Nephrogenic adenoma in renal transplant recipients: a truly benign lesion?

Expression of L1 Cell Adhesion Molecule, a Nephronal Principal Cell Marker, in Nephrogenic Adenoma

Nephrogenic adenoma (NA) is a benign, reactive lesion seen predominantly in the urinary bladder and often associated with antecedent inflammation, instrumentation, or an operative history. Its histopathologic diversity can create diagnostic dilemmas and pathologists use morphologic evaluation along with available immunohistochemical (IHC) markers to navigate these challenges. IHC assays currently do not designate or specify NA's potential putative cell of origin. Leveraging single-cell RNA-sequencing technology, we nominated a principal (P) cell-collecting duct marker, L1 cell adhesion molecule (L1CAM), as a potential biomarker for NA. IHC characterization revealed L1CAM to be positive in all 35 (100%) patient samples of NA; negative expression was seen in the benign urothelium, benign prostatic glands, urothelial carcinoma (UCA) in situ, prostatic adenocarcinoma, majority of high-grade UCA, and metastatic UCA. In the study, we also used single-cell RNA sequencing to nominate a novel compendium of biomarkers specific for the proximal tubule, loop of Henle, and distal tubule (DT) (including P and intercalated cells), which can be used to perform nephronal mapping using RNA in situ hybridization and IHC technology. Employing this technique on NA we found enrichment of both the P-cell marker L1CAM and, the proximal tubule type-A and -B cell markers, PDZKI1P1 and PIGR, respectively. The cell-type markers for the intercalated cell of DTs (LINC01187 and FOXI1), and the loop of Henle (UMOD and IRX5), were found to be uniformly absent in NA. Overall, our findings show that based on cell type-specific implications of L1CAM expression, the shared expression pattern of L1CAM between DT P cells and NA. L1CAM expression will be of potential value in assisting surgical pathologists toward a diagnosis of NA in challenging patient samples.

Acute post-renal kidney graft dysfunction due to cytomegalovirus-positive nephrogenic adenoma-case report and review of the literature

Tissue-invasive cytomegalovirus (CMV) disease represents a well-recognized complication after kidney transplantation. However, direct involvement of the urogenital tract and CMV-ureteritis occur less frequently. Nephrogenic adenomas are benign lesions of the urinary tract preferentially reported in kidney transplant recipients. We herein report a second case of a 33-year-old male kidney transplant recipient with acute post-renal allograft dysfunction due to CMV-positive ureteral nephrogenic adenoma. A causal connection might be suspected but remains to be proven.

Nephrogenic Adenoma Complicating Renal Transplantation: A Case Report and Discussion

Nephrogenic adenoma (NA) is a benign adenomatous lesion of the urinary tract. Long considered to be a rare phenomenon, case series from the renal transplant population suggest that it may be much more common within this group. Although NA is considered to be a lesion with low premalignant potential, hematuria, lower urinary tract symptoms, and recurrent urinary tract infections (UTIs) are frequently observed in the context of NA. Furthermore, after resection of NA, lesion recurrence and persistent symptoms are frequently observed. Here we present the case of a 69-year-old male renal transplant recipient with NA and associated recurrent UTIs despite cystoscopic resection of the primary lesion. This case is illustrative of the clinical impact of NA and the need for ongoing work into the development of strategies to manage this problematic phenomenon.

