Diagnostic implications of transcription factor Pax 2 protein and transmembrane enzyme complex carbonic anhydrase IX immunoreactivity in adult renal epithelial neoplasms.

Pax 2, expressed by metanephric mesenchyme is vital for renal tubule formation and development. Carbonic anhydrase IX (CA IX) is implicated in cell proliferation, adhesion, and invasion. Data regarding expression in renal epithelial tumors other than clear cell renal cell carcinoma (RCC) are limited, conflicting, from tissue microarrays, and do not encompass the entire spectrum or novel uncommon variants. Conventional sections from 200 renal tumors comprising clear cell RCC (n=30), oncocytoma (n=17), papillary RCC (n=30), chromophobe RCC (n=50), urothelial carcinomas (n=30), collecting duct carcinomas (n=5), renal tumors with Xp11.2 translocation (n=15), tubulocystic carcinoma (n=19), and mucinous tubular spindle cell carcinoma (n=4) were immunostained for Pax 2 and CA IX. Clear cell RCC (28/30, 93%), oncocytoma (17/17, 100%), papillary RCC (16/30, 53%), and mucinous tubular spindle cell carcinoma (3/4, 75%) demonstrated nuclear immunoreactivity with Pax 2, whereas the other subtypes were nonreactive. Clear cell RCC (30/30, 100%), urothelial carcinoma (27/30, 90%), papillary RCC (17/30, 57%), and renal tumors with Xp11.2 translocation (6/15, 40%) exhibited membranous immunoreactivity with CA IX, whereas the other subtypes were nonreactive. This suggests potential diagnostic utility of Pax 2 in distinction of (i) oncocytoma (positive) from chromophobe RCC (negative), (ii) clear cell RCC and papillary RCC (positive) from renal tumors with Xp11.2 translocation (negative), and (iii) high-grade clear cell RCC (positive) from urothelial carcinoma (negative). CA IX expression has potential diagnostic implications including (i) clear cell RCC (positive) versus chromophobe RCC (negative) and (ii) urothelial carcinoma (positive) versus collecting duct carcinoma (negative). These antibodies may reliably discriminate between clinically significant subtypes of RCC with overlapping cytoarchitectural features.