Nephrogenic adenoma (nephrogenic metaplasia)

Definition

A benign urogenital proliferation that may be found in the bladder, urethra, renal pelvis or ureters. It is thought to represent a reaction of the urothelium to injury² by instrumentation, surgery or calculi. When the lesion develops in renal transplant recipients, the lesions are composed of donor cells, indicating that they probably represent implanted detached renal tubules³.

Epidemiology

This is an uncommon lesion of adults.

Macroscopic appearances

The lesions may be single or multiple.

Histopathology

Nephrogenic adenoma has a variable architecture; papillary, tubular, nested, hobnail or solid. The hobnails may line vessels-like structures. Small tubules may have a pseudoinfiltrative pattern. Dilated tubules filled with eosinophilic material produce a thyroidised appearance. A basal layer is lacking. There may be cytological atypia with focally prominent nucleoli, but mitoses are absent. The stroma may be oedematous or inflammatory. Calcification and ossification occur³.

Immunohistochemistry

		various sites	bladder	prostate
	P504S	22/38 (diffuse in 10 cases, focal in 6 cases, patchy in 6 cases)3	3/16 (intensity and extent less than in prostatic cases)1	4/4 (3 cases, luminal / subluminal staining of >75% of tubular component, strong in 2 cases, moderate in one case. The remaining case showed staining of <10% of tubules.)1
	PSA	0/223	0/161	0/41, 1/11 (focal positivity in one case. Three other cases showed staining of the secretions only.)2
	PSAP			3/10 (weakly diffusely positive in two cases, focal positivity in one case. Two other cases showed staining of the secretions only.)2
	CK7			9/92
	34bE12	10/26 (6 cases were negative for 34bE12 but positive for P504S)3	4/161	1/4 (<25% of tubules in one case)1, 5/92
	p63		0/161	0/41

Differential diagnosis

• In prostatic urethra / extending into prostate: prostatic carcinoma. Demonstration of origin from the urethra helps in the diagnosis of nephrogenic adenoma. Both may express P504S¹. Positivity for PSA favours prostatic adenocarcinoma, while negativity suggest nephrogenic adenoma.

• signet ring cell, clear cell or papillary adenocarcinoma

References

¹Skinnider, B. F., E. Oliva, et al. (2004). "Expression of alpha-methylacyl-CoA racemase (P504S) in nephrogenic adenoma: a significant immunohistochemical pitfall compounding the differential diagnosis with prostatic adenocarcinoma." Am J Surg Pathol 28(6): 701-5.

²Allan, C. H. and J. I. Epstein (2001). "Nephrogenic adenoma of the prostatic urethra: a mimicker of prostate adenocarcinoma." Am J Surg Pathol 25(6): 802-8.

³Gupta, A., H. L. Wang, et al. (2004). "Expression of alpha-methylacyl-coenzyme A racemase in nephrogenic adenoma." Am J Surg Pathol 28(9): 1224-9.

This page last revised 1.11.2004.

©SMUHT/PW Bishop