Nephrogenic Adenoma of the Urinary Bladder: A Review of the Literature

Background. Nephrogenic adenoma of the urinary bladder (NAUB) is a rare lesion associated with nonspecific symptoms and could inadvertently be misdiagnosed. Aim. To review the literature. Methods. Various internet search engines were used. Results. NAUB is a benign tubular and papillary lesion of the bladder, is more common in men and adults, and has been associated with chronic inflammation/irritation, previous bladder surgery, diverticula, renal transplantation, and intravesical BCG; recurrences and malignant transformations have been reported. Differential diagnoses include clear cell adenocarcinoma, endocervicosis, papillary urothelial carcinoma, prostatic adenocarcinoma of bladder, and nested variant of urothelial carcinoma; most NAUBs have both surface papillary and submucosal tubular components; both the papillae and tubules tend to be lined by a single layer of mitotically inactive bland cells which have pale to clear cytoplasm. Diagnosis may be established by using immunohistochemistry (positive staining with racemase; PAX2; keratins stain positive with fibromyxoid variant), electron microscopy, DNA analysis, and cytological studies. Treatment. Endoscopic resection is the treatment but recurrences including sporadic malignant transformation have been reported. Conclusions. There is no consensus on best treatment. A multicentre study is required to identify the treatment that would reduce the recurrence rate, taking into consideration that intravesical BCG is associated with NAUB.

Nonneoplastic lesions of the prostate and bladder

CONTEXT

Specimens from the prostate and bladder are commonly encountered by the general surgical pathologist. Emphasis is usually placed on neoplasms of the bladder and prostate, particularly if malignant, owing to their therapeutic consequences. A good command of benign lesions occurring in the bladder and prostate, and knowledge of their preneoplastic potential will help pathologists confidently diagnose malignancy versus its benign mimickers and guide the urologists in choosing the appropriate therapy and follow-up for the patient.

OBJECTIVE

To present a mixture of benign entities, and discuss their histologic and clinical characteristics, hoping to provide a practical review for the general surgical pathologist.

DATA SOURCES

An extensive review of the literature on the entities discussed was performed.

CONCLUSIONS

A wide variety of benign entities are present in the prostate and bladder. Benign lesions in the prostate can be age related, such as prostatic atrophy and benign prostatic hyperplasia; transition zone associated, such as basal cell hyperplasia, adenosis, and sclerosing adenosis; or prostatic urethra associated. Benign lesions of the bladder encompass a wide variety of reactive changes that can occur in the urothelium, as well as hyperplastic lesions or reactive proliferations that could be misdiagnosed as malignant. The bladder responds to chronic irritation through several reactive/metaplastic lesions such as cystitis cystica/glandularis, keratinizing squamous metaplasia, or nephrogenic metaplasia. The urothelium can also give rise to hyperplastic/proliferative lesions, in particular von Brunn nest hyperplasia, papillary polypoid cystitis, and pseudocarcinomatous proliferation, which should be distinguished from malignant processes. Ectopic tissue, such as prostatic or mullerian, can also be seen.

Nephrogenic Adenoma of the Urinary Tract

Nephrogenic adenoma (NA) is an uncommon and intriguing lesion in the urinary tract. The pathogenesis of NA is not entirely clear. NA was considered to be a metaplastic process of the urothelium in response to chronic irritation of the urinary tract. However, recent evidence has shown that NA is not a metaplastic lesion but rather a proliferation of exfoliated and implanted renal epithelial cells in the urinary tract. Histologically, NAs exhibit, singly or in combination, tubules, small papillae, and microcystic structures lined by cells with little cytological atypia and focal hobnail changes. Solid formations and compressed spindled cells within a fibromyxoid background are rarely observed. Differential diagnosis includes, but is not limited to, malignant neoplasms occurring at the same sites, in particular urothelial carcinoma with deceptively bland morphology (with small tubules, microcystic and nested variants), prostatic adenocarcinoma, and clear cell adenocarcinoma. Immunohistochemical studies with antibodies targeting members of the paired box gene family (PAX2 and/or PAX8) in NAs may be helpful in the differential diagnosis of urothelial lesions and prostatic adenocarcinoma. NAs are most likely to be confused with clear cell adenocarcinoma, especially in small biopsy specimens. This is confounded by both lesions being frequently positive for PAX2, PAX8, and CK7 and not infrequently positive for p504S (α-methylacyl-CoA-racemase, AMACR) by immunohistochemistry. Recognition of its characteristic morphological patterns and awareness of its unusual architectural and cytological features are important in making the diagnosis of NA and distinguishing this lesion from its mimickers.

