[983] Nephrogenic Adenoma Showing a Flat Pattern. Description of a New Histological Variant of a Rare Benign Lesion Using PAX-2 and PAX-8 Immunohistochemistry

Sergio Pina-Oviedo, Jae Y Ro. The Methodist Hospital, Houston, TX

Background: Nephrogenic adenoma (NA) is a rare benign lesion of the bladder that mostly occurs in males. Its histogenesis is uncertain but possible origin from mesonephric embryologic remnants of the bladder, metaplastic urothelial changes after chronic inflammation, or renal cell shedding and implanation into the bladder have been postulated. Several histological patterns including a tubular, tubulocystic, polypoid and papillary patterns have been described. NA consists of tubules, cysts or papillae lined by flat to polygonal cells with large nucleus and middle-sized nucleolus, occasionally separated by stroma with associated chronic inflammation. Although a benign entity, NA is a gross and microscopic mimicker of malignant lesions. By immunohistochemistry, NAs are positive for the renal tubule markers PAX-2, PAX-8, AMACR, CD10 and CK7, and negative for urothelial (thrombomodulin, p63) and/or prostate markers (PSA). We described for the first time the presence of NA with a flat pattern adjacent to tubular and papillary NAs, and the utility of PAX-8 along with PAX-2 for the diagnosis of this lesion.
Design: Fifteen (15) cases of NA were retrieved from the archives of our institution. The following immunostains were performed: PAX-8, PAX-2, thrombomodulin and p63. Appropiate positive and negative controls were used.
Results: PAX-8 immunostain was positive in 9 cases (60%) of NAs; PAX-2 was positive in 14 (93%) of the cases. Thrombomodulin and p63 were positive in 1 case (<1%), each. By immunohistochemical evaluation with PAX-2 and PAX-8, we were able to identified that at least 9 cases (60%) of NAs not only presented tubular or papillary patterns, but also featured a flat pattern that extended into the adjacent urothelium or spreaded in a Pagetoid fashion.
Conclusions: We report the presence of NA with a flat pattern in at least 60% of our cases after immunohistochemical evaluation of adjacent areas of tubular or papillary NAs. PAX-8, along with PAX-2, may be also considered as a marker for the detection and diagnosis of NA. PAX-2 and PAX-8 expression also supports the hypothesis of its possible renal epithelial origin. Recognition of a flat pattern in NA may be important for differential diagnosis, however, its clinical implications are uncertain.
Category: Genitourinary (including renal tumors)

Tuesday, March 20, 2012 1:00 PM

Poster Session IV # 89, Tuesday Afternoon


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