur Sangoi, MD (Stanford)

ureter/renal pelvis

ureter, fibromyxoid, nephrogenic adenoma, PAX8