Nephrogenic adenoma of the bladder in a prune belly syndrome patient: case report and review of the literature

Nephrogenic adenoma (NA) is a rare lesion of the urinary tract widely considered to be a metaplastic response to urothelial injury. Herein, we present the case of an 8-year-old male with prune belly syndrome who presented with gross hematuria. Investigation revealed a bladder mass; however, upon cystoscopic examination, multiple polypoid lesions were identified. Microscopic examination revealed NA of the bladder. To our knowledge, this is the second reported case of NA of the bladder in association with prune belly syndrome.

Clear cell adenocarcinoma of the bladder and urethra: cases diffusely mimicking nephrogenic adenoma

Although clear cell adenocarcinoma have been described focally mimicking nephrogenic adenoma, we have identified a subset of clear cell adenocarcinoma that diffusely resembles nephrogenic adenoma (nephrogenic adenoma-like clear cell adenocarcinoma). Twelve classic clear cell adenocarcinomas of the bladder and urethra and 7 nephrogenic adenoma-like clear cell adenocarcinomas were compared to 10 nephrogenic adenomas. Classic clear cell adenocarcinomas and nephrogenic adenoma-like clear cell adenocarcinomas comprised 4 men and 15 women. The following features were seen in classic clear cell adenocarcinomas: nephrogenic adenoma-like clear cell adenocarcinomas: predominantly solid pattern (7/12:0/7), marked nuclear pleomorphism (7/12:1/7), prominent nucleoli (5/12:1/7), clear cytoplasm in 50% or greater of tumor (7/12:0/7), and necrosis (8/12:3/7), although the necrosis in nephrogenic adenoma-like clear cell adenocarcinomas was often focal and intraluminal. Both patterns of clear cell adenocarcinomas showed prominent hobnail features, although more pronounced in nephrogenic adenoma-like clear cell adenocarcinomas. Muscularis propria invasion was seen in 5 of 9 classic clear cell adenocarcinomas and 6 of 6 nephrogenic adenoma-like clear cell adenocarcinomas, where evaluable. Classic clear cell adenocarcinoma was associated with urothelial carcinoma (n = 2) and endometriosis (n = 1). The Ki-67 rate in clear cell adenocarcinomas ranged from 10% to 80% compared with 0% to 5% in nephrogenic adenoma. The following antibodies were not helpful in distinguishing nephrogenic adenoma-like clear cell adenocarcinoma from nephrogenic adenoma: CD10, estrogen receptor, p63, high-molecular-weight cytokeratin, and alpha-methylacyl coenzyme-A racemase. PAX2 expression was more frequent in nephrogenic adenoma (89%) compared to both patterns of clear cell adenocarcinoma (29%-32%). The key features discriminating between nephrogenic adenoma-like clear cell adenocarcinoma and nephrogenic adenoma include occasional clear cells, more prominent pleomorphism especially hyperchromatic enlarged nuclei, and extensive muscular invasion. Presence of mitoses and a high rate of Ki-67 expression in lesions resembling nephrogenic adenoma require clinical correlation, close follow-up, and repeat biopsy with more extensive sampling.

Expression of PAX8 in nephrogenic adenoma and clear cell adenocarcinoma of the lower urinary tract: evidence of related histogenesis?

Recent evidence has showed that nephrogenic adenoma is a true "nephrogenic" lesion derived from the proliferation of exfoliated and implanted renal tubular cells in the urinary tract, a process that closely resembles the formation of endometriosis. This new concept has led to the identification of renal transcription factor PAX2 as a diagnostic marker for nephrogenic adenoma. PAX8 is another transcription factor structurally and functionally related to PAX2. Both are cell lineage restricted transcription factors expressed in normal and neoplastic tissues of related origin, including renal tubular cells in both fetal and adult kidneys. In this study, we investigated the expression of PAX8 in nephrogenic adenoma and its mimics. We report here that PAX8 was detected in all nephrogenic adenomas (N=35) and clear cell adenocarcinoma of the lower urinary tract (N=7), but not in prostate adenocarcinoma (N=100), adenocarcinoma (N=9), squamous cell carcinoma (N=5), or urothelial carcinoma (N=48) of the urinary bladder and its variants. PAX8 was neither detected in normal urothelium of the urinary bladder nor in prostate glands and stroma. PAX2 was also detected in 2 of the 7 clear cell adenocarcinomas of the lower urinary tract. We suggest that PAX8 is an additional marker for identifying nephrogenic adenoma. Expression of PAX8 or PAX2 in both nephrogenic adenoma and clear cell adenocarcinoma of the lower urinary tract may indicate a possible related tissue origin for these 2 lesions; both may be derived from proliferating renal tubular cells in the urinary tract. In addition, detection of PAX8 or PAX2 in clear cell adenocarcinoma of the lower urinary tract is helpful in differentiating it from urothelial carcinoma and its variants and adenocarcinomas of the urinary bladder or of the prostate.

Nephrogenic adenoma of the ureter: case report

Nephrogenic adenoma is a rare metaplastic benign lesion of urothelium in response to genitourinary tract procedures, chronic infection, trauma, urinary calculi and immunosuppressive therapy after renal transplantation. It has been reported to occur throughout the urinary tract especially, in the urinary bladder. We report a case of nephrogenic adenoma arising from the lower end of the right ureter with clinical and radiological features suspicious of carcinoma.

Nephrogenic adenoma: an update on an innocuous but troublesome entity

Nephrogenic adenoma (NA) is a rare benign lesion of the urothelial tract that is typically preceded by some form of genitourinary insult. The pathogenesis of NA is not entirely clear. Although generally presumed to be a metaplastic process of the urothelium, recent evidence suggests that NA may in fact be derived from detached renal tubular cells implanting along the urothelial tract in previously injured areas, at least in cases associated with a kidney transplant. On light microscopy, NA shows a variety of patterns, including tubulocystic, papillary, and much less frequently solid, that often coexist. Recognition of its characteristic patterns, and awareness of its unusual architectural and cytologic features, is key to making the diagnosis of NA and distinguishing this lesion from malignant neoplasms occurring at the same sites, in particular, clear cell carcinoma, nested or microcystic variants of urothelial carcinoma and prostatic adenocarcinoma. Although straightforward in most cases, the correct diagnosis may be difficult to make on limited tissue samples. A number of immunohistochemical markers have been studied in an attempt to characterize NA; however, to date there is no specific immunohistochemical profile to distinguish this lesion from its malignant mimickers, although PAX2, a new marker, may prove to be helpful in this regard. Clinicopathologic correlation with careful attention to morphology remains the pillar in establishing the correct diagnosis.

A case series of nephrogenic adenoma of the urethra and bladder in children: review of this rare diagnosis, its natural history and management, with reference to the literature

Nephrogenic adenoma (NA) is a rare benign tumour of the urinary tract and is found most commonly in the bladder. Here are presented four cases of paediatric NA, two bladder and two urethral. Their diagnostic and management features in the context of differential diagnosis and natural history are discussed. A 3-year-old girl presented with recurrent urinary tract infections (UTIs) and haematuria. She had undergone a previous hemi-nephro-ureterectomy. An ultrasound scan suggested a large bladder tumour, which was biopsied cystoscopically, and histology confirmed an NA. She then underwent open resection of the tumour. A 4-year-old girl presented with recurrent UTIs and a history of previous bilateral duplex ureterostomies and subsequent trans-uretero-ureterostomy with ureteric re-implantation. A cystoscopy showed a papillary tumour, which was confirmed as NA on histology. An 11-year-old boy presented with haematuria and dysuria and no other relevant history. At urethroscopy a ragged area biopsied in the bulbar urethra showed NA. A 7-year-old boy presented with haematuria and no other relevant history. At urethroscopy an inflamed nodular area was biopsied and nephrogenic adenoma confirmed. In the two bladder cases, but not the urethral cases, a causative factor could be identified. Recurrence was noted in both of the bladder cases. The urethral cases had persistent symptoms suggestive of continuing NA. Treatment consisted of endoscopic and open ablation of the tumours, and endoscopic fulguration of recurrences for the bladder cases, and surveillance for the urethral cases. Only two previous cases of urethral and 25 cases of bladder NA have been reported in children.

PAX2: a reliable marker for nephrogenic adenoma

Nephrogenic adenoma is a rare lesion of the urinary tract. The diagnosis usually is straightforward when characteristic microscopic and clinical findings are present, and the entity is familiar. However, misdiagnosis, in particular of adenocarcinoma of the prostate gland, may occur. Immunohistochemical stains often are needed to make such a distinction, but currently available markers offered only partial help. It recently was demonstrated that nephrogenic adenoma in renal transplant patients originated from the renal tubular epithelium. This newly proved, but long sought information may be helpful in the differential diagnosis of nephrogenic adenoma. In this study, we investigated the expression of a renal transcription factor, PAX2, in 39 nonrenal transplant-related nephrogenic adenomas, 100 adenocarcinomas of the prostate gland, and 47 urothelial carcinomas of the urinary tract. A strong and distinct nuclear staining of PAX2 was found in all 39 cases of nephrogenic adenoma (100%), but not in normal prostate tissue, normal urothelium, adenocarcinomas of the prostate gland, and invasive urothelial carcinomas. Focal CD10 was detected in six of 13 nephrogenic adenomas in the superficial papillary component and in normal prostate epithelium, normal urothelium, lymphocytes, adenocarcinoma of the prostate gland, and urothelial carcinoma. There was no uroplakins detected in nephrogenic adenoma. Therefore, these findings are suggesting that nephrogenic adenoma in nonrenal transplant patients may also arise from the renal epithelium, as did the comparable lesions after transplantation. PAX2 is a specific and sensitive immunohistochemical marker in identification and differential diagnosis of nephrogenic adenoma.

Nephrogenic Adenoma of the Urinary Bladder

INTRODUCTION

The nephrogenic adenoma (NA) is a benign metaplastic lesion of the urothelium and is attributed to chronic irritation of the mucosa, by injury, infection, stone disease or intravesical instrumentations. We present our experience on this morbid entity, its clinical appearance in the urinary bladder, its frequency and relapses. Furthermore we reviewed the related recent literature and focused on its potential to neoplastic degeneration and the value of the new diagnostic modalities.

PATIENTS AND METHODS

Four patients with NA of the urinary bladder are presented. The papilloid or polypoid formations observed by the cystoscopy were identified after the TUR, as NA of the urinary bladder. Their mean follow-up was 3.5 years.

RESULTS

Remission of the symptoms was observed after TUR in all patients. Three out of four patients presented 1-7 relapses, while in one case, after seven NA relapses, a urothelial carcinoma of the bladder was diagnosed.

CONCLUSIONS

Unlike histological features, the clinical - endoscopic characteristics of NA are non-specific. Even if it is not definitely considered like a premalignant condition, NA has to be followed up frequently and long lasting, because of its high recurrence rate. The combination of Cytology, Flow cytometry, DNA image analysis and Fluorescence in situ hybridization of bladder washings or voided urine, are of high value in monitoring NA of the urothelium.

Nephrogenic adenoma of the urinary bladder

INTRODUCTION

The nephrogenic adenoma (NA) is a benign metaplastic lesion of the urothelium and is attributed to chronic irritation of the mucosa, by injury, infection, stone disease or intravesical instrumentations. We present our experience on this morbid entity, its clinical appearance in the urinary bladder, its frequency and relapses. Furthermore we reviewed the related recent literature and focused on its potential to neoplastic degeneration and the value of the new diagnostic modalities.

PATIENTS AND METHODS

Four patients with NA of the urinary bladder are presented. The papilloid or polypoid formations observed by the cystoscopy were identified after the TUR, as NA of the urinary bladder. Their mean follow-up was 3.5 years.

RESULTS

Remission of the symptoms was observed after TUR in all patients. Three out of four patients presented 1-7 relapses, while in one case, after seven NA relapses, a urothelial carcinoma of the bladder was diagnosed.

CONCLUSIONS

Unlike histological features, the clinical--endoscopic characteristics of NA are non-specific. Even if it is not definitely considered like a premalignant condition, NA has to be followed up frequently and long lasting, because of its high recurrence rate. The combination of Cytology, Flow cytometry, DNA image analysis and Fluorescence in situ hybridisation of bladder washings or voided urine, are of high value in monitoring NA of the urothelium.

Expression of alpha-methylacyl-coenzyme A racemase in nephrogenic adenoma

Nephrogenic adenoma is a benign lesion composed of small glandular structures that develops along the urothelium with uncertain pathogenesis. Some investigators believe that nephrogenic adenoma develops by a metaplastic process in response to injury to the urothelium, while others believe that it arises from detached renal tubules. Nephrogenic adenoma may be present in the prostatic urethra and morphologically mimic prostatic adenocarcinoma. Alpha-methylacyl-coenzyme A racemase (AMACR), a recently identified prostate cancer marker, is typically negative in normal urothelium and prostatic glands, and positive in distal convoluted renal tubules in addition to prostatic adenocarcinomas. Therefore, evaluation of AMACR expression in nephrogenic adenoma will have significance in the pathologic diagnosis and in understanding pathogenesis of this lesion. We studied 38 nephrogenic adenomas by clinical, histologic, and immunohistochemical analyses for AMACR (P504S) and high molecular weight cytokeratin (34betaE12). Twenty-two of 38 nephrogenic adenomas (58%) demonstrated strong cytoplasmic positivity for AMACR, ranging from patchy, focal to diffuse staining. In addition, 16 of 26 (62%) nephrogenic adenomas were negative for 34betaE12. To our knowledge, this is one of the first report of a completely benign lesion, which can be found in the prostate, showing strong AMACR immunoreactivity. Our findings suggest using caution when interpreting positive AMACR immunostaining in prostatic specimens. These findings could be explained by possible renal tubular origin or renal differentiation, at least in a subset, of nephrogenic adenomas.

Derivation of nephrogenic adenomas from renal tubular cells in kidney-transplant recipients

BACKGROUND

Nephrogenic adenomas are benign, tumor-like lesions within the urothelial mucosa of the urinary tract that are not uncommon in renal-transplant recipients. We investigated the origin of nephrogenic adenomas in renal-transplant recipients.

METHODS

Tissue sections were analyzed by fluorescence in situ hybridization with the use of probes for the X and Y chromosomes, by immunohistochemical methods with the use of antibodies to renal tubular antigens, and by lectin histochemical methods. Forty-six nephrogenic adenomas from 29 patients were analyzed.

RESULTS

All nephrogenic adenomas in 14 female recipients of transplants from male donors and 10 male recipients of transplants from female donors showed the same sex-chromosome status as the donor kidney, but not the same sex-chromosome status as the recipient's surrounding bladder tissue. The nephrogenic adenomas from all 6 female recipients of transplants from female donors showed female chromosomes, and those from the 16 male recipients of transplants from male donors showed male chromosomes. The presence of aquaporin 1, PAX2, and lectin-binding capacity for peanut agglutinin, Lotus tetragonolobus agglutinin, and Sophora japonica agglutinin in nephrogenic adenomas indicated an origin from renal tubular cells.

CONCLUSIONS

Nephrogenic adenomas in renal-transplant recipients are derived from tubular cells of the renal transplants and are not metaplastic proliferations of the recipient's bladder urothelium.

DNA profiles and numeric histogram classifiers in nephrogenic adenoma

BACKGROUND

The malignant potential of nephrogenic adenoma is still a matter of controversy and therapeutic regimens of this morphologic entity range from partial, even total cystectomy to watchful waiting. The objective of the current study was to evaluate several robust image cytometry-DNA histogram classifiers and to search among those for factors that separate a biologically nonaggressive metaplastic lesion from lesions with increased malignant potential.

METHODS

The study included bladder irrigation specimens, 23 preceding transurethral resection of nephrogenic adenoma and 24 preceding resection of papillary bladder carcinoma. Feulgen-stained nuclei were imported to a static image analysis system, and densitometric data were interpreted by two different software programs. Histograms were described numerically by DNA index, 2c deviation index, and by 5c/9c-exceeding and euploid polyploidy rates. In addition, an interpretation algorithm based on a dual parameter analysis with an integrated automatic threshold was used.

RESULTS

The numeric classification of DNA histograms of patients suffering from nephrogenic adenoma resulted in DNA indices between 0.91 and 1.15. The 2c deviation indices ranged from 0.03 to 0.43, and the 5c exceeding rates ranged from 0.0 to 1.58. None of the measurements showed nuclei exceeding 9c. The p25-75 ranges of 2c deviation indices in nephrogenic adenoma and papillary urothelial carcinoma did not overlap. These findings might be explained by minor proliferative activity in nephrogenic adenoma. Euploid polyploidy rates less than 5% confirm this explanation. Risk analysis documented high risk only for those patients with nephrogenic adenomas who had proven transitional cell carcinoma in their history.

CONCLUSIONS

DNA estimation by image cytometry of urinary bladder irrigation specimens appears able to separate papillary bladder lesions. The method detects those lesions with higher malignant potential but is limited in separating entities with low malignant potential. Comparison of the discriminative power of robust numeric DNA classifiers reveals the 2c deviation index superior to the widely used DNA index and the 5c exceeding rate in this material.

Atypical nephrogenic metaplasia of the urinary tract: a precursor lesion?

BACKGROUND

Nephrogenic metaplasia with cytologic atypia (atypical nephrogenic metaplasia) is occasionally encountered and its biologic potential is uncertain.

METHODS

The authors describe 18 cases of atypical nephrogenic metaplasia characterized by the presence of prominent cytologic atypia, including nuclear enlargement, nuclear hyperchromasia, and enlarged nucleoli. DNA ploidy analysis by digital image analysis and immunostaining for high-molecular-weight cytokeratin (34betaE12), cytokeratin 7, cytokeratin 20, carcinoembryonic antigen (CEA), epithelial membrane antigen (EMA), p53, and MIB-1 were performed in 9 cases.

RESULTS

The mean patient age was 62 years (median, 65 years; range, 39-84 years). The male-to-female ratio was 2.6:1. Two patients had a history of noninvasive papillary urothelial carcinoma. The typical clinical presentation was hematuria (8 patients) and voiding symptoms (5 patients). Cystoscopic findings were suspicious for neoplasm in 7 of 13 cases. The neoplastic cells were positive for high-molecular-weight cytokeratin, cytokeratin 7, and EMA, and were usually negative for cytokeratin 20 and CEA. p53 nuclear accumulation and increased MIB-1 labeling index were seen in 4 cases. DNA ploidy analysis showed aneuploid pattern in 2 of 9 cases. The mean patient follow-up was 3.5 years (range, 0.5-10.6 years); 2 patients had recurrent nephrogenic metaplasia, and the remainder were alive without recurrence or urothelial carcinoma.

CONCLUSIONS

Atypical nephrogenic metaplasia is benign; it occasionally displays substantial cytologic abnormalities of no apparent clinical significance. Awareness of the spectrum of cytologic changes within this entity is critical to prevent overdiagnosis of cancer and avoid unnecessary treatment. There is no direct evidence that links atypical nephrogenic metaplasia to cancer.